Converter circuit and motor driving apparatus

A converter circuit for converting an output voltage from an AC power supply includes a rectifier circuit for rectifying the output voltage of the AC power supply; first and second capacitors connected in series, for smoothing the output of the rectifier circuit; and a switch circuit for switching the connections between the respective capacitors and the AC power supply so that the output voltage of the AC power supply is applied to each of the respective capacitors at a cycle that is shorter than the cycle of the AC power supply.

FIELD OF THE INVENTION

The present invention relates to a converter circuit and a motor driving apparatus and, more particularly, to a converter circuit which is capable of boosting an input voltage, and a motor driving apparatus using the converter circuit.

BACKGROUND OF THE INVENTION

Conventionally, a full-wave voltage doubler circuit has been employed to boost an input voltage from 100V to 200V.

FIG. 16is a diagram illustrating an example of a conventional full-wave voltage doubler circuit.

The full-wave voltage doubler circuit10comprises a bridge diode circuit4for rectifying an output voltage of an AC power supply1, a power-factor improvement reactor3which is connected in series between the AC power supply1and the bridge diode circuit4, two electrolytic capacitors5and6which are connected in series to each other and in parallel to the bridge diode circuit4, and an electrolytic capacitor9which is connected in parallel to the electrolytic capacitors5and6.

With reference toFIG. 16, input terminals1aand1bof the full-wave voltage doubler circuit are connected to an output terminal of the AC power supply1. The bridge diode circuit4comprises two diodes4aand4bwhich are connected in series between output terminals1cand1dof the full-wave voltage doubler circuit10, and a connection node4cof the diodes4aand4bis connected to the input terminal1aof the full-wave voltage doubler circuit10through the power-factor improvement reactor3. Further, the other input terminal1bof the full-wave voltage doubler circuit10is connected to a connection node of the electrolytic capacitors5and6, and protection diodes7and8are connected in parallel to the electrolytic capacitors5and6, respectively.

In the full-wave voltage doubler circuit10thus constituted, the output voltage of the AC power supply1is full-wave-rectified by the diodes4aand4bwhich are components of the bridge diode circuit4, and the electrolytic capacitors5and6are alternately charged by a full-wave-rectified output from the bridge diode circuit4at a cycle equal to the cycle of the output voltage of the AC power supply1. A voltage twice as high as the output voltage of the AC power supply1, which is caused by this charging at both ends of the capacitors5and6connected in series, is smoothed by the electrolytic capacitor9, and a smoothed double-high voltage is generated between the output terminals1cand1dof the full-wave voltage doubler circuit10.

On the other hand, there has also been proposed another example of a full-wave voltage doubler circuit wherein, in order to increase efficiency, a metallized film capacitor is used as a voltage doubler capacitor to be charged by a rectified output of diodes connected in series, and two bridge diode circuits are connected in parallel (for example, refer to Japanese Published Patent Application No. 2001-211651 (FIG. 1)).

Further, there has also been proposed a circuit system wherein a rectifier circuit is provided with a booster circuit, in order to increase the power factor of an input power supply and boost the input voltage to an arbitrary voltage (for example, refer to Japanese Patent No. 3308993 (FIG. 1)).

FIG. 17is a diagram for explaining a voltage conversion circuit disclosed in Japanese Patent No. 3308993.

The voltage conversion circuit11comprises a rectifier circuit20for rectifying an output voltage of an AC power supply1which is applied to input terminals2aand2b, a booster circuit13for boosting an output voltage of the rectifier circuit20, and an electrolytic capacitor17which is charged by an output voltage of the booster circuit13.

The rectifier circuit20comprises first and second diodes21and22which are connected in series, and third and fourth diodes23and24which are connected in series. A connection node20aof the first and second diodes21and22is connected to an input terminal2aof the voltage conversion circuit11, and a connection node20bof the third and fourth diodes23and24is connected to the other input terminal2bof the voltage conversion circuit11. Further, the cathodes of the first and third diodes21and23are connected to each other, and the connection node of the first and third diodes21and23is an output terminal of the rectifier circuit20. The anodes of the second and fourth diodes22and24are connected to each other, and the connection node of the second and fourth diodes22and24is the other output terminal of the rectifier circuit20.

The booster circuit13comprises a reactor14having an end connected to the other end of the rectifier circuit20, a diode16ahaving an anode connected to the other end of the reactor14and a cathode connected to the output terminal2cof the voltage conversion circuit11, and a switching element15which is connected between the connection node of the reactor14and the diode16aand the other output terminal of the rectifier circuit20. The switching element15is an IGBT (Insulated Gate type Bipolar Transistor), and a diode16bis connected in inverse-parallel to the IGBT15.

In the voltage conversion circuit11, the AC voltage supplied from the AC power supply1is rectified by the rectifier circuit20, and the output of the rectifier circuit20is input to the booster circuit13. In the booster circuit13, the output of the rectifier circuit20is boosted by on-off of the switching element15. That is, an electric path at the output side of the reactor14is short-circuited when the switching element15is turned on, whereby a DC current flows from the rectifier circuit20into the reactor14, and energy is stored in the reactor14. Thereafter, when the switching element15is turned off, an induced voltage is generated in the reactor14, and the capacitor17is charged by a sum voltage of the induced voltage and the output voltage of the rectifier circuit20, whereby a voltage higher than the output voltage of the rectifier circuit20is generated between the terminals of the capacitor17.

In the voltage conversion circuit11having the booster circuit13of this type, the current supplied from the AC power supply1is controlled so as to have a sinusoidal waveform by adjusting the time ratio between the on period and the off period of the switching element15, whereby the power factor is improved. Further, the magnitude (absolute value) of the input current is controlled by adjusting the time ratio, whereby the level of the output DC voltage can be controlled.

However, the conventional full-wave voltage doubler circuit10shown inFIG. 16requires the large-capacitance voltage-doubler capacitors5and6and the reactor3for improving the power factor. Further, if the capacitance of the voltage-doubler capacitor is small, the capacitor does not operate as a voltage-doubler capacitor.

In brief, the operation of the voltage-doubler circuit is as follows. That is, the two capacitors connected in series are alternately charged at every half period of the input AC voltage, and a sum voltage of the terminal voltages of the two capacitors is outputted. Therefore, when the capacitances of the capacitors are small, the terminal voltages of the charged capacitors are undesirably lowered during the half period of the input voltage when no charging is carried out, and the output voltage of the voltage-doubler circuit10, which is output as a sum voltage of the terminal voltages of the two capacitors, is not double the input voltage.

On the other hand, the conventional voltage conversion circuit11shown inFIG. 17is a component of, for example, a motor driving apparatus, and the capacitance of the reactor14as a component of the booster circuit13and the capacitance of the capacitor17charged by the output of the booster circuit13are determined according to the switching frequency of the switching element15. That is, in order to reduce the capacitance of the reactor14, the switching frequency must be increased so as to reduce the harmonic current that appears at the input end. Further, since the ripple of the voltage charged in the capacitor17is increased as the capacitance of the capacitor17is reduced, the switching frequency must be increased to reduce the ripple.

However, considering the efficiency of the voltage conversion circuit11or the cost of the harmonic switching element, there is a limitation in actually increasing the switching frequency by the booster circuit13, and therefore, the capacitances of the reactor14and the capacitor17cannot be reduced by a predetermined value or more.

As described above, in the circuit structures such as the conventional full-wave voltage doubler circuit10and the voltage conversion circuit11, since the capacitances of the capacitors and the reactors, which are components of these circuits, cannot be reduced by a predetermined value or more, the circuit scale of the full-wave voltage doubler circuit10or the voltage conversion circuit11cannot be reduced. Therefore, it is difficult to reduce the size of a motor driving apparatus including these circuits.

SUMMARY OF THE INVENTION

The present invention is made to solve the above-described problems and has for its object to provide a small-footprint converter circuit capable of generating a voltage that is double an input voltage, without using large-capacitance capacitors and reactors.

It is another object of the present invention to provide a compact motor driving apparatus employing the converter circuit.

Other objects and advantages of the invention will become apparent from the detailed description that follows. The detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the scope of the invention will be apparent to those of skill in the art from the detailed description.

According to a first aspect of the present invention, there is provided a converter circuit having a pair of input terminals and a pair of output terminals, and boosting an AC voltage. The converter circuit comprises: a rectifier circuit for rectifying an output voltage of an AC power supply, which is input to the input terminals, and outputting the rectified voltage to the output terminals; plural capacitors connected in series between the two output terminals; and a switch circuit for switching the connections between the respective capacitors and the AC power supply so that the output voltage of the AC power supply is applied to each of the respective capacitors at a cycle that is shorter than the cycle of the AC power supply. Therefore, it is possible to significantly reduce the capacitances of the respective capacitors in the converter circuit which are required for generating a voltage that is twice as high as the input voltage in this converter circuit. Further, the reduction in the capacitances of the capacitors which are components of the converter circuit leads to a reduction in the capacitance of a reactor which is used for improving the power factor of the converter circuit. As a result, the capacitors and the reactor, which occupy a greater part of the volume of the converter circuit, can be reduced in size, whereby the volume of the converter circuit itself can be significantly reduced.

According to a second aspect of the present invention, in the converter circuit according to the first aspect, the plural capacitors are first and second capacitors connected in series. In addition, the switch circuit comprises first and second switching elements connected in series, first and second diodes connected in series and connected in parallel to the switching elements connected in series, and third and fourth diodes connected in series and connected in parallel to the switching elements connected in series. Furthermore, a connection node of the first and second diodes is connected to one of the input terminals, a connection node of the third and fourth diodes is connected to the other input terminal, and a connection node of both the switching elements is connected to a connection node of the both capacitors. Therefore, it is possible to avoid high-speed switching operations of the respective switching elements, whereby an increase in a harmonic current in the converter circuit can be minimized. Further, since no high-speed switching elements are required, the converter circuit is realized at a reduced cost.

According to a third aspect of the present invention, in the converter circuit according to the first aspect, the switch circuit includes a first bidirectional switch connected between one of the input terminals and a connection node of both the capacitors, and a second bidirectional switch connected between the other input terminal and the connection node of both the capacitors. Therefore, it is possible to reduce the number of components of the converter circuit, in addition to the effect of reducing the capacitances of the capacitors which are required for generating a voltage twice as high as the input voltage.

According to a fourth aspect of the present invention, there is provided a converter circuit having a pair of input terminals and a pair of output terminals, and boosting an AC voltage. The converter circuit comprises: a rectifier circuit for rectifying an output voltage of an AC power supply, which is applied to the input terminals, and outputting the rectified voltage to the output terminals; a first capacitor connected between the output terminals; a second capacitor having an end connected to one of the output terminals; and a switch circuit for switching the connections between the other end of the second capacitor and the one and the other input terminals so that the output voltage of the AC power supply is applied to the second capacitor, while a sum voltage of the terminal voltage of the second capacitor and the output voltage of the AC power supply is applied to the first capacitor, at a cycle that is shorter than the cycle of the AC power supply. Therefore, it is possible to significantly reduce the capacitances of the respective capacitors which are required for generating a voltage that is twice as high as the input voltage in this converter circuit. Further, the reduction in the capacitances of the capacitors which are components of the converter circuit leads to a reduction in the capacitance of a reactor which is used for improving the power factor of the converter circuit. As a result, it is possible to realize a compact converter circuit in which the capacitors and the reactor, which occupy a greater part of the volume of the converter circuit, are reduced in size.

According to a fifth aspect of the present invention, in the converter circuit according to the fourth aspect, the switch circuit includes first and second switching elements connected in series, first and second diodes connected in series and connected in parallel to the switching elements connected in series, and third and fourth diodes connected in series and connected in parallel to the switching elements connected in series. In addition, a connection node of the first and second diodes is connected to one of the input terminals, a connection node of the third and fourth diodes is connected to the other input terminal, and a connection node of both the switching elements is connected to the other end of the second capacitor. Therefore, it is possible to avoid high-speed switching operations of the respective switching elements, whereby an increase in a harmonic current in the converter circuit can be minimized. Further, since no high-speed switching elements are required, the converter circuit is realized at a reduced cost.

According to a sixth aspect of the present invention, in the converter circuit according to the fourth aspect, the switch circuit includes a first bidirectional switch connected between one of the input terminals and the other end of the second capacitor, and a second bidirectional switch connected between the other input terminal and the other end of the second capacitor. Therefore, it is possible to reduce the number of components of the converter circuit, in addition to the effect of reducing the capacitances of the capacitors required for generating a voltage twice as high as the input voltage.

According to a seventh aspect of the present invention, there is provided a motor driving apparatus receiving an output voltage of an AC power supply, converting the output voltage of the AC power supply into a driving voltage, and outputting the driving voltage to a motor. The motor driving apparatus comprises: a converter circuit having a pair of input terminals and a pair of output terminals, and boosting the output voltage of the AC power supply; and an inverter circuit for converting an output voltage of the converter circuit into a three-phase AC voltage, and outputting the three-phase AC voltage as a driving voltage to the motor. The converter circuit comprises a rectifier circuit for rectifying the output voltage of the AC power supply, which is applied to the input terminals, and outputting the rectified voltage to the output terminals, plural capacitors connected in series between the output terminals, and a switch circuit for switching the connections between the respective capacitors and the AC power supply so that the output voltage of the AC power supply is applied to each of the plural capacitors at a cycle that is shorter than the cycle of the AC power supply. Therefore, it is possible to significantly reduce the capacitances of the respective capacitors which are required for generating a voltage that is twice as high as the input voltage in this converter circuit. Further, the reduction in the capacitances of the capacitors in the converter circuit leads to a reduction in the capacitance of a reactor which is used for improving the power factor of the converter circuit. As a result, it is possible to realize a compact converter circuit in which the capacitors and the reactor, which occupy a greater part of the volume of the converter circuit, are reduced in size, leading to a reduction in size of the motor driving apparatus.

According to an eighth aspect of the present invention, in the motor driving apparatus according to the seventh aspect, the plural capacitors are first and second capacitors connected in series. In addition, the switch circuit comprises first and second switching elements connected in series, first and second diodes connected in series and connected in parallel to the switching elements connected in series, and third and fourth diodes connected in series and connected in parallel to the switching elements connected in series. Furthermore, a connection node of the first and second diodes is connected to one of the input terminals, a connection node of the third and fourth diodes is connected to the other input terminal, and a connection node of both the switching elements is connected to a connection node of the both capacitors. Therefore, it is possible to avoid high-speed switching operations of the respective switching elements, whereby an increase in a harmonic current in the converter circuit can be minimized. Further, since no high-speed switching elements are required, the converter circuit is realized at reduced cost.

According to a ninth aspect of the present invention, there is provided a motor driving apparatus receiving an output voltage of an AC power supply, converting the output voltage of the AC power supply into a driving voltage, and outputting the driving voltage to a motor. The motor driving apparatus comprises: a converter circuit having a pair of input terminals and a pair of output terminals, and boosting the output voltage of the AC power supply; and an inverter circuit for converting an output voltage of the converter circuit into a three-phase AC voltage, and outputting the three-phase AC voltage as a driving voltage to the motor. The converter circuit comprises: a rectifier circuit for rectifying an output voltage of an AC power supply, which is applied to the input terminals, and outputting the rectified voltage to the output terminals; a first capacitor connected between the output terminals; a second capacitor having an end connected to one of the output terminals; and a switch circuit for switching the connections between the other end of the second-capacitor and the one and the other input terminals so that the output voltage of the AC power supply is applied to the second capacitor, while a sum voltage of the terminal voltage of the second capacitor and the output voltage of the AC power supply is applied to the first capacitor, at a cycle that is shorter than the cycle of the AC power supply. Therefore, it is possible to significantly reduce the capacitances of the respective capacitors which are required for generating a voltage that is twice as high as the input voltage in this converter circuit. Further, the reduction in the capacitances of the capacitors in the converter circuit leads to a reduction in the capacitance of a reactor which is used for improving the power factor of the converter circuit. As a result, it is possible to realize a compact converter circuit in which the capacitors and the reactor, which occupy a greater part of the volume of the converter circuit, are reduced in size, leading to a reduction in size of the motor driving apparatus.

According to a tenth aspect of the present invention, in the motor driving apparatus according to an eighth aspect, the switch circuit repeatedly turns the first and second switching elements on and off alternately so that the first and second capacitors are alternately charged, and the capacitances of the first and second capacitors are set to such large values that the terminal voltages of the first and second capacitors do not drop to zero during one switching period of the switching elements when the motor is at the maximum output. Therefore, the boosting operation of the converter circuit can be ensured over the whole driving area of the motor.

According to an eleventh aspect of the present invention, in the motor driving apparatus according to the eighth aspect, the switch circuit repeatedly turns the first and second switching elements on and off alternately so that the first and second capacitors are alternately charged, and the switching cycle of the switching elements is set to such a short period that the terminal voltages of the first and second capacitors do not drop to zero when the motor is at the maximum output. Therefore, the boosting operation of the converter circuit can be ensured over the whole driving area of the motor.

According to a twelfth aspect of the present invention, in the motor driving apparatus according to the eighth aspect, the switch circuit stops the on-off operations of the first and second switching elements when the torque of the motor satisfies a required torque. Therefore, power loss in the converter circuit can be minimized. That is, since the boosting operation of the converter circuit is stopped in a low load area where no boosting operation is needed, only the rectifier circuit can be operated to improve the operation efficiency of the converter circuit.

According to a thirteenth aspect of the present invention, in the motor driving apparatus according to the twelfth aspect, the switch circuit judges whether the torque of the motor is excessive or deficient, on the basis of the voltage supplied to the motor. Therefore, it is possible to easily judge as to whether the torque of the motor is excessive or deficient, whereby a switch circuit that operates according to the motor torque can easily be realized.

According to a fourteenth aspect of the present invention, in the motor driving apparatus according to the twelfth aspect, the switch circuit judges whether the torque of the motor is excessive or deficient, on the basis of an ordered rpm and an actual rpm of the motor. Therefore, it is possible to accurately detect as to whether the torque of the motor is excessive or deficient, whereby the switch circuit can correctly be operated according to the motor torque.

According to a fifteenth aspect of the present invention, in the motor driving apparatus according to the twelfth aspect, the switch circuit judges whether the torque of the motor is excessive or deficient, on the basis of the amplitude of a current supplied to the motor. Therefore, a switch circuit that operates according to the motor torque can easily be realized.

According to a sixteenth aspect of the present invention, in the motor driving apparatus according to the eighth embodiment, the switch circuit uses a power supply for driving the inverter circuit, as a power supply for driving the first and second switching elements. Therefore, it becomes unnecessary to prepare a special power supply for driving the first and second switching elements, whereby the number of components of the converter circuit is significantly reduced, resulting in reductions in circuit space and cost.

According to a seventeenth aspect of the present invention, in the motor driving apparatus according to the sixteenth aspect, a power supply for driving a lower-potential-side element between the first and second switching elements comprises a DC power supply for driving the inverter, a diode having an anode connected to a higher-potential-side terminal of the DC power supply, and a capacitor connected between a cathode of the diode and a lower-potential end of the lower-potential-side switching element. In addition, a power supply for driving a higher-potential-side element between the first and second switching elements comprises a diode having an anode connected to the cathode of the diode which is a component of the driving power supply for driving the lower-potential-side element, and a capacitor connected between a cathode of the diode and a connection node of the two switching elements. Therefore, a power supply for driving the first and second switching elements can be realized in a relatively simple circuit construction, whereby the number of components of the converter circuit is significantly reduced, resulting in reductions in circuit space and cost.

According to an eighteenth aspect of the present invention, in the motor driving apparatus according to the seventh aspect, the switch circuit changes the switching cycle for turning the first and second switching elements on and off, according to the output of the motor. Therefore, the converter circuit is able to carry out an appropriate boosting operation according to the motor output, whereby the operation efficiency of the converter circuit is improved.

According to a nineteenth aspect of the present invention, in the motor driving apparatus according to the eighth aspect, the switching cycle for turning the first and second switching elements on and off is equal to the switching cycle for turning on and off the switching elements which are components of the inverter circuit. Therefore, the frequency of the harmonic current that occurs in the motor driving apparatus is unified, whereby the number of noise filters to be provided at the input end is also unified, resulting in a significant cost reduction.

According to a twentieth aspect of the present invention, in the motor driving apparatus according to the eighth aspect, the switch circuit turns the first and second switching elements on and off so that harmonic components of the current inputted to the converter circuit are decreased. Since the harmonic current is reduced, a noise filter to be provided at the input end can be reduced in size, or dispensed with.

According to a twenty-first aspect of the present invention, in the motor driving apparatus according to the eighth aspect, the diodes as components of the rectifier circuit have an inverse recovery time as short as that of the diodes constituting the switch circuit. Therefore, it is possible to reduce losses at commutation in the rectifier circuit in which a cut-off of current is carried out for every carrier period of the first and second switching elements, whereby operation efficiency of the rectifier circuit is improved.

According to a twenty-second aspect of the present invention, in the motor driving apparatus according to the eighth aspect, the converter circuit includes a capacitor for charging a regenerative current that occurs when the motor is stopped, where such capacitor is connected to the output end of the converter circuit. Therefore, it is possible to prevent the inverter from being destroyed due to the regenerative current even when the motor is suddenly stopped, whereby reliability of the motor driving apparatus is improved.

According to a twenty-third aspect of the present invention, in the motor driving apparatus according to the eighth aspect, the switch circuit is a switching module which is obtained by modularizing the first to fourth diodes, and the first and second switching elements. Therefore, the motor driving apparatus that does not need boosting and the motor driving apparatus that needs boosting can share the circuit substrate, whereby design efficiency is enhanced.

According to a twenty-fourth aspect of the present invention, in the motor driving apparatus according to the twenty-third aspect, the switching module is operated with a driving signal that is supplied from an inverter drive unit for driving the inverter circuit. Therefore, it becomes unnecessary to provide a special apparatus for driving the switching module, resulting in a cost reduction.

According to a twenty-fifth aspect of the present invention, in the motor driving apparatus according to the eighth aspect, the converter circuit includes a reactor for cutting off noises that occur in the switch circuit included in the converter circuit, where such reactor is connected to the input end of the converter circuit. Therefore, the power factor of the input current is increased, whereby occurrence of a harmonic current at the input end can be reduced.

According to a twenty-sixth aspect of the present invention, in the motor driving apparatus according to the twenty-fifth aspect, the switch circuit turns the first and second switching elements on and off so that the on periods of both the elements are overlapped, thereby to boost the output voltage of the converter circuit to double or more of the output voltage of the AC power supply. Therefore, it is possible to drive a motor that requires a voltage that is twice or more as high as the power supply voltage.

According to a twenty-seventh aspect of the present invention, in the motor driving apparatus according to the eighth aspect, the inverter circuit controls a supply current to the motor so as to increase the power factor of the current inputted to the converter circuit. Therefore, the power factor of the input current is increased, whereby occurrence of a harmonic current at the input end can be reduced.

According to a twenty-eighth aspect of the present invention, in the motor driving apparatus according to the eighth aspect, the switch circuit turns the first and second switching elements on and off so as to increase the power factor of the current inputted to the converter circuit. Therefore, the power factor of the input current is increased, whereby occurrence of a harmonic current at the input end can be reduced.

According to a twenty-ninth aspect of the present invention, there is provided a compressor for receiving a voltage from an AC power supply. The compressor comprises a motor, a motor driving apparatus for driving the motor. The motor driving apparatus is a motor driving apparatus according to the seventh aspect of the present invention. Therefore, the capacitances of the capacitors used in the converter circuit of the motor driving apparatus can be reduced, whereby the motor driving apparatus is reduced in size and cost, leading to reductions in size and cost of the compressor.

According to a thirtieth aspect of the present invention, there is provided an air conditioner for receiving a voltage from an AC power supply, and having a compressor. The air conditioner comprises a motor driving apparatus for driving a motor of the compressor. The motor driving apparatus is a motor driving apparatus according to the seventh aspect of the present invention. Therefore, the capacitances of the capacitors used in the converter circuit of the motor driving apparatus can be reduced, whereby the motor driving apparatus is reduced in size and cost, leading to reductions in size and cost of the refrigerator.

According to a thirty-first aspect of the present invention, there is provided a refrigerator for receiving a voltage from an AC power supply, and having a compressor. The refrigerator comprises a motor driving apparatus for driving a motor of the compressor. The motor driving apparatus is a motor driving apparatus according to the seventh aspect of the present invention. Therefore, the capacitances of the capacitors used in the converter circuit of the motor driving apparatus can be reduced, whereby the motor driving apparatus is reduced in size and cost, leading to reductions in size and cost of the compressor.

According to a thirty-second aspect of the present invention, there is provided an electric washing machine for receiving a voltage from an AC power supply. The electric washing machine comprises a motor, and a motor driving apparatus for driving a motor of the compressor. The motor driving apparatus is a motor driving apparatus according to the seventh aspect of the present invention. Therefore, the capacitances of the capacitors used in the converter circuit of the motor driving apparatus can be reduced, whereby the motor driving apparatus is reduced in size and cost, leading to reductions in size and cost of the washing machine.

According to a thirty-third aspect of the present invention, there is provided an air blower for receiving a voltage from an AC power supply. The air blower comprises a motor, and a motor driving apparatus for driving the motor. The motor driving apparatus is a motor driving apparatus according to the seventh aspect of the present invention. Therefore, the capacitances of the capacitors used in the converter circuit of the motor driving apparatus can be reduced, whereby the size and cost of the air blower can be reduced.

According to a thirty-fourth aspect of the present invention, there is provided an electric vacuum cleaner for receiving a voltage from an AC power supply. The electric vacuum cleaner comprises a motor, and a motor driving apparatus for driving the motor. The motor driving apparatus is a motor driving apparatus according to the seventh aspect of the present invention. Therefore, the capacitances of the capacitors used in the converter circuit of the motor driving apparatus can be reduced, whereby the size and cost of the vacuum cleaner can be reduced.

According to a thirty-fifth aspect of the present invention, there is provided a heat-pump type hot-water supply unit for receiving a voltage from an AC power supply, and having a compressor. The heat-pump type hot-water supply unit comprises a motor driving apparatus for driving a motor of the compressor. The motor driving apparatus is a motor driving apparatus according to the seventh aspect of the present invention. Therefore, the capacitances of the capacitors used in the converter circuit of the motor driving apparatus can be reduced, whereby the motor driving apparatus is reduced in size and cost, leading to reductions in size and cost of the heat-pump type hot-water supply unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 1is a diagram for explaining a converter circuit according to a first embodiment of the present invention.

The converter circuit100according to the first embodiment receives an AC voltage supplied from an AC power supply1, and converts the input voltage into a non-negative voltage that is equal to or larger than the amplitude of the input voltage. The converter circuit100has a pair of input terminals a1and a2to which the output voltage of the AC power supply1is applied, and a pair of output terminals b1and b2from which the non-negative voltage equal to or larger than the amplitude of the input voltage is output.

To be specific, the converter circuit100comprises: a rectifier circuit20for rectifying the output voltage of the AC power supply1, which is applied to the input terminals a1and a2; first and second capacitors31and32which are connected in series between the output terminals b1and b2; and a switch circuit40for connecting a connection node10fof the first and second capacitors31and32to the two input terminals a1and a2, alternately, so that charging of the first capacitor31and charging of the second capacitor32are alternately repeated by the output voltage of the AC power supply1at a cycle that is shorter than the cycle of the output voltage of the AC power supply1. The first and second capacitors31and32constitute a capacitor circuit30for generating an output voltage between the output terminals b1and b2.

The rectifier circuit20comprises four diodes21to24, similar to the rectifier circuit of the conventional voltage conversion circuit11shown inFIG. 17. A connection node10aof the diodes21and22connected in series is connected to the input terminal a1, while a connection node10bof the diodes23and24connected in series is connected to the input terminal a2. Further, the cathodes of the diodes21and23are connected to each other, and the connection node of the diodes21and23is connected to the output terminal b1. The anodes of the diodes22and24are connected to each other, and the connection node of the diodes22and24is connected to the output terminal b2.

The switch circuit40comprises: first and second switching elements45and46connected in series; first and second diodes41and42which are connected in series with each other and in parallel with the switching elements45and46connected in series; and third and fourth diodes43and44which are connected in series with each other and in parallel with the switching elements45and46connected in series. A connection node10cof the first and second diodes41and42is connected to the input terminal a1, and a connection node10dof the third and fourth diodes43and44is connected to the input terminal a2. Further, a connection node10eof the switching elements45and46is connected to the connection node10fof capacitors31and32, which are connected in series and constitute the capacitor circuit30. In this first embodiment, IGBTs (Insulating Gate Bipolar Transistors) are used as the switching elements45and46.

Next, the operation of the converter circuit100will be described.

When the output voltage of the AC power supply1is applied to the input terminals a1and a2of the converter circuit100, the output voltage of the AC power supply1is rectified by the rectifier circuit20of the converter circuit100, and the capacitors31and32of the capacitor circuit30are charged by the output of the rectifier circuit20so that the potential at the output terminal b1becomes higher than the potential at the output terminal b2.

That is, when the potential at the input terminal a1is higher than the potential at the input terminal a2, a current flows from the input terminal a1through the diode21, the capacitor circuit30, and the diode24to reach the input terminal a2, by the output voltage of the AC power supply1, in the converter circuit100. On the other hand, when the potential at the input terminal a1is lower than the potential at the input terminal a2, a current flows from the input terminal a2through the diode23, the capacitor circuit30, and the diode22to reach the input terminal a1, by the output voltage of the AC power supply1, in the converter circuit100. Thereby, the two capacitors31and32in the capacitor circuit30are charged.

At this time, when on-off of the first and second switching elements45and46in the switch circuit40is complementarily carried out so that one is turned on while the other one is turned off according to a switch control signal (not shown), the first and second capacitors31and32in the capacitor circuit30are alternately charged by the output voltage of the AC power supply1. It is assumed that on-off of the switching elements45and46is carried out at a cycle (e.g., 1/1000 (sec)) that is shorter than the cycle ( 1/60 (sec)) corresponding to the frequency (60 Hz) of the AC power supply1. That is, the output voltage of the AC power supply1is applied to each of the first and second capacitors31and32at a cycle that is shorter than the cycle of the AC power supply1, by turning the first and second switching elements45and46on and off.

Hereinafter, current flow in the switch circuit40and the capacitor circuit30will be described with respect to two cases having different polarities of the output voltage of the AC power supply.

Initially, a description will be given of the case where the potential at the input terminal a1of the converter circuit100is higher than the potential at the other input terminal a2.

When the switching element45is turned on and the switching element46is turned off, a current flows from the input terminal a1through the diode41, the switching element45, the second capacitor32, and the diode24to reach the input terminal a2, whereby the second capacitor32is charged by the output voltage of the AC power supply1so that the potential at the connection node10fbecomes higher than the potential at the output terminal b2.

On the other hand, when the switching element45is turned off and the switching element46is turned on, a current flows from the input terminal a1through the diode21, the first capacitor31, the switching element46, and the diode44to reach the input terminal a2, whereby the first capacitor31is charged by the output voltage of the AC power supply1so that the potential at the output terminal b1becomes higher than the potential at the connection node10f.

Thereby, a sum voltage of the terminal voltage of the first capacitor31and the terminal voltage of the second capacitor32is generated between the output terminals b1and b2of the capacitor circuit100, and the maximum value of this sum voltage is double the input voltage.

Next, a description will be given of the case where the potential at the input terminal a1of the converter circuit100is lower than the potential of the other input terminal a2.

When the switching element45is turned on and the switching element46is turned off, a current flows from the input terminal a2through the diode43, the switching element45, the second capacitor32, and the diode22to reach the input terminal a1, whereby the second capacitor32is charged by the output voltage of the AC power supply1so that the potential at the connection node10fbecomes higher than the potential at the output terminal b2.

On the other hand, when the switching element45is turned off and the switching element46is turned on, a current flows from the input terminal a2through the diode23, the first capacitor31, the switching element46, and the diode42to reach the input terminal a1, whereby the first capacitor31is charged by the output voltage of the AC power supply1so that the potential at the output terminal b1becomes higher than the potential at the connection node10f.

Thereby, a sum voltage of the terminal voltage of the first capacitor31and the terminal voltage of the second capacitor32is generated between the output terminals b1and b2of the capacitor circuit100, and the maximum value of this sum voltage is double the input voltage.

As a result, regardless of the polarity of the output voltage of the AC power supply1, a rectified voltage that is higher than the output voltage of the AC power supply applied to the input terminals a1and a2is output from the output terminals b1and b2.

As described above, the converter circuit100according to the first embodiment is provided with the rectifier circuit20for rectifying the output voltage of the AC power supply1, the first and second capacitors31and32connected in series for smoothing the output of the rectifier circuit20, and the switch circuit40for switching the connections of the capacitors31and32with the AC power supply1so that the first and second capacitors31and32are alternately charged at a cycle that is shorter than the cycle of the output voltage of the AC power supply1. Therefore, the number of charging times per unit time for the capacitors31and32connected in series becomes larger than the frequency of the AC power supply1, whereby the capacitances of the capacitors31and32which are required for generating a voltage that is twice as high as the input voltage can be reduced.

Further, since the output voltage of the AC power supply1is alternately applied to the first and second capacitors31and32, either of the two capacitors is always charged. Therefore, charging of the capacitors for generating a voltage that is double the input voltage can be carried out with efficiency, whereby the capacitances of the capacitors can be further reduced.

Furthermore, since the sum voltage of the terminal voltages of the first and second capacitors31and32connected in series is the output voltage of the converter circuit100, the withstand voltages of the respective capacitors31and32can be reduced to about half the maximum output voltage of the converter circuit100.

While in this first embodiment the capacitor circuit30comprises two capacitors connected in series, the capacitor circuit30is not restricted thereto. For example, the capacitor circuit30may comprise three or more capacitors. In this case, the connection node10eof the switch circuit40may be connected to any connection node as long as it is a connection node of capacitors connected in series. Further, the capacitor circuit30may be constituted by replacing the first and second capacitors with first and second capacitor units each comprising plural capacitors.

While in this first embodiment IGBTs are used as the switching elements45and46constituting the switch circuit40, the switching elements45and46are not restricted thereto. The switching elements45and46may be implemented by any circuit element that cuts off the current path, such as an FET that electrically cuts off the current path, or a relay that physically cuts off the current path.

While in this first embodiment the first and second switching elements45and46are complementarily turned on and off in the switch circuit40, the switch circuit40may have a period during which both of the first and second switching elements45and46are turned off.

Second Embodiment

FIG. 2is a block diagram for explaining a converter circuit according to a second embodiment of the present invention.

The converter circuit101according to the second embodiment boosts the output voltage of the AC power supply1similar to the converter circuit100according to the first embodiment, and the converter circuit101is composed of a rectifier circuit20, a capacitor circuit30, and a switch circuit40a.

The rectifier circuit20and the capacitor circuit30are identical to those of the first embodiment. The switch circuit40acomprises a first bidirectional switching element71which is connected between the input terminal a1of the converter circuit101and the connection node10fof the capacitor circuit30, and a second bidirectional switching element72which is connected between the input terminal a2of the converter circuit101and the connection node10fof the capacitor circuit30.

In the switch circuit40a, on-off of the first and second bidirectional switching elements71and72is complementarily repeated so that one is turned off while the other is turned on. At this time, the on-off repetition is carried out at a cycle (e.g., 1/1000 (sec)) that is shorter than a cycle ( 1/60 (sec)) corresponding to the frequency of the AC power supply1(e.g., 60 Hz), similar to the switch circuit40of the first embodiment.

Next, the operation of the converter circuit101will be described.

In this second embodiment, since the operations other than that of the switch circuit40aare identical to those described for the first embodiment, only the operation of the switch circuit40awill be described hereinafter with respect to the two cases having different polarities of the output voltage of the AC power supply1.

When the voltage at an input terminal a1of the converter circuit101is higher than the voltage at the other input terminal a2thereof, if the first bidirectional switching element71is turned on and the second bidirectional switching element72is turned off, a current flows from the input terminal a1through the first bidirectional switching element71, the second capacitor32, and the diode24to reach the input terminal a2, whereby the second capacitor32is charged by the output voltage of the AC power supply1so that the voltage at the connection node10fbecomes higher than the voltage at the output terminal b2.

On the other hand, when the first bidirectional switching element71is turned off and the second bidirectional switching element72is turned on, a current flows from the input terminal a1through the diode21, the first capacitor31, and the second bidirectional switching element72to reach the input terminal a2, whereby the first capacitor31is charged by the output voltage of the AC power supply1so that the voltage at the output terminal b1becomes higher than the voltage at the connection node10f.

Further, when the voltage at the input terminal a1of the converter circuit101is lower than the voltage at the input terminal a2thereof, if the first bidirectional switching element71is turned on and the second bidirectional switching element72is turned off, a current flows from the input terminal a2through the diode23, the first capacitor31, and the first bidirectional switching element71to reach the input terminal a1, whereby the second capacitor32is charged by the output voltage of the AC power supply so that the voltage at the connection node10fbecomes higher than the voltage at the output terminal b2.

On the other hand, when the first bidirectional switching element71is turned off and the second bidirectional switching element72is turned on, a current flows from the input terminal a2through the second bidirectional switching element72, the second capacitor32, and the diode22to reach the input terminal a1, whereby the second capacitor32is charged by the output voltage of the AC power supply so that the voltage at the connection node10fbecomes higher than the voltage at the output terminal b2.

Thereby, a sum voltage of the terminal voltage of the first capacitor31and the terminal voltage of the second capacitor32is continuously generated between the two output terminals b1and b2of the converter circuit101, and the sum voltage is double the input voltage at maximum.

As described above, the converter circuit101according to the second embodiment is provided with the switch circuit40acomprising two bidirectional switches71and72, instead of the switch circuit40comprising four diodes and two switching elements, which is included in the converter circuit100of the first embodiment. Therefore, as in the first embodiment, the capacitances of the capacitors31and32for generating a voltage that is double the input voltage can be reduced, and the withstand voltages of the respective capacitors31and32can be minimized.

Moreover, since the switch circuit40ais composed of the two bidirectional switching elements71and72, the number of components of the converter circuit can be reduced.

While in this second embodiment the switch circuit40acomprises the first and second bidirectional switching elements71and72which are complementarily turned on and off, the switch circuit40amay have a period during which both of the first and second switching elements71and72are turned off.

Third Embodiment

FIG. 3is a diagram for explaining a converter circuit according to a third embodiment of the present invention.

The converter circuit102according to the third embodiment boosts the output voltage of the AC power supply1similar to the converter circuit100according to the first embodiment, and the converter circuit102is composed of a rectifier circuit20, a capacitor circuit30a, and a switch circuit40.

The rectifier circuit20and the switch circuit40are identical to those of the first embodiment. The capacitor circuit30acomprises a third capacitor33connected between the output terminals b1and b2, and a fourth capacitor34connected between the output terminal b2and the connection node10eof the first and second switching elements of the switch circuit40. While the capacitor circuit30acomprises the two capacitors33and34, the capacitor circuit30amay comprise third and fourth capacitor units each comprising plural capacitors connected, instead of the third and fourth capacitors.

Next, the operation of converter circuit102will be described.

When the output voltage of the AC power supply1is input to the input terminals a1and a2of the converter circuit102, the output voltage is rectified by the rectifier circuit20in the converter circuit102, and the capacitor33of the capacitor circuit30ais charged by the output of the rectifier circuit20so that the voltage at the output terminal b1becomes higher than the voltage at the output terminal b2.

That is, when the voltage at the input terminal a1is higher than the voltage at the input terminal a2, a current flows in the converter circuit102from the input terminal a1through the diode21, the third capacitor33, and the diode24to reach the input terminal a2due to the output voltage of the AC power supply1. On the other hand, when the voltage at the input terminal a1is lower than the voltage at the input terminal a2, a current flows in the converter circuit102from the input terminal a2through the diode23, the third capacitor33, and the diode22to reach the input terminal a1due to the output voltage of the AC power supply1. Thereby, the third capacitor33of the capacitor circuit30ais charged.

At this time, on-off of the first and second switching elements45and46of the switch circuit40is complementarily carried out by a switch control signal (not shown) so that one of the switching elements45and46is turned off while the other one is turned on, whereby the third and fourth capacitors33and34of the capacitor circuit30aare alternately charged. The on-off of the switching elements45and46is carried out at a cycle (e.g., 1/1000 (sec)) that is shorter than a cycle ( 1/60 (sec)) corresponding to the frequency of the AC power supply1(e.g., 60 Hz). That is, by turning on and off the switching elements45and46, the output voltage of the AC power supply1is applied to the fourth capacitor34while the sum voltage of the terminal voltage of the fourth capacitor34and the output voltage of the AC power supply1is applied to the third capacitor33at a cycle that is shorter than the cycle of the AC power supply1.

Hereinafter, current flow in the switch circuit40and the capacitor circuit30awill be described with respect to two cases having different polarities of the output voltage of the AC power supply1.

Initially, a description will be given of the case where the voltage at one input terminal a1of the converter circuit102is higher than the voltage at the other input terminal a2.

When the switching element45is turned on and the switching element46is turned off, a current flows from the input terminal a1through the diode41, the switching element45, the fourth capacitor34, and the diode24to reach the input terminal a2, whereby the fourth capacitor34is charged by the output voltage of the AC power supply1so that the voltage at the connection node10ebecomes higher than the voltage at the output terminal b2.

On the other hand, when the switching element45is turned off and the switching element46is turned on, a current flows from the input terminal a1through the diode21, the third capacitor33, the fourth capacitor34, the switching element46, and the diode44to reach the input terminal a2, whereby the third capacitor33is charged by the sum voltage of the output voltage of the AC power supply1and the terminal voltage of the fourth capacitor34so that the voltage at the output terminal b1becomes higher than the voltage at the output terminal b2.

Thereby, when the voltage at the input terminal a1is higher than the voltage at the input terminal a2, a terminal voltage of the third capacitor33, which is charged by the output voltage of the AC power supply1and the terminal voltage of the fourth capacitor34, is generated between the output terminals b1and b2of the converter circuit102, and this terminal voltage is double the input voltage at maximum.

Next, a description will be given of the case where the voltage at the input terminal a1is lower than the voltage at the input terminal a2.

When the switching element45is turned on and the switching element46is turned off, a current flows from the input terminal a2through the diode41, the switching element45, the fourth capacitor34, and the diode22to reach the input terminal a1, whereby the fourth capacitor34is charged by the output voltage of the AC power supply1so that the voltage at the connection node10ebecomes higher than the voltage at the output terminal b2.

On the other hand, when the switching element45is turned off and the switching element46is turned on, a current flows from the input terminal a2through the diode23, the third capacitor33, the fourth capacitor34, the switching element46, and the diode42to reach the input terminal a1, whereby the third capacitor33is charged by the sum voltage of the output voltage of the AC power supply1and the terminal voltage of the fourth capacitor34so that the voltage at the output terminal b1becomes higher than the voltage at the output terminal b2.

Thereby, even when the voltage at the input terminal a1is lower than the voltage at the input terminal a2, a terminal voltage of the third capacitor33, which is charged by the output voltage of the AC power supply1and the terminal voltage of the fourth capacitor34, is generated between the output terminals b1and b2of the converter circuit102, and this terminal voltage is double the input voltage at maximum.

As a result, regardless of the polarity of the output voltage of the AC power supply1, a rectified voltage, which is higher than the output voltage of the AC power supply1that is applied to the input terminals a1and a2, is output from the output terminals b1and b2of the converter circuit102.

As described above, the converter circuit102according to the third embodiment is provided with the rectifier circuit20for rectifying the output voltage of the AC power supply1, the third capacitor33connected between the output terminals b1and b2, the fourth capacitor34having an end connected to the output terminal b2, and the switch circuit40afor connecting the terminal10eof the fourth capacitor34alternately to the input terminals a1and a2of the AC power supply1so that the output voltage of the AC power supply1is applied to the fourth capacitor34while the sum voltage of the terminal voltage of the fourth capacitor34and the output voltage of the AC power supply1is applied to the third capacitor33at a cycle that is shorter than the cycle of the output voltage of the AC power supply1. Therefore, the number of charging times per unit time for the capacitors33and34becomes larger than the frequency of polarity inversion of the AC power supply1, whereby the capacitances of the both capacitors33and34can be reduced as compared with the case where the capacitors33and34are alternately charged at every polarity inversion of the AC power supply1.

Further, in this third embodiment, since the output voltage of the AC power supply1is applied to the fourth capacitor34during one half period of the switching cycle while the sum voltage of the terminal voltage of the fourth capacitor34and the output voltage of the AC power supply1is applied to the third capacitor33during the other half period of the switching cycle, either of the two capacitors is always charged as in the first embodiment. Therefore, charging of the capacitors for generating a voltage that is double the input voltage can be carried out with efficiency, and the capacitances of the capacitors can be further reduced.

Furthermore, in the converter circuit102according to the third embodiment, the terminal voltage of the fourth capacitor34is used for boosting the terminal voltage of the third capacitor33, and the terminal voltage of the third capacitor33is the output voltage of the converter circuit102. Therefore, the converter circuit102is constructed such that the two capacitors for generating the output voltage have different capacitances from each other, whereby the converter circuit102is made resistant to variations in capacitances of the two capacitors, and is easily manufactured. Moreover, in the circuit construction according to the third embodiment, only the capacitor33that is a component of the capacitor circuit30ais connected between the output terminals b1and b2of the converter circuit102, whereby the capacitances of the capacitors33and34can be further reduced as compared with the circuit construction in which plural capacitors are connected in series between the output terminals b1and b2.

While in this third embodiment the first and second switching elements45and46are complementarily turned on and off in the switch circuit40, the switch circuit40may have a period during which both of the first and second switching elements45and46are turned off.

Fourth Embodiment

FIG. 4is a diagram for explaining a converter circuit according to a fourth embodiment of the present invention.

The converter circuit103of the fourth embodiment boosts the output voltage of the AC power supply1similar to the converter circuit102of the third embodiment, and comprises a rectifier circuit20, a capacitor circuit30a, and a switch circuit40b.

The rectifier circuit20and the capacitor circuit30aare identical to those of the third embodiment. The switch circuit40bcomprises a first bidirectional switching element71which is connected between the input terminal a1of the converter circuit103and the connection node10eof the fourth capacitor of the capacitor circuit30a, and a second bidirectional switching element72which is connected between the input terminal a2of the converter circuit103and the connection node10eof the capacitor circuit30a, similar to the switch circuit40aaccording to the second embodiment.

In the switch circuit40b, on-off of the first and second bidirectional switching elements71and72is complementarily repeated so that one of the switching elements71and72is turned off while the other one is turned on. At this time, the on-off repetition is carried out at a cycle (e.g., 1/1000 (sec)) that is shorter than a cycle ( 1/60 (sec)) corresponding to the frequency of the AC power supply1(e.g., 60 Hz). That is, by turning the first and second bidirectional switching elements71and72on and off, the output voltage of the AC power supply1is applied to the fourth capacitor34while the sum voltage of the terminal voltage of the fourth capacitor34and the output voltage of the AC power supply1is applied to the third capacitor33at a cycle that is shorter than the cycle of the AC power supply1.

Next, the operation of the converter circuit103will be described.

In this fourth embodiment, since the operations other than that of the switch circuit40bare identical to those described for the third embodiment, the operation of the switch circuit40bwill be mainly described hereinafter with respect to two cases having different polarities of the output voltage of the AC power supply1.

When the voltage of one input terminal a1of the converter circuit103is higher than the voltage at the other input terminal a2thereof, if the first bidirectional switching element71is turned on and the second bidirectional switching element72is turned off, a current flows from the input terminal a1through the first bidirectional switching element71, the fourth capacitor34, and the diode24to reach the input terminal a2, whereby the fourth capacitor34is charged by the output voltage of the AC power supply1so that the voltage at the connection node10ebecomes higher than the voltage at the output terminal b2.

On the other hand, when the first bidirectional switching element71is turned off and the second bidirectional switching element72is turned on, a current flows from the input terminal a1through the diode21, the third capacitor33, the fourth capacitor34, and the second bidirectional switching element72to reach the input terminal a2, whereby the third capacitor33is charged by the sum voltage of the output voltage of the AC power supply1and the terminal voltage of the capacitor34so that the voltage at the output terminal b1becomes higher than the voltage at the output terminal b2.

Thereby, when the voltage at the input terminal a1is higher than the voltage at the input terminal a2, a terminal voltage of the third capacitor33, which is charged by the output voltage of the AC power supply1and the terminal voltage of the fourth capacitor34, is generated between the output terminals b1and b2of the converter circuit103, and this terminal voltage is double the input voltage at maximum.

Further, when the voltage at the input terminal a1of the converter circuit103is lower than the voltage at the input terminal a2thereof, if the first bidirectional switching element71is turned on and the second bidirectional switching element72is turned off, a current flows from the input terminal a2through the second bidirectional switching element72, the fourth capacitor34, and the diode22to reach the input terminal a1, whereby the fourth capacitor34is charged by the output voltage of the AC power supply1so that the voltage at the connection node10ebecomes higher than the voltage at the output terminal b2.

On the other hand, when the first bidirectional switching element71is turned on and the second bidirectional switching element72is turned off, a current flows from the input terminal a2through the diode23, the third capacitor33, the fourth capacitor34, and the first bidirectional switching element71to reach the input terminal a1, whereby the third capacitor33is charged by the sum voltage of the output voltage of the AC power supply1and the terminal voltage of the capacitor34so that the voltage at the output terminal b1becomes higher than the voltage at the output terminal b2.

Thereby, even when the voltage at the input terminal a1is lower than the voltage at the other input terminal a2, a terminal voltage of the third capacitor33, which is charged by the sum voltage of the output voltage of the AC power supply1and the terminal voltage of the fourth capacitor34, is generated between the output terminals b1and b2of the converter circuit103, and this terminal voltage is double the input voltage at maximum.

As a result, regardless of the polarity of the output voltage of the AC power supply1, a rectified voltage that is higher than the output voltage of the AC power supply1which is applied to the input terminals a1and a2is output from the output terminals b1and b2of the converter circuit13.

As described above, the converter circuit103according to the fourth embodiment of the present invention is provided with the switch circuit40bcomprising two bidirectional switching elements71and72, instead of the switch circuit40comprising four diodes and two switching element according to the third embodiment. Therefore, the capacitances of the capacitors which are required for generating a voltage that is double the input voltage can be reduced, as in the third embodiment, and further, the converter circuit103can be resistant to variations in the capacitances of the two capacitors, and be easily manufactured.

Furthermore, in this fourth embodiment, since the switch circuit40bis composed of two bidirectional switching elements71and72, the number of parts of the converter circuit can be reduced.

While in this fourth embodiment the first and second bidirectional switching elements71and72are complementarily turned on and off in the switch circuit40b, the switch circuit40bmay have a period during which both of the first and second switching elements71and72are turned off.

Fifth Embodiment

FIG. 5is a circuit diagram for explaining a motor driving apparatus according to a fifth embodiment of the present invention.

The motor driving apparatus200according to the fifth embodiment is provided with a converter circuit100athat boosts an output voltage of an AC power supply1, and an inverter circuit50that converts the boosted AC voltage into a three-phase AC voltage to be applied to a motor2.

Hereinafter, the converter circuit100aand the inverter circuit50will be described in detail.

The converter circuit100ais identical to the converter circuit100according to the first embodiment. That is, the converter circuit100acomprises: a rectifier circuit20for rectifying the output voltage of the AC power supply1, which is applied to the input terminals a1and a2, to output the rectified voltage to the output terminals b1and b2; a capacitor circuit30for smoothing the output of the rectifier circuit20, which is connected between the output terminals b1and b2; and a switch circuit40for connecting a connection node10fof first and second capacitors31and32, which are components of the capacitor circuit30and are connected in series, alternately to the two input terminals a1and a2so that the first and second capacitors31and32are alternately charged with the output voltage of the AC power supply1. The switch circuit40comprises four diodes41to44and two switching elements45and46as in the first embodiment, and the switching elements are turned on and off by a open-close control signal Cs supplied from a driving apparatus (not shown) for the switching elements. Accordingly, in the converter circuit100aof the motor driving apparatus200according to the fifth embodiment, as in the first embodiment, by turning the first and second switching elements45and46on and off, the output voltage of the AC power supply1is applied to each of the first and second capacitors31and32at a cycle that is shorter than the cycle of the AC power supply1.

The inverter circuit50has switching elements51and52connected in series, switching elements53and54connected in series, and switching elements55and56connected in series. One of the ends of the switching elements51,53, and55are connected to each other, and the connection node of the switching elements51,533, and55is connected to one output terminal b1of the converter circuit100a. One of the ends of the switching elements52,54, and56are connected to each other, and the connection node of the switching elements52,54, and56is connected to the other output terminal b2of the converter circuit100a. Further, diodes61to66are connected in inverse parallel to the respective switching elements51to56. A connection node50aof the switching elements51and52is a first output node of the inverter circuit50, a connection node50bof the switching elements53and54is a second output node of the inverter circuit50, and a connection node50cof the switching elements55and56is a third output node of the inverter circuit50. The first to third output nodes50ato50cof the inverter circuit50are connected to input nodes of the respective phases of the three-phase motor2. The switching elements are IGBT (Insulated Gate type Bipolar Transistor) elements.

A typical circuit structure of the inverter circuit50comprises six pieces of circuit elements each comprising an IGBT (switching element) and a diode connected in inverse parallel to the IGBT as shown inFIG. 5. However, the switching elements may be FETs like MOSFETs, power transistors, and the like. Further, the type of the motor2is not restricted to that mentioned above.

The switching elements51to56as components of the inverter circuit50are turned on and off so that an AC voltage having a frequency according to the rpm (revolutions per minute) of the motor2is supplied from the inverter circuit50to the motor2, by a drive signal Ds. The output of the motor2is controlled by the duty ratio of on-off of the switching elements.

Further, in this fifth embodiment, under the condition that the carrier cycle of the switch circuit40, i.e., the cycle in which the first and second switching elements45and46are turned on and off alternately, is shorter than the cycle of the output voltage of the AC power supply1, the capacitances of the capacitors31and32connected in series are set so that the terminal voltages of the capacitors31and32are not lowered to zero even when any motor is driven. Therefore, regardless of the type of the motor2, the converter circuit100acan output a voltage that is equal to or larger than the amplitude of the input voltage. The capacitances of the capacitors31and32are desired to be larger than the capacitance at which the terminal voltage of the capacitor is lowered to zero at the maximum output of the motor2, that is, when the load to the converter circuit100ais maximum, under the condition that the carrier cycle is shorter than the cycle of the output voltage of the AC power supply1.

Next, the operation of the motor driving apparatus200will be described.

When the output voltage of the AC power supply1is applied to the motor driving apparatus200and the open-close control signal Cs is applied to the switching elements45and46while the drive signal Ds is applied to the switching elements51to56of the inverter circuit50, the converter circuit100aoperates in a manner similar to the converter circuit100of the first embodiment to output a voltage that is equal to or higher than the power supply voltage.

Further, in the inverter circuit50, the drive signal Ds is applied to the respective switching elements51to56as a gate signal, whereby the switching elements51to56are turned on and off. Then, in the inverter circuit50, the output voltage of the converter circuit100ais converted into a three-phase AC voltage, and the three-phase AC voltage is output to the motor2, whereby the motor2is driven by the three-phase AC voltage.

Hereinafter, a description will be given of the carrier frequency of the switch circuit and the capacitances of the capacitors31and32, in an example of use of the motor driving apparatus200according to the fifth embodiment.

For example, in the motor driving apparatus200, when the carrier frequency of the switch circuit40is set to 10 kHz and the motor is driven with a motor load corresponding to a motor driving current of about 15 A, the capacitances of the respective capacitors31and32as components of the capacitor circuit30are about 4 μF.

On the other hand, in order to drive the motor with the same motor load as mentioned above without operating the switch circuit40of the motor driving apparatus200, a capacitance of about 1000 μF is required for the whole capacitor circuit30of the motor driving apparatus200. That is, in the conventional full-wave voltage double circuit10having no switch circuit as shown inFIG. 16, the capacitance of the capacitor9must be about 1000 μF.

Further, in the conventional voltage conversion circuit11shown inFIG. 17, when driving the motor with the same motor load as described above, the capacitance of the capacitor17becomes about 100 μF which is considerably larger than the capacitances of the capacitors in the converter circuit100aof the fifth embodiment, even if the switching frequency of the booster circuit13is equal to or higher than 20 kHz. The reason is as follows. In the booster circuit13of the conventional voltage conversion circuit11shown inFIG. 17, the capacitor17is charged by the reactor14during only a very short period immediately after the switching element15is turned off, thereby to boost the output voltage of the rectifier circuit20.

In brief, in the conventional voltage conversion circuit11, boosting by the booster circuit13is carried out in a very short period just after a turn-off of the switching element15, of the switching cycle of the booster circuit13. On the other hand, in the converter circuit100aof the fifth embodiment, boosting of the output voltage of the rectifier circuit20is substantially carried out over the entire switching cycle. To be specific, in the switch circuit40of the fifth embodiment, during a period when the switching element45is on while the switching element46is off, the output voltage of the AC power supply1is applied to the capacitor32between the two capacitors31and32connected in series. On the other hand, during a period when the switching element45is off while the switching element46is on, the output voltage of the AC power supply1is applied to the capacitor31between the two capacitors31and32connected in series. As described above, in this fifth embodiment, the boosting operation of applying the output voltage of the AC power supply1to the respective capacitors by the switch circuit40is carried out with higher efficiency as compared with the conventional voltage conversion circuit11.

Since the capacitances of the two capacitors31and32of the converter circuit100aare merely employed in one example of use of the motor driving apparatus200, the capacitors may have different capacitances when the carrier frequency of the switch circuit40and the motor load are different from those mentioned above. The higher the carrier frequency is or the smaller the motor load is, the smaller the capacitances of the capacitors31and32are.

As described above, the motor driving apparatus200according to the fifth embodiment is provided with the converter circuit100awhich includes the rectifier circuit20for rectifying the output voltage of the AC power supply1, and the two capacitors31and32connected in series for smoothing the output of the rectifier circuit20, wherein the output voltage of the AC power supply1is applied alternately to the first and second capacitors31and32at a cycle that is shorter than the cycle of the AC power supply1, and the output of the converter circuit is converted into a three-phase AC voltage and applied to the motor2. Therefore, as in the first embodiment, the number of charging times per unit time for the capacitors31and32connected in series becomes larger than the frequency of the AC power supply1, whereby the capacitances of the capacitors31and32can be reduced as compared with the case where both the capacitors are alternately charged for every polarity inversion of the AC power supply1. As a result, the size of the motor driving apparatus equipped with the converter circuit100acan be reduced.

While in this fifth embodiment the first and second switching elements45and46are complementarily turned on and off in the converter circuit100a, the converter circuit100amay have a period during which both of the first and second switching elements45and46are turned off.

Furthermore, in this fifth embodiment, the capacitances of the capacitors31and32of the converter circuit100aare set at a value that is larger than a threshold value at which the terminal voltage of the capacitor drops to zero when the output of the motor2is maximum, under the condition that the carrier cycle of the switch circuit is fixed to a constant cycle that is smaller than the cycle of the output voltage of the AC power supply. However, if the capacitances of the capacitors31and32cannot be set at a value that is equal to or larger than the threshold value, the carrier cycle of the switch circuit40may be adjusted so that the voltages of the capacitors31and32are not lowered to zero when the output of the motor2is maximum, under the state where the capacitances of the capacitors31and32are set at a possible largest value that is smaller than the threshold value. Also, in this case, the boosting operation of the converter circuit100acan be ensured in the whole driving area of the motor2.

Further, in the converter circuit100aof the fifth embodiment, the first and second switching elements45and46continuously perform switching operations while the motor2is being driven. However, the first and second switching elements45and46may stop the switching operations when the torque of the motor2satisfies a required value and a voltage whose amplitude is equal to or larger than the amplitude of the input voltage, i.e., the output voltage of the AC power supply1, is not needed as the output of the converter circuit100a, for example, when the load on the motor2is light or the rpm of the motor2is low.

In this case, in a low load area where boosting of the input voltage is not required, a boosting operation of the converter circuit100ais stopped and only the full-wave rectifier circuit20is operated, whereby the operation efficiency of the converter circuit can be improved. That is, power loss in the converter circuit can be reduced by avoiding that useless current flows in the first and second switching elements45and46and the first to fourth diodes21to24.

Whether or not the torque of the motor2satisfies a required torque can be judged from the power supplied to the motor2. To be specific, a constant reference power is set with respect to the power supplied to the motor and, when the power supplied to the motor21is equal to or larger than the constant reference voltage, it is judged that a power equal to or larger than the reference voltage cannot be supplied to the motor without boosting the converter circuit100a, and boosting of the converter circuit100ais started. In this case, excess and deficiency of the torque of the motor can be easily estimated, and a switch circuit that operates according to the motor torque can be easily realized.

The reference voltage to be used for judgement as to whether or not boosting of the converter circuit100ais required may be set so that a hysteresis of variations in the supply voltage is reflected in the judgement. That is, a first reference voltage for starting boosting and a second reference voltage for stopping boosting are used, and the first reference voltage is set to be larger than the second reference voltage. Thereby, it is possible to make the converter circuit100aperform a stable operation.

Further, the voltage supplied to the motor2can be detected from the state of the load connected to the motor2. However, the supply voltage to the motor2may be detected from the voltage and current inputted to the motor2, or the voltage and current inputted to the inverter circuit50, or the voltage and current inputted to the converter circuit100a.

Further, in order to judge whether or not the torque of the motor2satisfies a required torque, a difference between a command rpm to the motor2and the actual rpm may be used. In this method, when control of the inverter circuit50is carried out to adjust the amplitude of the current or voltage to be supplied to the motor so that a difference between the required rpm and the actual rpm of the motor2is minimized, since the amplitude of the output voltage of the inverter circuit50peaks out if the motor is short of torque, a difference between the command rpm and the actual rpm increases, and the difference is never reduced. In this case, excess and deficiency of the torque of the motor can be accurately detected, whereby the switch circuit can be correctly operated according to the motor torque.

Furthermore, whether or not the torque of the motor2satisfies a required torque may be judged from the amplitude of the current supplied to the motor2. In this case, when a permanent magnet motor or the like is employed as the motor2, the inverter circuit50sends a current to the motor2to cancel the magnetic flux if the input voltage to the inverter circuit50is insufficient, thereby to output torque. More specifically, when the amount of current supplied to the motor2is equal to or larger than a constant reference current, the converter circuit100astarts boosting. In this case, a switch circuit that operates according to the motor torque can be easily realized.

Further, the reference current to be used for judging whether or not boosting of the converter circuit100ashould be carried out may be set so that a hysteresis of variations in the supply voltage is reflected in the judgement. That is, a first reference current for starting boosting and a second reference current for stopping boosting are employed, and the first reference current is set to be larger than the second reference current. Thereby, it is possible to make the converter circuit100aperform a more stable operation.

Sixth Embodiment

FIG. 6is a diagram for explaining a motor driving apparatus according to a sixth embodiment of the present invention.

The motor driving apparatus201is provided with a converter circuit100bthat shares a driving power supply with the inverter circuit50, instead of the converter circuit100aof the motor driving apparatus200of the fifth embodiment.

That is, the inverter circuit50of the motor driving apparatus201is identical to that of the fifth embodiment. The converter circuit100bincludes, like the converter circuit100aof the fifth embodiment, a rectifier circuit20for rectifying the output voltage of the AC power supply1, a capacitor circuit30for smoothing the output of the rectifier circuit20, and a switch circuit40cfor alternately charging capacitors31and32, which are components of the capacitor circuit30and which are connected in series, with the output voltage of the AC power supply1.

The switch circuit40cincludes, in addition to the elements41to46constituting the switch circuit40aof the fifth embodiment, a diode81and a capacitor84which are connected in series between the plus terminal of the DC power supply80for driving the switching elements51to56of the inverter circuit50, and the emitter of the second switching element46; and a diode82and a capacitor83which are connected in series between the connection node of the elements81and84and the connection node of the first and second switching elements45and46.

A power supply circuit for driving the second switching element46comprises the driving power supply80of the inverter circuit50, the diode81having a cathode connected to the plus terminal of the power supply80, and the capacitor84connected between the anode of the diode81and the emitter of the second switching element46. Further, a power supply circuit for driving the first switching element45comprises the power supply circuit for driving the second switching element46, the diode82having a cathode connected to the anode of the diode81, and the capacitor83connected between the anode of the diode82and the connection node10eof the switching elements45and46.

Next, the operation of the motor driving apparatus201will be described.

In the motor driving apparatus201according to the sixth embodiment, the fundamental operation of the converter circuit100bis identical to that of the converter circuit100aaccording to the fifth embodiment, and the inverter circuit50operates in the same manner as described for the fifth embodiment.

Therefore, only the operation of the power supply circuit for driving the first switching element45of the converter circuit100band the operation of the power supply circuit for driving the second switching element46will be described hereinafter.

When the voltage at the connection node of the emitter of the second switching element46and the anodes of the second and fourth diodes42and44becomes equal to the voltage at the output terminal b2of the converter circuit100b, a current flows from the driving power supply80of the inverter circuit50through the diode81to the capacitor84, whereby the capacitor84is charged. The second switching element46is driven by a terminal voltage that is generated by the charging of the capacitor84. That is, the terminal voltage of the capacitor84is applied between the gate and emitter of the switching element46according to the open-close control signal Cs.

On the other hand, when the voltage at the connection node10eof the first and second switching elements45and46becomes equal to the voltage at the output terminal b2of the converter circuit100b, a current flows from the driving power supply80of the inverter circuit50through the diodes81and82to the capacitor83, whereby the capacitor83is charged. When the second switching element46is turned on and both the ends thereof are at the same voltage, a current flows from the capacitor84through the diode82to the capacitor83, whereby the capacitor83is charged. The first switching element45is driven by a terminal voltage that is generated by the charging of the capacitor83. That is, the terminal voltage of the capacitor83is applied between the gate and emitter of the switching element45according to the open-close control signal Cs.

As described above, according to the sixth embodiment, FET elements or the like which are able to perform electrical switching are used as the first and second switching elements45and46, and the driving power supply for the switching elements45and46is created from the power supply for driving the inverter circuit50. Therefore, it becomes unnecessary to specially prepare a power supply for driving the first and second switching elements45and46, whereby the number of circuit components can be significantly reduced, resulting in reductions in circuit space and cost.

While in the fifth and sixth embodiments the carrier cycle for turning on and off the first and second switching elements45and46is constant, the carrier cycle may be varied according to the load on the motor2. That is, when the motor load is not so heavy, the switching loss can be reduced by increasing the carrier cycle. At this time, the carrier cycle is not necessarily varied linearly, but several cycles may be changed in stages.

Further, the carrier cycle for turning the first and second switching elements45and46on and off may be equal to the carrier cycle for turning switching of the inverter circuit50on and off. Thereby, the frequency of the harmonic current generated by the motor driving apparatus200is unified, and the number of noise filters to be provided at the input side is reduced to one, resulting in significant reduction in cost.

Furthermore, the first and second switching elements45and46may perform switching so as to reduce the harmonic component of the current inputted to the converter circuit100b. To be specific, the switching elements45and46may perform switching by adjusting the phase obtained from the timing of switching of the inverter circuit50. The harmonic current that appears at the input side of the converter circuit100bis detected, and the first and second switching elements45and46may perform switching so as to cancel the harmonic current.

Thereby, the harmonic current is reduced, and the size of the noise filter to be provided at the input side can be reduced, or the noise filter can be dispensed with.

Further, the diode as a component of the rectifier circuit20of the converter circuit100bmay be implemented by an element having an inverse recovery time as short as that of the diode as a component of the converter circuit100b. In this case, it is possible to reduce the loss at commutation in the rectifier circuit20in which the current is cut off at every carrier cycle of the first and second switching elements45and46, whereby efficiency of the circuit operation is enhanced.

Seventh Embodiment

FIG. 7is a diagram for explaining a motor driving apparatus according to a seventh embodiment of the present invention.

The motor driving apparatus202according to the seventh embodiment is provided with a converter circuit100bwhich is obtained by adding a capacitor57for charging a regenerative current from the motor2at the output side of the converter circuit100aof the motor driving apparatus200of the fifth embodiment. The components of the motor driving apparatus202other than the converter circuit100care identical to those of the motor driving apparatus200of the fifth embodiment.

To be specific, the converter circuit100cincludes, like the converter circuit100aof the fifth embodiment, a rectifier circuit20for rectifying the output voltage of the AC power supply1, a capacitor circuit30for smoothing the output of the rectifier circuit20, and a switch circuit40for alternately charging two capacitors31and32which are components of the capacitor circuit30and are connected in series. In the converter circuit100c, the capacitor57is connected in parallel to the two capacitors31and32connected in series, between the output terminals b1and b2of the converter circuit100c.

The capacitance of the capacitor57may be set to a value at which the inverter circuit is prevented from being damaged by the motor regenerative current. For example, when the motor driving apparatus is one for controlling a motor of a compressor that is used in a home-use air conditioner, the capacitance of the capacitor57is about 1 μF to 50 μF. This capacitance is a minimum threshold value which is obtained from the capacitance of the inductance of the motor, the maximum variation allowed for the inverter input voltage, and the maximum value of the current applied to the motor.

That is, the energy possessed by the motor when the maximum current is applied to the motor can be obtained from the capacitance of the inductance. Then, the capacitance of the capacitor is determined on the basis of the extent to which an increase in the terminal voltage of the capacitor, which occurs when the energy is applied to the capacitor as a motor regenerative current, is allowed.

Next, the operation of the motor driving apparatus202will be described.

In the motor driving apparatus202according to the seventh embodiment, since the rectifier circuit20, the capacitor circuit30, the switch circuit40, and the inverter circuit50are operated in the same manner as described for the fifth embodiment, only the operation which is different from those mentioned for the fifth embodiment will be described hereinafter.

When the motor2is stopped or the switching operation of the inverter circuit50is stopped, the current that flows in the motor2is regenerated at the input end of the inverter circuit50. When this regenerative current is large, the voltage at the input end of the inverter circuit50becomes excessively large, whereby the motor driving apparatus, especially the inverter circuit50, might be damaged.

In the motor driving apparatus202according to the seventh embodiment, however, since the capacitor57is added at the output end of the converter circuit100cas shown inFIG. 7, the regenerative current from the motor2is charged to the capacitor57when the motor2is stopped, thereby minimizing increase in the voltage at the input end of the inverter circuit50due to the regenerative current.

Thereby, the elements of the inverter circuit50are prevented from being destroyed by the motor regenerative current that occurs when the motor is stopped, resulting in a more safe motor driving apparatus.

As described above, the motor driving apparatus202of the seventh embodiment is provided with the converter circuit100chaving the capacitor57, which is added between the output terminals b1and b2and which charges the regenerative current from the motor2, in addition to the rectifier circuit20, the switch circuit40, and the capacitor circuit30which constitute the converter circuit100aof the fifth embodiment. Therefore, in addition to the effects of the fifth embodiment, the elements of the inverter circuit50are prevented from being destroyed by the regenerative current even when the motor2is suddenly stopped, whereby reliability of the motor driving apparatus is improved.

The switch circuit comprising the first to fourth diodes41to44and the first and second switching elements45and46, which swift circuit is included in the converter circuit according to any of the fifth to seventh embodiments, may be modularized. In this case, the motor driving apparatus that does not need boosting can be implemented by only removing the module. In other words, the circuit substrate can be shared by the motor driving apparatus that does not need boosting of the power supply voltage and the motor driving apparatus that needs boosting of the power supply voltage, resulting in an improved design efficiency.

Further, the modularized switch circuit may be supplied with a driving signal from the driving unit of the inverter circuit50. In this case, a driving unit for driving the module as the switch circuit is dispensed with, resulting in a reduction in cost of the motor driving apparatus.

Eighth Embodiment

FIG. 8is a diagram for explaining a motor driving apparatus according to an eighth embodiment of the present invention.

The motor driving apparatus203according to the eighth embodiment is provided with a converter circuit100dwhich is obtained by adding a reactor58to the input end of the converter circuit100aof the motor driving apparatus200according to the fifth embodiment. The components of the motor driving apparatus203other than the converter circuit100dare identical to those of the motor driving apparatus200of the fifth embodiment.

To be specific, the converter circuit100dincludes, like the converter circuit100aof the fifth embodiment, a rectifier circuit20for rectifying the output voltage of the AC power supply1, a capacitor circuit30for smoothing the output of the rectifier circuit20, and a switch circuit40for alternately charging two capacitors31and32which are components of the capacitor circuit30and are connected in series. The converter circuit100dincludes the reactor58which is connected between the connection node10aof the rectifier circuit20and the input terminal a1to which the output of the AC power supply1is applied.

The capacitance of the reactor58may be set to a value at which switching current noise that occurs with the switching operation of the inverter circuit is removed, and the waveform of the output current of the AC power supply is not distorted. For example, when the motor driving apparatus is one for driving a motor of a compressor that is used in a home-use air conditioner, the capacitance of the reactor58is about 0.1 mH to 1.0 mH. This value depends on the carrier frequency of the converter circuit100d, i.e., the on-off repetition cycle of the switching element, and is determined so as to reduce harmonics of the carrier component.

Next, the operation of the motor driving apparatus203will be described.

In the motor driving apparatus203according to the eighth embodiment, the rectifier circuit20, the capacitor circuit30, the switch circuit40, and the inverter circuit50are operated in the same manner as described for the fifth embodiment, and therefore, only the operation which is different from those mentioned for the fifth embodiment will be described hereinafter.

The output current of the AC power supply1is influenced by the switching operation of the converter circuit100d, and the switching current is superposed as noise.

In the motor driving apparatus203, as shown inFIG. 8, the noise generated in the converter circuit100dis cut off by the reactor58that is inserted between the AC power supply1and the converter circuit100d, whereby the switching noise superposed on the output current of the AC power supply1is reduced. Thereby, the waveform of the output current of the AC power supply1is prevented from being distorted, and the power factor of the input current is improved.

As described above, the motor driving apparatus203according to the eighth embodiment is provided with the converter circuit100dincluding the reactor58which is inserted between the input end of the rectifier circuit20and the AC power supply1, and cuts off the noise generated in the switch circuit40, in addition to the rectifier circuit20, the switch circuit40, and the capacitor circuit30which constitute the converter circuit100aof the fifth embodiment. Therefore, in addition to the effects of the fifth embodiment, the switching noise superposed on the output of the AC power supply1can be reduced, thereby increasing the power factor of the input current, and suppressing occurrence of harmonic current.

While in this eighth embodiment the switching elements45and46, which are components of the switch circuit40of the converter circuit100d, complementary perform an on-off operation, the on periods of the first and second switching elements45and46may be slightly overlapped. In this case, the output voltage of the converter circuit can be boosted to a voltage that is twice or more than the power supply voltage, whereby a motor that needs a voltage that is twice or more than the power supply voltage can also be driven.

Further, in the motor driving apparatus of the eighth embodiment, the inverter circuit50is controlled so that a driving current having a frequency according to the rpm of the motor is applied to the motor. However, the motor driving apparatus may control the current supplied from the inverter circuit50to the motor2so as to improve the power factor of the current inputted to the converter circuit100d. Thereby, the power factor of the input current to the converter circuit100dis improved, and the harmonic current is reduced. Further, the motor driving apparatus of the eighth embodiment may control on-off of the first and second switching elements45and46so as to improve the power factor of the current inputted to the converter circuit100d. Thereby, the power factor of the input current can be improved, and the harmonic current can be reduced.

The motor driving apparatus according to the eighth embodiment may be provided with the switch circuit40aof the converter circuit101according to the second embodiment, instead of the switch circuit40as a component of the converter circuit100d. Also in this case, the same effects as described for the eighth embodiment can be achieved.

Furthermore, the motor driving apparatus according to the seventh embodiment is provided with the capacitor at the input end of the converter circuit, and the motor driving apparatus according to the eighth embodiment is provided with the reactor between the converter circuit and the AC power supply. However, the motor driving apparatus may be provided with both of the capacitor and the reactor.

Ninth Embodiment

FIG. 9is a motor driving apparatus according to a ninth embodiment of the present invention.

The motor driving apparatus204according to the ninth embodiment receives a voltage supplied from the AC power supply1, and drives the motor2. The motor driving apparatus204includes a converter circuit102athat is able to output a non-negative voltage having an amplitude equal to or larger than the amplitude of the input voltage, and an inverter circuit50that converts the non-negative voltage outputted from the circuit into a three-phase AC voltage to be applied to the motor2.

The converter circuit102ais identical to the converter circuit102according to the third embodiment. That is, the converter circuit102aincludes a rectifier circuit20for rectifying the output voltage of the AC power supply1, a third capacitor33connected between the output ends b1and b2, a fourth capacitor34having an end connected to the output terminal b2, and a switch circuit40which connects the other end10eof the fourth capacitor34alternately to the input terminals a1and a2which are connected to the AC power supply so that charging of the third capacitor33and charging of the fourth capacitor34are alternately repeated at a cycle that is shorter than the cycle of the output voltage of the AC power supply1. In the switch circuit40of the converter circuit102a, the respective switching elements45and46are turned on and off according to an open-close control signal Cs as in the third embodiment. Accordingly, also in the converter circuit102aof the motor driving apparatus204according to the ninth embodiment, as in the third embodiment, by turning the switching elements45and46on and off, the output voltage of the AC power supply1is applied to the fourth capacitor34while a sum voltage of the terminal voltage of the fourth capacitor34and the output voltage of AC power supply1is applied to the third capacitor33, at a cycle that is shorter than the cycle of the AC power supply1.

Further, in the motor driving apparatus204according to the ninth embodiment, only one capacitor33that is a component of the capacitor circuit30ais connected between the output terminals b1and b2of the converter circuit102a. Accordingly, in the converter circuit102a, the capacitances of the capacitors33and34which are components of the capacitor circuit30aare further reduced as compared with those in the circuit structure in which plural capacitors are connected in series between the output terminals b1and b2. For example, in the motor driving apparatus204, when the carrier frequency of the switch circuit40is set at 10 kHz and the motor is driven with a motor load corresponding to a motor driving current of about 15 A as in the fifth embodiment, the capacitance required of the third capacitor33of the capacitor circuit30ais about 2 μF, and the capacitance required of the fourth capacitor34of the capacitor circuit30is about 1 μF.

The inverter circuit50is identical to the inverter circuit50according to the fifth embodiment.

As described above, the motor driving apparatus204according to the ninth embodiment is provided with the converter circuit102athat is identical to the converter circuit102according to the third embodiment, instead of the converter circuit100aof the motor driving apparatus200according to the fifth embodiment. Therefore, as in the third embodiment, the number of charging per unit time of the capacitors33and34becomes larger than the frequency of polarity inversion of the AC power supply, and the capacitances of the capacitors33and34can be reduced as compared with the case where the both capacitors are alternately charged for every polarity inversion of the AC power supply1, whereby the size of the motor driving apparatus equipped with the converter circuit can be reduced.

While in this ninth embodiment the converter circuit102ais identical to the converter circuit102according to the third embodiment, the converter circuit102amay be identical to the converter circuit103according to the fourth embodiment. Also, in this case, the same effects as those of the motor driving apparatus according to the ninth embodiment can be achieved.

Further, the motor driving apparatus according to the ninth embodiment is not restricted to that mentioned above. The motor driving apparatus according to the ninth embodiment may be provided with a capacitor for charging a regenerative current from the motor, at the output end of the converter circuit102a, like the motor driving apparatus202of the seventh embodiment, or the motor driving apparatus may be provided with a reactor at the input end of the converter circuit102a, like the motor driving apparatus203according to the eighth embodiment.

Tenth Embodiment

FIG. 10is a block diagram for explaining an air conditioner according to a tenth embodiment of the present invention.

An air conditioner250according to the tenth embodiment has an indoor unit255and an outdoor unit256, and performs cooling and heating.

The air conditioner250is provided with a compressor250afor circulating a refrigerant between the indoor unit255and the outdoor unit256, and a motor driving unit250bfor driving a motor (not shown) of the compressor250awith a voltage supplied from an AC power supply1. InFIG. 10, the AC power supply1, the motor of the compressor250a, and a motor driving apparatus250bare identical to the AC power supply1, the motor2, and the motor driving apparatus200according to the fifth embodiment, respectively.

Further, the air conditioner250has a four-way valve254, a throttle253, an indoor heat exchanger251, and an outdoor heat exchanger252. The indoor heat exchanger251is a component of the indoor unit255, while the throttle253, the outdoor heat exchanger252, the compressor250a, the four-way valve254, and the motor driving apparatus250bare components of the outdoor unit256.

The indoor heat exchanger251has an air blower251afor increasing the efficiency of heat exchange, and a temperature sensor251bfor measuring the temperature of the heat exchanger251or the ambient temperature thereof. The outdoor heat exchanger252has an air blower252afor increasing the efficiency of heat exchange, and a temperature sensor252bfor measuring the temperature of the heat exchanger252or the ambient temperature thereof.

In this tenth embodiment, the compressor250aand the four-way valve254are placed in the refrigerant path between the indoor heat exchanger251and the outdoor heat exchanger252. That is, in this air conditioner250, the four-way valve254selects either of the following two states: the state where the refrigerant flows in the direction of arrow A, the refrigerant that has passed through the outdoor heat exchanger252is sucked into the linear compressor250a, and the refrigerant discharged from the linear compressor250ais supplied to the indoor heat exchanger251; and the state where the refrigerant flows in the direction of arrow B, the refrigerant that has passed through the indoor heat exchanger251is sucked into the linear compressor250a, and the refrigerant discharged from the linear compressor250ais supplied to the outdoor heat exchanger252.

Further, the throttle253has both the function of reducing the flow rate of the circulating refrigerant, and the function as a valve for automatically controlling the flow rate of the refrigerant. That is, under the state where the refrigerant is circulating in the refrigerant circulation path, the throttle253reduces the flow rate of the fluid refrigerant outputted from the condenser to the evaporator to expand the fluid refrigerant, and supplies a proper amount of refrigerant that is required for the evaporator.

The indoor heat exchanger251operates as the condenser during heating, and as the evaporator during cooling. The outdoor heat exchanger252operates as the evaporator during heating, and as the condenser during cooling. In the condenser, the high-temperature and high-pressure refrigerant gradually liquefies while losing heat to the air that is blown into the condenser, resulting in a high-pressure fluid refrigerant in the vicinity of the outlet of the condenser. This is equivalent to where the refrigerant liquefies while radiating heat into the air. Further, the fluid refrigerant whose temperature and pressure are reduced by the throttle253flows into the evaporator. When the indoor air is blown into the evaporator under this state, the fluid refrigerant takes a great amount of heat from the air and evaporates, resulting in a low-temperature and low-pressure gas refrigerant. The air which has lost a great amount of heat in the evaporator is discharged as cool air from the blowoff port of the air conditioner.

Next, the operation of the air conditioner250will be described.

In the air conditioner250, when an output voltage of the AC power supply1is applied to the motor driving apparatus250b, the output voltage of the AC power supply1is rectified and boosted by the converter circuit as in the motor driving apparatus200of the fifth embodiment, and further, the output of the converter circuit100ais converted into a three-phase motor driving voltage by the inverter circuit50(refer toFIG. 5).

When the three-phase motor driving voltage is applied to a motor (not shown) of the compressor250a, the compressor250ais driven and thereby the refrigerant circulates in the refrigerant circulation path, and heat exchange is carried out in the heat exchanger251of the indoor unit255and the heat exchanger252of the outdoor unit256. That is, in the air conditioner250, a well-known heat pump cycle is created in the refrigerant circulation path by circulating the refrigerant that is sealed in the circulation path, by using the compressor250a. Thereby, heating or cooling is carried out.

For example, when the air conditioner250performs heating, the four-way valve254is set by a user operation so that the refrigerant flows in the direction of arrow A. In this case, the indoor heat exchanger251operates as a condenser, and discharges heat by circulation of the refrigerant in the refrigerant circulation path. Thereby, the room is heated.

Conversely, when the air conditioner250performs cooling, the four-way valve254is set by a user operation so that the refrigerant flows in the direction of arrow B. In this case, the indoor heat exchanger251operates as an evaporator, and absorbs heat from the ambient air by circulation of the refrigerant in the refrigerant circulation path. Thereby, the room is cooled.

In the air conditioner250, a command rpm is determined on the basis of the target temperature that is set on the air conditioner250, the actual room temperature and outdoor temperature, and the motor driving apparatus250bcontrols the rpm of the motor of the compressor250aon the basis of the command rpm. Thereby, comfortable cooling or heating is carried out by the air conditioner250.

As described above, in the air conditioner250according to the tenth embodiment, the motor driving apparatus250bfor driving the motor as a power source of the compressor250ais provided with the converter circuit which includes the rectifier circuit for rectifying the output voltage of the AC power supply, and two capacitors connected in series for smoothing the output of the rectifier circuit. Further, the motor driving apparatus250bapplies the output voltage of the AC power supply1to both the capacitors alternately at a cycle that is shorter than the cycle of the output voltage of the AC power supply1. The output voltage of the converter circuit is converted into a three-phase AC voltage to be applied to the motor of the compressor250a. Therefore, as in the fifth embodiment, the capacitances of the capacitors constituting the converter circuit can be reduced, whereby the motor driving apparatus250bequipped with the converter circuit can be reduced in size and price, leading to reductions in size and price of the air conditioner250.

Eleventh Embodiment

FIG. 11is a block diagram for explaining a refrigerator according to an eleventh embodiment of the present invention.

A refrigerator260according to this eleventh embodiment comprises a compressor260a, a motor driving apparatus260b, a condenser261, an evaporator262, and a throttle263.

The compressor260a, the condenser261, the throttle263, and the evaporator262form a refrigerant circulation path. The motor driving apparatus260bhas an input connected to an AC power supply1, and drives a motor (not shown) as a drive source of the compressor260a. The power supply1, the motor of the compressor260a, and the motor driving apparatus260bare identical to AC the power supply1, the motor2, and the motor driving apparatus200according to the fifth embodiment, respectively.

The throttle263reduces the flow rate of the fluid refrigerant outputted from the condenser261to expand the fluid refrigerant under the state where the refrigerant is circulating in the refrigerant circulation path, and supplies a proper amount of refrigerant that is required for the evaporator262, like the throttle253of the air conditioner250according to the tenth embodiment.

The condenser261condenses the high-temperature and high-pressure refrigerant gas that flows therein, and discharges the heat of the refrigerant to the outside air. The refrigerant gas sent into the condenser261gradually liquefies while losing heat to the outside air, resulting in a high-pressure fluid refrigerant in the vicinity of the outlet of the condenser.

The evaporator262evaporates the low-temperature fluid refrigerant to cool the inside of the refrigerator260. The evaporator262has an air blower262afor increasing efficiency of heat exchange, and a temperature sensor262bfor detecting the temperature inside the refrigerator.

Next, the operation of the refrigerator260will be described.

In the refrigerator260according to the eleventh embodiment, when an output voltage of the AC power supply1is input to the motor driving apparatus260b, the output voltage of the AC power supply1is rectified and boosted by the converter circuit100aas in the motor driving apparatus200according to the fifth embodiment, and further, the output of the converter circuit100ais converted into a three-phase motor driving voltage by the inverter circuit50(refer toFIG. 5).

When the three-phase motor driving voltage is applied to a motor (not shown) of the compressor260a, the compressor260ais driven and thereby the refrigerant circulates in the direction of arrow C in the refrigerant circulation path, whereby heat exchange is carried out between the condenser261and the evaporator262. Thus, the inside of the refrigerator260is cooled.

That is, the flow rate of the refrigerant, which is liquefied in the condenser261, is reduced by the throttle263, and thereby the refrigerant expands, resulting in a low-temperature fluid refrigerant. When the low-temperature fluid refrigerant is sent into the evaporator262, it is evaporated in the evaporator262, whereby the inside of the refrigerator260is cooled. At this time, the air in the refrigerator260is compulsorily sent into the evaporator262by the air blower262a, and thereby heat exchange is efficiently carried out in the evaporator262.

As described above, in the refrigerator260according to the eleventh embodiment, the motor driving apparatus260bfor driving the motor as a power source of the compressor260ais provided with the converter circuit which includes the rectifier circuit for rectifying the output voltage of the AC power supply, and two capacitors connected in series for smoothing the output of the rectifier circuit. The motor driving apparatus260, and applies the output voltage of the AC power supply1to both the capacitors alternately at a cycle that is shorter than the cycle of the output voltage of the AC power supply1. The output voltage of the converter circuit is converted into a three-phase AC voltage to be applied to the motor of the compressor260a. Therefore, as in the fifth embodiment, the capacitances of the capacitors constituting the converter circuit can be reduced, whereby the motor driving apparatus260bequipped with the converter circuit can be reduced in size and price, leading to reductions in size and price of the refrigerator260.

Twelfth Embodiment

FIG. 12is a block diagram for explaining an electric washing machine according to a twelfth embodiment of the present invention.

A washing machine270according to the twelfth embodiment has a washing machine outer frame271, and an outer bath273is hung by a bar272in the outer frame271. A washing/dewatering bath274is rotatably placed in the outer frame273, and an agitation blade275is rotatably attached to the bottom of the washing/dewatering bath274.

A motor276for rotating the washing/dewatering bath274and the agitation blade275are placed in a space beneath the outer bath273in the outer frame271, and a motor driving apparatus277that is connected to an external AC power supply1and drives the motor276is attached to the outer frame271.

The AC power supply1, the motor276, and the motor driving apparatus277are identical to the AC power supply1, the motor2, and the motor driving apparatus200according to the fifth embodiment, respectively. A command signal indicating a command rpm according to a user operation is input to the motor driving apparatus277from a microcomputer (not shown) that controls the operation of the washing machine270.

Next, the operation of the washing machine270will be described.

In the washing machine270, when the user performs a predetermined operation, a command signal is output from the microcomputer to the motor driving apparatus277that receives a voltage from the AC power supply1. In the motor driving apparatus277, the output voltage of the AC power supply1is rectified and boosted by the converter circuit100aas in the motor driving apparatus200of the fifth embodiment, and further, the output voltage of the converter circuit100ais converted into a three-phase motor driving voltage by the inverter circuit50(refer toFIG. 5).

When the three-phase motor driving voltage is applied to the motor276, the agitation blade275or the washing/dewatering bath274is rotated by the motor276, and washing or dewatering of laundry such as clothes in the bath274is carried out.

As described above, in the washing machine270according to the twelfth embodiment, the motor driving apparatus277for driving the motor276as a power source is provided with the converter circuit which includes the rectifier circuit for rectifying the output voltage of the AC power supply1, and two capacitors connected in series for smoothing the output of the rectifier circuit. The motor driving apparatus277applies the output voltage of the AC power supply1to both the capacitors alternately at a cycle that is shorter than the cycle of the output voltage of the AC power supply1. The output voltage of the converter circuit is converted into a three-phase AC voltage to be applied to the motor276. Therefore, as in the fifth embodiment, the capacitances of the capacitors constituting the converter circuit can be reduced, whereby the motor driving apparatus277equipped with the converter circuit can be reduced in size and price, leading to reductions in size and price of the washing machine270.

Thirteenth Embodiment

FIG. 13is a block diagram for explaining an air blower according to a thirteenth embodiment of the present invention.

An air blower280according to the thirteenth embodiment is provided with a fan281, a motor282for rotating the fan281, and a motor driving apparatus283that is connected to an AC power supply1and drives the motor282.

The AC power supply1, the motor282, and the motor driving apparatus283are identical to the AC power supply1, the motor2, and the motor driving apparatus200according to the fifth embodiment, respectively, and a command signal indicating a command rpm according to a user operation is input to the motor driving apparatus283from a microcomputer (not shown) that controls the operation of the air blower280.

Next, the operation of the air blower280will be described.

In the air blower280, when the user performs a predetermined operation, a command signal is output from the microcomputer to the motor driving apparatus283that receives a voltage from the AC power supply1. Then, in the motor driving apparatus283, the output voltage of the AC power supply1is rectified and boosted by the converter circuit100a, and further, the output of the converter circuit100ais converted into a three-phase motor driving voltage by the inverter circuit50(refer toFIG. 5).

When the three-phase motor driving voltage is applied to the motor282, the motor282is driven and the fan281is rotated, whereby air blowing is carried out.

As described above, in the air blower280according to the thirteenth embodiment, the motor driving apparatus283for driving the motor282as a power source is provided with the converter circuit which includes the rectifier circuit for rectifying the output voltage of the AC power supply1, and two capacitors connected in series for smoothing the output of the rectifier circuit. The motor driving apparatus283applies the output voltage of the AC power supply1to both the capacitors alternately at a cycle that is shorter than the cycle of the output voltage of the AC power supply1. The output voltage of the converter circuit is converted into a three-phase AC voltage to be applied to the motor282. Therefore, as in the fifth embodiment, the capacitances of the capacitors constituting the converter circuit can be reduced, whereby the motor driving apparatus283equipped with the converter circuit can be reduced in size and price, leading to reductions in size and price of the air blower280.

Fourteenth Embodiment

FIG. 14is a block diagram for explaining an electric vacuum cleaner according to a fourteenth embodiment of the present invention.

A vacuum cleaner290according to the fourteenth embodiment is provided with a floor suction head297having an inlet at its bottom, a vacuum cleaner body290afor sucking air, and a dust suction hose having an end connected to the floor suction head297and the other end connected to the cleaner body290a.

The cleaner body290acomprises a dust collection chamber295having a front surface at which the other end of the dust suction hose296is opened, and an electric air blower291placed at the rear surface of the dust collecting chamber295.

The electric air blower291comprises a fan292placed opposite to the rear surface of the dust collection chamber295, a motor293for rotating the fan, and a motor driving apparatus294that is connected to an AC power supply1and drives the motor293. The air blower291performs air blowing so that suction of air is carried out by rotation of the fan292.

The AC power supply1, the motor293, and the motor driving apparatus294are identical to the AC power supply1, the motor2, and the motor driving apparatus200according to the fifth embodiment, respectively, and a command signal indicating a command rpm according to a user operation is input to the motor driving apparatus294from a microcomputer (not shown) that controls the operation of the air blower290.

Next, the operation of the vacuum cleaner290will be described.

In the vacuum cleaner290, when the user performs a predetermined operation, a command signal is output from the microcomputer to the motor driving apparatus294that receives a voltage from the AC power supply1. Then, the output voltage of the AC power supply1is rectified and boosted by the converter circuit100a, and further, the output of the converter circuit100ais converted into a three-phase motor driving voltage by the inverter circuit50(refer toFIG. 5).

When the three-phase motor driving voltage is applied to the motor293, the fan292is rotated by the motor293, and a suction force is generated in the cleaner body290a. The suction force generated in the cleaner body290aacts on the inlet (not shown) at the bottom of the floor suction head297through the hose296, and dust on the floor is sucked from the inlet of the floor suction head297to be collected into the dust collection chamber295of the cleaner body290a.

As described above, in the vacuum cleaner290according to the fourteenth embodiment, the motor driving apparatus294for driving the motor293as a power source is provided with the converter circuit which includes the rectifier circuit for rectifying the output voltage of the AC power supply1, and two capacitors connected in series for smoothing the output of the rectifier circuit. The motor driving apparatus294applies the output voltage of the AC power supply1to the both capacitors alternately at a cycle that is shorter than the cycle of the output voltage of the AC power supply1. The output voltage of the converter circuit is converted into a three-phase AC voltage to be applied to the motor293. Therefore, as in the fifth embodiment, the capacitances of the capacitors constituting the converter circuit can be reduced, whereby the motor driving apparatus294equipped with the converter circuit can be reduced in size and price, leading to reductions in size and price of the vacuum cleaner280.

Fifteenth Embodiment

FIG. 15is a block diagram for explaining a heat pump type hot-water supply unit according to a fifteenth embodiment of the present invention.

A heat pump type hot-water supply unit380according to the fifteenth embodiment includes a refrigeration cycle unit381afor heating supplied water to discharge hot water, a hot-water storage381bin which the hot water discharged from the refrigeration cycle unit381ais stored, and pipes386a,386b,387a, and387bconnecting the refrigeration cycle unit381aand the hot-water storage381b.

The refrigeration cycle unit381aincludes a compressor380a, an air-refrigerant heat exchanger382, a throttle383, and a water-refrigerant heat exchanger385, which constitute a refrigerant circulation path, and a motor driving apparatus380bthat receives a voltage from an AC power supply1and drives the motor of the compressor380a.

The AC power supply1, the motor of the compressor380a, and the motor driving apparatus380bare identical to the AC power supply1, the motor2, and the motor driving apparatus200according to the fifth embodiment, respectively.

The throttle383reduces the flow rate of the fluid refrigerant that is sent from the water-refrigerant heat exchanger385to the air-refrigerant heat exchanger382to expand the fluid refrigerant, like the throttle253of the air conditioner250of the tenth embodiment.

The water-refrigerant heat exchanger385is a condenser that heats up the water supplied to the refrigeration cycle unit381a, and has a temperature sensor385afor detecting the temperature of the heated water. The air-refrigerant heat exchanger382is an evaporator that absorbs heat from the ambient atmosphere. The air-refrigerant heat exchanger382has an air blower382afor increasing the efficiency of heat exchange, and a temperature sensor382bfor detecting the ambient temperature.

InFIG. 15, reference numeral384denotes a refrigerant pipe for circulating the refrigerant along the refrigerant circulation path that is formed by the compressor380a, the water-refrigerant heat exchanger385, the throttle383, and the air-refrigerant heat exchanger382. The refrigerant pipe284is connected to a defrost bypass pipe384afor supplying the refrigerant discharged from the linear compressor380ato the air-refrigerant heat exchanger382, bypassing the water-refrigerant heat exchanger385and the throttle383, and a defrost bypass valve384bis provided in a portion of the bypass pipe384a.

The hot-water storage381bhas a hot-water storage tank388for keeping water or hot water. A water supply pipe388cfor supplying water from the outside to the storage tank388is connected to a water intake port388c1of the storage tank388, and a hot-water supply pipe388dfor supplying hot-water from the storage tank388to a bathtub is connected to a hot-water discharge port388d1of the storage tank388. Further, a hot-water supply pipe389for supplying the hot water stored in the storage tank388to the outside is connected to a water intake/discharge port388aof the storage tank388.

The storage tank388and the water-refrigerant heat exchanger385of the refrigeration cycle unit381aare connected through pipes386a,386b,387a, and387b, and a water circulation path is formed between the storage tank388and the water-refrigerant heat exchanger385.

The water supply pipe386bis a pipe for supplying water from the storage tank388to the water-refrigerant heat exchanger385. An end of the water supply pipe386bis connected to a water discharge port388bof the storage tank388, while the other end of the water supply pipe386bis connected to a water intake side pipe387bof the water-refrigerant heat exchanger385through a joint387b1. Further, a discharge valve388b1for discharging the water or hot water stored in the storage tank388is fixed to an end of the water supply pipe386b. The water supply pipe386ais a pipe for returning the water from the water-refrigerant heat exchanger385to the storage tank388. An end of the water supply pipe386ais connected to the water intake/discharge port388aof the storage tank388, while the other end of the water supply pipe386ais connected to a discharge side pipe387aof the water-refrigerant heat exchanger385through a joint387a1.

A pump387for circulating the water in the water circulation path is provided in a portion of the water intake side pipe387bof the water-refrigerant heat exchanger385.

Further, in the hot-water supply unit380, a command rpm of the motor is determined on the basis of the operating state of the hot-water supply unit, that is, the target temperature of hot water which is set on the supply unit, the temperature of the water that is supplied from the hot-water storage381bto the water-refrigerant heat exchanger385aof refrigeration cycle unit381a, and the outdoor temperature. The motor driving apparatus380bdetermines a motor output required for the motor of the compressor380aon the basis of the command rpm.

Next, the operation of the hot-water supply unit380will be described.

In the hot-wafer supply unit380, when the output voltage of the AC power supply1is input to the motor driving apparatus380b, the output voltage of the AC power supply1is rectified and boosted by the converter circuit100, further, the output of the converter circuit100ais converted into a three-phase motor driving voltage by the inverter circuit50, as in the motor driving apparatus200according to the fifth embodiment (refer toFIG. 5).

When the three-phase motor driving voltage is applied to the motor of the compressor380a, the compressor380ais driven, whereby the high-temperature refrigerant compressed by the compressor380acirculates in the direction of arrow E, that is, the refrigerant passes through the refrigerant pipe384and is supplied to the water-refrigerant heat exchanger385. Further, when the pump387in the water circulation path is driven, water is supplied from the storage tank388to the water-refrigerant heat exchanger385.

In the water-refrigerant heat exchanger385, heat exchange is carried out between the refrigerant and the water that is supplied from the storage tank388, whereby heat moves from the refrigerant to the water. That is, the supplied water is heated, and the heated water is supplied to the storage tank388. At this time, the temperature of the heated water is observed by the condensation temperature sensor385a.

Further, in the water-refrigerant heat exchanger385, the refrigerant is condensed by the above-mentioned heat exchange, the flow rate of the condensed fluid refrigerant is reduced by the throttle383to expand the refrigerant, and the refrigerant is sent to the air-refrigerant heat exchanger382. In the hot-water supply unit380, the air-refrigerant heat exchanger382serves as an evaporator. That is, the air-refrigerant heat exchanger382absorbs heat from the outside air that is sent by the air blower382bto evaporate the low-temperature fluid refrigerant. At this time, the temperature of the ambient atmosphere of the air-refrigerant heat exchanger382is observed by the temperature sensor382b.

Further, in the refrigeration cycle unit381a, when the air-refrigerant heat exchanger382is frosted, the defrost bypass valve384bis opened, and the high-temperature refrigerant is supplied to the air-refrigerant heat exchanger382through the defrost bypass line384a. Thereby, the air-refrigerant heat exchanger382is defrosted.

On the other hand, the hot water is supplied from the water-refrigerant heat exchanger385of the refrigeration cycle unit381ato the hot-water storage81bthrough the pipes87aand86a, and the supplied hot water is stored in the storage tank388. The hot water in the storage tank388is supplied to the outside through the hot-water supply pipe389as required. Especially when the hot water is supplied to a bathtub, the hot water in the storage tank388is supplied to the bathtub through a hot-water supply pipe388dfor the bathtub.

Further, when the amount of water or hot water stored in the storage tank388becomes lower than a predetermined amount, water is supplied from the outside through the water supply pipe388c.

As described above, in the heat pump type hot-water supply unit380according to the fifteenth embodiment, the motor driving apparatus380bfor driving the motor as a power source of the compressor380ais provided with the converter circuit which includes the rectifier circuit for rectifying the output voltage of the AC power supply1, and two capacitors connected in series for smoothing the output of the rectifier circuit. The motor driving apparatus380bapplies the output voltage of the AC power supply1to both the capacitors alternately at a cycle that is shorter than the cycle of the output voltage of the AC power supply1. The output voltage of the converter circuit is converted into a three-phase AC voltage to be applied to the compressor380a. Therefore, as in the fifth embodiment, the capacitances of the capacitors constituting the converter circuit can be reduced, whereby the motor driving apparatus380bequipped with the converter circuit can be reduced in size and price, leading to reductions in size and price of the heat pump type hot-water supply unit380.

While in the tenth to fifteenth embodiments, the motor driving apparatus for driving the motor as a power supply is identical to the motor driving apparatus200according to the fifth embodiment, the motor driving apparatus may be identical to any of the motor driving apparatuses according to the sixth to ninth embodiments.

According to the present invention, a converter circuit that receives a voltage from an AC power supply is provided with a switch circuit which applies an output voltage of the AC power supply alternately to two capacitors connected in series, to an output terminal of the converter circuit, at a cycle that is shorter than a polarity inversion cycle of the output voltage. Therefore, it is possible to significantly reduce the capacitances of the capacitors which are required for generating a voltage that is twice as high as an input voltage.