Electric vehicle control apparatus and electric vehicle

According to one embodiment, an electric vehicle control apparatus is provided with a converter having a diode and a switching device which convert an AC voltage or a DC voltage supplied from an input side into a DC voltage, whose output side is connected to a main motor through an inverter, a battery connected to the converter through a reactor, to provide a power source for the main motor, and a boosting chopper circuit composed the diode and the switching device which the converter has, so as to boost a voltage of the battery.

FIELD

Embodiments described herein relate to an electric vehicle control apparatus and an electric vehicle.

BACKGROUND

An electric railway vehicle is driven using a power supplied from an overhead line through a pantograph. By the way, it would appear that, in typical foreign railway systems, an overhead line is not set up over a yard line of a train shed and a pit line for performing maintenance. In this case, when moving an electric vehicle to a pit line over which an overhead line is not set up, a locomotive with a diesel power not requiring an overhead power moves the electric vehicle to the pit line. In this case, each time the necessity to move the electric vehicle to the pit line occurs, the locomotive with diesel power becomes necessary, and therefore there was a problem that the working efficiency is bad.

Accordingly, a method to drive a main motor at low speed using a battery for control power source which is usually provided in an electric vehicle has been proposed. However, since the voltage of the battery for a control power source is lower compared with a voltage which is usually applied to a DC side of a VVVF inverter for driving the motor, a voltage so as to obtain a prescribed speed, that is a rotational frequency of the motor, will be insufficient.

In such a case, as a configuration so as to boost a voltage of the battery for control power source to a voltage required for a VVVF inverter, technology which is provided with a boosting chopper has been proposed.

DETAILED DESCRIPTION

According to an embodiment, an electric vehicle control apparatus is provided with a converter having a diode and a switching device which convert an AC voltage or a DC voltage supplied from an input side into a DC voltage, whose output side is connected to a main motor through an inverter, a battery connected to the converter through a reactor, to provide a power source for the main motor, and a boosting chopper circuit composed of the diode and the switching device which the converter has, so as to boost a voltage of the battery.

Hereinafter, further embodiments will be described with reference to the drawings.

First Embodiment

FIG. 1is a diagram showing a main circuit configuration of an electric vehicle control apparatus100of an electric vehicle according to an embodiment. As shown inFIG. 1, a power collector (hereinafter, pantograph)1is connected to an AC overhead line not shown, and thereby an electric power is supplied to the electric vehicle control apparatus100. And, the pantograph1, an AC high-speed circuit breaker2, and a transformer3are connected to the electric vehicle control apparatus100at the overhead line side thereof. And, a negative side of the transformer3is earthed through a wheel4. The transformer3transforms an AC voltage supplied through the pantograph1from the AC overhead line, and supplies the transformed AC voltage to an AC/DC converter20side.

As shown inFIG. 1, the electric vehicle control apparatus100according to the present embodiment is provided with a contactor5for passing electric current through a charging resistor, a contactor6for short-circuiting the charging resistor, a charging resistor7, and the AC/DC converter20at the secondary side of the transformer3. In addition, the electric vehicle control apparatus100is provided with a filter capacitor12, and a VVVF inverter13at the DC side of the AC/DC converter20. Furthermore, the electric vehicle control apparatus100is provided with a main motor (MM)14such as a traction motor at the AC side of the VVVF inverter13. In addition, the electric vehicle control apparatus100is provided with a battery15for control power source, a backflow preventing diode16, a reactor17, a positive side opening contactor18, and a negative side opening contactor19.

The battery15for control power source (hereinafter, referred also to as a battery15) is a battery to supply electric power to various systems performing control in the electric vehicle control apparatus100and so on. The battery15for control power source according to the present embodiment is used for supplying electric power to the VVVF inverter13, when an electric vehicle moves on a place where no overhead line is installed. When a power supplying source such as the overhead line, and a third rail is present, since the battery15for control power source is charged by a charger not shown, the battery15becomes to a full charge state.

The AC/DC converter20according to the present embodiment has two phases of a U-phase and a V-phase. The U-phase includes a U-phase upper side device8, and a U-phase lower side device9. The V-phase includes a V-phase upper side device10, and a V-phase lower side device11. Each of the U-phase upper side device8, the U-phase lower side device9, the V-phase upper side device10, and the V-phase lower side device11is composed of a diode (10a,11a) and a switching device (10b,11b) such as an IGBT which are connected in anti-parallel. In the present embodiment, it is illustrated that the V-phase of the AC/DC converter20is used to form a boosting chopper circuit for boosting a voltage of the battery15. However, the U-phase of the AC/DC converter20can be used to form the boosting chopper circuit.

In the electric vehicle control apparatus100according to the present embodiment, when the electric vehicle runs on a place where an overhead line is installed, the AC high-speed circuit breaker2, the contactor5, and the contactor6are connected, and the positive side opening contactor18, and the negative side opening contactor19are opened. By this means, the electric power supplied from the transformer3is supplied to the AC/DC converter20through the charging resistor7. And, the AC/DC converter20converts an AC voltage of the supplied electric power into a DC voltage. And, the electric power is supplied from the AC/DC converter20to the filter capacitor12and the VVVF inverter13which are arranged in parallel. The VVVF inverter13converts the DC voltage outputted from the AC/DC converter20into an AC voltage of variable voltage variable frequency, and supplies the AC voltage to the main motor14to drive the electric vehicle. By this means, the electric vehicle can run on a place where an overhead line is installed. However, in many cases, in foreign railway systems, an overhead line may not be set up over a yard line of a train shed, and a pit line for performing maintenance. In order to run an electric vehicle in a condition like this, the battery15is required for driving the main motor.

According to the electric vehicle control apparatus100of the present embodiment, the AC/DC converter20is connected to the battery15, and part of the semiconductor devices of the AC/DC converter20is utilized for forming the boosting chopper. Namely, the AC/DC converter20and the boosting chopper share common semiconductor devices. Hereinafter, an explanation on how the boosting chopper is realized will be provided.

FIG. 2is a diagram showing a boosting chopper to which part of the configuration included in the AC/DC converter20provided in the electric vehicle control apparatus100is applied. In the example shown inFIG. 2, a boosting chopper circuit201is realized by the configuration on the route shown by bold lines. That is, the boosting chopper circuit201is composed of the battery15, the backflow preventing diode16, the reactor17, the switching device (IGBT or the like, for example)11bincluded in the V-phase lower side device11, the diode10aincluded in the V-phase upper side device10, and the filter capacitor12. As shown inFIG. 2, the boosting chopper circuit201shares the switching device11b, and the diode10aincluded in the V-phase upper side device10with the AC/DC converter20.

The reactor17used in the boosting chopper circuit201is determined by a battery discharge current and a switching frequency. For example, if the running by the battery15is limited to the running at a speed of about 3 km/h, and also the driving force is limited to about ⅕ of the maximum driving force, the power consumption becomes about 30 kw. And if the voltage of the battery15is 110 V, and when the battery discharge current is 270 A, the switching frequency is 500 Hz, and if allowable current pulsation is ±50 A, that is, peak to peak thereof is 100 A, the inductance value may be about 1 mH. For this reason, in the present embodiment, the reactor17with an inductance value of 1 mH and a rated current of 270 A may be selected. Accordingly, the additional component does not become such a large component as to affect the size of the whole electric vehicle control apparatus100.

The backflow preventing diode16is provided for preventing the battery15from being charged by backflow of the current.

When the electric vehicle according to the present embodiment moves on a place where an overhead line is installed, an operator performs an operation to switch to the battery running, and thereby the pantograph1comes down, and a circuit is established so that electric power is supplied from the battery15to the VVVF inverter13.

When the electric vehicle according to the present embodiment runs on a place where no overhead line by using the electric power of the battery15, the electric vehicle control apparatus100makes the AC high-speed circuit breaker2, the contactor5for inputting the charging resistor and the contactor6for short-circuiting the charging resistor to be opened, and connects the positive side opening contactor18, and the negative side opening contactor19. And, the boosting chopper circuit201performs boosting in accordance with the conduction ratio of the switching device11b.

By this means, the electric vehicle control apparatus100according to the present embodiment, even if the voltage of the battery15is 110 V, for example, after the boosting chopper circuit201boosts the voltage to a voltage of 200-300 V, can charge the filter capacitor12. Since the electric power is supplied to the VVVF inverter13with the boosted voltage, it is possible to drive the main motor14. By this means, the electric vehicle control apparatus100can move the electric vehicle on which the electric vehicle control apparatus100is loaded can move at a place where no overhead line is installed.

FIG. 3is a diagram showing a main circuit configuration to control the boosting chopper circuit201in the electric vehicle control apparatus100. The main circuit configuration shown inFIG. 3is provided with a switch control unit301, and operates by the energization from the battery15. In addition the configuration shown inFIG. 3is shown as an example of a control system to control the boosting chopper circuit201, and other control system may be used.

The switch control unit301shown inFIG. 3turns on/off the switching device11bincluded in the V-phase lower side device11, and thereby a discharge current IBATTfrom the battery15flows. That is, when the switch control unit301turns on the switching device11bincluded in the V-phase lower side device11, since the battery is short-circuited through the reactor17, the current increases. Then, when the switch control unit301turns off the switching device11b, the current passes through the diode10aside of the V-phase upper side device10into the filter capacitor12, by the energy stored in the reactor17. At this time, the discharge current IBATTgradually decreases. When the switch control unit301again turns on the switching device11bincluded in the V-phase lower side device11, the discharge current IBATTre-increases.

In the electric vehicle control apparatus100according to the present embodiment, this operation is repeated, and thereby the current from the battery15is charged into the filter capacitor12. In this manner, the switch control unit301adequately changes the ON/OFF cycle, that is the conduction ratio, of the switching device11bof the V-phase lower side device11, and consequently the voltage of the filter capacitor12becomes higher than the voltage of the battery15.

Next, the configuration of the switch control unit301will be described with reference toFIG. 3. In the present embodiment, a filter capacitor voltage required for driving the main motor14is predetermined as a command value (referred to also as a filter capacitor voltage command value). When a voltage applied to the filter capacitor12is to be made 300 V, 300 V is set as the filter capacitor voltage command value.

And, a subtractor311outputs a difference voltage value which is obtained by subtracting a voltage measured from the filter capacitor12, from the filter capacitor voltage command value, to a proportional integral controller (PI)312. And the proportional integral controller312calculates a command value (a battery discharge current command value) for determining a discharge current flowing from the battery15, from the inputted difference voltage value.

And, a subtractor313outputs a difference current value which is obtained by subtracting an actual battery discharge current value from the battery discharge current command value, to a proportional integral controller (PI)314. The proportional integral controller314calculates a conduction ratio (a ratio of a time when the switching device11bis ON) of the switching device11bof the boosting chopper circuit201from the inputted difference current value.

And a PWM signal generator315generates a switching signal QYfor the switching device11b, with a method such as to compare a conduction ratio and a triangular wave, so that the switching frequency becomes a prescribed switching frequency.

FIG. 4is a diagram showing an example of the switching signal QYwhich is generated according to the relation between the voltage command value and the triangular wave. As shown inFIG. 4, the PWM signal generator315compares the conduction ratio with the triangular wave, and in a case where the conduction ratio is larger than the triangular wave, the PWM signal generator315outputs the switching signal QYas ON. On the other hand, in a case where the conduction ratio is not more than the triangular wave, the PWM signal generator315outputs the switching signal QYas OFF. By this means, the ON/OFF cycle of the switching device11bis controlled in accordance with the switching signal QY.

FIG. 5is a diagram showing the discharge current IBATTwhich increases and decreases in accordance with the ON/OFF cycle of the switching signal QY. As shown inFIG. 5, the discharge current IBATTgradually increases during a time period when the switching signal QYis ON, and the discharge current IBATTgradually decreases during a time period when the switching signal QYis OFF.

In addition, the electric vehicle control apparatus100according to the present embodiment is provided with a configuration to control the inverter13in accordance with the voltage of the battery15.FIG. 6is a diagram showing a configuration to control the VVVF inverter13of the electric vehicle control apparatus100. As shown inFIG. 6, the electric vehicle control apparatus100is provided with a battery SOC (State of Charge: charging state of a battery) detection unit601, and a battery SOC determination unit602.

As shown inFIG. 6, the battery SOC detection unit601detects the SOC (charging state of the battery) of the battery15, and outputs the detection result to the SOC determination unit602. And, the battery SOC determination unit602has a function to output a startup command to the VVVF inverter13, based on the detection result. In this manner, in the present embodiment, when determining that the SOC of the battery15is not less than a predetermined value, the battery SOC determination unit602outputs the startup command to the VVVF inverter13, to make the driving main motor14to be driven.

As described above, it becomes possible to make the voltage of the filter capacitor12higher than the voltage of battery15. By this means, it becomes possible that the VVVF inverter13applies a sufficient voltage to the main motor14.

In addition, when the battery SOC determination unit602determines that the SOC of the battery15is smaller than a predetermined value, since the power supply from the battery15is suppressed, the over discharge can be suppressed. By this means, it is possible to suppress that the battery15deteriorates.

Incidentally,FIG. 2shows the exemplary configuration in which the diode10aof the V-phase upper side device10and the switching device11bof the V-phase lower side device11are made to perform chopper operation, to boost the voltage. However, if the chopper operation as in the present embodiment is not carried out, and a switching signal to control the switching device11bis kept in the OFF state, the discharge current from the battery15flows into the diode10aof the V-phase upper side device10. By this means, the same voltage as the battery15is applied to the filter capacitor12. When the sufficient driving force is obtained even by this voltage of the battery15, the main motor14may be driven from the VVVF inverter13without boosting. Even in such a case, the reactor17functions as a smoothing circuit for the discharge current from the battery15. By this means, the ripple (vibration component) of the discharge current from the battery15can be decreased, and the heat generation from the battery15can be suppressed, and thereby it is possible to prevent that the life of the battery is made to be shortened.

In the electric vehicle control apparatus100according to the present embodiment, the example has been described in which, in order to perform driving by the battery15for control power source, the battery15is connected to one phase of the AC/DC converter20, that is the V-phase in the example shown inFIG. 1, through the reactor17and the backflow preventing diode16, and through the positive side opening contactor18and the negative side opening contactor19. In this manner, in the present embodiment, the case in which a main circuit line from the battery15for control power source is connected to the V-phase has been shown, but a configuration in which the main circuit line is connected to the U-phase may be used. Furthermore, in the present embodiment, the example has been described in which the electric vehicle control apparatus100according to present embodiment is provided with the converter to convert the AC voltage into the DC voltage, but an example provided with a converter to convert a DC voltage supplied from an input side into a DC voltage may be used.

In the electric vehicle control apparatus100according to the present embodiment, the voltage is boosted using part of the configuration of the AC/DC converter20configured as a main circuit for an AC overhead line as a boosting chopper, and thereby it has become possible to apply the voltage higher than the voltage of the battery15to the VVVF inverter13. By this means, it has become possible that the VVVF inverter13applies the sufficient voltage to the main motor14.

That is to say, in the electric vehicle control apparatus100of the present embodiment, since boosting function has been ensured without providing semiconductor devices for a boosting chopper, it becomes possible to achieve miniaturization of the whole electric vehicle control apparatus.

In other words, in the electric vehicle control apparatus of the present embodiment, since the boosting chopper is realized using part the configuration of the converter, at the time of driving the main motor by the battery, although the voltage supplied to the main motor is boosted, resulting in that the electric vehicle control apparatus is not provided with the boosting chopper.

Second Embodiment

The example to use part of the configuration of the AC/DC converter as the boosting chopper is not limited to the first embodiment, but other aspect may be applied. Accordingly, in a second embodiment, a case in which a main circuit configuration is another aspect will be described.

FIG. 7is a diagram showing a main circuit configuration of an electric vehicle control apparatus700according to a second embodiment. Furthermore, in the second embodiment, the same symbols are given to the same constituent elements as the above-described first embodiment, and the description thereof will be omitted.

The electric vehicle control apparatus700shown inFIG. 7is an example in which, compared with the electric vehicle control apparatus100of the first embodiment, the reactor17is removed, and a secondary winding701of the transformer3is used in place of the reactor17.

FIG. 8is a diagram showing a boosting chopper to which part of the configuration included in the AC/DC converter20provided in the electric vehicle control apparatus700is applied. In the example shown inFIG. 8, a boosting chopper801is realized by the configuration on the route shown by bold lines. That is, the boosting chopper801is composed of the battery15, the backflow preventing diode16, the secondary winding701of the transformer3, the switching device (a transistor, for example)11bincluded in the V-phase lower side device11, the diode10aincluded in the V-phase upper side device10, and the filter capacitor12.

As shown inFIG. 8, the boosting chopper801shares the switching device11band the diode10aincluded in the V-phase upper side device10with the AC/DC converter20, and in addition uses the secondary winding701of the transformer3as a reactor.

Generally, an inductance of a secondary winding of a transformer is about 1 mH to 2 mH. For this reason, the secondary winding701of the transformer3can be used as an inductance sufficient for a reactor for a boosting chopper.

In this manner, the electric vehicle control apparatus700according to the present embodiment shares part of the devices included in the AC/DC converter20, similarly as the first embodiment, and in addition uses the secondary winding701of the transformer3as a reactor, and boosts the voltage of the battery15to apply the boosted voltage to the VVVF inverter13, to thereby make the main motor14to be driven. Furthermore, the control and so on at the time of driving are the same as in the first embodiment, and the description thereof will be omitted.

In this manner, in the electric vehicle control apparatus700according to the present embodiment, a new reactor is suppressed from being provided, and thereby further reduction of the number of components is made possible. By this means, it is possible to suppress cost increase.

Furthermore, the electric vehicle control apparatus700according to the present embodiment uses the secondary winding701of the transformer3as a reactor, and thereby realizes smoothing of the discharge current similarly as the first embodiment.

The above-described electric vehicle control apparatuses according to the first to second embodiments have used part of the configuration of the AC/DC converter to convert the AC overhead line voltage to the DC voltage in an electric vehicle of an AC overhead line, as the boosting chopper.

By this means, in the electric vehicle control apparatuses according to the first to second embodiments, it has become possible to solve the problem that, conventionally in the case of trying to drive a vehicle by a battery for control power source, since the battery voltage is low, if the battery voltage is directly connected to a DC side of a driving VVVF inverter, since the voltage is insufficient for a voltage for driving the main motor, the sufficient speed and driving force cannot be obtained.

Furthermore, conventionally, there was a problem that when using the voltage of a battery, the voltage is applied to a VVVF inverter, a discharge current from the battery includes ripple (vibration component) caused by the switching of the VVVF inverter, and the battery generates heat, and thereby the life of the battery is caused to be shortened. Whereas, according to the electric vehicle control apparatuses of the first to second embodiments, since the reactor17or the secondary winding701of the transformer3is placed between the battery15and the VVVF inverter13, the discharge current can be smoothed, and therefore generation of heat in the battery15can be prevented.

The electric vehicle control apparatus of the configuration described above shares the semiconductor devices and the reactor composing the boosting chopper, with the converter and the main transformer provided in the main circuit. Thus, in addition to the effect of the first embodiment, the number of components necessary for the electric vehicle control apparatus having boosting function can be reduced and miniaturization can be realized. In addition, since the number of the components can be reduced, cost reduction can be made. Furthermore, since it is unnecessary to ensure a space to install the boosting chopper, it becomes possible to provide flexibility in the arrangement of other components.

Third Embodiment

FIG. 9is a diagram showing a main circuit configuration of the electric vehicle control apparatus700according to a third embodiment. Furthermore, in the third embodiment, the same symbols are given to the same constituent elements as the above-described first embodiment, and the description thereof will be omitted.

The electric vehicle control apparatus700according to the third embodiment connects the battery15of a low voltage through the reactor17between the U-phase and the V-phase of the AC/DC converter (single-phase PWM converter)20.

The filter capacitor (smoothing capacitor)12, the VVVF inverter13, and the main motor14are connected to the DC side of the AC/DC converter (single-phase PWM converter)20.

And, in the electric vehicle control apparatus700according to the present embodiment, a rotation detector901to detect the rotational frequency of the main motor14is mounted to the main motor14. And, the present embodiment is an example in which a control unit900performs control in accordance with the rotation of the main motor14detected by the rotation detector901.

The control unit900according to the present embodiment is provided with a PWM controller911, a boosting controller912, a PWM controller913, a damping controller914, an adder915, a current/vector controller916, and a command calculator917.

And, a torque command calculated based on a command from an operator's cab, and the rotational frequency of the main motor14are inputted to the command calculator917of the control unit900. The command calculator917calculates and outputs a D-axis current command, a Q-axis current command, and a boosting voltage command, based on the torque command and the rotational frequency. Next, a D-axis current and a Q-axis current will be described.

FIG. 10is a diagram showing an example of the main motor14which is driven by the electric power supplied from the VVVF inverter13. As shown inFIG. 10, the main motor14is provided with electric circuits (field coils) corresponding to three phases of a V-phase1003, a U-phase1004, and a W-phase1005. The main motor14rotates a shaft1002by the rotating field generated by flowing currents to the field coils of the respective phases.

And, the present embodiment is an example in which three phases (U, V, W) are converted into an αβ-axis coordinate system at rest of orthogonal two phases, and then further converted into a DQ-axis rotating coordinate system, to perform control of the main motor14. In addition, since the conversion method of these coordinate systems is well-known technology, the description thereof will be omitted.

And, in the DQ-axis rotating coordinate system, when the D-axis is set to the direction of the secondary magnetic flux of the main motor14, the D-axis becomes an excitation component, and the Q-axis becomes a torque component. That is, a D-axis current becomes an excitation current component, and a Q-axis current becomes a torque current component. And, the command calculator917outputs the D-axis current command, and the Q-axis current command, based on the DQ-axis rotating coordinate system.

Returning toFIG. 9, the damping controller914performs pseudo differentiation of the voltage of the filter capacitor (smoothing capacitor)12detected by a voltage detector918, and multiplies the result of the psude differentiation by a gain, to calculate a compensation amount to the Q-axis current command. And the adder915adds the compensation amount to the Q-axis current command outputted from the damping controller914to the Q-axis current command value outputted from the command calculator917, to output the Q-axis current command after compensation.

The Q-axis current command after compensation and the D-axis current command are inputted to the current/vector controller916. And, the current/vector controller916outputs a three-phase voltage command to the PWM controller911. And, the PWM controller911controls the switching devices incorporated in the VVVF inverter13, based on the inputted three-phase voltage command.

In addition, the command calculator917outputs a boosting voltage command to the boosting controller912. The boosting controller912outputs a conduction ratio command of the AC/DC converter (single-phase PWM converter)20to the PWM controller913, by means of PI control and so on so that the voltage of the smoothing capacitor12coincides with the boosting voltage command. Also in the electric vehicle control apparatus according to the present embodiment, the boosting chopper is realized using part of the configuration of the AC/DC converter20.

The PWM controller913switches the devices included in the U-phase in accordance with the inputted conduction ratio command, and on the other hand, keeps the lower device included in the V-phase ON.

Furthermore, the boosting voltage command may become equal to the voltage of the smoothing capacitor. In this case, a boosting rate command indicates a boosting rate of 100%, and the conduction ratio command becomes a conduction ratio of 100%. And, the PWM controller913keeps the upper device included in the U-phase ON, and keeps the lower device included in the V-phase ON.

Furthermore, in the present embodiment, the example using the boosting voltage command has been described, but the boosting rate command may be used in place of the boosting voltage command. Even in the case to control the boosting rate using the boosting rate command, the same operation and effect can be obtained as in the case to use the boosting voltage command.

Furthermore, the boosting rate is expressed by a ratio of the DC voltage of the AC/DC converter20at the VVVF inverter13side, to the DC voltage of the AC/DC converter (single-phase PWM converter)20at the battery side15. For example, when the boosting rate is 100%, the conduction ratio becomes 100% (the upper device included in the U-phase is kept ON), and when the boosting rate is 200%, the conduction ratio becomes 50% (the upper device and the lower device of the U-phase are switched with a duty of 50%).

The damping controller914performs pseudo differentiation of the voltage of the smoothing capacitor12detected by the voltage detector918, and multiplies the result of the psude differentiation by the gain, to calculate the compensation amount to the Q-axis current command. And, when the DC voltage rises, the Q-axis current command increases, that is, increasing the torque to thereby increase the current flowing from the smoothing capacitor12achieves the same operation and effect as providing a resistor in parallel with the smoothing capacitor12. Since the energy is consumed by the operation that the resistor is connected in parallel with the smoothing capacitor12, the resonance can be suppressed.

When controlling the AC/DC converter (single-phase PWM converter)20, as described above, the boosting controller912in the control unit900, in response to a boosting rate of 100% designated in the boosting rate command, controls both of the upper device included in the U-phase and the lower device included in the V-phase to be kept ON. In this case, the damping controller914behaves the same operation as the resistor connected in parallel with the smoothing capacitor12, and consequently suppresses the resonance generated between the smoothing capacitor12and the reactor17. Meanwhile, since switching of all devices in the AD/DC converter (single-phase PWM converter)20is halted and the voltage applied to the VVVF inverter13is reduced when a boosting rate of 100% is set to the boosting rate command, the switching loss of the AC/DC converter (single-phase PWM converter)20and the VVVF inverter13can be reduced, and the current of the battery15can be reduced.

The command calculator917determines the D-axis current command, the Q-axis current command, the boosting voltage command based on the torque command and the rotational frequency of the main motor14, so as to reduce the total loss composed of a motor loss and a power conversion loss. For this reason, the electric vehicle control apparatus according to the present embodiment can reduce the generation of heat of the low voltage battery15, and therefore can suppress the deterioration of the life. In addition, since the high efficiency thereof improves, it becomes possible to make the electric vehicle run a long distance within the limited battery capacity.

FIG. 11is a diagram showing the relation between the D-axis current and the Q-axis current required for outputting the same torque, and a copper loss of the motor that is a heating loss generated with the operation of the motor, when the rotational frequency and the DC voltage inputted to the VVVF inverter13are previously determined. In the case of rotating at extremely low speed, the motor efficiency is low compared with the power conversion efficiency, and the copper loss is dominant in the motor loss. As shown inFIG. 11, in order to make the motor copper loss minimum, it is only necessary to set the D-axis current to about 130 A. In this case, since a modulation rate is about 90%, VVVF inverter13can be controlled to output the necessary torque.

Furthermore, when the DC voltage inputted to the VVVF inverter13further drops more than the DC voltage determined inFIG. 11, since the modulation rate increases in inverse proportion to the DC voltage, it is supposed that the modulation rate exceeds 100%. If the modulation rate exceeds 100%, the control cannot be performed. In case that the DC voltage drops and the modulation rate exceeds 100%, the command calculator917outputs the D-axis current command so as to reduce the D-axis current, as shown in an arrow inFIG. 11. As the D-axis current decreases in accordance with the D-axis current command, the modulation rate decreases. Thus, even in case that the DC voltage drops and the modulation rate exceeds 100%, it is possible to adjust the modulation rate to a value lower than 100%. That is, it is possible to suppress the modulation rate from exceeding 100%, with the change of the DC voltage.

Above embodiment focuses on the case where the DC current becomes low level. However, an embodiment regarding a case where the Q-axis current command is further large as shown inFIG. 11will be described hereinafter. As shown inFIG. 11, the modulation rate might exceed 100%, under the condition that the Q-axis current command is large in order to output a high torque, and the loss is small. In this case, the command calculator917outputs the D-axis current command so as to reduce the D-axis current. Consequently, the modulation rate can be suppressed within 100%, while enabling a high torque output.

The command calculator917performs control so that the necessary torque is outputted, in terms of minimizing the loss, by the D-axis current command, and the modulation rate does not exceed 100%.

The control unit900according to the present embodiment performs various commands so that the electric vehicle can run with low loss within the range that the modulation rate does not to exceed 100%, for the torque command in each rotation, as described above. For example, theoretically, the modulation rate can optionally be changed by the boosting control of the boosting chopper (the single-phase PWM converter20in the present embodiment), but actually, when the boosting rate is increased, a voltage and a current of any portion increase, and receive restriction of a protection voltage and a protection current, and in addition, the boosting has become a factor to increase the loss of the single-phase PWM converter20and the VVVF inverter13.

Accordingly, the command calculator917according to the present embodiment has determined the D-axis current command, the Q-axis current command, the boosting voltage command, so as to minimize the total loss in accordance with the torque command and the rotation. By this means, it has become possible to suppress the loss.

Particularly, when a vehicle runs with the power supplied from the battery15, a large torque and a large output are required while the vehicle is being accelerated, but the required torque and output decreases when a constant speed operation at a prescribed speed is started. That is, while the vehicle is being accelerated, the command calculator917outputs various commands so that the boosting operation is performed. In this case, a current value smaller than the current value in which the loss becomes minimum is set for the D-axis current command, so that a large output can be obtained though the loss is large.

And, when the constant operation is started, and a low torque and a low output are required, the command calculator917outputs various commands (conduction ratio command 0) so that the boosting operation is not performed. In this case, a current value in which the loss becomes minimum is set for the D-axis current command.

In addition, there may be an apparatus which is not equipped with a boosting chopper or the above described single-phase PWM converter20. However, such an apparatus will be able to modulate a DC voltage to a given DC voltage by using the method of setting the D-axis current command and the Q-axis current command.

For example, in an embodiment, the filter capacitor12of the boosting chopper circuit201is composed of a capacitor, but may be composed of two capacitors connected in series, and the position between them may be earthed.