Power regenerative converter

There are provided a smoothing capacitor (71) for storing an induced electromotive force generated by a three-phase induction motor (5), a regenerative transistor (81 to 86) for switching a terminal voltage of the smoothing capacitor to carry out a power regenerating operation over a three-phase AC power supply (3), a line voltage detecting portion (6) for detecting a line voltage of the three-phase AC power supply, a fundamental waveform generating portion (10) for generating, from a signal output from the line voltage detecting portion, a fundamental waveform defined to be a line voltage waveform of the three-phase AC power supply in which a source voltage distortion component is not mixed, a base driving signal creating portion (7) for creating a base driving signal to be used for an ON/OFF control of the regenerative transistor based on a signal output from the fundamental waveform generating portion, and a base driving signal output portion (9) for outputting the base driving signal.

TECHNICAL FIELD

The present invention relates to a power regenerative converter.

BACKGROUND ART

A power regenerative converter is disposed between an inverter device for variable speed controlling a three-phase induction motor and a three-phase AC power supply and a reactor is provided between the three-phase AC power supply and the power regenerative converter. The power regenerative converter regenerates, in a three-phase AC power supply, an induced electromotive force generated in a speed reduction of a three-phase induction motor (hereinafter referred to as a motor). When a speed of the motor is reduced, a current obtained by the induced electromotive force thus generated flows into both terminals of a smoothing capacitor in the power regenerative converter. When a regenerative transistor of the power regenerative converter is turned ON, a regenerative current flows from the smoothing capacitor into a power supply.

Thus, a difference between a voltage of the smoothing capacitor of the power regenerative converter and a source voltage is utilized to cause a current to flow with a current limitation by the reactor. If a phase of the regenerative transistor to be turned ON is taken erroneously, therefore, the difference in a voltage is increased and a large current suddenly flows so that an apparatus might be stopped or broken down. For this reason, a DC bus voltage value is compared with a regeneration starting voltage value, and a regenerating operation is started when the DC bus voltage value is higher than the regeneration starting voltage. For a command to be given to each regenerative transistor during the regenerating operation, moreover, an ON/OFF signal of the regenerative transistor which is generated based on a phase of a detected three-phase line voltage is used to carry out the power regenerating operation (for example, see Patent Document 1).

DISCLOSURE OF THE INVENTION

Problems to be Solved

However, a conventional power regenerative converter detects a line voltage phase through zero cross point monitoring of a line voltage. In some cases in which a source voltage distortion is mixed into the three-phase AC power supply, therefore, the detection of the line voltage phase is disordered. Moreover, an ON/OFF control signal of the regenerative transistor is created from a phase detecting signal. For this reason, a switching ON/OFF timing is disordered so that an excessively large current flows in some cases. There is a possibility that a system might be stopped due to a breakage of a power supply or an apparatus.

In order to solve the problems, it is an object of the invention to obtain a power regenerative converter capable of carrying out a stable regenerating operation also in the case in which a source voltage distortion is mixed into a three-phase AC power supply.

Means for Solving the Problems

The invention provides a power regenerative converter including a smoothing capacitor for storing an induced electromotive force generated by a three-phase induction motor, a regenerative transistor for switching a terminal voltage of the smoothing capacitor to carry out a power regenerating operation over a three-phase AC power supply, a line voltage detecting portion for detecting a line voltage of the three-phase AC power supply, a fundamental waveform generating portion for generating, from a signal output from the line voltage detecting portion, a fundamental waveform defined to be a line voltage waveform of the three-phase AC power supply in which a source voltage distortion component is not mixed, a base driving signal creating portion for creating a base driving signal to be used for an ON/OFF control of the regenerative transistor based on a signal output from the fundamental waveform generating portion, and a base driving signal output portion for outputting the base driving signal.

Advantage of the Invention

According to the invention, the voltage phase can be accurately detected from the fundamental waveform of the source voltage. Therefore, it is possible to generate the ON/OFF control signal of the regenerative transistor without an influence of a distortion component. Consequently, it is possible to implement a power regenerative converter which can prevent an apparatus or a power supply from being broken down due to an overvoltage or an overcurrent, thereby hindering a system from being stopped.

EXPLANATION OF THE DESIGNATION

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

FIG. 1is a block diagram showing a structure of a power regenerative converter according to the embodiment. The structure will be described below. A power regenerative converter1is disposed between a three-phase AC power supply3for generating AC powers having three phases (R, S and T phases) and an inverter device4for variable speed controlling a motor5. The power regenerative converter1includes AC power terminals51,52,53,54,55and56. The AC power terminals51,52and53are connected to respective power terminals of the three-phase AC power supply3through a reactor2, and the AC power terminals54,55and56are connected to the respective power terminals of the three-phase AC power supply3without the reactor2. Moreover, DC power terminals57and58of the power regenerative converter1are connected to DC buses in the inverter device4. DC buses59and60connected to the DC power terminals57and58are disposed in the power regenerative converter1, and a smoothing capacitor71is connected between the DC buses59and60. Both terminals of the smoothing capacitor71are connected to a PN bus voltage detecting portion8for detecting voltages on both terminals of the smoothing capacitor71.

A regenerating portion70including regenerative transistors81,82,83,84,85and86and diodes91,92,93,94,95and96is provided between the DC buses59and60in the power regenerative converter1, and three sets of the regenerative transistors81and82, the regenerative transistors83and84and the regenerative transistors85and86which are connected in series are connected in parallel between the DC buses59and60. More specifically, collector terminals of the regenerative transistors81,83and85constituting an upper arm are connected to the DC bus59, and emitter terminals of the regenerative transistors82,84and86constituting a lower arm are connected to the DC bus60. An emitter terminal of the regenerative transistor81and a collector terminal of the regenerative transistor82are, connected to the AC power terminal51in common. Similarly, an emitter terminal of the regenerative transistor83and a collector terminal of the regenerative transistor84are connected to the AC power terminal52, and an emitter terminal of the regenerative transistor85and a collector terminal of the regenerative transistor86are connected to the AC power terminal53. The diodes91,92,93,94,95and96are connected to the regenerative transistor81,82,83,84,85and86in parallel, respectively. More specifically, an anode terminal of the diode is connected to the emitter terminal of the regenerative transistor, and a cathode terminal of the diode is connected to the collector terminal of the regenerative transistor.

The AC power terminals54,55and56are connected to a line voltage detecting portion6for detecting a source voltage waveform among the three phases of the three-phase AC power supply3, and an output terminal of the line voltage detecting portion6is connected to a fundamental waveform generating portion10for generating a fundamental waveform defined to be a line voltage waveform of the three-phase AC power supply into which a distortion component is not mixed. An output terminal of the fundamental waveform generating portion10is connected to a base driving signal creating portion7for creating a base driving signal to carry out an ON/OFF control of the regenerative transistor based on a voltage phase of the three-phase AC power supply3and a reference voltage detecting portion12for calculating a voltage value of the three-phase AC power supply3based on an output of the fundamental waveform generating portion10. Output terminals of the base driving signal creating portion7, the reference voltage detecting portion12and the PN bus voltage detecting portion8are connected to a base driving signal output portion9for outputting a base driving signal to carry out an ON/OFF control of the regenerative transistor based on the voltage value of the three-phase AC power supply3and voltage values of the both terminals of the smoothing capacitor71, and an output terminal of the base driving signal output portion9is connected to corresponding base terminals of the regenerative transistors81,82,83,84,85and86, respectively.

Although a signal input to the line voltage detecting portion6is set to be the voltage of each of the phases in the three-phase AC power supply3without the reactor2inFIG. 1, it may be a voltage of each of the phases in the three-phase AC power supply3through the reactor2.

Next, description will be given to a flow of a regenerative current in the power regenerative converter shown inFIG. 1. First of all, a current obtained by an induced electromotive force generated by a speed reduction of a motor flows into the both terminals of the smoothing capacitor71. Consequently, a voltage of the smoothing capacitor71is raised. For this reason, an electric potential of one of the phases which is indicative of a maximum electric potential in the three-phase source voltages supplied from the power supply is lower than a positive electrode of the smoothing capacitor71, and an electric potential of one of the phases which is indicative of a minimum electric potential in the three-phase source voltages is higher than an electric potential of a negative electrode of the smoothing capacitor71. Accordingly, a difference in an electric potential is generated between the three-phase source voltages which are supplied and the smoothing capacitor71. Therefore, a regenerative current flows from the smoothing capacitor71to the power supply by an ON operation of the regenerative transistor.

Thus, the difference between the voltage of the smoothing capacitor in the power regenerative converter and the source voltage is utilized to cause the current to flow with a current limitation through the reactor. When the phase of the regenerative transistor to be turned ON is taken erroneously, therefore, the difference in a voltage is increased. Consequently, there is a possibility that a large current might suddenly flow, resulting in a stoppage or breakage of an apparatus. For this reason, it is important to detect the phase of the power supply and to carry out the ON/OFF control of the regenerative transistor.

The ON/OFF control of the regenerative transistor using a base driving signal will be described below.

FIG. 2is a block diagram showing a part from the line voltage detecting portion6to the base driving signal creating portion7.FIG. 3is a block diagram showing an internal structure of the fundamental waveform generating portion10.FIG. 4is a chart showing an output waveform of the line voltage detecting portion6and that of the fundamental waveform generating portion10.FIG. 5is a Bode diagram for a primary low-pass filter I(s) and a quaternary low-pass filter H(s).

As shown inFIG. 2, the line voltage detecting portion6inputs voltage waveforms VR, VS and VT of the three-phases of the three-phase AC power supply3and detects and outputs line voltage waveforms VR-S, VS-T and VT-R of the three phases, respectively. The fundamental waveform generating portion10inputs the line voltage waveforms VR-S, VS-T and VT-R output from the line voltage detecting portion6, and generates fundamental waveforms V′R-S, V′S-T and V′T-R from the line voltage waveforms and outputs them to the base driving signal creating portion7. The base driving signal creating portion7uses the fundamental waveforms V′R-S, V′S-T and V′T-R to create base driving signals to be utilized for the ON/OFF control of the regenerative transistor (six signals corresponding to the respective regenerative transistors in the embodiment).

Next, the line voltage detecting portion6will be described.

The line voltage detecting portion6detects the line voltage waveforms VR-S, VS-T and VT-R among R-S, S-T and T-R lines through the three-phase AC power supply3. An S-R line voltage waveform is obtained by leading or lagging a phase of the R-S line voltage waveform by 180 degrees, a T-S line voltage waveform is obtained by leading or lagging a phase of the S-T line voltage waveform by 180 degrees, and an R-T line voltage waveform is obtained by leading or lagging a phase of the T-R line voltage waveform by 180 degrees. Accordingly, the S-R, T-S and R-T line voltage waveforms can be calculated from the R-S, S-T and T-R line voltage waveforms which are detected by the line voltage detecting portion6. Therefore, it is sufficient to detect only the three line voltage waveforms VR-S, VS-T and VT-R.

Next, the fundamental waveform generating portion10will be described.

In order to create the base driving signal to be used for the ON/OFF control of the regenerative transistor without an influence of a distortion component of the three-phase AC power supply3, the fundamental waveform generating portion10is set to have the following structure. As shown inFIG. 3, the fundamental waveform generating portion10includes a radio frequency component removing filter21for removing distortion components from the line voltage waveforms VR-S, VS-T and VT-R of the three-phase AC power supply3, a frequency calculating portion22for calculating a fundamental frequency of the line voltage waveform of the three-phase AC power supply3from an output of the radio frequency component removing filter21, and a correcting portion23for correcting an output of the radio frequency component removing filter21. As shown inFIG. 4, although the distortion component mixed in the line voltage waveform is removed in the radio frequency component removing filter21, a waveform obtained after the removal has a phase and an amplitude changed. Therefore, the correcting portion23uses the fundamental frequency of the line voltage waveform of the three-phase AC power supply3which is calculated by the frequency calculating portion22to correct the phase and the amplitude changed by removing the distortion component through the radio frequency component removing filter21so as to be the same as those of the line voltage waveform of the three-phase AC power supply3in the case in which the distortion component is not contained. Accordingly, the fundamental waveform generating portion10inputs the line voltage waveforms VR-S, VS-T and VT-R of the three-phase AC power supply3and outputs the fundamental waveforms V′R-S, V′S-T and V′T-R to be the line voltage waveforms of the three-phase AC power supply3which do not contain the distortion component.

Next, detailed description will be given to the radio frequency component removing filter21and an output waveform signal thereof and the correcting portion23in the fundamental waveform generating portion10.

Although the radio frequency component removing filter21can be implemented by a system having an FFT analyzer function, and furthermore, can implement the function by various filters such as a low-pass filter and a band-pass filter, description will be given to the case of a quaternary low-pass filter using a secondary low-pass filter in two stages. By the low-pass filter, a distortion component having a radio frequency is removed and the frequency is identical to a frequency of the three-phase AC power supply3which does not contain the distortion component.

First of all, the secondary low-pass filter will be described. When ωn represents a break frequency and s represents a Laplace operator, a transfer function G(s) of the secondary low-pass filter is expressed in Equation (1).

[Equation⁢⁢1]G⁡(s)=ωn2s2+2⁢ωn⁢s+ωn2(1)
The transfer function G(s) of the secondary low-pass filter which is expressed in the Equation (1) can be rewritten as Equation (2).

[Equation⁢⁢2]G⁡(s)=⁢ωn2s2+2⁢ωn⁢s+ωn2=⁢(ωns+ωn)2(2)
The Equation (2) indicates that the secondary low-pass filter is equivalent to have a primary low-pass filter with a break frequency ωn[rad/sec] in two stages.

Next, there will be supposed the case of a quaternary low-pass filter using the secondary low-pass filter in two stages. In that case, a quaternary low-pass filter transmission function H(s) is expressed in Equation (3).

[Equation⁢⁢3]H⁡(s)=⁢ωn2s2+2⁢ωn⁢s+ωn2×ωn2s2+2⁢ωn⁢s+ωn2=⁢(ωns+ωn)4(3)
The Equation (3) indicates that the quaternary low-pass filter is equivalent to have the primary low-pass filter with the break frequency ωn[rad/sec] in four stages.

When the transmission function of the primary low-pass filter is represented by I(s), a gain attenuation g and a phase lag amount φ after a passage through I(s) are expressed in Equations (4) and (5) (ω is an optional frequency).

In the case in which the radio frequency component removing filter21is the quaternary low-pass filter H(s) using the secondary low-pass filter in two stages, accordingly, it is apparent, from the Equations (6) and (7), that the gain attenuation gh and the phase lag amount φh in the radio frequency component removing filter21are four times as large as the gain attenuation g and the phase lag amount φ in the primary low-pass filter I(s).

Moreover,FIG. 5is a Bode diagram in which a gain to frequency relationship and a phase to frequency relationship are represented on rectangular coordinates and are caused to make a set respectively for each of the primary low-pass filter I(s) and the quaternary low-pass filter H(s). From the Bode diagram, it is apparent that the gain attenuation gh and the phase lag amount φh in the quaternary low-pass filter H(s) are four times as large as the gain attenuation g and the phase lag amount φ in the primary low-pass filter I(s), respectively.

As shown inFIG. 4, the frequency of the output waveform of the radio frequency component removing filter21is equal to that of the line voltage waveform of the three-phase AC power supply3. After the fundamental frequency of the line voltage waveform of the three-phase AC power supply3is calculated in the frequency calculating portion22, therefore, the break frequency on of the radio frequency component removing filter21is changed to be the fundamental frequency. The phase lag amount φ of a waveform signal output from the filter which is expressed in the Equation (3) with respect to the line voltage waveform signal of the three-phase AC power supply3which does not contain the distortion is calculated by the Equation (7) and is 180 degrees (=π). Although the phase of the line voltage is detected without an influence, furthermore, the amplitude of the waveform signal output from the filter which is expressed in the Equation (3) is calculated by using the Equation (6) and is a quarter of the amplitude of the line voltage waveform of the three-phase AC power supply3which does not contain the distortion. Accordingly, the output of the radio frequency removing filter21is a waveform signal obtained by lagging the amplitude and the phase by ¼ and 180 degrees as compared with the line voltage waveform of the three-phase AC power supply3which does not contain the distortion.

An operation of the fundamental waveform generating portion10will be described below by using a specific line voltage waveform.

When a line voltage waveform between two certain phases in the three-phase AC power supply3is set to be a sin waveform, a line voltage waveform y1(t) to be a signal which has not been input to the radio frequency component removing filter21can be expressed in Equation (8). A represents an amplitude and t represents a time. It is supposed that the distortion component is not mixed at all.
[Equation 8]
y1(t)=Asin(ωnt)   (8)
In an output waveform signal y2(t) of the radio frequency component removing filter21in an input of the line voltage expressed in the Equation (8), an amplitude is a quarter and a phase is lagged by 180 degrees (=π) with respect to the line voltage waveform having no distortion as described above. Therefore, Equation (9) is obtained.

In order to cause the output waveform signal y2(t) of the radio frequency component removing filter21which is expressed in the Equation (9) to be equal to the line voltage waveform y1(t) of the three-phase AC power supply3which is expressed in the Equation (8), the phase lag and the amplitude attenuation are corrected by the correcting portion23. In this case, the correcting portion23is constituted by a filter for carrying out a constant multiplication over the amplitude. If the output signal y2(t) of the radio frequency component removing filter21is multiplied by −4, the amplitude is corrected and the phase lag is also corrected. Consequently, it is possible to generate a false fundamental waveform corresponding to the line voltage waveform between the two phases.

The correcting portion23has a function for calculating a phase lag amount and a gain attenuation in addition to the filter for carrying out the constant multiplication, and these functions can be implemented by various techniques. For example, it is possible to propose a method of correcting a phase lag by means of an all-pass filter having zero amplitude attenuation and capable of operating only a phase.

As described above, the fundamental waveform generating portion10inputs the line voltage waveforms VR-S, VS-T and VT-R of the three-phase AC power supply3, removes the distortion portion of the line voltage waveforms of the three-phase AC power supply3by means of the radio frequency component removing filter21, corrects the amplitudes and phases of the waveforms thus obtained so as to be equal to those of the line voltage waveforms of the three-phase AC power supply3through the correcting portion23, and generates and outputs the fundamental waveforms V′R-S, V′S-T and V′T-R to be the line voltage waveforms of the three-phase AC power supply3which do not contain the distortion component.

The base driving signal creating portion7will be described below.

FIG. 6is a time chart in the regenerating operation of the power regenerative converter, showing a temporal change in a phase detecting signal, a regenerative transistor and a regenerative current which corresponds to a change in a voltage of a fundamental waveform.

The base driving signal creating portion7shown inFIG. 1inputs the fundamental waveforms V′R-S, V′S-T and V′T-R which are generated by the fundamental waveform generating portion10. The phases of the fundamental waveforms V′R-S, V′S-T and V′T-R which are input are led or lagged by 180 degrees to calculate fundamental waveforms V′S-R, V′T-S and V′R-T. More specifically, it is sufficient to multiply the fundamental waveforms V′R-S, V′S-T and V′T-R by −1. A zero cross of each of the fundamental waveforms is detected and the phase detecting signal for each of the fundamental waveforms is created in such a manner that the amplitudes of the fundamental waveforms V′R-S, V′S-T, V′T-R, V′S-R, V′T-S and V′R-T are ON between positive phases and are OFF between negative phases as shown inFIG. 6, for example. The line voltage waveform of the three-phase AC power supply in which the distortion component is not mixed is an almost sin waveform. Therefore, the fundamental waveform is also a sin waveform, and an electric potential of the fundamental waveform is a maximum on a center in an ON phase section of the phase detecting signal and the electric potential of the fundamental waveform is a minimum on a center of an OFF phase section of the phase detecting signal. Accordingly, it is possible to grasp phases indicative of the maximum and minimum electric potentials of the fundamental waveform through each of the phase detecting signals. For each of the regenerative transistors81to86, there is created a base driving signal for carrying out an ON/OFF control of the regenerative transistors81to86which serves to turn ON any of the regenerative transistors81,83and85that is connected to the phase indicative of the maximum electric potential of the three-phase AC source voltage, to turn ON any of the regenerative transistors82,84and86that is connected to the phase indicative of the minimum electric potential of the three-phase AC source voltage and to turn OFF the other regenerative transistors. The base driving signal thus created is output to the base driving signal output portion9.

Next, the regenerating operation will be described.

In the PN bus voltage detecting portion8shown inFIG. 1, the voltages on both terminals of the smoothing capacitor71are detected as DC bus voltages and are output to the base driving signal output portion9. In the reference voltage detecting portion12, a moving average filter is used to integrate waveforms taking absolute values of the fundamental waveforms V′R-S, V′S-T and V′T-R by one cycle of the fundamental waveform (an inverse number of a frequency), thereby detecting a voltage amplitude. The voltage amplitude value thus detected is set to be a line voltage value of the three-phase AC power supply3in the case in which the distortion component is not mixed, and is output to the base driving signal output portion9.FIG. 7is a block diagram showing an internal structure of the base driving signal output portion9. In the base driving signal output portion9, a signal output from the reference voltage detecting portion12and a signal output from the PN bus voltage detecting portion8are input to a subtractor41to calculate a difference between the voltage value of the three-phase AC power supply3and the DC bus voltage value. Then, there is carried out a regenerating operation for inputting, to a comparator43, a regeneration starting voltage value Von which is preset as a threshold for starting a regenerating operation and the difference between the voltage value of the three-phase AC power supply3and the DC bus voltage value which is an output of the subtractor41and comparing them with each other, and outputting, to the regenerative transistors81to86, the base driving signal for performing the ON/OFF control of the regenerative transistor which is created by the base driving signal creating portion7when the difference between the voltage value of the three-phase AC power supply3and the DC bus voltage value is higher than the regeneration starting voltage.

As shown in the time chart for the regenerating operation of the power regenerative converter1inFIG. 6, the regenerative transistors81and84are turned ON when the electric potential of the fundamental waveform V′R-S is a maximum. When the electric potential of the fundamental waveform V′R-T is a maximum, the regenerative transistors81and86are turned ON. When the electric potential of the fundamental waveform V′S-T is a maximum, the regenerative transistors83and86are turned ON. When the electric potential of the fundamental waveform V′S-R is a maximum, the regenerative transistors82and83are turned ON. When the electric potential of the fundamental waveform V′T-R is a maximum, the regenerative transistors85and82are turned ON. When the electric potential of the fundamental waveform V′T-S is a maximum, the regenerative transistors84and85are turned ON.

More specifically, the electric potential of the fundamental waveform V′R-S is a maximum at a time of t20to t40. Therefore, the regenerative transistors81and84are turned ON and the other regenerative transistors are turned OFF. Consequently, the smoothing capacitor71and the S-R phase of the three-phase AC power supply are connected to the reactor through a power impedance so that the regenerative current flows from the R phase to the S phase. Similarly, the electric potential of the fundamental waveform V′R-T is a maximum at a time of t40to t60. Therefore, the regenerative transistors81and86are turned ON and the other regenerative transistors are turned OFF. Consequently, the regenerative current flows from the R phase to the T phase.

As described above, if the fundamental waveform of the line voltage of the three-phase AC power supply3is generated, it is possible to detect the fundamental frequency of the line voltage waveform of the three-phase AC power supply, thereby detecting an accurate voltage phase of the three-phase AC power supply from the fundamental waveform without the influence of the distortion component also in the case in which the distortion component is mixed into the three-phase AC power supply3. In the creation of the base driving signal, by using the fundamental waveform to be the line voltage waveform of the three-phase AC power supply3which does not contain the distortion component, it is possible to accurately create, for the voltage phase of the three-phase AC power supply, the base driving signal for carrying out the ON/OFF control of the regenerative transistor which serves to turn ON only the regenerative transistor for connecting two phases of any of the line voltages which is a maximum and to turn OFF the other regenerative transistors. Accordingly, an overvoltage and an overcurrent can be prevented from being applied to the power supply and the regenerative converter in the regenerating operation. Therefore, it is possible to prevent a system from being stopped due to a breakage of the power supply or the regenerative converter due to them.

Second Embodiment

Description will be given to an embodiment in which a function for extracting a distortion component of a three-phase AC power supply and obtaining a distortion frequency, a distortion amplitude and a distortion ratio of the distortion component is added to the first embodiment in order to grasp the distortion component in the case in which the distortion component is mixed into the three-phase AC power supply.

FIG. 8is a block diagram showing a structure of a power regenerative converter according to the embodiment.FIG. 9is a diagram showing an internal structure of a distortion component extracting portion. In a power regenerative converter1A according to the embodiment shown inFIG. 8, a distortion component extracting portion11for extracting a distortion component to be mixed into a line voltage waveform of a three-phase AC power supply3is provided after the fundamental waveform generating portion10in the power regenerative converter1according to the first embodiment, and furthermore, a distortion component frequency detecting portion24for detecting a frequency of the distortion component thus extracted, a distortion voltage detecting portion25for detecting a voltage amplitude of the distortion component thus extracted and a distortion ratio calculating portion26for calculating a distortion ratio of a source voltage distortion (a voltage amplitude of the distortion component/an amplitude of the source voltage) are provided after the distortion component extracting portion11.

As shown inFIG. 9, the distortion component extracting portion11inputs line voltage waveforms VR-S, VS-T and VT-R containing a distortion component in the three-phase AC power supply3through an output from a line voltage detecting portion6and fundamental waveforms V′R-S, V′S-T and V′T-R which do not contain the distortion component but have an equal frequency to the line voltage waveform and an almost equal amplitude thereto through an output from the fundamental waveform generating portion10. In the distortion component extracting portion11, the fundamental waveform V′R-S is subtracted from the line voltage waveform VR-S through a subtractor27. Similarly, the fundamental waveform V′S-T is subtracted from the line voltage waveform VS-T through a subtractor28and the fundamental waveform V′T-R is subtracted from the line voltage waveform VT-R through a subtractor29. Accordingly, distortion components VfR-S, VfS-T and VfT-R of the line voltage waveform of the three-phase AC power supply3are extracted by the subtractors27,28and29and are output from the distortion component extracting portion11, respectively. The distortion components VfR-S, VfS-T and VfT-R output from the distortion component extracting portion11are input to the distortion component frequency detecting portion24and the distortion voltage detecting portion25.

As shown inFIG. 8, the distortion component frequency detecting portion24inputs the distortion components VfR-S, VfS-T and VfT-R from the distortion component extracting portion11and detects frequencies of the distortion components. Moreover, the distortion voltage detecting portion25inputs the distortion components VfR-S, VfS-T and VfT-R from the distortion component extracting portion11and uses a moving average filter to integrate waveforms taking absolute values of the distortion components VfR-S, VfS-T and VfT-R by one cycle of each of the distortion components (an inverse number of the frequency), thereby detecting voltage amplitudes of the distortion components. Furthermore, the distortion ratio calculating portion26inputs an output (a source voltage) of a reference voltage detecting portion12and an output (a distortion component voltage) of the distortion voltage detecting portion25and divides them, thereby calculating a distortion ratio (the voltage amplitude of the distortion component/an amplitude of the source voltage).

By providing the distortion component extracting portion11, the distortion component frequency detecting portion24, the distortion voltage detecting portion25and the distortion ratio calculating portion26, thus, it is possible to obtain the distortion frequency, the distortion amplitude and the distortion ratio of the distortion component of the line voltage waveform in the three-phase AC power supply3without using a special measuring device. By displaying the distortion frequency, the distortion amplitude and the distortion ratio of the distortion component of the line voltage waveform in the three-phase AC power supply3or giving a warning such as an alarm when the values depart from a predetermined range, it is possible to monitor a power state.

By monitoring the power state through the display or the warning, moreover, it is possible to grasp the power state before carrying out a regenerating operation. In the case in which the distortion component is mixed into the power supply and greatly influences the regenerating operation, therefore, it is possible to prevent the regenerating operation from being carried out, for example, to hinder a base driving signal from being output. Accordingly, it is possible to prevent the power supply and the regenerative converter from being broken down due to a flow of an overcurrent to them through the regenerating operation.

Third Embodiment

Description will be given to an embodiment in which a function for carrying out an ON/OFF control of a regenerative transistor depending on a state of a distortion component when the distortion component is mixed into a three-phase AC power supply is added to the first embodiment.

FIG. 10is a block diagram showing a structure of a power regenerative converter according to the embodiment.FIG. 11is a block diagram showing an internal structure of a base driving signal output portion9A according to the embodiment.FIG. 12is a time chart in a regenerating operation of a power regenerative converter1B, showing a temporal change in a regenerative transistor and a regenerative current which correspond to a line voltage waveform and a fundamental waveform of a three-phase AC power supply3in which a distortion component is mixed.

In the power regenerative converter1B according to the embodiment shown inFIG. 10, a distortion component extracting portion11for extracting a distortion component mixed into a source voltage waveform between three phases of the three-phase AC power supply3is provided after the fundamental waveform generating portion10of the power regenerative converter according to the first embodiment, and the base driving signal output portion9A is provided in place of the base driving signal output portion9according to the first embodiment. An output of the distortion component extracting portion11is input to the base driving signal output potion9A.

An operation in the base driving signal output portion9A will be described with reference toFIG. 11.

The base driving signal output portion9A inputs a signal output from the distortion component extracting portion11, a signal output from a base driving signal creating portion7, a signal output from a reference voltage detecting portion12and a signal output from a PN bus voltage detecting portion8respectively, and outputs a base driving signal to be used for an ON/OFF control of six regenerative transistors. The base driving signal output portion9A has such a structure as to output the base driving signal and to start the regenerating operation when a difference value between a voltage value of the three-phase AC power supply3and a DC bus voltage value is equal to or greater than a certain threshold.

A line voltage value of the three-phase AC power supply3which is output from the reference voltage detecting portion12and has no distortion component mixed therein and the DC bus voltage value output from the PN bus voltage detecting portion8are input to a subtractor41in the base driving signal output portion9A to calculate a difference between the line voltage value of the three-phase AC power supply3having no distortion component mixed therein and the DC bus voltage value. On the other hand, in order to prevent the regenerating operation from being carried out when the line voltage value of the three-phase AC power supply3is greater than the DC bus voltage, a voltage threshold for starting the regenerating operation corresponding to a drop or rise in a source voltage due to the distortion component is generated by using a regeneration starting voltage Von and the distortion component extracting portion11in the case in which the distortion component is not mixed. First of all, the signal output from the distortion component extracting portion11is input to a distortion component correcting portion40and is thus corrected, and the corrected signal is output. The distortion component correcting portion40maintains a cycle of the distortion component and carries out a correction except for the cycle (for example, an amplitude). Accordingly, the distortion component correcting portion40may multiply the output signal of the distortion component extracting portion11by a constant, for example. A signal output from the distortion component correcting portion40and the regeneration starting voltage Von are input to an adder42. The regeneration starting voltage Von is a constant which is predetermined as a threshold for starting the regenerating operation. Therefore, a signal output from the adder42is synchronized with a cycle of a drop or rise in a voltage of a power supply which is caused by the distortion component. Accordingly, the signal output from the adder42can be set to be a voltage threshold for starting the regenerating operation corresponding to a drop or rise in a source voltage which is caused by the distortion component.

The output of the adder42and that of the subtractor41are input to a comparator43, and the signal output from the subtractor41is compared with the signal output from the adder42. Moreover, the signal output from the base driving signal creating portion7is input to a collector portion of a switch44and a signal output from the comparator43is connected to a gate portion of the switch44. An emitter portion of the switch44is connected to gate portions of regenerative transistors81to86, respectively. When the signal output from the subtractor41is larger than the signal output from the adder42, the switch44is turned ON. When the switch44is turned ON, a base driving signal created by the base driving signal creating portion7is output from the base driving signal output portion9A. The base driving signal which is output is input to the respective regenerative transistors to carry out the ON/OFF control of the regenerative transistors.

As described above, by extracting the distortion component of the three-phase AC power supply3and changing the voltage threshold of the regenerating start corresponding to the distortion component, it is possible to carry out the ON/OFF control of the regenerative transistors in an accurate timing. Accordingly, also in the case in which an influence of the distortion component on the regenerating operation is great, conventionally, it is possible to execute a stable regenerating operation. Consequently, an overvoltage or an overcurrent can be prevented from being applied to the power supply or the regenerative converter due to the regenerating operation. Thus, it is possible to prevent the power supply or the regenerative converter from being broken down due to the regenerating operation. As a result, it is possible to prevent a system from being stopped.

Industrial Applicability

The power regenerative converter according to the invention is suitable for the case in which a stable regenerating operation can be obtained in a three-phase AC power supply in which a source voltage distortion is mixed.