Drive system

Abstract

To provide a drive system capable of suppressing occurrence of over-voltage while preventing merchantability from reducing.SOLUTION: A drive system for an electric vehicle for driving, using power of a battery, a motor for traveling having a plurality of phases each including a first coil group and a second coil group whose connection state is switchable to serial connection of being connected in series to each other and to parallel connection of being connected in parallel to each other, comprises: a drive circuit comprising a first inverter connected to the first coil group and a second inverter connected to the second coil group for each phase of the motor for traveling; and a control section for performing switching control that when a request for discharging a capacitor connected in parallel between positive and negative electrodes of the battery is received in a state of the capacitor and the battery being separated electrically, switches the first coil group and the second coil group into parallel connection when the first coil group and the second coil group are connected in series and regenerative power is generated by electric motive force by the first coil group and the second coil group.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a drive system. [Background technology]

[0002] BACKGROUND ART Conventionally, a system for driving a motor such as a traction motor of an electric vehicle has been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-259570 Summary of the Invention [Problem to be solved by the invention]

[0004] In relation to this, in the prior art, when regenerative power is consumed by a resistor, the number and size of parts increases, and when regenerative power is absorbed by shorting each phase of a three-phase motor, braking torque is generated in the motor, causing vibration and noise, resulting in problems in terms of marketability. In other words, with the prior art, it has been difficult to simultaneously reduce the occurrence of overvoltage and prevent a decline in marketability.

[0005] The present invention has been made to solve the above problems, and an object of the present invention is to provide a drive system that can reduce the occurrence of overvoltage while preventing a decrease in marketability. [Means for solving the problem]

[0006] One embodiment of the present invention is a drive system for an electric vehicle that uses battery power to drive a traction motor having multiple phases with a first coil group and a second coil group whose connection state can be switched between a series connection connected to each other and a parallel connection connected to each other.The drive system includes a drive circuit that has, for each phase of the traction motor, a first inverter connected to the first coil group and a second inverter connected to the second coil group; a capacitor connected in parallel between the positive and negative poles of the battery; and a control unit that performs switching control to switch the first coil group and the second coil group to a parallel connection when the battery is electrically disconnected and there is a request to discharge the capacitor, and when regenerative power is generated by the electromotive force generated by the first coil group and the second coil group. [Effects of the Invention]

[0007] According to this invention, it is possible to reduce the occurrence of overvoltage while preventing a decrease in merchantability. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a drive system according to an embodiment of the present invention. [Figure 2] 1 is a diagram illustrating a schematic configuration of a magnetic circuit of a traction motor according to an embodiment of the present invention. [Figure 3] FIG. 2 is a diagram illustrating a schematic configuration of coil phases of a traction motor according to the present embodiment. [Figure 4] FIG. 2 is a diagram illustrating an example of the configuration of a drive circuit according to the present embodiment. [Figure 5] FIG. 4 is a diagram illustrating an example of the flow of operation of the control device of the present embodiment. [Figure 6] FIG. 10 is a diagram illustrating an example of reverse-phase discharge control by the control unit of the present embodiment. [Figure 7] FIG. 4 is a diagram illustrating an example of a current path in the negative-phase discharge control of the present embodiment. [Figure 8] FIG. 10 is a diagram showing a modified example of the configuration of the drive system of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Overall configuration of drive system] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 is a diagram showing an example of the configuration of a drive system 1 according to this embodiment. In this example of this embodiment, the drive system 1 is applied to an electric vehicle. The drive system 1 includes a control device 10, a traction motor 20, a battery 30, and a drive circuit 40.

[0010] The control device 10 includes a control unit 110 and a storage unit 120. The control unit 110 includes, for example, a CPU (central processing unit), and provides various functions based on the programs and data stored in the storage unit 120 . The storage unit 120 includes a storage element such as a nonvolatile semiconductor memory, and stores programs and data for the control unit 110 to operate.

[0011] The traction motor 20 includes a rotor 21, a coil 22, and a stator 23, and is driven under the control of the control device 10. A specific example of the configuration of the traction motor 20 will be described with reference to FIG.

[0012] 2 is a diagram showing a schematic configuration of a magnetic circuit of the traction motor 20 of this embodiment. In this embodiment, the traction motor 20 is a so-called two-phase open-winding switching motor. In one example of this embodiment, the traction motor 20 is configured with two-phase coils 22, an α-phase and a β-phase, which are shifted in phase by 90 degrees from each other.

[0013] In the traction motor 20, a first coil group L1 and a second coil group L2 are wound around the teeth 23 of a certain phase. Specific examples of the first coil group L1 and the second coil group L2 will be described.

[0014] The stator 23 includes α-phase teeth 23-1 and β-phase teeth 23-2. An α-phase coil 221-1 (coil α1) and an α-phase coil 221-2 (coil α2) are wound around the α-phase tooth 23-1. The α-phase coil 221-1 (coil α1) is also referred to as the first α-phase coil group L1, and the α-phase coil 221-2 (coil α2) is also referred to as the second α-phase coil group L2.

[0015] A β-phase coil 222-1 (coil β1) and a β-phase coil 222-2 (coil β2) are wound around the β-phase tooth 23-2. The β-phase coil 222-1 (coil β1) is also referred to as a first β-phase coil group L1, and the β-phase coil 222-2 (coil β2) is also referred to as a second β-phase coil group L2.

[0016] That is, the traction motor 20 includes a plurality of phases each having a first coil group L1 and a second coil group L2 configured to include common teeth.

[0017] The α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) generate magnetic flux in the direction A in the figure. The β-phase coil 222-1 (coil β1) and the β-phase coil 222-2 (coil β2) generate magnetic flux in the direction B in the figure. The direction A and the direction B are perpendicular to each other.

[0018] The traction motor 20 of this embodiment is a so-called two-phase motor (or a spatial phase orthogonal motor). In the traction motor 20, an α-phase coil 221-1 (coil α1) and an α-phase coil 221-2 (coil α2) are wound around a common tooth 23 (α-phase tooth 23-1) and are magnetically coupled to each other. In addition, a β-phase coil 222-1 (coil β1) and a β-phase coil 222-2 (coil β2) are wound around a common tooth 23 (β-phase tooth 23-2) and are magnetically coupled to each other. In the traction motor 20, the direction in which the α-phase magnetic flux is generated (direction A in the figure) and the direction in which the β-phase magnetic flux is generated (direction B in the figure) are perpendicular to each other, so there is no magnetic interference between the phases.

[0019] Furthermore, each coil 22 of the traction motor 20 is configured as a so-called open winding. Therefore, the electrical coupling state between the coils 22 of the traction motor 20 can be switched by a switching circuit external to the traction motor 20. For example, the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) can be connected in series or in parallel. Similarly, the β-phase coil 222-1 (coil β1) and the β-phase coil 222-2 (coil β2) can be connected in series or in parallel.

[0020] In other words, the traction motor 20 can be said to have multiple phases having a first coil group L1 and a second coil group L2 whose connection state can be switched between a series connection where the coils are connected in series with each other and a parallel connection where the coils are connected in parallel with each other.

[0021] The first coil group L1 and the second coil group L2 can also be said to be open windings in which a plurality of phases are connected to the inverter (drive circuit 40) independently of one another.

[0022] According to the traction motor 20 configured in this manner, the current of each phase can be controlled individually, and therefore it is possible to control the current taking into consideration overheating of a specific phase.

[0023] 3 is a diagram showing a schematic diagram of the phase configuration of the coil 22 of the traction motor 20 of this embodiment. As described above, the α-phase and the β-phase are orthogonal to each other.

[0024] Here, the phase difference δ between the coils 22 wound around the common stator 23 will be described. The phase difference δα between the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) is 0 (zero). Similarly, the phase difference δβ between the β-phase coil 222-1 (coil β1) and the β-phase coil 222-2 (coil β2) is 0 (zero).

[0025] Therefore, if currents of the same magnitude are passed through the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) so as to generate magnetic fluxes in opposite directions, the magnetic fluxes will cancel each other out, and the overall magnetic flux in the α-phase tooth 23-1 will be 0 (zero). Similarly, if currents of the same magnitude are passed through the β-phase coil 222-1 (coil β1) and the β-phase coil 222-2 (coil β2) so as to generate magnetic fluxes in opposite directions, the magnetic fluxes will cancel each other out, and the overall magnetic flux in the β-phase tooth 23-2 will be 0 (zero).

[0026] Returning to Figure 1, the traction motor 20 has four types of coils 22, namely the above-mentioned α-phase coil 221-1 (coil α1), α-phase coil 221-2 (coil α2), β-phase coil 222-1 (coil β1), and β-phase coil 222-2 (coil β2), each configured as an open winding.

[0027] The battery 30 includes a secondary battery and the like, and supplies the driving motor 20 with electric power for driving the vehicle.

[0028] The capacitor 50 is connected in parallel with the battery 30 between the positive and negative electrodes of the battery 30, and temporarily stores the power generated between the positive and negative electrodes of the battery 30.

[0029] That is, the capacitor 50 is connected in parallel between the positive and negative electrodes of the battery 30 .

[0030] A battery contactor 31 is provided between the battery 30 and the capacitor 50. The battery contactor 31 cuts off the supply of power from the battery 30 based on the control of a higher-level system (not shown). In other words, the battery contactor 31 cuts off the electrical connection between the battery 30 and the capacitor 50.

[0031] As an example, the upper system cuts off the battery contactor 31 when the electric vehicle equipped with the drive system 1 is stopped (for example, when the driver operates the control stop switch), when maintenance is performed on the high-voltage electrical system such as the battery 30, drive circuit 40, and traction motor 20, or when an accident such as a collision occurs.

[0032] When the battery contactor 31 is in a conductive state (ON state), the potential difference between the two electrodes of the capacitor 50 is equal to the voltage between the positive and negative electrodes of the battery 30. In the following description, the voltage between the positive and negative electrodes of the battery 30 is also referred to as the battery voltage VBatt. The battery voltage VBatt when the battery contactor 31 is disconnected is also referred to as the minimum battery voltage VBattL. In other words, the voltage across the capacitor 50 immediately after the battery contactor 31 is disconnected is equal to the minimum battery voltage VBattL.

[0033] The drive circuit 40 is connected to each of the coils 22, which are made up of open windings, of the traction motor 20. Based on the control of the control device 10, the drive circuit 40 controls the connection state of the coils 22 and the exchange of power between the battery 30 and the traction motor 20. More specifically, the drive circuit 40 changes the connection state between the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) and the connection state between the β-phase coil 222-1 (coil β1) and the β-phase coil 222-2 (coil β2) to a series connection or a parallel connection. Based on the control of the control device 10, the drive circuit 40 supplies power supplied from the battery 30 to the traction motor 20, or supplies (e.g., regenerates) power generated by the traction motor 20 to the battery 30. A specific example of the configuration of this drive circuit 40 will be described with reference to FIG.

[0034] 4 is a diagram showing an example of the configuration of the drive circuit 40 of this embodiment. The drive circuit 40 includes a first inverter 41 and a second inverter 42. The first inverter 41 is connected to the α-phase coil 221. The second inverter 42 is connected to the β-phase coil 222.

[0035] The first inverter 41 includes an eleventh inverter 411 and a twelfth inverter 412 . The eleventh inverter 411 includes a first switch 411A, a second switch 411B, a third switch 411C, and a fourth switch 411D configured as an H-bridge, and drives the α-phase coil 221-1 (coil α1). The twelfth inverter 412 includes a first switch 412A, a second switch 412B, a third switch 412C, and a fourth switch 412D configured as an H-bridge, and drives the α-phase coil 221-2 (coil α2). As described above, the α-phase coil 221-1 (coil α1) is in the first coil group L1, and the α-phase coil 221-2 (coil α2) is in the second coil group L2.

[0036] Similarly, for the β phase, the second inverter 42 includes a twelfth inverter 412 and a twenty-second inverter 422. The twenty-first inverter 421 includes a first switch 421A, a second switch 421B, a third switch 421C, and a fourth switch 421D configured as an H bridge, and drives the β-phase coil 222-1 (coil β1). The twenty-second inverter 422 includes a first switch 422A, a second switch 422B, a third switch 422C, and a fourth switch 422D configured as an H-bridge, and drives the β-phase coil 222-2 (coil β2). As described above, the β-phase coil 222-1 (coil β1) is in the first coil group L1, and the β-phase coil 222-2 (coil β2) is in the second coil group L2.

[0037] That is, the drive circuit 40 includes, for each phase of the traction motor 20, a first inverter (e.g., an eleventh inverter 411 or a twenty-first inverter 421) connected to the first coil group L1 and a second inverter (e.g., a twelfth inverter 412 or a twenty-second inverter 422) connected to the second coil group L2.

[0038] [Switching the connection state of coil 22] The first connection changeover switch 413 is disposed between the eleventh inverter 411 and the twelfth inverter 412. The first connection changeover switch 413 switches between an on state and an off state based on the control of the control device 10, thereby switching the connection state between the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) between a parallel connection and a series connection.

[0039] (1) When the coil 22 is connected in parallel The control device 10 turns the first connection changeover switch 413 to the OFF state. When the first connection changeover switch 413 is turned to the OFF state, the eleventh inverter 411 and the twelfth inverter 412 are electrically disconnected. As a result, the eleventh inverter 411 drives the α-phase coil 221-1 (coil α1). The twelfth inverter 412 drives the α-phase coil 221-2 (coil α2).

[0040] More specifically, the control device 10 turns on the first switch 411A and the fourth switch 411D and turns off the second switch 411B and the third switch 411C for the eleventh inverter 411. As a result, a current path is formed between the first switch 411A and the fourth switch 411D in the α-phase coil 221-1 (coil α1). The control device 10 turns on the first switch 412A and the fourth switch 412D and turns off the second switch 412B and the third switch 412C for the twelfth inverter 412. As a result, a current path is formed between the first switch 412A and the fourth switch 412D in the α-phase coil 221-2 (coil α2).

[0041] When power is supplied to the traction motor 20 from the battery 30 or the capacitor 50, a drive current flows through the α-phase coil 221-1 (coil α1) in the direction from the first switch 411A to the fourth switch 411D in the eleventh inverter 411. Similarly, a drive current flows through the α-phase coil 221-2 (coil α2) in the twelfth inverter 412 in the direction from the first switch 412A to the fourth switch 412D.

[0042] As shown in the figure, a black circle is attached to the end of the α-phase coil 221-1 (coil α1) that is connected to the first switch 411A, and a black circle is attached to the end of the α-phase coil 221-2 (coil α2) that is connected to the first switch 412A.

[0043] When a drive current flows from the black circle side attached to coil 22, the direction of the magnetic flux generated in α-phase tooth 23-1 by the drive current flowing through α-phase coil 221-1 (coil α1) coincides with the direction of the magnetic flux generated in α-phase tooth 23-1 by the drive current flowing through α-phase coil 221-2 (coil α2). That is, the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) generate magnetic flux in the same direction in the stator 23.

[0044] When the direction of the drive current flowing through the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) is reversed, the control device 10 reverses the on / off states of each switch of the 11th inverter 411 and the 12th inverter 412 from the above-mentioned state. As described above, the control device 10 connects the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) in parallel and controls the drive current therefor.

[0045] The mechanism for parallel connection of the coils 22 in the second inverter 42 is the same as that of the first inverter 41 except that it operates with a phase shift of 90 degrees relative to the first inverter 41, and therefore a description thereof will be omitted.

[0046] (2) When the coil 22 is connected in series The control device 10 turns the first connection changeover switch 413 on, and turns the third switch 411C and fourth switch 411D of the first inverter 41 and the first switch 412A and second switch 412B of the second inverter 42 off. When the first connection changeover switch 413 is turned on, the eleventh inverter 411 and the twelfth inverter 412 are electrically connected to each other. As a result, the first inverter 41 configures an H-bridge by the first switch 411A, the second switch 411B, the third switch 412C, and the fourth switch 412D. The control device 10 switches the first switch 411A and the fourth switch 412D, and the second switch 411B and the third switch 412C, between the on and off states, respectively, as a pair. As a result, the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) are driven in a state in which they are connected in series.

[0047] [Charging mode function] Here, a case will be described in which the first inverter 41 and the second inverter 42 are used as a charging circuit when charging the battery 30 with an external charger (not shown) in a so-called plug-in electric vehicle. Generally, a charging circuit that connects an external charger includes a reactor and a switching element for voltage adjustment, and an isolation transformer.

[0048] As described above, the traction motor 20 of this embodiment is configured with spatial phase orthogonal and open windings, and therefore, by electrically separating the α phase and the β phase and controlling them individually, it is possible to give the phases different functions.

[0049] For example, the traction motor 20 can have the α phase function as an insulating transformer and the β phase function as a reactor. The drive circuit 40 of this embodiment causes the coil 22 of the first inverter 41 to function as an insulating transformer, and causes the coil 22 of the second inverter 42 to function as a reactor.

[0050] (1) When the coil 22 of the second inverter 42 functions as a reactor The drive circuit 40 includes a disconnection switch 424 in the second inverter 42. The disconnection switch 424 includes a first disconnection switch 424A and a second disconnection switch 424B. The first disconnecting switch 424A is connected in series to the β-phase coil 222-1 (coil β1), and the second disconnecting switch 424B is connected in series to the β-phase coil 222-2 (coil β2).

[0051] When the coil 22 of the second inverter 42 is caused to function as a charging reactor, the control device 10 turns off the disconnection switches 424 (the first disconnection switch 424A and the second disconnection switch 424B). As a result, one end of the β-phase coil 222-1 (coil β1) and one end of the β-phase coil 222-2 (coil β2) are both open. By connecting each phase of an external charger to one end of the coil 22 opened by the disconnection switch 424, the β-phase coil 222-1 (coil β1) and the β-phase coil 222-2 (coil β2) can function as a reactor for charging.

[0052] As an example, a charger connection circuit (not shown) connects the U phase of an external charger to one end of the β-phase coil 222-1 (coil β1), the V phase to the midpoint of the second connection changeover switch 423, and the W phase to one end of the β-phase coil 222-2 (coil β2). In this case, each switch element of the second inverter 42 functions as an inverter that converts the power supplied from the external charger into a charging current for the battery 30.

[0053] (2) When the coil 22 of the first inverter 41 functions as an insulating transformer When the battery 30 is charged with power supplied from an external charger, it is preferable that the external charger (not shown) and the battery 30 are electrically insulated. For example, when an external charger is connected to the second inverter 42 side, by placing an isolation transformer between the second inverter 42 and the battery 30, the second inverter 42 and the battery 30 can be electrically isolated from each other. When charging from an external charger, the drive system 1 causes the first inverter 41 to function as an isolation transformer.

[0054] The drive circuit 40 includes a disconnection switch 414 in the first inverter 41. The disconnection switch 414 includes a first disconnection switch 414A and a second disconnection switch 414B. The first disconnection switch 414A is disposed on the positive side (high potential side) of the battery 30 in the power supply wiring between the eleventh inverter 411 and the twelfth inverter 412. The second disconnection switch 414B is disposed on the negative side (low potential side) of the battery 30 in the power supply wiring between the eleventh inverter 411 and the twelfth inverter 412.

[0055] When the coil 22 of the first inverter 41 is made to function as an isolation transformer, the control device 10 turns off the disconnection switches 414 (the first disconnection switch 414A and the second disconnection switch 414B). As a result, the power supply wiring of the eleventh inverter 411 and the power supply wiring of the twelfth inverter 412 are insulated from each other.

[0056] As described above, the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) are wound around the common tooth 23 (α-phase tooth 23-1) and are magnetically coupled to each other. Therefore, AC power supplied to the twelfth inverter 412 from an external charger connected to the second inverter 42 side is transmitted from the α-phase coil 221-2 (coil α2) to the α-phase coil 221-1 (coil α1) via the magnetic coupling. As a result, the battery 30 is charged with the power transmitted to the α-phase coil 221-1 (coil α1). That is, the first inverter 41 functions as an isolation transformer, electrically insulating the second inverter 42 side from the battery 30, while transmitting power by magnetic coupling.

[0057] As described above, the first inverter 41 and the second inverter 42 of this embodiment function as a circuit for driving the traction motor 20, and also function as a circuit for charging the battery 30 when an external charger is connected. In other words, the drive circuit 40 of this embodiment can serve as a charging reactor, inverter, and isolation transformer, which reduces the number of parts and enables weight and cost reduction compared to when these functions are configured in a circuit dedicated to charging.

[0058] [Discharge Control by Control Device 10] Next, the discharge control by the control device 10 will be described. The control device 10 of this embodiment controls the traction motor 20 based on a request from a higher-level system (e.g., a power plant control system) of the electric vehicle. As an example, the request from the higher-level system includes a discharge request RD. The discharge request RD is an instruction to the control device 10 to discharge the power stored in the capacitor 50 when the battery contactor 31 is disconnected.

[0059] An example of the flow of the discharge control operation of the control device 10 will be described with reference to FIG. FIG. 5 is a diagram showing an example of the flow of operations of the control device 10 of this embodiment.

[0060] (Step S10) The control unit 110 of the control device 10 determines the connection state of the battery contactor 31 based on the control of the higher-level system. If the control unit 110 determines that the battery contactor 31 is not released (open) (i.e., is in the ON state) (step S10; NO), the process proceeds to step S20.

[0061] (Step S20) If the battery contactor 31 is in the ON state, the control unit 110 performs normal control. Here, normal control refers to general control other than overvoltage avoidance control. The control unit 110 returns the process to step S10 and continues to determine the connection state of the battery contactor 31.

[0062] On the other hand, in step S10, if the control unit 110 determines that the battery contactor 31 is released (that is, in the OFF state) (step S10; YES), the process proceeds to step S30.

[0063] (Step S30) When the battery contactor 31 is released, the control unit 110 performs gate-off control. Specifically, the control unit 110 turns off the inter-phase switch 45 (switch unit). As a result, the first inverter 41 and the second inverter 42 are electrically isolated from each other.

[0064] The electric vehicle, which is the object of control of the drive system 1, continues to run by inertia even after the battery contactor 31 is released. As a result, a back electromotive force generated in the traction motor 20 is applied to the drive circuit 40. When the battery contactor 31 is released, a charging path is formed from the coil 22 to the capacitor 50 via a parasitic diode of the inverter (first inverter 41 or second inverter 42). If the back electromotive force is greater than the voltage between the electrodes of the capacitor 50 (i.e., the battery minimum voltage VBattL), a charging current flows to the capacitor 50 via the charging path to the capacitor 50, and regenerative power is generated. Therefore, depending on the state of inertial running of the electric vehicle, an overvoltage may be applied to the capacitor 50. The control unit 110 performs control to avoid an overvoltage so that an overvoltage is not applied to the capacitor 50. A specific flow of the operation of the control unit 110 to avoid an overvoltage will be described.

[0065] (Step S40) The control unit 110 acquires the battery voltage VBatt and the back electromotive force generated by the coil 22 using a voltage sensor (not shown). The control unit 110 compares the battery voltage VBatt immediately after the battery contactor 31 is released (i.e., the battery minimum voltage VBattL) with the back electromotive force generated in the traction motor 20 to determine whether regenerative power is being generated.

[0066] The battery minimum voltage VBattL indicates the voltage across the capacitor 50 immediately after the battery contactor 31 is released. If the battery minimum voltage VBattL≧the back electromotive force, the control unit 110 determines that an overvoltage is not applied to the capacitor 50 (step S40; NO), and ends the control for avoiding the overvoltage. On the other hand, if the battery minimum voltage VBattL<the back electromotive voltage (step S40; YES), the control unit 110 advances the process to step S50. In this example, the control unit 110 determines the generation of regenerative power by comparing the back electromotive force voltage with the battery voltage, but the generation of regenerative power may be determined by detecting current instead of comparing voltages. In this case, the regenerative power can be detected by a known method, such as providing a current sensor in the current path to the capacitor.

[0067] (Step S50) The control unit 110 determines whether the coils 22 of each phase are in a series connection state (i.e., series operation). If the control unit 110 determines that the coils 22 of each phase are in a parallel connection state (step S50; NO), the control unit 110 proceeds to step S70. If the control unit 110 determines that the coils 22 of each phase are in a series connection state (step S50; YES), the control unit 110 proceeds to step S60.

[0068] (Step S60) The control unit 110 switches the coils 22 of each phase to a parallel connection state (i.e., parallel operation). Specifically, the control unit 110 switches the first connection changeover switch 413 of the first inverter 41 to the OFF state, and operates the eleventh inverter 411 and the twelfth inverter 412 individually. Furthermore, the control unit 110 switches the second connection changeover switch 423 of the second inverter 42 to the OFF state, and operates the twenty-first inverter 421 and the twenty-second inverter 422 individually.

[0069] 6 is a diagram showing an example of the back electromotive force in the drive circuit 40 of this embodiment. When the coils 22 are operated in series, the back electromotive force generated in the first coil group L1 and the back electromotive force generated in the second coil group L2 are superimposed.

[0070] For example, a case will be described in which a back electromotive force V1 is generated in each of the α-phase coil 221-1 (coil α1) of the first coil group L1 and the α-phase coil 221-2 (coil α2) of the second coil group L2 in the first inverter 41.

[0071] As described above, the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) are wound around the common α-phase tooth 23-1, and the phase difference δα is 0 (zero). Therefore, when the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) are connected in series, the combined back electromotive force becomes a back electromotive force V2 that is twice the back electromotive force V1.

[0072] The back electromotive force V2 is a relatively high voltage. Therefore, the back electromotive force V2 may become higher than the capacitor voltage V3, which is the voltage between the electrodes of the capacitor 50 immediately after the battery contactor 31 is released (i.e., the battery minimum voltage VBattL). In this case, depending on the state of inertial running of the electric vehicle, a charging current may flow from the coil 22 to the capacitor 50, causing an overvoltage of the capacitor 50.

[0073] On the other hand, when the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) are connected in parallel, the combined back electromotive force remains at back electromotive force V1. That is, when the first coil group L1 and the second coil group L2 are connected in parallel, the combined back electromotive force is lower than when they are connected in series. For this reason, the back electromotive force V2 is unlikely to become higher than the capacitor voltage V3, which is the voltage between the electrodes of the capacitor 50 immediately after the battery contactor 31 is released (i.e., the battery minimum voltage VBattL). Therefore, when the first coil group L1 and the second coil group L2 are operated in parallel, it is easier to prevent the capacitor 50 from becoming overvoltage than when they are operated in series. That is, according to the drive system 1 configured as described above, it is easy to avoid an overvoltage on the capacitor 50.

[0074] The control unit 110 may control the second inverter 42 in the same manner as the first inverter 41. The control of the second inverter 42 by the control unit 110 is similar to the control of the first inverter 41, and therefore a description thereof will be omitted.

[0075] (Step S70) Returning to FIG. 5, the control unit 110 determines whether the back electromotive force has decreased. Specifically, the control unit 110 determines whether the back electromotive force has decreased below a predetermined threshold. The predetermined threshold is, for example, a threshold set by subtracting a voltage value that takes a predetermined safety factor into account from the battery minimum voltage VBattL.

[0076] When the control unit 110 determines that the back electromotive force has become lower than the predetermined threshold value (step S70; YES), it ends the control for avoiding the overvoltage. On the other hand, if the control unit 110 determines that the back electromotive force has not decreased (step S70; NO), the control unit 110 advances the process to step S80. In this example, the control unit 110 determines the generation of regenerative power by comparing the back electromotive force voltage with the battery voltage, but the generation of regenerative power may be determined by detecting current instead of comparing voltages. In this case, the regenerative power can be detected by a known method, such as providing a current sensor in the current path to the capacitor.

[0077] (Step S80) If the back electromotive force has not decreased, the control unit 110 performs overvoltage avoidance control. An example of the overvoltage avoidance control will be described with reference to FIG.

[0078] 7 shows an example of the settings of each switch in the overvoltage avoidance control of this embodiment. The control unit 110 controls the on / off state of each switch of the drive circuit 40 based on the settings shown in FIG. 7. The setting information shown in FIG. 7 is stored in advance in the storage unit 120 as overvoltage avoidance control information. The control unit 110 controls each switch of the drive circuit 40 by reading out the overvoltage avoidance control information stored in the storage unit 120. An example of a current circuit formed as a result of controlling each switch based on the lower overvoltage avoidance control information shown in the figure will be described with reference to FIG.

[0079] FIG. 8 is a diagram showing an example of a current circuit formed in the overvoltage avoidance control of this embodiment. In the first inverter 41, a circuit is formed that passes through the α-phase coil 221-1 (coil α1), the second switch 411B, the second disconnect switch 414B, the second switch 412B, the α-phase coil 221-2 (coil α2), the third switch 412C, the first disconnect switch 414A, the third switch 411C, and returns to the α-phase coil 221-1 (coil α1).

[0080] In the second inverter 42, a circuit is formed that passes through the β-phase coil 222-1 (coil β1), the first disconnect switch 424A, the second switch 421B, the second switch 422B, the second disconnect switch 424B, the β-phase coil 222-2 (coil β2), the third switch 422C, the third switch 421C, and returns to the β-phase coil 222-1 (coil β1).

[0081] As a result, the capacitor 50 is disconnected from the current circuit including the coil 22, and therefore no overvoltage is applied to the capacitor 50.

[0082] In addition, in the circuit shown in the figure, the black circle side of the first coil group L1 is connected to the black circle side of the second coil group L2, that is, the first coil group L1 and the second coil group L2 are connected in opposite phases. As described above, the α-phase coil 221-1 (coil α1) and the α-phase coil 221-2 (coil α2) are wound around the common α-phase tooth 23-1, and the phase difference δα is 0. Therefore, even if a back electromotive force is generated in the coil 22 due to the inertial running of the electric vehicle, no back electromotive force flows in the current circuit described above. Because no back electromotive force flows through the drive circuit 40, the generation of Joule heat is suppressed and no back electromotive force is consumed. With the drive system 1 configured in this way, no braking torque is generated in the traction motor 20 due to power consumption, and vibrations and noise caused by torque fluctuations can be suppressed.

[0083] The control unit 110 returns the process to step S70 and determines whether or not the back electromotive force has decreased. If the control unit 110 determines that the back electromotive force has decreased, it ends the overvoltage avoidance control.

[0084] As described above, according to the drive system 1 of this embodiment, it is possible to prevent the capacitor 50 from becoming overvoltage when the battery contactor 31 is released.

[0085] Furthermore, the drive system 1 of this embodiment can prevent overvoltage of the capacitor 50 by simple control of the traction motor 20 without using a control method that requires a relatively large amount of calculation, such as vector control.

[0086] For example, in a configuration in which overvoltage is avoided while controlling the traction motor 20 by vector control, it is necessary to sense the rotation angle of the rotor 21 and perform feedback calculations based on the sensed rotation angle. In this case, feedback calculations based on the sensed rotation angle are essential to prevent the traction motor 20 from generating torque when performing discharge control.

[0087] On the other hand, the drive system 1 of this embodiment does not rely on vector control, but simply controls the circuit configuration through the winding configuration and magnetic design of the coil 22, thereby avoiding the occurrence of overvoltage without generating torque in the traction motor 20.

[0088] [Variations] In the above-described embodiment, it is assumed that the drive circuit 40 and the control device 10 are configured as separate devices. In the above-described embodiment, the control unit 110 of the control device 10 performs the overvoltage avoidance control, but this is not limited to this. In this modification, among the functions of the control unit 110 described above, at least a circuit that performs overvoltage avoidance control may be provided in the drive circuit 40. Also, in the above embodiment, the generation of regenerative power is determined by comparing the back electromotive force with the battery voltage, but the generation of regenerative power may be determined by detecting current instead of comparing voltages. In that case, the regenerative power can be detected by a known method, such as providing a current sensor in the current path to the capacitor.

[0089] The drive circuit 40 may include gate drive circuits for the transistors (for example, the first switch 421A to the fourth switch 422D) that constitute the first inverter 41 and the second inverter . When the drive circuit 40 is configured with a gate drive circuit in this way, the overvoltage prevention control may be configured as an integral part of the gate drive circuit.

[0090] Here, "integrated" refers to a case where the gate drive circuit and the overvoltage avoidance control circuit are configured on the same board, or a case where the gate drive circuit and the overvoltage avoidance control circuit are configured on separate boards and these boards are connected to each other by jumper wires or removable (or non-removable) stacking connectors.

[0091] In some cases, the drive circuit 40 is housed in a case (enclosure) for waterproofing, dustproofing, and strength enhancement. In this case, integration refers to the case where the gate drive circuit and the overvoltage avoidance control circuit are configured in the same case.

[0092] In general, the control device 10 is required to perform relatively complex calculations to drive the traction motor 20, and therefore is configured by a computer with relatively high calculation performance. On the other hand, as described above, the overvoltage avoidance control effectively utilizes the characteristic of the coils 22 of the traction motor 20, that is, the phase difference δ between the coils 22 of each phase is 0 (zero). That is, by connecting the coils 22 of the traction motor 20 in opposite phase, the overvoltage avoidance control suppresses the generation of current and prevents the traction motor 20 from generating torque, while also preventing the application of overvoltage to the capacitor 50. In other words, the overvoltage avoidance control can be realized with a relatively simple circuit that turns predetermined switches of the first inverter 41 and the second inverter 42 on or off. Therefore, the overvoltage prevention control circuit can be easily integrated with the gate drive circuit.

[0093] In the drive system 1 of this modified example, the gate drive circuits of the transistors that make up the first inverter 41 and the second inverter 42 are integrated with the overvoltage avoidance control, so even if the sensor for sensing the rotation angle of the rotor 21 cannot be used due to an impact such as a collision, or if the relatively high-performance computer required for feedback calculations does not work, the driving motor 20 can be discharged without generating torque.

[0094] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment and can be appropriately modified without departing from the spirit of the present invention. The configurations described in the above-described embodiments may be combined.

[0095] Each unit included in each device in the above-described embodiments may be realized by dedicated hardware, or may be realized by a memory and a microprocessor.

[0096] In addition, each part of each device may be composed of a memory and a CPU (central processing unit), and the functions of each part of each device may be realized by loading a program into memory and executing it. [Explanation of symbols]

[0097] 1... drive system, 10... control device, 110... control unit, 120... memory unit, 20... traction motor, 21... rotor, 22... coil, L1... first coil group, α1... eleventh coil, α2... twelfth coil, L2... second coil group, β1... 21st coil, β2... 22nd coil, 23... stator, 30... battery, 31... battery contactor, 40... drive circuit, 41... first inverter, 411... eleventh inverter (first inverter), 411A... first switch, 411B... second switch, 411C... third switch, 411E... fourth switch, 412... twelfth inverter (second inverter), 412A... first switch, 412B... second switch, 412C... third switch, 412D... fourth switch , 413...first connection changeover switch, 414...disconnection switch, 414A...first disconnection switch, 414B...second disconnection switch, 42...second inverter, 421...21st inverter (first inverter), 421A...first switch, 421B...second switch, 421C...third switch, 421D...fourth switch, 422...22nd inverter (second inverter), 422A...first switch, 422B...second switch, 422C...third switch, 422D...fourth switch, 423...second connection changeover switch, 424...disconnection switch, 424A...first disconnection switch, 424B...second disconnection switch, 45...interphase switch (switch unit), 450...power supply unit, 460...discharge control unit, 50...capacitor

Claims

1. A drive system for an electric vehicle that uses battery power to drive a traction motor having a plurality of phases, each phase having a first coil group and a second coil group whose connection state can be switched between a series connection connected in series with each other and a parallel connection connected in parallel with each other, a drive circuit including a first inverter connected to the first coil group and a second inverter connected to the second coil group for each phase of the traction motor; a control unit that performs switching control to switch the first coil group and the second coil group to a parallel connection when a capacitor connected in parallel between the positive and negative electrodes of the battery and the battery are electrically disconnected and there is a request to discharge the capacitor, the first coil group and the second coil group are connected in series, and regenerative power is generated by electromotive forces generated by the first coil group and the second coil group; A drive system comprising:

2. The drive circuit a respective phase inverter, which is a pair of the first inverter and the second inverter, provided for each phase of the traction motor; a switch unit that controls the exchange of power between the plurality of phase inverters by connecting and disconnecting a power supply line that supplies power from the battery to each of the plurality of phase inverters; Equipped with The control unit turns the switch unit into a disconnected state when the discharge request is received. The drive system of claim 1 .

3. When the discharge request is received and regenerative power is generated by electromotive forces generated by the first coil group and the second coil group in a state in which the series connection is switched to the parallel connection, the control unit sets the switch unit to a disconnected state. The drive system of claim 2 .

4. When the discharge request is received and the first coil group and the second coil group are connected in parallel, the control unit controls a connection state of the first inverter and the second inverter to connect the same poles of the first coil group and the second coil group in a closed circuit passing through the first coil group and the second coil group. The drive system of claim 1 .

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