Drive system

Abstract

This driving system (1) comprises a motor (M1), a power conversion unit (11), and a control unit (12). The motor (M1) is a reluctance motor that rotates by receiving the supply of power. The power conversion unit (11) has a plurality of switching elements (SW11, SW12, SW13, SW14, SW15, SW16), is directly connected to the motor (M1), converts power supplied from a power supply to power to be supplied to the motor (M1), and supplies the converted power to the motor (M1). The control unit (12) controls the plurality of switching elements (SW11, SW12, SW13, SW14, SW15, SW16) possessed by the power conversion unit (11).

Description

Drive system

[0001] The present disclosure relates to drive systems.

[0002] Some drive systems installed in electric railway vehicles convert DC power supplied from a substation via overhead lines into desired AC power, and then supply the converted AC power to an electric motor to drive the motor and generate propulsive force for the electric railway vehicle. Because the space under the floor of a railway vehicle is limited, it is preferable to generate propulsive force for the railway vehicle to travel at a target speed using a small number of electric motors.

[0003] Therefore, synchronous motors, which are more efficient than induction motors, are sometimes used as electric motors. An example of this type of drive system is disclosed in Patent Document 1. The electric vehicle control device disclosed in Patent Document 1 includes a plurality of permanent magnet synchronous motors, a plurality of inverters each associated with the permanent magnet synchronous motors, and a gate control device that controls the plurality of inverters.

[0004] Japanese Patent Application Laid-Open No. 2012-075317

[0005] In a permanent magnet synchronous motor, when there is no load, for example, if a short circuit occurs in the inverter and the inverter stops, a no-load induced voltage proportional to the motor rotation speed is generated due to the permanent magnet. As a result, in the electric vehicle control device disclosed in Patent Document 1, current flows from the permanent magnet synchronous motor to the inverter when the inverter stops. To prevent a failure due to current caused by the no-load induced voltage flowing from the permanent magnet synchronous motor to the inverter, the electric vehicle control device disclosed in Patent Document 1 includes a contactor provided between the inverter and the permanent magnet synchronous motor.

[0006] Since it is necessary to provide the same number of contactors as the permanent magnet synchronous motors, the electric vehicle control device disclosed in Patent Document 1 becomes complex in structure and large in size. Note that this problem is not limited to traction systems that receive power from overhead lines, but can occur in traction systems that drive permanent magnet synchronous motors with power supplied from a power source.

[0007] The present disclosure has been made in consideration of the above circumstances, and has an object to provide a drive system with a simple structure.

[0008] To achieve the above object, a drive system according to the present disclosure includes a reluctance motor, a power conversion unit, and a control unit. The reluctance motor rotates upon receiving a supply of electric power. The power conversion unit has a plurality of switching elements and is directly connected to the reluctance motor to convert electric power supplied from a power source into electric power to be supplied to the reluctance motor, and supplies the converted electric power to the reluctance motor. The control unit controls the plurality of switching elements of the power conversion unit.

[0009] According to the present disclosure, the power conversion unit is directly connected to the reluctance motor, and there is no need to provide a contactor between the power conversion unit and the reluctance motor, which simplifies the structure of the drive system.

[0010] Block diagram of a drive system according to an embodiment. Block diagram of a control unit according to an embodiment. Block diagram of a gate signal generator according to an embodiment. Block diagram of a first modified example of a drive system according to an embodiment. Block diagram of a second modified example of a drive system according to an embodiment.

[0011] Hereinafter, a drive system according to an embodiment of the present disclosure will be described in detail with reference to the drawings, in which the same or equivalent parts are designated by the same reference numerals.

[0012] A drive system 1 according to an embodiment will be described below, taking as an example a drive system that generates propulsive force for a railway vehicle. The drive system 1 shown in Fig. 1 is installed, for example, under the floor of the railway vehicle, converts DC power into three-phase AC power, and supplies the three-phase AC power to a motor to drive the motor, thereby generating propulsive force for the railway vehicle.

[0013] The drive system 1 includes a terminal 1a connected to a power supply, a grounded terminal 1b, a filter capacitor FC1 charged with DC power supplied from the power supply, and a power conversion unit 11 which is a DC-to-three-phase conversion device that converts the DC power supplied from the power supply via the filter capacitor FC1 into three-phase AC power. The drive system 1 further includes a motor M1 which is a reluctance motor that rotates upon receiving three-phase AC power from the power conversion unit 11, current sensors CT11, CT12, and CT13 that measure values ​​of phase currents of the motor M1, and a control unit 12 that controls a plurality of switching elements SW11, SW12, SW13, SW14, SW15, and SW16 included in the power conversion unit 11.

[0014] The power conversion unit 11 is directly connected to the motor M1. Direct connection means that the power conversion unit 11 is connected without an active element. Specifically, the power conversion unit 11 is connected to the motor M1 without a switch circuit that electrically disconnects the motor M1 from the power conversion unit 11. The switch circuit includes, for example, an electromagnetic contactor, a semiconductor switch, a manually operated mechanical switch, etc. Because the power conversion unit 11 is directly connected to the motor M1, the structure of the drive system 1 is simpler than a drive system in which a contactor is provided between the power conversion unit and a permanent magnet synchronous motor.

[0015] Each part of the traction system 1 will be described in detail below. Terminal 1a is electrically connected to a power source (not shown). The power source is, for example, a current collector that acquires power from a power supply line. The power supply line is, for example, an overhead line or a third rail. The current collector is, for example, a pantograph or a current collector shoe. Terminal 1a is preferably electrically connected to the current collector via a contactor, a filter reactor, or the like. Terminal 1b is grounded via the wheel.

[0016] One end of the filter capacitor FC1 is electrically connected to the terminal 1a, and the other end is electrically connected to the terminal 1b. As described above, the filter capacitor FC1 forms a filter together with the filter reactor provided between the terminal 1a and the current collector, thereby reducing harmonic components.

[0017] The power conversion unit 11 is an inverter that converts DC power into three-phase AC power, for example, an inverter capable of variable voltage and variable frequency control. In this embodiment, the power conversion unit 11 includes switching elements SW11 and SW12 connected to a U-phase coil of the motor M1, switching elements SW13 and SW14 connected to a V-phase coil of the motor M1, and switching elements SW15 and SW16 connected to a W-phase coil of the motor M1. The power conversion unit 11 further includes freewheeling diodes D11, D12, D13, D14, D15, and D16 connected in parallel to the switching elements SW11, SW12, SW13, SW14, SW15, and SW16, respectively.

[0018] Switching elements SW11 and SW12 are connected in series, switching elements SW13 and SW14 are connected in series, and switching elements SW15 and SW16 are connected in series. The connection point of switching elements SW11 and SW12 is directly connected to the U-phase coil of motor M1. The connection point of switching elements SW13 and SW14 is directly connected to the V-phase coil of motor M1. The connection point of switching elements SW15 and SW16 is directly connected to the W-phase coil of motor M1. The series-connected switching elements SW11 and SW12, the series-connected switching elements SW13 and SW14, and the series-connected switching elements SW15 and SW16 are connected in parallel with one another.

[0019] The switching elements SW11, SW12, SW13, SW14, SW15, and SW16 are switched on and off by the control unit 12. As a result, the power conversion unit 11 converts DC power supplied from the power supply via the filter capacitor FC1 into three-phase AC power for supply to the motor M1. The power conversion unit 11 then supplies the three-phase AC power to the motor M1. For example, the switching elements SW11, SW12, SW13, SW14, SW15, and SW16 are IGBTs (Insulated Gate Bipolar Transistors).

[0020] The motor M1, which receives three-phase AC power from the power conversion unit 11, is a reluctance motor, which has a low power factor and requires reactive current. Therefore, increasing the capacity of the power conversion unit 11 is an option, but increasing the capacity of the power conversion unit 11 would result in an increase in the size of the power conversion unit 11. High-frequency switching in the power conversion unit 11 is necessary to reduce iron loss in the motor M1. If semiconductor elements made of silicon are used as the switching elements SW11, SW12, SW13, SW14, SW15, and SW16, the amount of heat generated by high-frequency switching increases, resulting in an increase in the size of a cooling device for cooling the switching elements SW11, SW12, SW13, SW14, SW15, and SW16.

[0021] Because it is difficult to install a vehicle control device including a large power conversion unit and a large cooling device under the floor or on the roof of a railway vehicle, where space is limited, reluctance motors have not been used in railway vehicle motors until now. Therefore, in this embodiment, wide-gap semiconductors are used for the switching elements SW11, SW12, SW13, SW14, SW15, and SW16 of the power conversion unit 11. As a result, it is possible to increase the capacity and perform high-frequency switching of the power conversion unit 11 while suppressing an increase in the size of the power conversion unit 11, and it becomes possible to use a reluctance motor as the motor M1. A wide-gap semiconductor is a semiconductor formed using a material with a band gap larger than that of silicon, such as silicon carbide, a gallium nitride-based material, or diamond.

[0022] The anodes of the freewheeling diodes D11, D12, D13, D14, D15, and D16 are connected to the emitters of the switching elements SW11, SW12, SW13, SW14, SW15, and SW16, respectively, and the cathodes are connected to the collectors of the switching elements SW11, SW12, SW13, SW14, SW15, and SW16, respectively, thereby preventing a reverse current from flowing through the switching elements SW11, SW12, SW13, SW14, SW15, and SW16.

[0023] The motor M1 is a reluctance motor that rotates upon receiving a supply of three-phase AC power from the power conversion unit 11. In this embodiment, the motor M1 is a synchronous reluctance motor that does not have a permanent magnet. Because the motor M1 does not have a permanent magnet, no no-load induced voltage is generated. Therefore, there is no need to provide a contactor between the power conversion unit 11 and the motor M1 to electrically separate the motor M1 from the power conversion unit 11 in order to prevent current from flowing from the motor M1 to the power conversion unit 11 when the power conversion unit 11 is stopped. In other words, the power conversion unit 11 can be directly connected to the motor M1.

[0024] The current sensors CT11, CT12, and CT13 measure the values ​​of phase currents flowing through the motor M1 and send the current measurements to the control unit 12. For example, the current sensors CT11, CT12, and CT13 are CT (current transformer) type sensors. Specifically, the current sensor CT11 is attached to a bus bar connecting the connection point of the switching elements SW11 and SW12 to the U-phase coil of the motor M1 and measures the value of the U-phase current flowing from the power conversion unit 11 to the motor M1. The current sensor CT12 is attached to a bus bar connecting the connection point of the switching elements SW13 and SW14 to the V-phase coil of the motor M1 and measures the value of the V-phase current flowing from the power conversion unit 11 to the motor M1. The current sensor CT13 is attached to a bus bar connecting the connection point of the switching elements SW15 and SW16 to the W-phase coil of the motor M1 and measures the value of the W-phase current flowing from the power conversion unit 11 to the motor M1.

[0025] The control unit 12 outputs a torque command value τ in response to an operation of a master controller provided in the driver's cab of the railway vehicle (not shown). ＊ Based on the current measurement values ​​obtained from the current sensors CT11, CT12, and CT13, the control circuit CT1 generates and outputs a gate signal S1 that controls the switching elements SW11, SW12, SW13, SW14, SW15, and SW16.

[0026] As shown in FIG. 2, the control unit 12 calculates a torque command value τ ＊The control unit 12 includes a current command calculator 21 that calculates a current command value from the current command value, a voltage command calculator 22 that calculates a voltage command value from the current command value, and a rotating coordinate inverse converter 23 that performs coordinate conversion of the voltage command value. The control unit 12 further includes a position estimator 24 that estimates the magnetic pole position of a rotor of the motor M1, a rotating coordinate converter 25 that performs coordinate conversion of current measurement values, and a gate signal generator 26 that generates a gate signal S1.

[0027] The current command calculator 21 calculates a torque command value τ ＊ The current command value i on the rotation coordinate system for obtaining the target torque of the motor M1 is ＊ ｄ , i ＊ ｑ For example, the current command value i ＊ ｄ , i ＊ ｑ is the effective current value for the torque, i.e., the value that minimizes the copper loss of the motor M1. The voltage command calculator 22 calculates the current command value i ＊ ｄ , i ＊ ｑ and the current measurement value i generated by the rotating coordinate converter 25. ｄ , i ｑ The difference between (i ＊ ｄ -i ｄ ), (i ＊ ｑ -i ｑ ) to obtain the voltage command value v ＊ ｄ , v ＊ ｑ Calculate.

[0028] The rotating coordinate inverse converter 23 calculates the voltage command value v on the rotating coordinate system based on a transformation matrix using the estimated position θ̂, which is the magnetic pole position of the rotor of the motor M1 estimated by the position estimator 24. ＊ ｄ , v ＊ ｑ The voltage command value v on the two-phase coordinate system ＊ α , v ＊ βThen, the rotating coordinate inverse converter 23 converts the voltage command value v on the two-phase coordinate system into ＊ α , v ＊ β The voltage command value v on the three-phase coordinate system ＊ ｕ , v ＊ ｖ , v ＊ ｗ Convert to.

[0029] The position estimator 24 calculates the current measurement values ​​i obtained from the current sensors CT11, CT12, and CT13. ｕ , i ｖ , i ｗ and the voltage command value v on the three-phase coordinate system calculated by the rotating coordinate inverse converter 23. ＊ ｕ , v ＊ ｖ , v ＊ ｗ The magnetic pole position of the rotor of the motor M1 is estimated based on the above. The estimated position θ^, which is the magnetic pole position of the rotor estimated by the position estimator 24, is expressed in electrical angle.

[0030] The rotating coordinate converter 25 converts the current measurement value i in the three-phase coordinate system using a three-phase-to-two-phase conversion matrix. ｕ , i ｖ , i ｗ is expressed as the current measurement value i on the two-phase coordinate system. α , i β Then, the rotating coordinate converter 25 converts the current measurement value i on the two-phase coordinate system into α , i β The current measurement value i on the rotating coordinate system ｄ , i ｑ Convert to.

[0031] The gate signal generator 26 performs PWM (Pulse Width Modulation) control to generate the gate signal S1. In detail, as shown in FIG. 3, the gate signal generator 26 generates a voltage command value v ＊ ｕ , v ＊ ｖ , v ＊ ｗa differentiator 32 that differentiates the estimated position θ^ to calculate the rotation speed ω^ of the motor M1; a carrier wave generator 33 that generates a carrier wave in accordance with the rotation speed ω^ of the motor M1; and a comparator 34 that generates a gate signal based on a comparison between the modulated wave and the carrier wave.

[0032] The modulated wave generator 31 generates a voltage command value v on the three-phase coordinate system obtained from the rotating coordinate inverse converter 23. ＊ ｕ , v ＊ ｖ , v ＊ ｗ The modulated wave is generated based on the voltage command value v ＊ ｕ , v ＊ ｖ , v ＊ ｗ is a signal obtained by normalizing the estimated position θ^ with the value of the voltage between the terminals of the filter capacitor FC1. A differentiator 32 differentiates the estimated position θ^ to calculate the rotation speed ω^ of the motor M1.

[0033] The carrier wave generator 33 generates a carrier wave according to the rotation speed ω^ of the motor M1 calculated by the differentiator 32. The frequency of the carrier wave increases as the rotation speed of the motor M1 increases. In other words, the frequency of the carrier wave has a positive correlation with the rotation speed of the motor M1. In this embodiment, the carrier wave generator 33 uses a signal obtained by multiplying the modulated wave as the carrier wave. When the carrier wave and the modulated wave are synchronized and the carrier wave is a signal obtained by multiplying the modulated wave, the operating mode of the gate signal generator 26 is set to the synchronous multi-pulse mode. For example, when the gate signal generator 26 operates in the synchronous multi-pulse mode, the carrier wave generator 33 uses a carrier wave whose frequency is 15 times the frequency of the modulated wave.

[0034] The comparator 34 generates a gate signal S1 based on a comparison between the modulated wave generated by the modulated wave generator 31 and the carrier wave generated by the carrier wave generator 33, and outputs the gate signal S1 to the switching elements SW11, SW12, SW13, SW14, SW15, and SW16. Specifically, the gate signal S1 for the switching elements SW11, SW13, and SW15 is at an H (High) level when the value of the modulated wave is equal to or greater than the value of the carrier wave, and is at an L (Low) level when the value of the modulated wave is less than the value of the carrier wave. The gate signal S1 for the switching elements SW12, SW14, and SW16 is at an L level when the value of the modulated wave is equal to or greater than the value of the carrier wave, and is at an H level when the value of the modulated wave is less than the value of the carrier wave.

[0035] The switching elements SW11, SW12, SW13, SW14, SW15, and SW16 are switched on and off in response to the gate signal S1 output from the comparator 34. When the gate signal generator 26 operates in the synchronous multi-pulse mode, distortion of the current flowing through the motor M1 is reduced, allowing the motor M1 to operate with high efficiency.

[0036] As described above, the motor M1 included in the drive system 1 according to the embodiment is a synchronous reluctance motor that does not have a permanent magnet, and therefore does not generate a no-load induced voltage. Therefore, if, for example, a short-circuit fault occurs in the inverter and the inverter stops, there is no need to provide a contactor to disconnect the motor M1 from the power conversion unit 11, and the power conversion unit 11 is directly connected to the motor M1. Because there is no need to provide a contactor, the structure of the drive system 1 according to the embodiment is simpler than a drive system that includes a contactor between the power conversion unit and the motor.

[0037] The present disclosure is not limited to the above example. The drive system 1 may include a plurality of power conversion units 11 and a plurality of motors M1. Because the power conversion units 11 and the motors M1 must be associated one-to-one, the number of power conversion units 11 and the number of motors M1 included in the drive system 1 are the same.

[0038] As an example, the drive system 2 shown in Fig. 4 includes two power conversion units 11 and 13, two motors M1 and M2, and two filter capacitors FC1 and FC2 that are charged with power supplied from a power source (not shown). The power conversion units 11 and 13 have the same configuration. The motors M1 and M2 have the same configuration. The filter capacitors FC1 and FC2 have the same configuration. The drive system 2 further includes current sensors CT11, CT12, and CT13 that measure the value of the phase current of the motor M1, current sensors CT21, CT22, and CT23 that measure the value of the phase current of the motor M2, and a control unit 12 that controls multiple switching elements included in each of the power conversion units 11 and 13.

[0039] The filter capacitors FC1 and FC2 are connected in parallel to the power supply. Specifically, one end of the filter capacitor FC1 is connected to the terminal 1a, and the other end is connected to the terminal 1b. The filter capacitor FC2 is connected to the terminal 1a, and the other end is connected to the terminal 1b. The filter capacitors FC1 and FC2 are charged with power supplied from the power supply.

[0040] As in the embodiment, current sensors CT11, CT12, and CT13 measure the values ​​of phase currents flowing through motor M1 and send the current measurement values ​​to control unit 12. Current sensors CT21, CT22, and CT23 measure the values ​​of phase currents flowing through motor M2 and send the current measurement values ​​to control unit 12. As with current sensors CT11, CT12, and CT13, current sensors CT21, CT22, and CT23 are attached to the bus bar connecting power conversion unit 13 and motor M2.

[0041] As in the embodiment, the control unit 12 calculates a torque command value τ ＊ Based on the current measurements of the current sensors CT11, CT12, and CT13, the control unit 12 generates and outputs a gate signal S1 that controls a plurality of switching elements of the power conversion unit 11. The control unit 12 further generates a torque command value τ ＊Based on the measured values ​​of the current sensors CT21, CT22, and CT23, the control circuit 11 generates and outputs a gate signal S2 that controls a plurality of switching elements included in the power conversion unit 13. The method of generating the gate signals S1 and S2 is the same as in the embodiment.

[0042] In the drive system 2 having multiple motors M1 and M2, the power conversion unit 11 is directly connected to the motor M1, and the power conversion unit 13 is directly connected to the motor M2. Therefore, the structure of the drive system 2 is simpler than a drive system having contactors between each power conversion unit and each motor.

[0043] In the example of Fig. 4, the drive system 2 includes the same number of filter capacitors FC1 and FC2 as the power conversion units 11 and 13, but the power conversion units 11 and 13 may be connected to a single filter capacitor in common. The drive system 3 shown in Fig. 5 includes only the filter capacitor FC1. The drive system 3 differs from the drive system 2 in that the power conversion units 11 and 13 are connected to a common filter capacitor FC1.

[0044] The drive system 1-3 may include only two of the current sensors CT11, CT12, and CT13, rather than all of them. For example, the drive system 1-3 may measure the U-phase current and V-phase current flowing through the motor M1 using the current sensors CT11 and CT12, and calculate the W-phase current from the measured U-phase current and V-phase current. In this case, the control unit 12 may generate the gate signal S1 based on the measured U-phase current, measured V-phase current, and the calculated W-phase current value.

[0045] The number of power conversion units 11, 13 and the number of motors M1, M2 included in the drive systems 2, 3 are arbitrary as long as the number of power conversion units and the number of motors are the same. The drive systems 2, 3 may also include two independent control units 12. In this case, one control unit 12 controls the power conversion unit 11, and the other control unit 12 controls the power conversion unit 13.

[0046] In the embodiment, direct connection means connection without an active element, but the power conversion unit 11 and the motor M1 may be connected without an active element or a passive element. The same applies to the connection between the power conversion unit 13 and the motor M2.

[0047] The direct connection between the power conversion unit 11 and the motor M1 includes a connection via a relay terminal, a relay cable, etc. For example, when the power conversion unit 11 and the motor M1 are mounted on different vehicles, the power conversion unit 11 and the motor M1 are connected via a relay terminal. The same applies to a direct connection between the power conversion unit 13 and the motor M2.

[0048] The carrier wave and modulating wave do not have to be synchronized. When the carrier wave and modulating wave are not synchronized and the frequency of the carrier wave is higher than the frequency of the modulating wave, this is referred to as asynchronous multi-pulse mode. When the gate signal generator 26 operates in asynchronous multi-pulse mode, distortion of the current flowing through the motor M1 is reduced, as in the synchronous multi-pulse mode, allowing the motor M1 to operate with high efficiency.

[0049] When the rotation speed of the motor M1 is low, the carrier frequency may be set to the same value as the modulating frequency.

[0050] The control unit 12 may acquire a measurement value from a position sensor that measures the magnetic pole position of the rotor of the motor M1, and generate the gate signal S1 in accordance with the measurement value of the position sensor. In this case, the gate signal generator 26 does not need to include the position estimator 24, and may generate the gate signal S1 in accordance with the measurement value of the position sensor.

[0051] The motor M1 may be any synchronous motor that does not include a permanent magnet, and may be, for example, a switched reluctance motor.

[0052] The switching elements SW11, SW12, SW13, SW14, SW15, and SW16 may be semiconductor elements made of silicon, and the freewheeling diodes D11, D12, D13, D14, D15, and D16 may be wide-gap semiconductors.

[0053] The traction system 1-3 is not limited to being installed under the floor of the railway vehicle, but can be installed anywhere. As an example, the traction system 1-3 may be installed on the roof of the railway vehicle. The traction system 1-3 can be installed not only on railway vehicles that use DC power feeding, but also on railway vehicles that use AC power feeding. When the traction system 1-3 is installed on a railway vehicle that uses AC power feeding, the power is stepped down by a transformer, and the AC power is converted to DC power by a converter, and the power is supplied to the traction system 1-3.

[0054] The railway vehicle on which the drive system 1-3 is mounted is not limited to an electric railway vehicle. As one example, the drive system 1-3 may be mounted on a diesel railcar and receive a supply of electric power from a generator that generates electricity when driven by an internal combustion engine. As another example, the drive system 1-3 may be mounted on a battery car and receive a supply of electric power from a storage battery. The drive system 1-3 is not limited to a railway vehicle and may be mounted on any moving object such as an automobile, a ship, or an aircraft.

[0055] The present disclosure allows various embodiments and modifications without departing from the broad spirit and scope of the present disclosure. Furthermore, the above-described embodiments are intended to illustrate the present disclosure and do not limit the scope of the present disclosure. That is, the scope of the present disclosure is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and the meaning of equivalent disclosures are considered to be within the scope of the present disclosure.

[0056] 1, 2, 3 Drive system, 1a, 1b Terminal, 11, 13 Power conversion unit, 12 Control unit, 21 Current command calculator, 22 Voltage command calculator, 23 Rotation coordinate inverse converter, 24 Position estimator, 25 Rotation coordinate estimator, 26 Gate signal generator, 31 Modulation wave generator, 32 Differentiator, 33 Carrier wave generator, 34 Comparator, CT11, CT12, CT13, CT21, CT22, CT23 Current sensor, D11, D12, D13, D14, D15, D16 Freewheeling diode, FC1, FC2 Filter capacitor, M1, M2 Motor, S1, S2 Gate signal, SW11, SW12, SW13, SW14, SW15, SW16 Switching element.

Claims

1. A drive system comprising: a reluctance motor that rotates when supplied with electric power; a power conversion unit that has a plurality of switching elements and is directly connected to the reluctance motor, converts electric power supplied from a power source into electric power to be supplied to the reluctance motor, and supplies the converted electric power to the reluctance motor; and a control unit that controls the plurality of switching elements of the power conversion unit.

2. The drive system according to claim 1, wherein the plurality of switching elements are formed of wide-gap semiconductors.

3. The drive system according to claim 1, wherein a free wheel diode is connected in parallel to each of the plurality of switching elements, and at least one of the switching elements and the free wheel diode is formed from a wide gap semiconductor.

4. A drive system as claimed in any one of claims 1 to 3, wherein the control unit uses a modulated wave corresponding to a voltage command value for obtaining a target torque of the reluctance motor and a carrier wave whose frequency increases in accordance with an increase in the rotation speed of the reluctance motor, and generates gate signals for the plurality of switching elements based on a comparison between the modulated wave and the carrier wave.

5. A drive system according to any one of claims 1 to 4, wherein the control unit generates gate signals for the plurality of switching elements in accordance with the magnetic pole position of a rotor of the reluctance motor.

6. A drive system according to any one of claims 1 to 5, comprising: a plurality of power conversion units; and the same number of reluctance motors as the plurality of power conversion units, wherein the power conversion units are directly connected to the corresponding reluctance motors in a one-to-one correspondence.

7. The drive system according to claim 6, further comprising a filter capacitor that is charged with power supplied from the power supply, and the plurality of power conversion units are commonly connected to the filter capacitor.

8. The drive system according to claim 6, further comprising the same number of filter capacitors as the plurality of power conversion units charged with power supplied from the power source, the filter capacitors being connected in one-to-one correspondence with the power conversion units.

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