Motor drive system

Abstract

This motor drive system, for an electric vehicle comprising a motor having one rotor and two stators, comprises: a motor that outputs driving power for vehicle wheels and is capable of generating regenerative power; an inverter that controls each of electric power supplied to the two stators and the regenerative power; a battery that is capable of charging the regenerative power generated by the motor; a booster circuit provided between the inverter and the battery; a switching unit that switches the connection states of the two stators with respect to the inverter between a series connection and a parallel connection; and a control unit that controls the operation of the switching unit, wherein when the regenerative power is generated, the control unit controls the operation of the switching unit and switches the two stators into the series connection or the parallel connection.

Description

Technical Field

[0001] The present disclosure relates to a motor drive system.

Background Art

[0002] Hybrid electric vehicles and pure electric vehicles without an internal combustion engine (hereinafter collectively referred to as electric vehicles) are equipped with a drive motor that outputs the driving force of the vehicle. The drive motor is also used as a regenerative brake when the vehicle decelerates and has a function of generating electricity using the rotational torque of the wheels (hereinafter also referred to as "regenerative power generation"). The electricity generated by regenerative power generation (regenerative power generation electricity) is charged to the battery. Electric vehicles that have been put into practical use so far are equipped with one drive motor, and the drive of the drive motor is controlled by one inverter (see, for example, Patent Document 1).

[0003] In recent years, the practical application of electric vehicles equipped with multiple drive motors has been promoted. For example, there are electric vehicles equipped with a front-wheel drive motor and a rear-wheel drive motor, and electric vehicles equipped with a drive motor corresponding to each wheel. Furthermore, electric vehicles using a double-stator type axial gap motor having two stators as a drive motor have also been studied (see, for example, Patent Document 2). In such electric vehicles, a plurality of inverters that drive each drive motor or stator are connected in parallel to the battery.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, it is known that the voltage of the regenerative power generated from the inverter when the drive motor is used as a regenerative brake (hereinafter also referred to as "regenerative power generation voltage") is proportional to the rotational speed of the drive motor. Therefore, when the vehicle decelerates while traveling at a low or medium speed, there is a possibility that the regenerative power generation voltage may be insufficient with respect to the charging voltage of the battery. In fact, vehicle deceleration often occurs while the vehicle is traveling at a low or medium speed compared to when it is traveling at a high speed.

[0006] On the other hand, there is a technique of providing a boost - buck circuit between the inverter and the battery. However, when the difference between the regenerative power generation voltage and the charging voltage of the battery is large, it is necessary to increase the current of the regenerative power generated from the inverter on the low - voltage side (hereinafter also referred to as "regenerative power generation current"). When increasing the regenerative power generation current to boost up to the charging voltage of the battery, the driving frequency of the switching elements provided in the inverter increases. Therefore, the energy lost due to heat increases, and there is a possibility that the regeneration efficiency may decrease.

[0007] The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a motor drive system for an electric vehicle including a motor having one rotor and two stators, which can suppress a decrease in regeneration efficiency when charging the battery with regenerative power.

Means for Solving the Problems

[0008] In order to solve the above problems, according to an aspect of the present disclosure, a motor including one rotor and two stators, capable of outputting a driving force for a wheel and generating regenerative power, an inverter that controls the power supplied to the two stators and the regenerative power respectively, a battery that can be charged with the regenerative power generated by the motor, a boost - buck circuit provided between the inverter and the battery, a switching unit that switches the connection state of the two stators to the inverter between series and parallel, A control unit that controls the operation of the switching unit, and when generating the regenerative power, the control unit controls the operation of the switching unit to switch the two stators in series or in parallel, and a motor drive system for an electric vehicle is provided.

Advantages of the Invention

[0009] As described above, according to the present disclosure, in a motor drive system for an electric vehicle including a motor having one rotor and two stators, it is possible to suppress a decrease in regeneration efficiency when charging a battery with regenerative power generation power.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0011] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0012] <1. Configuration Example of Vehicle> First, an example of the overall configuration of a vehicle to which the motor drive system according to the embodiment of the present disclosure is applied will be described. The motor drive system according to the present embodiment includes a front-wheel drive motor for driving the front wheels and a rear-wheel drive motor for driving the rear wheels. In the present embodiment, a double-stator type axial gap motor is used as the front-wheel drive motor and the rear-wheel drive motor.

[0013] FIG. 1 is a schematic diagram showing a configuration example of a vehicle to which the motor drive system according to the present embodiment is applied. The vehicle 1 shown in FIG. 1 is an electric vehicle with four-wheel drive equipped with a left front wheel 3LF, a right front wheel 3RF, a left rear wheel 3LR, and a right rear wheel 3RR (hereinafter, collectively referred to as "wheel 3" when no particular distinction is required). The vehicle 1 includes a front-wheel drive motor 10F and a rear-wheel drive motor 10R as driving power sources for generating the driving torque of the vehicle 1. The driving torque output from the front-wheel drive motor 10F is transmitted to the left front wheel 3LF and the right front wheel 3RF (hereinafter, collectively referred to as "front wheel 3F" when no particular distinction is required). The driving torque output from the rear-wheel drive motor 10R is transmitted to the left rear wheel 3LR and the right rear wheel 3RR.

[0014] The vehicle 1 includes a motor drive system 2 and a hydraulic brake system 16. Among these, the hydraulic brake system 16 includes brake devices 17LF, 17RF, 17LR, 17RR provided on each wheel 3 (hereinafter, collectively referred to as brake device 17) and a brake hydraulic control device 19 for controlling the hydraulic pressure supplied to each brake device 17. Each brake device 17 is configured as a device that applies a braking force to the wheel 3 by sandwiching a brake disk that rotates with the wheel 3 with brake pads using the supplied hydraulic pressure.

[0015] The brake hydraulic control device 19 includes an electric motor pump that discharges brake fluid, a plurality of solenoid valves that adjust the hydraulic pressure supplied to each brake device 17, and a brake control device that controls the driving of these electric motor pump and solenoid valves. The hydraulic brake system 16 generates a predetermined braking force on each of the front, rear, left, and right drive wheels 3LF, 3RF, 3LR, and 3RR by controlling the hydraulic pressure supplied to each brake device 17. The hydraulic brake system 16 is used in combination with a regenerative brake using the front-wheel drive motor 10F and the rear-wheel drive motor 10R.

[0016] The motor drive system 2 includes a front-wheel drive motor 10F, a front-wheel inverter unit 20F, a rear-wheel drive motor 10R, a rear-wheel inverter unit 20R, a battery 40, and a control device 50. The specific configuration of the motor drive system 2 will be described in detail later.

[0017] Also, the vehicle 1 is provided with a vehicle state sensor 45. The vehicle state sensor 45 is connected to the control device 50 via a dedicated line or via communication means such as CAN (Controller Area Network) or LIN (Local Inter Net).

[0018] The vehicle state sensor 45 consists of one or more sensors that detect the operating state and behavior of the vehicle 1 (hereinafter also collectively referred to as "vehicle state"). The vehicle state sensor 45 includes at least one of, for example, a steering angle sensor, an accelerator position sensor, a brake stroke sensor, a brake pressure sensor, or an engine speed sensor, and detects the operating state of the vehicle 1 such as the steering angle of the steering wheel or the steering wheel, the accelerator opening, the brake operation amount, or the engine speed. Further, the vehicle state sensor 45 includes at least one of, for example, a vehicle speed sensor, an acceleration sensor, or an angular velocity sensor, and detects the behavior of the vehicle 1 such as the vehicle speed, the longitudinal acceleration, the lateral acceleration, or the yaw rate. The vehicle state sensor 45 transmits a sensor signal including the detected information to the control device 50.

[0019] In this embodiment, the vehicle state sensor 45 includes at least an accelerator position sensor, a brake stroke sensor, and a vehicle speed sensor. The accelerator position sensor detects the amount of operation of the accelerator pedal by the driver. For example, the accelerator position sensor may be a sensor that detects the amount of rotation of the rotation axis of the accelerator pedal, but is not particularly limited. The brake stroke sensor detects the amount of operation of the brake pedal by the driver. The brake stroke sensor may be a sensor that detects the amount of movement of the output rod connected to the brake pedal, a sensor that detects the amount of rotation of the rotation axis of the brake pedal, or a sensor that detects the stepping force of the brake pedal, but is not particularly limited. The vehicle speed sensor may be, for example, a sensor that detects the number of rotations of the rotation axis of the front-wheel drive motor 10F and the rear-wheel drive motor 10R, or either the front-wheel drive shaft 5F or the rear-wheel drive shaft 5R, but is not particularly limited.

[0020] <2. Motor Drive System> Subsequently, the configuration of the motor drive system 2 according to this embodiment will be specifically described. The motor drive system according to this embodiment includes one rotor and two stators, a motor that outputs the driving force of the wheels and can generate regenerative power, an inverter that controls the power supplied to the two stators and the regenerative power respectively, a battery that can charge the regenerative power generated by the motor, a boost circuit provided between the inverter and the battery, a switching unit that switches the connection state of the two stators to the inverter in series and parallel, and a control unit that controls the operation of the switching unit. In the motor drive system of an electric vehicle, when generating regenerative power, the control unit has a configuration that controls the operation of the switching unit to switch the two stators in series or parallel.

[0021] Note that the state in which two stators are connected in parallel refers to a connection state in which the current supplied to one of the two stators via an inverter returns to the inverter without passing through the other stator. Also, the state in which two stators are connected in series refers to a connection state in which the current supplied to one of the two stators via an inverter returns to the inverter via the other stator.

[0022] Also, the inverter corresponds to the inverter circuit in the following embodiments. The boost circuit corresponds to the buck-boost circuit in the following embodiments. The battery indicates, for example, a battery pack in which a plurality of battery cells are connected in series.

[0023] (2-1. System Configuration) FIG. 2 is an explanatory diagram showing the configuration of the motor drive system according to the present embodiment. FIG. 2 is a block diagram schematically showing the configuration of the motor drive system.

[0024] The motor drive system 2 includes a front-wheel drive motor 10F, a front-wheel inverter unit 20F, a front-wheel converter unit 30F, a rear-wheel drive motor 10R, a rear-wheel inverter unit 20R, a rear-wheel converter unit 30R, a battery 40, and a control device 50. The battery 40 is a rechargeable secondary battery. The battery 40 may be, for example, a lithium-ion battery with a rated voltage of 200V, but the rated voltage and type of the battery 40 are not particularly limited.

[0025] The battery 40 is connected to the front-wheel drive motor 10F via the front-wheel converter unit 30F and the front-wheel inverter unit 20F, and is also connected to the rear-wheel drive motor 10R via the rear-wheel converter unit 30R and the rear-wheel inverter unit 20R. The battery 40 stores the electric power supplied to the front-wheel drive motor 10F and the rear-wheel drive motor 10R. The battery 40 is provided with a battery management device 41 that detects the open-circuit voltage, output voltage, battery temperature, etc. of the battery 40 and transmits them to the control device 50.

[0026] The front-wheel drive motor 10F outputs a driving torque that is transmitted to the front wheels 3F via the front-wheel differential mechanism 7F and the front-wheel drive shaft 5F. The rear-wheel drive motor 10R outputs a driving torque that is transmitted to the rear wheels 3R via the rear-wheel differential mechanism 7R and the rear-wheel drive shaft 5R. The driving of the front-wheel drive motor 10F and the rear-wheel drive motor 10R is controlled by the control device 50. In the present embodiment, a double-stator type axial gap motor is used as the front-wheel drive motor 10F and the rear-wheel drive motor 10R.

[0027] The double-stator type axial gap motor has an axial gap structure in which the rotors 13F and 13R are sandwiched by a first stator 11Fa, 11Ra and a second stator 11Fb, 11Rb provided on both sides in the rotational axis direction of the rotors 13F, 13R via gaps, respectively.

[0028] In the present embodiment, the front-wheel drive motor 10F and the rear-wheel drive motor 10R are configured as three-phase alternating current motors. However, the number of phases is not particularly limited. The front-wheel drive motor 10F rotates the rotor 13F by a rotating magnetic field formed by supplying three-phase alternating current to the first stator 11Fa and the second stator 11Fb, respectively, and outputs a driving torque. Further, the front-wheel drive motor 10F has a function of performing regenerative power generation by rotating the rotor 13F in response to the rotational torque of the front wheels 3F transmitted via the front-wheel drive shaft 5F in a state where three-phase alternating current is not supplied to the first stator 11Fa and the second stator 11Fb. The rear-wheel drive motor 10R connected to the rear wheels 3R has the same function.

[0029] The front-wheel inverter unit 20F includes a boost-buck circuit 31F, an inverter circuit 21F, and a switching unit 29F. The rear-wheel inverter unit 20R includes a boost-buck circuit 31R, an inverter circuit 21R, and a switching unit 29R. The front-wheel inverter unit 20F and the rear-wheel inverter unit 20R have the same function. Hereinafter, the configuration and function of the inverter unit will be described by taking the front-wheel inverter unit 20F as an example.

[0030] The step-up / down circuit 31F adjusts the voltage of the power generated by regeneration by the first stator 11Fa and the second stator 11Fb of the front-wheel drive motor 10F and output from the inverter circuit 21F, and supplies it to the battery 40. The step-up / down circuit 31F may have a function of adjusting the voltage of the supply current when supplying current to the inverter circuit 21F. The drive of the step-up / down circuit 31F is controlled by the control device 50.

[0031] The inverter circuit 21F converts the DC power drawn from the battery 40 into three-phase AC power and supplies it to the first stator 11Fa and the second stator 11Fb of the front-wheel drive motor 10F. Further, the inverter circuit 21F converts the three-phase AC power regenerated by the first stator 11Fa and the second stator 11Fb into DC power and supplies it to the step-up / down circuit 31F. The drive of the inverter circuit 21F is controlled by the control device 50.

[0032] The switching unit 29F switches the connection state of the first stator 11Fa and the second stator 11Fb to the inverter circuit 21F between series and parallel. The switching unit 29F includes a plurality of switches provided for each coil of each phase of the first stator 11Fa and the second stator 11Fb. The switch may be, for example, a relay, but may be a switch other than a relay as long as it can be driven and controlled by the control device 50.

[0033] Subsequently, the configuration of the drive circuit of the drive motor will be described in detail. The drive circuits of the front-wheel drive motor 10F and the rear-wheel drive motor 11R have the same configuration. Hereinafter, the configuration of the drive circuit of the front-wheel drive motor 10F will be described, and the description of the configuration of the drive circuit of the front-wheel drive motor 10F will be omitted as appropriate.

[0034] FIG. 3 shows a circuit diagram of the drive circuit of the front-wheel drive motor. The buck-boost circuit 31F is configured to include a coil 39, two switching elements 35 and 37, and a smoothing capacitor 33. The buck-boost circuit 31F includes an upper arm electrically connected to the upper arm side of the inverter circuit 21, and a lower arm electrically connected to the lower arm side of the inverter circuit 21F. Switching elements 35 and 37 with diodes electrically connected in anti-parallel are respectively provided on the upper arm and the lower arm. The switching elements 35 and 37 may be, for example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) or IGBTs (Insulated Gate Bipolar Transistors), but other switching elements may also be used.

[0035] One end of the coil 39 is electrically connected to the positive electrode side of the battery 40, and the other end of the coil 39 is electrically connected between the two switching elements 35 and 37. The smoothing capacitor 33 is connected in parallel with the battery 40 with respect to the inverter circuit 21F. The driving of each of the switching elements 35 and 37 is controlled by the control device 50.

[0036] The inverter circuit 21F is configured to include a plurality of switching elements. The driving of each switching element of the inverter circuit 21F is controlled by the control device 50. The inverter circuit 21F includes three arm circuits 23u, 23v, and 23w (hereinafter, simply referred to as the arm circuit 23 in general unless otherwise distinguished).

[0037] The arm circuit 23u is electrically connected to the u-phase coils of the first stator 11Fa and the second stator 11Fb of the front-wheel drive motor 10F. The arm circuit 23u, the u-phase coil of the first stator 11Fa, and the u-phase coil of the second stator 11Fb are electrically connected at the branching portion 26u. The arm circuit 23v is electrically connected to the v-phase coils of the first stator 11Fa and the second stator 11Fb of the front-wheel drive motor 10F. The arm circuit 23v, the v-phase coil of the first stator 11Fa, and the v-phase coil of the second stator 11Fb are electrically connected at the branching portion 26v. The arm circuit 23w is electrically connected to the w-phase coils of the first stator 11Fa and the second stator 11Fb of the front-wheel drive motor 10F. The arm circuit 23w, the w-phase coil of the first stator 11Fa, and the w-phase coil of the second stator 11Fb are electrically connected at the branching portion 26w.

[0038] Each arm circuit 23 includes an upper arm on the upstream side of the current and a lower arm on the downstream side of the current. Switching elements 25u, 27u, 25v, 27v, 25w, and 27w, in which diodes are electrically connected in antiparallel, are respectively provided on the upper arm and the lower arm of each arm circuit 23. The switching elements 25u, 27u, 25v, 27v, 25w, and 27w may be, for example, MOSFETs or IGBTs, but may also be other switching elements.

[0039] The u-phase, v-phase, and w-phase coils of the first stator 11Fa of the front-wheel drive motor 10F are electrically connected to the connection portions between the upper arm and the lower arm of each of the arm circuits 23u, 23v, and 23w, respectively. Also, the u-phase, v-phase, and w-phase coils of the first stator 11Fa are electrically connected to each other at the connection portion 28a. The driving of the switching elements 25u, 27u, 25v, 27v, 25w, and 27w of each arm circuit 23u, 23v, and 23w is controlled by the control device 50. Thereby, the rotational drive of the rotor 13F by the first stator 11Fa of the front-wheel drive motor 10F and the regenerative power generation by the first stator 11Fa are controlled.

[0040] Similarly, the coils of the u-phase, v-phase, and w-phase of the second stator 11Fb of the front-wheel drive motor 10F are electrically connected to the connection parts between the upper arms and the lower arms of the respective arm circuits 23u, 23v, and 23w. The coils of the u-phase, v-phase, and w-phase of the second stator 11Fb are electrically connected to each other at the connection part 28b. The driving of the switching elements 25u, 27u, 25v, 27v, 25w, and 27w of the respective arm circuits 23u, 23v, and 23w is controlled by the control device 50. Thereby, the rotational drive of the rotor 13F by the second stator 11Fb and the regenerative power generation by the second stator 11Fb are controlled.

[0041] The switching unit 29F includes a first switch 29aa, a second switch 29ab, and a third switch 29ac provided for each of the coils of the u-phase, v-phase, and w-phase of the first stator 11Fa. Further, the switching unit 29F includes a fourth switch 29ba, a fifth switch 29bb, and a sixth switch 29bc provided for each of the coils of the u-phase, v-phase, and w-phase of the second stator 11Fb.

[0042] The first switch 29aa is provided between the coil of the u-phase of the first stator 11Fa and the branching part 26u. The first switch 29aa switches the electrical connection and disconnection (on / off) between the branching part 26u and the coil of the u-phase. The second switch 29ab is provided between the coil of the v-phase of the first stator 11Fa and the branching part 26v. The second switch 29ab switches the electrical connection and disconnection (on / off) between the branching part 26v and the coil of the v-phase. The third switch 29ac is provided between the coil of the w-phase of the first stator 11Fa and the branching part 26w. The third switch 29ac switches the electrical connection and disconnection (on / off) between the branching part 26w and the coil of the w-phase.

[0043] The fourth switch 29ba is provided between the u-phase coil of the second stator 11Fb and the connection part 28b. The fourth switch 29ba switches between a first connection state in which the u-phase coil is connected to the connection part 28b of the second stator 11Fb and a second connection state in which the u-phase coil is connected to the u-phase coil of the first stator 11Fa. The fifth switch 29bb is provided between the v-phase coil of the second stator 11Fb and the connection part 28b. The fifth switch 29bb switches between a first connection state in which the v-phase coil is connected to the connection part 28b of the second stator 11Fb and a second connection state in which the v-phase coil is connected to the v-phase coil of the first stator 11Fa. The sixth switch 29bc is provided between the w-phase coil of the second stator 11Fb and the connection part 28b. The sixth switch 29bc switches between a first connection state in which the w-phase coil is connected to the connection part 28b of the second stator 11Fb and a second connection state in which the w-phase coil is connected to the w-phase coil of the first stator 11Fa.

[0044] By turning on the first switch 29aa, the second switch 29ab, and the third switch 29ac and setting the fourth switch 29ba, the fifth switch 29bb, and the sixth switch 29bc to the first connection state, the first stator 11Fa and the second stator Fb are connected in parallel to the inverter circuit 21F. On the other hand, by turning off the first switch 29aa, the second switch 29ab, and the third switch 29ac and setting the fourth switch 29ba, the fifth switch 29bb, and the sixth switch 29bc to the second connection state, the first stator 11Fa and the second stator Fb are connected in series to the inverter circuit 21F.

[0045] When the control device 50 controls the power running of the front-wheel drive motor 10F, the first stator 11Fa and the second stator 11Fb are connected in parallel to the inverter circuit 21F. In this state, the control device 50 controls the driving of the switching element of the boost-buck circuit 31F, boosts the output power of the battery 40, and supplies it to the inverter circuit 21F. The boost ratio is adjusted by the duty ratio of the on / off of the switching element. Further, the control device 50 controls the driving of the switching element of the inverter circuit 21F, converts the DC power supplied through the boost-buck circuit 31F into three-phase AC power, and supplies it to the first stator 11Fa and the second stator 11Fb of the front-wheel drive motor 10F.

[0046] Also, when the control device 50 controls the regenerative drive of the front-wheel drive motor 10F, according to the regeneration efficiency, it switches the connection state of the first stator 11Fa and the second stator 11Fb to the inverter circuit 21F in series or in parallel. In this state, the control device 50 controls the driving of the switching element of the inverter circuit 21F, converts the three-phase AC regenerative power generated from the front-wheel drive motor 10F into DC power, and supplies it to the boost-buck circuit 31F. Further, the control device 50 controls the driving of the switching element of the boost-buck circuit 31F, and boosts the voltage of the charging current supplied to the battery 40 to the required charging voltage of the battery 40.

[0047] <3. Regeneration Efficiency> Here, the regeneration efficiency will be described in detail taking the drive circuit of the front-wheel drive motor as an example.

[0048] When charging the battery 40 with the regenerative power generated by the front-wheel drive motor 10F, it is necessary to adjust the charging voltage within the range of the required charging voltage of the battery 40. The control device 50 controls the driving of the switching element of the buck-boost circuit 31F to adjust the regenerative voltage so that the charging voltage is within the range of the required charging voltage of the battery 40. At this time, if the regenerative voltage output from the front-wheel drive motor 10F is small, the boost ratio of the buck-boost circuit 31F increases, so the regenerative current required by the buck-boost circuit 31F increases. In this case, the control device 50 controls the driving of the switching element of the inverter circuit 21F to increase the regenerative current supplied to the buck-boost circuit 31F.

[0049] When increasing the regenerative current supplied to the buck-boost circuit 31F, the number of driving times of the switching element of the inverter circuit 21F increases, so the heat generation amount due to the driving of the switching element increases. That is, the amount of energy lost due to heat increases, and the regeneration efficiency decreases. Therefore, in order to suppress the decrease in the regeneration efficiency, it is effective to increase the regenerative voltage output from the front-wheel drive motor 10F and decrease the boost ratio in the buck-boost circuit 31F.

[0050] In the case of the configuration of the motor drive system 2 according to the present embodiment, the regenerative voltages of the first stator 11Fa and the second stator 11Fb generated by the rotation of the common rotor 13F are the same value. When the first stator 11Fa and the second stator 11Fb are connected in parallel to the inverter circuit 21F, regenerative power of voltages corresponding to the rotational speed of the rotor 13F is output from the first stator 11Fa and the second stator 11Fb, respectively. On the other hand, when the first stator 11Fa and the second stator 11Fb are connected in parallel to the inverter circuit 21F, the regenerative voltage (the second regenerative voltage) output from the front-wheel drive motor 10F is the sum of the regenerative voltages of the first stator 11Fa and the second stator 11Fb.

[0051] When decelerating from a high vehicle speed, the rotational speed of the rotor 13F is relatively high, and the regenerative power generation voltage of the first stator 11Fa and the second stator 11Fb increases. Therefore, even when the first stator 11Fa and the second stator 11Fb are connected in parallel to the inverter circuit 21F, the boost ratio in the boost - buck circuit 31F can be kept small, and the regenerative efficiency can be maintained relatively high.

[0052] On the other hand, when decelerating from a low vehicle speed, the rotational speed of the rotor 13F is low, and the regenerative power generation voltage of the first stator 11Fa and the second stator 11Fb decreases. However, by connecting the first stator 11Fa and the second stator 11Fb in series to the inverter circuit 21F, the regenerative power generation voltage (the first regenerative power generation voltage) output from the front - wheel drive motor 10F can be doubled. As a result, the boost ratio in the boost - buck circuit 31F becomes small, and a decrease in the regenerative efficiency can be suppressed.

[0053] Note that the motor drive system 2 according to this embodiment includes a front - wheel drive motor 10F and a rear - wheel drive motor 10R. Therefore, when the deceleration torque on the front - wheel side becomes large during deceleration of the vehicle 1, the regenerative torque of the front - wheel drive motor 10F may be larger than the regenerative torque of the rear - wheel drive motor 10R. When the regenerative torque changes under a predetermined regenerative power generation voltage, the regenerative torque is proportional to the regenerative power generation current. That is, when the regenerative power generation voltage is the same, the difference in the regenerative torque appears as the difference in the regenerative power generation current. Therefore, in the motor drive system 2, the switching between series connection and parallel connection during regenerative drive is independently performed in the drive circuits of the front - wheel drive motor 10F and the rear - wheel drive motor 10R respectively.

[0054] Hereinafter, after explaining the configuration of the control device 50 that executes the control process of the motor drive system 2 according to this embodiment, the process when the front - wheel drive motor 10F and the rear - wheel drive motor 10R are regeneratively driven, which is a feature of the motor drive system 2, will be described in detail.

[0055] <3. Control Device> (3-1. Configuration) The control device 50 functions as a device that controls the operation of the motor drive system 2 by a processor such as one or more CPUs (Central Processing Units) executing a computer program. The computer program is a computer program for causing the processor to execute operations described later that the control device 50 should execute. The computer program executed by the processor may be recorded on a recording medium that functions as a storage unit (memory) 53 provided in the control device 50, or may be recorded on a recording medium built into the control device 50 or any recording medium externally attachable to the control device 50.

[0056] Examples of the recording medium for recording the computer program include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical recording media such as CD-ROMs (Compact Disk Read Only Memories), DVDs (Digital Versatile Disks), and Blu-ray (registered trademark), magneto-optical media such as floptical disks, storage elements such as RAMs (Random Access Memories) and ROMs (Read Only Memories), and flash memories such as USB (Universal Serial Bus) memories and SSDs (Solid State Drives), and other media capable of storing programs.

[0057] As shown in FIG. 2, the control device 50 includes a processing unit 51 and a storage unit 53. The processing unit 51 is configured to include a processor such as one or more CPUs. Part or all of the processing unit 51 may be configured with updatable components such as firmware, or may be program modules executed by instructions from the processor. However, part or all of the processing unit 51 may be configured using analog circuits.

[0058] The storage unit 53 is composed of one or more storage elements (memories) such as a RAM or a ROM that is communicably connected to the processing unit 51. However, the number and type of the storage unit 53 are not particularly limited. The storage unit 53 stores a computer program executed by the processing unit 51, various parameters used for arithmetic processing, detection data, data such as arithmetic results, etc. In addition, the control device 50 includes an interface (not shown) for communicating with the battery management device 41, the vehicle state sensor 45, etc.

[0059] The processing unit 51 controls the power running drive of the front-wheel drive motor 10F and the rear-wheel drive motor 10R by controlling the drives of the inverter circuits 21F, 21R, the switching units 29F, 29R, and the boost - buck circuits 31F, 31R. Specifically, the processing unit 51 acquires information on the target acceleration of the vehicle 1, and when the target acceleration is a positive value, calculates the target drive torque of the front-wheel drive motor 10F and the rear-wheel drive motor 10R based on the vehicle speed and the information on the target acceleration.

[0060] When the target acceleration is a positive value, the processing unit 51 sets the state such that the first stator 11Fa (11Ra) and the second stator Fb (Rb) are connected in parallel to the inverter circuit 21F (21R). Then, the processing unit 51 controls the drives of the switching elements provided in the inverter circuits 21F, 21R and the boost - buck circuits 31F, 31R based on the target drive torque, and drives the front-wheel drive motor 10F and the rear-wheel drive motor 10R. Thereby, the front-wheel drive motor 10F and the rear-wheel drive motor 10R output the drive torque of the vehicle 1.

[0061] On the other hand, when the target acceleration is a negative value, the processing unit 51 calculates the target regeneration torque of the front-wheel drive motor 10F and the rear-wheel drive motor 10R based on the vehicle speed and the information on the target acceleration. Also, the processing unit 51 calculates the regeneration efficiency in the case where the first stator 11Fa (11Ra) and the second stator 11Fb (11Rb) are connected in parallel and in series to the inverter circuit 21F (21R), respectively. The processing unit 51 sets the states of the switching units 29F, 29R so as to obtain a connection state with a higher regeneration efficiency.

[0062] Then, based on the calculated target regeneration torque, the processing unit 51 controls the driving of each switching element provided in the inverter circuits 21F and 21R and the boost - buck circuits 31F and 31R, and controls the regeneration of the front - wheel drive motor 10F and the rear - wheel drive motor 10R. As a result, the regenerative power generated by the front - wheel drive motor 10F and the rear - wheel drive motor 10R is charged to the battery 40, and a regenerative braking torque is generated.

[0063] (3 - 2. Example of processing operation) Figs. 4 to 5 are flowcharts showing an example of the processing operation by the control device provided in the motor drive system according to the present embodiment. The flowcharts shown in Figs. 4 to 5 are repeatedly executed at a predetermined calculation cycle.

[0064] First, when the motor drive system 2 is started (step S11), the processing unit 51 acquires information on the vehicle state (step S13). The information on the vehicle state includes at least the operation amount of the accelerator pedal, the operation amount of the brake pedal, and the vehicle speed information. When the vehicle 1 is in the autonomous driving state, instead of the information on the operation amounts of the accelerator pedal and the brake pedal, the information on the required acceleration may be acquired.

[0065] Next, the processing unit 51 determines whether a deceleration request for the vehicle 1 has been made (step S15). Whether a deceleration request for the vehicle 1 has been made can be determined based on, for example, the sensor signals of the accelerator position sensor and the brake stroke sensor. When the accelerator pedal is depressed, the processing unit 51 determines that an acceleration request has been made by the driver. On the other hand, when the brake pedal is depressed, or when the speed at which the operation amount of the accelerator pedal is returned in the direction of zero exceeds a predetermined threshold value, the processing unit 51 determines that a deceleration request has been made by the driver.

[0066] When the vehicle 1 is in the autonomous driving state, the processing unit 51 determines that an acceleration request has been made when the required acceleration is a positive value, and determines that a deceleration request has been made when the required acceleration is a negative value.

[0067] When it is not determined that a deceleration requirement is present (S15 / No), the processing unit 51 controls the power running drive of the front-wheel drive motor 10F and the rear-wheel drive motor 10R (step S19). For example, the processing unit 51 calculates target drive torques Tq_drv_tgt_F and Tq_drv_tgt_R output from the front-wheel drive motor 10F and the rear-wheel drive motor 10R, respectively, based on information on the vehicle speed and the target acceleration. The target acceleration in the case where an acceleration requirement is present is a positive value. The target drive torques Tq_drv_tgt_F and Tq_drv_tgt_R become larger as the vehicle speed is higher and as the target acceleration is larger. Note that the target drive torque Tq_drv_tgt_F of the front-wheel drive motor 10F and the target drive torque Tq_drv_tgt_R of the rear-wheel drive motor 10R may be the same or different. Further, the processing unit 51 controls the driving of the switching elements of the boost / buck circuits 31F, 31R and the inverter circuits 21F, 21R based on the calculated target drive torques Tq_drv_tgt_F and Tq_drv_tgt_R, and power runs the front-wheel drive motor 10F and the rear-wheel drive motor 10R.

[0068] Taking the front-wheel drive motor 10F as an example, the control process of the power running drive of the front-wheel drive motor 10F will be specifically described. For example, the processing unit 51 sets the voltage of the direct current supplied to the inverter circuit 21F and the frequency of the three-phase alternating current supplied to the first stator 11Fa and the second stator 11Fb of the front-wheel drive motor 10F based on the target drive torque Tq_drv_tgt_F of the front-wheel drive motor 10F and the rotational speed of the front-wheel drive motor 10F.

[0069] Further, the processing unit 51 controls the driving of the switching elements 35 and 37 of the step-up / down circuit 31F based on the ratio between the output voltage of the battery 40 and the voltage of the direct current supplied to the inverter circuit 21F, and boosts the voltage of the direct current output from the battery 40 to a set voltage. Also, the processing unit 51 controls the driving of each switching element of the inverter circuit 21F, converts the direct current into a three-phase alternating current, and supplies it to the first stator 11Fa and the second stator 11Fb. Thereby, the front-wheel drive motor 10F is driven, and the driving torque of the vehicle 1 is output. Note that the arithmetic processing when the front-wheel drive motor 10F and the rear-wheel drive motor 10R are driven for power running is not particularly limited, and may be executed in accordance with a conventionally known arithmetic processing method.

[0070] On the other hand, in step S15 above, when it is determined that a deceleration request is being made (S15 / Yes), the processing unit 51 controls the regeneration by the front-wheel drive motor 10F and the rear-wheel drive motor 10R (step S17).

[0071] FIG. 5 shows a flowchart of the regeneration control process. The processing unit 51 calculates the target regeneration torques Tq_reg_tgt_F and Tq_reg_tgt_R of the front-wheel drive motor 10F and the rear-wheel drive motor 10R respectively based on the information on the vehicle speed and the target acceleration (step S31). The target acceleration in the case where a deceleration request is being made is a negative value. Also, the target regeneration torques Tq_reg_tgt_F and Tq_reg_tgt_R become larger as the vehicle speed is higher and as the target acceleration is smaller (larger on the negative side). Note that an upper limit may be set for the target regeneration torques Tq_reg_tgt_F and Tq_reg_tgt_R that can be set. In this case, information on the braking torque insufficient for the deceleration request may be transmitted to the brake fluid pressure control device 19 of the hydraulic brake system 16, and the insufficient braking torque may be supplemented by the hydraulic brake torque.

[0072] Next, the processing unit 51 calculates the regenerative power generation voltages V_inv_pal and V_inv_ser in the states where the first stator 11Fa (11Ra) and the second stator 11Fb (Rb) are connected in parallel and in series, respectively, to the inverter circuit 21F (21R) based on the rotational speeds of the front-wheel drive motor 10F and the rear-wheel drive motor 10R (step S33).

[0073] Here, generally, the induced power generation voltage E due to electromagnetic induction of a motor having a stator and a rotor can be expressed by the following formula (1).

[0074] [Number]

[0075] Φ: Magnetic flux t: Time B: Magnetic flux density S: Coil area ω: Rotor angular velocity θ: Angle formed by the direction parallel to the coil surface of the stator and the perpendicular to the direction of the magnetic flux density

[0076] As shown in formula (1), the regenerative power generation voltage V_inv of the regenerative power generated from the first stator 11Fa (11Ra) and the second stator 11Fb (Rb) is proportional to the angular velocity (ω) of the rotor 13F (11R), that is, the rotational speeds of the front-wheel drive motor 10F and the rear-wheel drive motor 10R. The rotational speeds of the front-wheel drive motor 10F and the rear-wheel drive motor 10R are proportional to the vehicle speed. The magnetic flux density (B) and the coil area (S) in the above formula (1) are information obtained in advance according to the specifications of the front-wheel drive motor 10F and the rear-wheel drive motor 10R. Therefore, the processing unit 51 can calculate the regenerative power generation voltage V_inv of the first stator 11Fa (11Ra) and the second stator 11Fb (Rb) based on the vehicle speed.

[0077] When the first stator 11Fa (11Ra) and the second stator 11Fb (Rb) are connected in parallel to the inverter circuit 21F (21R), the regenerative power generation voltage V_inv of the first stator 11Fa (11Ra) and the second stator 11Fb (Rb) becomes the regenerative power generation voltage V_inv_pal of the front-wheel drive motor 10F and the rear-wheel drive motor 10R. On the other hand, when the first stator 11Fa (11Ra) and the second stator 11Fb (Rb) are connected in series to the inverter circuit 21F (21R), the sum of the regenerative power generation voltages V_inv of the first stator 11Fa (11Ra) and the second stator 11Fb (Rb) (V_inv × 2) becomes the regenerative power generation voltage V_inv_ser of the front-wheel drive motor 10F and the rear-wheel drive motor 10R.

[0078] In addition, when a sensor or the like for detecting the rotational speeds of the front-wheel drive motor 10F and the rear-wheel drive motor 10R is provided, the processing unit 51 may calculate the regenerative power generation voltages V_inv_pal and V_inv_ser based on the rotational speeds of the front-wheel drive motor 10F and the rear-wheel drive motor 10R instead of the vehicle speed. The rotational speed of the motor may be detected using a sensor for detecting the rotational speed of the motor shaft, or may be calculated based on the rotational speed of the drive shaft detected by a sensor for detecting the rotational speed of the drive shaft of the wheel.

[0079] Next, the processing unit 51 acquires information on the required charging voltage V_bat_crg of the battery 40 and information on the maximum charging current value I_bat_max (step S35). The information on the required charging voltage V_bat_crg of the battery 40 and the information on the maximum charging current value I_bat_max are set in advance according to the specifications of the battery 40 and stored in the storage unit 53. The information on the required charging voltage V_bat_crg of the battery 40 and the information on the maximum charging current value I_bat_max may be acquired from the battery management device 41. For example, the higher the open-circuit voltage of the battery 40, the higher the range of the required charging voltage V_bat_crg is set, and the smaller the maximum charging current value I_bat_max is set. On the other hand, the lower the open-circuit voltage of the battery 40, the lower the range of the required charging voltage V_bat_crg is set, and the larger the maximum charging current value I_bat_max is set.

[0080] Next, the processing unit 51 calculates the respective regeneration efficiencies η_pal and η_ser when the first stator 11Fa (11Ra) and the second stator 11Fb (Rb) are connected in parallel and in series to the inverter circuit 21F (21R) (step S37). Specifically, the processing unit 51 adds the efficiencies of the boost-buck circuits 31F and 31R during regenerative driving and the efficiencies of the inverter circuits 21F and 21R during regenerative driving when connected in parallel and in series, respectively, and calculates the regeneration efficiency η_pal when connected in parallel and the regeneration efficiency η_ser when connected in series.

[0081] The efficiencies of the boost-buck circuits 31F and 31R and the inverter circuit 21F (21R) during regenerative driving can be obtained using efficiency maps, respectively. The efficiency maps of the boost-buck circuits 31F and 31R are created based on the data of the efficiencies obtained by obtaining in advance, using an actual machine or by simulation, the efficiency corresponding to the input voltage, input current, and output voltage. Since the loss due to the driving of the switching elements is dominant in the efficiency of the inverter circuits 21F and 21R, the efficiency maps of the inverter circuits 21F and 21R are created based on the data of the efficiencies obtained by obtaining in advance, using an actual machine or by simulation, the efficiency corresponding to the regenerative output.

[0082] Next, the processing unit 51 compares the regeneration efficiency η_pal in the parallel connection with the regeneration efficiency η_ser in the series connection, and determines whether the regeneration efficiency η_pal in the parallel connection is equal to or higher than the regeneration efficiency η_ser in the series connection (step S39). If the regeneration efficiency η_pal in the parallel connection is equal to or higher than the regeneration efficiency η_ser in the series connection (S39 / Yes), the processing unit 51 switches the connection state of the switching units 29F and 29R to a state in which the first stator 11Fa (11Ra) and the second stator 11Fb (Rb) are connected in parallel to the inverter circuit 21F (21R) (step S41). Specifically, the processing unit 51 turns on the first switch 29aa, the second switch 29ab, and the third switch 29ac, and sets the fourth switch 29ba, the fifth switch 29bb, and the sixth switch 29bc to the first connection state. In a configuration where the first switch 29aa, the second switch 29ab, and the third switch 29ac are turned on and the fourth switch 29ba, the fifth switch 29bb, and the sixth switch 29bc are in the first connection state in the non-energized state, the processing unit 51 sets the switching units 29F and 29R to the non-energized state.

[0083]

[0084] On the other hand, if the regeneration efficiency η_pal in the parallel connection is less than the regeneration efficiency η_ser in the series connection (S39 / No), the processing unit 51 switches the connection state of the switching units 29F and 29R to a state in which the first stator 11Fa (11Ra) and the second stator 11Fb (Rb) are connected in series to the inverter circuit 21F (21R) (step S43). Specifically, the processing unit 51 turns off the first switch 29aa, the second switch 29ab, and the third switch 29ac, and sets the fourth switch 29ba, the fifth switch 29bb, and the sixth switch 29bc to the second connection state. In a configuration where the first switch 29aa, the second switch 29ab, and the third switch 29ac are turned on and the fourth switch 29ba, the fifth switch 29bb, and the sixth switch 29bc are in the first connection state in the non-energized state, the processing unit 51 sets the switching units 29F and 29R to the energized state.In this embodiment, the connection state is switched to the one with higher regeneration efficiency between parallel connection and series connection. However, when the processing unit 51 performs parallel connection, it may control the boost ratios of the boost converters 31F and 31R so as to be equal to or lower than a predetermined reference value. Thereby, a decrease in the regeneration efficiency can be surely suppressed.

[0085] Next, based on the target regeneration torques Tq_reg_tgt_F and Tq_reg_tgt_R of the front-wheel drive motor 10F and the rear-wheel drive motor 10R and the target output voltages V_con_tgt of the boost converters 31F and 31R, the processing unit 51 controls the driving of the switching elements of the boost converters 31F and 31R and the inverter circuits 21F and 21R to cause the front-wheel drive motor 10F and the rear-wheel drive motor 10R to perform regenerative power generation (step S45).

[0086] Specifically, the processing unit 51 sets the on / off frequency of each switching element of the inverter circuit 21F based on the target regeneration torque Tq_reg_tgt_F of the front-wheel drive motor 10F and the rotational speed of the front-wheel drive motor 10F. Further, the processing unit 51 sets the drive duty ratio of the on / off of the switching element of the boost converter 31F based on the ratio (boost ratio) between the regenerative power generation voltage and the required charging voltage V_bat_crg. Similarly, for the rear-wheel drive motor 10R, the processing unit 51 sets the duty ratio of the on / off of each switching element of the inverter circuit 21R and the boost converter 31R.

[0087] Then, the processing unit 51 controls the driving of the switching elements of the inverter circuits 21F and 21R and the boost converters 31F and 31R. Thereby, the three-phase AC regenerative power generation current output from the first stators 11Fa and 11Ra and the second stators 11Fb and 11Rb of the front-wheel drive motor 10F and the rear-wheel drive motor 10R respectively is converted into a DC current, and further the charging voltage of the battery 40 is boosted to the required charging voltage to charge the battery 40.

[0088] Note that after the processing unit 51 starts regenerative power generation by the front-wheel drive motor 10F and the rear-wheel drive motor 10R in step S45, the target regenerative torques Tq_reg_tgt_F and Tq_reg_tgt_R of the front-wheel drive motor 10F and the rear-wheel drive motor 10R are controlled so that the charging current to the output battery 40 becomes equal to or less than the maximum charging current value I_bat_max of the battery 40. Specifically, when the charging current of the battery 40 exceeds the maximum charging current value I_bat_max, the processing unit 51 sets the target regenerative torques Tq_reg_tgt_F and Tq_reg_tgt_R to values obtained by subtracting the surplus regenerative torque. In this case, the braking torque corresponding to the surplus regenerative torque is added to the braking torque of the hydraulic brake system 16.

[0089] As described above, when a deceleration request for the vehicle is made, the control device switches the connection states of the first stator and the second stator to the inverter circuit in parallel and in series so that the regenerative efficiency is increased. For this reason, when decelerating in a state where the vehicle speed is relatively low, etc., when the voltage of the regenerative power generation power output from the first stator and the second stator is low, the first stator and the second stator are put in a series state, and the voltage of the regenerative power generation power output from the drive motor to the inverter circuit can be increased. Therefore, it is possible to suppress a decrease in the regenerative efficiency when charging the battery by boosting the regenerative power generation power by the drive motor with a boost-buck circuit.

[0090] As described above, the preferred embodiments of the present disclosure have been described in detail with reference to the accompanying drawings, but the present disclosure is not limited to such examples. It is obvious that those having ordinary knowledge in the technical field to which the present disclosure pertains can come up with various modification examples or correction examples within the scope of the technical idea described in the claims, and it is naturally understood that these also belong to the technical scope of the present disclosure.

[0091] For example, vehicles to which the technology of the present disclosure is applicable are not limited to electric vehicles equipped with a front-wheel drive motor and a rear-wheel drive motor. For example, the vehicle may be an electric vehicle equipped with either a front-wheel drive motor or a rear-wheel drive motor, or may be an electric vehicle equipped with one drive motor for each wheel. Even in such an electric vehicle, when regenerating each drive motor, by switching the connection states of the first inverter and the second inverter in parallel and in series so that the regeneration efficiency is increased, it is possible to control a decrease in the regeneration efficiency in the same manner as described above.

[0092] In addition, in the above embodiment, the motor drive system applied to an electric vehicle has been described as an example, but the motor drive system of the present disclosure is not limited to the motor drive system of an electric vehicle, and may be a railway or other motor drive system.

Explanation of Reference Numerals

[0093] 1: Vehicle, 2: Motor drive system, 10F: Front-wheel drive motor, 10R: Rear-wheel drive motor, 11Fa·11Ra: First stator, 11Fb·11Rb: Second stator, 13F·13R: Rotor, 20F: Front-wheel inverter unit, 20R: Rear-wheel inverter unit, 21F·21R: Inverter circuit, 29F·29R: Switching unit, 31F·31R: Boost-buck circuit, 40: Battery, 50: Control device, 51: Processing unit, 53: Storage unit

Claims

1. A motor including one rotor and two stators, which outputs the driving force of a wheel and can generate regenerative power, an inverter that controls the power supply and regenerative power to the two stators respectively, a battery that can charge the regenerative power generated by the motor, a boost circuit provided between the inverter and the battery, a switching unit that switches the connection state of the two stators to the inverter between series and parallel, and a control unit that controls the operation of the switching unit, wherein the control unit controls the operation of the switching unit to switch the two stators between series and parallel based on the required charging voltage of the battery, the rotational speed of the motor, and the target regenerative torque when generating the regenerative power. A motor drive system for an electric vehicle.

2. The control unit when generating the regenerative power, based on the rotational speed of the motor, obtains the first regenerative power generation voltage when the connection state of the two stators to the inverter is in series and the second regenerative power generation voltage when it is in parallel respectively, obtains the respective regenerative efficiencies when the connection state of the two stators to the inverter is in series and in parallel based on the first regenerative power generation voltage, the second regenerative power generation voltage, the required charging voltage of the battery, and the target regenerative torque, and switches the two stators between series and parallel so that the regenerative efficiency is increased. The motor drive system for an electric vehicle according to Claim 1.

3. The control unit when switching the two stators to parallel to generate the regenerative power, controls so that the boost ratio of the boost circuit is equal to or less than a predetermined reference value. The motor drive system for an electric vehicle according to Claim 2.

4. The electric vehicle is an electric car, and the motor is a single axial gap motor of a double stator type. The motor drive system for an electric vehicle according to Claim 1.

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