Electric vehicle control method and electric vehicle control device

Abstract

Provided is an electric vehicle control method for controlling an electric vehicle comprising: a drive system including an electric motor for traveling and an inverter that drives the electric motor; and a battery that is charged by electric power supplied from an external power source and that supplies electric power to the drive system. The electric vehicle includes two of the drive systems for front-wheel driving and for rear-wheel driving. One of the drive systems has a boost function for boosting the electric power supplied from the external power source by a switching operation of the inverter. In the electric vehicle control method, if the battery is at a low temperature when the external power source is connected, a controller executes, before boost charging is started, battery warming-up control in which the temperature of the battery is raised by operating the drive system for front-wheel driving and the drive system for rear-wheel driving in a state in which a driving force is not generated in the electric motor, and supplying a heat medium heated by heat exchange with both of the drive systems to the battery. When the battery temperature reaches a target temperature, the controller terminates the battery warming-up control of the drive system having the boost function and starts boosting by the boost function, and controls an inverter frequency and a current value of the drive system having the boost function during execution of the battery warming-up control to values determined from a magnitude of a thermal stress generated in the inverter due to a temperature difference ΔT between the heat medium and a heating element of the drive system and a required life of the inverter.

Description

Electric vehicle control method and electric vehicle control device

[0001] The present invention relates to an electric vehicle control method and an electric vehicle control device.

[0002] Electric vehicles capable of charging a battery with power supplied from an external power source are known. A known charging control for such electric vehicles is boost control, which boosts the power of the external power source to the rated voltage of the battery when the rated voltage of the external power source is lower than the rated voltage of the battery. A known boost control method uses a coil of a traction motor provided in the electric vehicle as an inductor to repeatedly turn on and off (hereinafter also referred to as switching operation) an element (switching element) of an inverter that drives the traction motor.

[0003] Also known is a system that includes a cooling circuit in which a heat medium circulates through the driving motor, inverter, and battery, and that warms up the battery by utilizing the heat generated by the driving motor and inverter when the battery is cold.

[0004] However, during the execution of the boost control, the amount of change in the current flowing through the switching element is large due to the switching operation, and the switching operation is repeated. Therefore, when the boost control is performed in an electric vehicle equipped with the above-mentioned cooling circuit, the thermal stress caused by the temperature difference between the switching element and the heat medium is large, and the number of inputs to the switching element increases, which accelerates the deterioration of the switching element.

[0005] JP2018-26946A discloses a method for diagnosing degradation due to temperature changes of a switching element. Specifically, the method detects a phase current flowing between an inverter circuit and a load, detects a change in the current characteristics of the switching element from the phase current, calculates the temperature of the switching element from the change, and diagnoses the degradation state of the inverter circuit from the temperature and phase current of the switching element.

[0006] However, in the above-mentioned document, the diagnosis of the deterioration state is performed while the switching element is being switched. This results in a huge amount of diagnostic data, which requires a large data capacity for the control unit. Furthermore, although the above-mentioned diagnosis can grasp the deterioration state of the switching element, it does not mention suppressing the deterioration.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an electric vehicle control method that can suppress deterioration of inverter elements due to voltage boost control.

[0008] According to one aspect of the present invention, there is provided an electric vehicle control method for controlling an electric vehicle having a drive system including an electric motor for driving and an inverter that drives the electric motor, and a battery that is charged with power supplied from an external power source and supplies power to the drive system, wherein the electric vehicle has two drive systems, one for driving and one for rear-wheel drive, and one of the drive systems has a boost function that boosts the power supplied from the external power source by switching the inverter. In this method, if the battery is cold when the external power source is connected, before starting boost charging, the controller operates the front-wheel drive drive system and the rear-wheel drive drive system in a state where no driving force is generated in the electric motor, and performs battery warm-up control to warm the battery by supplying a heat medium that has been heated by heat exchange with both drive systems to the battery, and when the battery temperature reaches a target temperature, ends the battery warm-up control for the drive system with the boost function, starts boosting the battery using the boost function, and while battery warm-up control is being performed, controls the inverter frequency and current value of the drive system with the boost function to values ​​determined from the magnitude of thermal stress generated in the inverter due to the temperature difference ΔT between the heat medium and the heating element of the drive system and the required life of the inverter.

[0009] FIG. 1 is a block diagram showing a schematic configuration of a rotating electrical machine system. FIG. 2 is a schematic circuit diagram of the rotating electrical machine system. FIG. 3 is a schematic circuit diagram of a temperature adjustment system. FIG. 4 is a time chart showing changes in the temperature difference ΔT between the refrigerant and the inverter element when a switching operation is performed. FIG. 5 is a diagram showing an example of the relationship between the magnitude of amplitude stress and the number of inputs of amplitude stress until the end of the life. FIG. 6 is a diagram showing an example of the magnitude relationship between the amplitude stress of the rear inverter and the front inverter during battery warm-up control. FIG. 7 is a flowchart showing a control routine for battery warm-up control.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] 1 is a block diagram showing a schematic configuration of a rotating electrical machine system 100. The rotating electrical machine system 100 is a vehicle drive system or a power generation system mounted on an electrically powered vehicle that can be charged by an external charger 15, such as an electric vehicle or a plug-in hybrid vehicle.

[0012] The rotating electrical machine system 100 includes a rear power train 14 that drives the rear wheels, a front power train 34 that drives the front wheels, a battery 10 , and a controller 13 .

[0013] The rear power train 14 is configured to include a rear inverter 11 and a rear motor 12. The rear inverter 11 and the rear motor 12 may be formed substantially integrally.

[0014] The front power train 34 is configured to include a front inverter 31 and a front motor 32. The front inverter 31 and the front motor 32 may be formed substantially integrally.

[0015] The battery 10 is a rechargeable DC power source. The battery 10 supplies power to drive the rear motor 12 and the front motor 32. That is, when driving the rear motor 12 and the front motor 32, the battery 10 supplies a DC voltage V ｄｃOn the other hand, when the rear motor 12 and the front motor 32 generate electric power, the battery 10 is charged by that electric power.

[0016] When the external charger 15 is connected, the battery 10 is charged by the power supplied by the external charger 15 via the rear power train 14. At this time, the input voltage V ＩＮ is boosted by the rear power train 14 as needed. This provides an output voltage V suitable for charging. ＯＵＴ In this embodiment, the battery 10 is charged by the voltage (DC voltage V ｄｃ ) is, for example, 800 V. The external charger 15 is a DC power supply, and its voltage (input voltage V ＩＮ ) is, for example, 400 V or 800 V. Therefore, when a 400 V external charger 15 is connected, the output voltage V ＯＵＴ is boosted to 800V.

[0017] The rear inverter 11 converts DC power output by the battery 10 into AC power and supplies it to the rear motor 12. This drives the rear motor 12. On the other hand, when the rear motor 12 generates electric power, the rear inverter 11 converts the AC power generated by the rear motor 12 into DC power and supplies it to the battery 10.

[0018] When an external charger 15 is connected to the rotating electrical machine system 100, the rear inverter 11 can configure a boost converter together with the rear motor 12. Specifically, all or part of the switching elements and free wheel diodes that configure the rear inverter 11 are used as elements of the boost converter. When the external charger 15 is a quick charger or the like, the rear inverter 11 configures a boost converter together with the rear motor 12, and the input voltage V ＩＮ The output voltage V ＯＵＴ is applied to the battery 10.

[0019] The rear motor 12 is an AC synchronous motor with embedded permanent magnets and has multiple phases. Therefore, the rear motor 12 includes a rotor with embedded permanent magnets and a stator with multiple independent coils. The rear motor 12 rotates due to the interaction between the magnetic flux generated by the permanent magnets (hereinafter referred to as permanent magnet magnetic flux) and a composite magnetic flux (hereinafter referred to as coil magnetic flux) of the magnetic flux generated by the multiple-phase coils. The multiple-phase coils are connected in a so-called star connection (Y connection) and have a neutral point. In this embodiment, the rear motor 12 is a three-phase AC synchronous motor with embedded permanent magnets. Therefore, the rear motor 12 includes a rotor with permanent magnets and a stator with UVW three-phase stator coils connected in a Y connection.

[0020] When configuring the boost converter, the coils of each phase of the rear motor 12 are used as inductors of the boost converter. At this time, one terminal of the external charger 15 is connected to the neutral point of the rear motor 12.

[0021] The current flowing through the coils of each phase (UVW) (hereinafter referred to as the three-phase current I ＵＶＷ ), and neutral point voltage V ｎ , the rotation angle θ of the rotor (permanent magnet 40) ｒ can be detected at any timing. ＵＶＷ is detected by the current sensor 16. The neutral point voltage V ｎ is detected by the voltage sensor 17. The rotation angle θ ｒ is detected by the rotation sensor 18. The rotation angle θ ｒ is measured counterclockwise in the UVW coordinate system, with the position of the U-phase coil (U) as the reference angle (0°).

[0022] The front power train 34 has the same configuration as the rear power train 14, except that it does not function as a boost converter. ＵＶＷ is detected by the current sensor 36, and the neutral point voltage V ｎ is detected by the voltage sensor 37, and the rotation angle θ ｒ is detected by the rotation sensor 38.

[0023] The rotating electrical machine system 100 also includes a temperature sensor 50 that detects the temperature of the battery 10, a temperature sensor 51 that detects the temperature of the rear inverter 11, a temperature sensor 52 that detects the temperature of the rear motor 12, a temperature sensor 53 that detects the temperature of the front inverter 31, and a temperature sensor 54 that detects the temperature of the front motor 32. The detected values ​​of each temperature sensor are read into the controller 13.

[0024] In this embodiment, as described above, the rear powertrain 14 functions as a boost converter, and the front powertrain 34 does not have this function, but it is sufficient if at least one of the rear powertrain 14 or the front powertrain 34 has this function.

[0025] The controller 13 is a control device that comprehensively controls the operation of each part of the rotating electrical machine system 100. The controller 13 is configured, for example, by one or more computers, and is programmed to cause each part to perform a predetermined operation. In this embodiment, the controller 13 is a charge / discharge control device that controls the charging or discharging of the battery 10 by configuring a DC / DC converter with the rear inverter 11 and the rear motor 12. A charge / discharge control program for operating the rear inverter 11 and the rear motor 12 as a DC / DC converter may be provided in the form of being stored in a storage medium.

[0026] Specifically, the controller 13 controls the overall operation of the rotating electrical machine system 100 by inputting a PWM (pulse width modulation) signal to the rear inverter 11. For example, the controller 13 generates a PWM signal (referred to as a rotation control PWM signal) for controlling the rotation of the rear motor 12, and controls the rotation speed and torque of the rear motor 12 by inputting this to the rear inverter 11. The controller 13 generates the rotation control PWM signal based on, for example, the amount of operation of the accelerator pedal.

[0027] In this embodiment, even when an external charger 15 is connected to the rotating electrical machine system 100, the controller 13 inputs a PWM signal (hereinafter referred to as a converter PWM signal) to the rear inverter 11 to operate the rear power train 14 as a DC / DC converter. This allows the rear inverter 11 and the rear motor 12 to function as a step-up converter or a step-down converter. The controller 13 controls the three-phase current I ＵＶＷ , neutral point voltage V ｎ , and the rotation angle θ ｒ A PWM signal for the converter is generated based on the

[0028] The external charger 15 is provided separately from the vehicle on which the rotating electrical machine system 100 is mounted, and is, for example, a rapid charger or other charger installed in a charging station.

[0029] Fig. 2 is a schematic circuit diagram of the rotating electrical machine system 100. As shown in Fig. 2, the battery 10 includes a battery main body 21 and relay switches 22a and 22b. The rear inverter 11 includes a rear smoothing capacitor 23 and a rear bridge circuit 24. The rear motor 12 includes a U-phase coil (U), a V-phase coil (V), and a W-phase coil (W) as multi-phase coils.

[0030] The rear bridge circuit 24 includes legs L corresponding to the UVW phases. Ｕ , L Ｖ , L Ｗ Each leg L Ｕ , L Ｖ , L Ｗ Each of the inverters 11 consists of two arms, an upper arm and a lower arm, and the coils U, V, and W of each phase are connected between them. Each arm is formed by a switching element and a freewheeling diode. The controller 13 inputs a PWM signal to the rear inverter 11 to control the timing of turning on (conducting) and off (disconnecting) the switching element of each arm.

[0031] Furthermore, the rotating electric machine system 100 includes rear relay switches 25, 26, and 27, a capacitor 28, and an external input / output terminal 29. These are components for connecting the external charger 15 and the rotating electric machine system 100.

[0032] The rear relay switch 25 is provided between a first terminal of the external input / output terminal 29 and one end of the battery 10, and the rear relay switch 26 is provided between a second terminal of the external input / output terminal 29 and the other end of the battery 10. The rear relay switch 27 is provided on a line connecting the first terminal of the external input / output terminal 29 and the neutral point of the rear motor 12. The rear capacitor 28 is provided between the rear relay switch 27 and the neutral point of the rear motor 12 so as to connect the first and second terminals of the external input / output terminal 29 in parallel.

[0033] The rear relay switches 25, 26, and 27 are each independently turned on / off by the controller 13. When the voltages of the external charger 15 and the battery 10 are the same and no boosting is required, the rear relay switches 25 and 26 are turned on (conductive) and the rear relay switch 27 is turned off (disconnected). As a result, the external charger 15 is directly connected to the battery 10 without going through the rear inverter 11 and the rear motor 12. On the other hand, when the voltage of the external charger 15 is lower than the voltage of the battery 10 and boosting is required, the rear relay switch 25 is turned off and the rear relay switches 26 and 27 are turned on, and a PWM signal for boosting the voltage is sent from the controller 13 to the rear inverter 11. As a result, the external charger 15 is connected to the battery 10 via the rear motor 12 and the rear inverter 11, the output voltage of the external charger 15 is boosted, and the output power of the external charger 15 charges the battery 10 (boost control using the neutral point).

[0034] A circuit including the battery 10, rear inverter 11, and rear motor 12 is referred to as a rear motor circuit 101. On the other hand, a circuit including the battery 10, front inverter 31, and front motor 32 is referred to as a front motor circuit 201.

[0035] The circuit configuration of the front motor circuit 201 is basically the same as that of the rear motor circuit 101, and includes relay switches 22c and 22d that turn on (connect) or off (disconnect) the battery 21, front inverter 31, and front motor 32, as well as a front smoothing capacitor 43 and a front bridge circuit 44 that constitute the front inverter 31. The front motor circuit 201 also includes a front relay switch 45 that is provided between a first terminal of the external input / output terminal 29 and one end of the battery 10, and a front relay switch 46 that is provided between a second terminal of the external input / output terminal 29 and the other end of the battery 10. However, the front motor circuit 201 does not have a line connecting the terminal of the external charger 15 to the neutral point of the front motor 32. In other words, the front motor circuit 201 does not perform voltage boost control using the neutral point. The operation of the front inverter 31 and the on / off of each relay switch in the front motor circuit 201 are controlled by the controller 13.

[0036] 3 is a schematic circuit diagram of a temperature adjustment system 301 for adjusting the temperature of the rotating electrical machine system 100. Note that the temperature adjustment system 301 described below is an example of a system that can be used to adjust the temperature of the rotating electrical machine system 100, and other configurations may also be used.

[0037] The temperature adjustment system 301 includes a first circuit 301A in which the battery 10 is disposed, a second circuit 301B in which the front power train 34 and the rear power train 14 are disposed, and a heat pump system 301C connecting the first circuit 301A and the second circuit 301B. The second circuit 101B also includes a bypass passage 64 that branches off from the second passage 60, passes through the radiator 61, and rejoins the second circuit 301B.

[0038] The first circuit 301A includes a first refrigerant pump 72 that circulates a refrigerant as a heat medium within the circuit, the battery 10, and a first heat exchanger 73 into which the refrigerant that has received heat from the battery 10 flows. In the first heat exchanger 73, heat is exchanged between the refrigerant in the first circuit 301A and the refrigerant in the heat pump system 301C.

[0039] The second circuit 301B includes a second refrigerant pump 63 that circulates the refrigerant within the circuit, a third heat exchanger 65 that exchanges heat between the refrigerant and the refrigerant that cools the front powertrain 34, a fourth heat exchanger 66 that exchanges heat between the refrigerant and the refrigerant that cools the rear powertrain 14, and a fifth heat exchanger 77 into which the refrigerant that has passed through the fourth heat exchanger 66 and the third heat exchanger 65 flows. A third pump 68 and a fourth pump 70 are respectively installed in the circuit 67 for the refrigerant that cools the front powertrain 34 and the circuit 69 for the refrigerant that cools the rear powertrain 14. The circuits 67 and 69 are each provided with a temperature sensor (not shown) that detects the temperature of the refrigerant flowing through the circuit.

[0040] The branch point of the second passage 60 and the bypass passage 64 is located downstream of the fifth heat exchanger 77, and is provided with a flow path switching valve 62. The flow path switching valve 62 switches whether the refrigerant that has passed through the fifth heat exchanger 77 flows directly through the second passage 60 or through the bypass passage 64.

[0041] The heat pump system 301C includes a circulation path in which a first heat exchanger 73, a compressor 75, a fifth heat exchanger 77, and an expansion valve 76 are arranged in this order. The compressor 75 can rotate in either the forward direction, which is the direction of rotation when the refrigerant that has passed through the first heat exchanger 73 is compressed and sent to the fifth heat exchanger 77, or the reverse direction, which is the direction of rotation when the refrigerant that has passed through the fifth heat exchanger 77 is compressed and sent to the first heat exchanger 73.

[0042] The pumps 72 , 63 , 68 , 70 , compressor 75 , and flow path switching valve 62 are controlled by a controller 13 .

[0043] Next, the battery warm-up control will be described.

[0044] When the battery 10 is at a low temperature, the upper limit of the current that can be input to the battery 10 (hereinafter also referred to as the input current limit value) is smaller than when the battery 10 is at an appropriate temperature, so there is a risk that the battery 10 cannot be charged efficiently.

[0045] Therefore, when the external charger 15 is connected while the battery 10 is at a low temperature, the controller 13 executes battery warm-up control to warm up the battery 10 before starting charging.

[0046] The battery warm-up control is a control for raising the temperature of the battery 10 by supplying heat generated in the rear power train 14 and the front power train 34 to the battery 10 via the refrigerant.

[0047] So-called d-axis current control can be applied as a method for generating heat in the rear power train 14 and the front power train 34. That is, for the rear motor 12 and the front motor 32, the component of current that contributes to torque (q-axis component) is set to zero, and only the component of current that does not contribute to torque (d-axis component) is passed through the electric motors, thereby utilizing the heat resulting from losses caused by the current flow.

[0048] Then, to supply the generated heat to the battery 10, the controller 13 operates the first refrigerant pump 72, the second refrigerant pump 63, the third pump 68, and the fourth pump 70, rotates the compressor 75 in the reverse direction, and sets the flow path switching valve 62 to a state where the refrigerant in the second circuit 301B passes through the bypass passage 64. As a result, the heat generated in the rear power train 14 and the front power train 34 moves to the first circuit 301A via the heat pump system 301C and is used to warm up the battery 10. Note that during the warm-up mode, the first refrigerant pump 72, the second refrigerant pump 63, the third pump 68, the fourth pump 70, and the compressor 75 are driven using surplus power supplied from the external charger 15 that cannot be fully taken in by the battery 10 due to input / output limitations caused by low temperatures.

[0049] The multiple components that make up the rear inverter 11 and the front inverter 31 are connected by soldering or the like, and when the temperature of the rear inverter 11 rises, thermal stress occurs in each component due to differences in the thermal expansion coefficients of the multiple components. Repeated input of this thermal stress leads to the accumulation of thermal fatigue in each component, ultimately resulting in the deterioration of switching elements, etc. In a configuration that uses refrigerant cooling, the temperature change associated with switching operations is large, resulting in large repetitive stress (amplitude stress). Furthermore, large changes in current value associated with switching operations, such as in boost control, also contribute to large amplitude stress.

[0050] That is, when voltage boost control is performed during charging, the rear inverter 11 is at a disadvantage in terms of lifespan compared to the front inverter 31. For this reason, if the same control is performed on the rear power train 14 and the front power train 34 during battery warm-up control, and voltage boost control is performed on the rear power train 14 after warm-up is complete, there is a risk that the rear inverter 11 will deteriorate more quickly.

[0051] Therefore, when battery warm-up control is performed when an external charger 15 that requires boost control is connected to the vehicle, the controller 13 executes the battery warm-up control described below to suppress deterioration of the rear inverter 11.

[0052] First, the outline of the battery warm-up control in this embodiment will be described with reference to FIGS.

[0053] FIG. 4 is a time chart showing the change in the temperature difference ΔT between the refrigerant and the inverter element when a switching operation is performed.

[0054] The temperature of the inverter element repeatedly rises and falls as a result of switching operations. The temperature change of the inverter element is determined by the inverter frequency and current value. As the temperature of the inverter element changes as described above, the temperature difference ΔT between the inverter element and the refrigerant repeatedly increases and decreases, as shown in Figure 4. The greater the difference between the maximum and minimum values ​​of this temperature difference ΔT, the greater the amplitude stress. The lifespan performance of the inverter element is correlated with the magnitude of the amplitude stress and the number of times the amplitude stress is input, as shown below.

[0055] 5 is a diagram showing an example of the relationship between the magnitude of amplitude stress and the number of inputs of amplitude stress (also referred to as the upper limit of inputs) until the end of the life span when a predetermined target life span is set. As shown in FIG. 5, for the same target life span, the upper limit of inputs becomes smaller as the amplitude stress becomes larger. For example, when the amplitude stress is σ1, the upper limit of inputs is N1, and when the amplitude stress is σ2, which is smaller than σ1, the upper limit of inputs is N2, which is larger than N1.

[0056] Therefore, in this embodiment, in consideration of deterioration due to voltage boost control, the frequency and / or current value of the rear inverter 11 is controlled so that the amplitude stress of the battery warm-up control is smaller than that of the front inverter 31. For example, in the battery warm-up control, the amplitude stress of the rear inverter 11 is set to σ2, and the amplitude stress of the front inverter 31 is set to σ1.

[0057] 6 shows the magnitude relationship between the amplitude stresses of the rear inverter 11 and the front inverter 31 during battery warm-up control. By controlling the amplitude stresses to be as described above, the front inverter 31 deteriorates more rapidly than the rear inverter 11 during battery warm-up control, but this difference in deterioration is offset by the subsequent voltage boost control. In other words, the rear powertrain 14, which is subject to strict voltage boost control in terms of life durability performance, is prevented from deteriorating due to battery warm-up control, while the front powertrain 34, which is not subject to voltage boost control, generates more heat. This allows the rear powertrain 14 and the front powertrain 34 to deteriorate at the same rate.

[0058] For the rear powertrain 14, the battery warm-up control is terminated and transitioned to voltage boost control when the temperature of the battery 10 reaches a predetermined temperature, but for the front powertrain 34, the battery warm-up control may be terminated or continued as is, as with the rear powertrain 14. Until the predetermined temperature is reached, the temperature rise of the battery 10 is controlled as the top priority, but after the predetermined temperature is reached, the inverter frequency and current value are set taking into consideration the SOC, refrigerant temperature, atmospheric temperature, and life durability performance of the battery 10.

[0059] Next, a specific example of a control routine for battery warm-up control will be described with reference to FIG.

[0060] FIG. 7 is a flowchart showing a control routine for battery warm-up control executed by the controller 13.

[0061] In step S10, the controller 13 sets a target value (hereinafter also referred to as target temperature difference tΔT) for the temperature difference ΔT between the refrigerant and the inverter element of the powertrain having the boost function (i.e., the rear powertrain 14). The target temperature difference tΔT is desirably set to a value that satisfies the endurance performance of the rear powertrain 14. For example, if the endurance performance requires a driving range of 100,000 km, the frequency of execution of the battery warm-up control and the frequency of execution of the boost control until the required driving range is reached are set, and the magnitude of the amplitude stress that satisfies the endurance performance is set according to the frequency. The target temperature difference tΔT is then set based on the amplitude stress. The frequency of execution of the battery warm-up control and the frequency of execution of the boost control may be set based on data from multiple other vehicles. The driving history of the vehicle may be learned, and the set values ​​of the frequencies may be corrected using the learned results.

[0062] In step S20, the controller 13 acquires the inverter temperature and the coil temperature of each phase of the rear power train 14.

[0063] In step S30, the controller 13 acquires the coolant temperature of the rear power train 14.

[0064] In step S40, the controller 13 calculates the actual value of the temperature difference ΔT between the refrigerant of the rear power train 14 and the inverter element (hereinafter also referred to as actual temperature difference rΔT) from the values ​​acquired in steps S20 and S30.

[0065] In step S50, the controller 13 sets the inverter frequency and current value to make the actual temperature difference rΔT equal to the target temperature difference tΔT, thereby controlling the amplitude stress to a value that satisfies the life durability performance.

[0066] In step S60, the controller 13 sets the inverter frequency and current of the front powertrain 34. For example, these values ​​are set to values ​​greater than those of the rear powertrain 14 set in step S50. The extent to which these values ​​are set to be greater is preferably determined based on the lifespan of the front powertrain 34, the frequency at which the battery warm-up control is executed, and the target heat recovery amount in the battery warm-up control. Because the battery warm-up control warms up the battery 10 using heat recovered from the rear powertrain 14 and the front powertrain 34, a large amount of recovered heat is desirable. However, because the inverter frequency and current of the rear powertrain 14 are set to values ​​that take into account deterioration due to voltage boost control, the amount of recovered heat is smaller than when voltage boost control is not executed. Therefore, by setting the inverter frequency and current of the front powertrain 34 as described above, the heat lost in the rear powertrain 14 can be recovered by the front powertrain 34, which does not execute voltage boost control. Note that either the inverter element or the current value may be set to be greater than that of the rear powertrain 14.

[0067] After the inverter frequency and current value for each power train are set by the processing of steps S10 to S60, the battery warm-up control continues until the battery temperature reaches a predetermined value. Whether or not the battery temperature has reached the predetermined value is determined by a battery temperature determination routine executed in parallel with this routine.

[0068] [Modification] Next, a modification of the battery warm-up control described above will be described. This modification also falls within the scope of the present invention, just like the embodiment described above.

[0069] The difference from the embodiment is that when battery warm-up control is executed, the output of the fourth pump 70 provided in the refrigerant circuit 69 that cools the rear power train 14 is made larger than when special control such as battery warm-up control is not executed (also referred to as normal operation).

[0070] Increasing the output of the fourth pump 70 increases the amount of heat recovered in the circuit 69, thereby improving the warm-up efficiency of the battery 10. Furthermore, an increase in the amount of recovered heat means an increase in cooling efficiency. If the cooling efficiency is improved, the amount of heat generated by the rear power train 14 can be increased by increasing at least one of the inverter frequency and current value. In other words, the improved cooling efficiency allows the amount of heat generated to be increased while maintaining the lifespan performance, thereby improving the warm-up efficiency of the battery 10.

[0071] As described above, in this embodiment, an electric vehicle is provided that includes a powertrain (drive system) 14, 34 including an electric motor 12, 32 for driving and an inverter 11, 31 that drives the electric motor 12, 32, and a battery 10 that is charged with power supplied from an external charger (external power source) 15 and supplies power to the powertrain 14, 34, and the powertrain 14, 34 is provided as one for front-wheel drive and one for rear-wheel drive, and one of the powertrains 14, 34 has a boost function that boosts the power supplied from the external charger 15 by switching the inverter 11. In this method, when the battery 10 is connected to the external charger 15, the controller 13 operates the front powertrain (front-wheel drive powertrain) 34 and the rear powertrain (rear-wheel drive powertrain) 14 without generating driving force from the electric motors 12, 32, before starting boost charging. The controller 13 executes battery warm-up control to warm the battery 10 by supplying a refrigerant (heat medium) heated by heat exchange with the powertrains to the battery 10. When the battery temperature reaches a target temperature, the controller 13 terminates the battery warm-up control for the rear powertrain 14, which has a boost function, and starts boosting the battery 10 using the boost function. During the battery warm-up control, the controller 13 controls the inverter frequency and current of the rear powertrain 14, which has a boost function, to values ​​determined by the magnitude of thermal stress generated in the inverter 11 due to the temperature difference ΔT between the refrigerant and the inverter elements (heat-generating elements of the drive system) and the required life of the inverter 11. This prevents deterioration of the life durability performance of the rear powertrain 14, which performs boost control, which may accelerate deterioration.

[0072] In this embodiment, during execution of the battery warm-up control, the controller 13 sets the current value of the front power train 34, which does not have a boost function, to be greater than the current value of the rear power train 14, which does have a boost function. This allows the front power train 34 to compensate for the reduced amount of heat recovered by the rear power train 14, thereby preventing a decrease in the warm-up efficiency of the battery 10.

[0073] In this embodiment, during execution of the battery warm-up control, the controller 13 sets the inverter frequency of the front power train 34, which does not have a boost function, to be higher than the inverter frequency of the rear power train 14, which has a boost function. This allows the front power train 34 to compensate for the reduced amount of heat recovered in the rear power train 14, thereby preventing a decrease in the warm-up efficiency of the battery 10.

[0074] In this modification, when executing battery warm-up control, the controller 13 increases the output of the fourth pump 70, which supplies refrigerant to the rear power train 14, which has a boost function, compared to the output of the third pump 68, which supplies refrigerant to the front power train 34, which does not have a boost function, and increases the inverter frequency of the rear power train 14, which has a boost function, in accordance with the increase in cooling efficiency due to the increase in output of the fourth pump 70. This improves the cooling efficiency of the rear power train 14, thereby increasing the amount of heat generated while maintaining the battery's lifespan performance, thereby improving the warm-up efficiency of the battery 10.

[0075] In this modification, when executing battery warm-up control, the controller 13 increases the output of the fourth pump 70, which supplies refrigerant to the rear power train 14, which has a boost function, compared to the output of the third pump 68, which supplies refrigerant to the front power train 34, which does not have a boost function, and increases the current value of the rear power train 14, which has a boost function, in accordance with the increase in cooling efficiency due to the increase in output of the fourth pump 70. This improves the cooling efficiency of the rear power train 14, thereby increasing the amount of heat generated while maintaining the battery's lifespan performance, thereby improving the warm-up efficiency of the battery 10.

[0076] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

Claims

1. An electric vehicle comprising: a drive system including an electric motor for driving and an inverter that drives the electric motor; and a battery that is charged with power supplied from an external power source and supplies power to the drive system, wherein the drive system has two drive systems, one for front-wheel drive and one for rear-wheel drive, and one of the drive systems has a boost function that boosts the power supplied from the external power source by switching the inverter, in a control method for controlling an electric vehicle, wherein: if the battery is at a low temperature when the external power source is connected, a controller operates the drive system for front-wheel drive and the drive system for rear-wheel drive in a state where no driving force is generated in the electric motor before starting boost charging, and performs battery warm-up control to warm the battery by supplying a heat medium that has been heated by heat exchange with both drive systems to the battery; and when the battery temperature reaches a target temperature, ends the battery warm-up control of the drive system with the boost function and starts boosting the battery using the boost function. an inverter frequency and a current value of the drive system having the boost function during execution of the battery warm-up control, to values ​​determined from the magnitude of thermal stress generated in the inverter due to a temperature difference ΔT between the heat medium and a heating element of the drive system and a required lifespan of the inverter.

2. The method for controlling an electric vehicle according to claim 1, wherein the controller determines the temperature difference ΔT as the difference between the temperature of the heat medium and the temperature of the inverter or the electric motor.

3. An electric vehicle control method as described in claim 1, wherein the controller, while executing the battery warm-up control, makes the current value of the drive system that does not have the boost function greater than the current value of the drive system that has the boost function.

4. An electric vehicle control method as described in claim 1, wherein the controller, while the battery warm-up control is being executed, makes the inverter frequency of the drive system that does not have the boost function higher than the inverter frequency of the drive system that has the boost function.

5. An electric vehicle control method as claimed in claim 1, wherein, when executing the battery warm-up control, the controller increases the output of the pump that circulates the heat medium in the drive system having the boost function compared to the output of the pump that circulates the heat medium in the drive system without the boost function, and increases the inverter frequency of the drive system having the boost function in accordance with the increase in cooling efficiency caused by the increase in output of the pump that circulates the heat medium in the drive system having the boost function.

6. An electric vehicle control method as claimed in claim 1, wherein, when executing the battery warm-up control, the controller increases the output of the pump that circulates the heat medium through the drive system having the boost function compared to the output of the pump that circulates the heat medium through the drive system not having the boost function, and increases the current value of the drive system having the boost function in accordance with an increase in cooling efficiency due to an increase in the output of the pump that circulates the heat medium through the drive system having the boost function.

7. An electric vehicle comprising: a drive system including an electric motor for driving and an inverter that drives the electric motor; and a battery that is charged with power supplied from an external power source and supplies power to the drive system, wherein the electric vehicle control device controls an electric vehicle that has two drive systems, one for front-wheel drive and one for rear-wheel drive, one of which has a boost function that boosts the power supplied from the external power source by switching the inverter, wherein if the battery is at a low temperature when the external power source is connected, the drive system for front-wheel drive and the drive system for rear-wheel drive are operated in a state where no driving force is generated in the electric motor before starting boost charging, and performs battery warm-up control that warms the battery by supplying a heat medium that has been heated by heat exchange with both drive systems to the battery; and when the battery temperature reaches a target temperature, the battery warm-up control of the drive system with the boost function is terminated and boosting by the boost function is started. an inverter frequency and a current value of the drive system having the boost function during execution of the battery warm-up control, to values ​​determined from the magnitude of thermal stress generated in the inverter due to a temperature difference ΔT between the heat medium and a heating element of the drive system and a required lifespan of the inverter.

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