Overvoltage prevention device for electric vehicle

Abstract

To suppress application of overvoltage to a battery even when a front wheel or a rear wheel of a four wheel electric vehicle slips.SOLUTION: An electric vehicle executes: when power consumption of one motor 21 among motors that respectively bear front wheels or rear wheels indicates a rapid decrease state satisfying a predetermined condition, torque compensation means that suppresses torque decrease in the entire vehicle by increasing power to the other motor 22; and when the torque compensation means is executed and when difference between upper limit current of a battery 16 and execution charging current charged to the battery 16 becomes equal to or less than a predetermined value T, overvoltage prevention means that consumes differential power by changing a phase of current to one motor having smaller power consumption out of the first motor 21 and the second motor 22 and controlling the current to flow through a d-axis.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an operation for preventing an overvoltage of a battery mounted on an electric vehicle having a power generation device. [Background technology]

[0002] Hybrid vehicles, which combine a power generating device such as an engine-driven generator or a fuel cell with a battery, are commonly used as electric vehicles that can achieve both environmental friendliness and fuel efficiency. Such electric vehicles are classified into two types: one in which the motor is driven by electricity from the power generating device, and another in which the battery is charged once and then the motor is driven by electricity from the battery.

[0003] In the former type, it is difficult to rapidly change the power output from the power generation device according to demand. As a result, power exceeding demand may be generated, resulting in overvoltage. When overvoltage occurs, the load on the circuits and devices increases, which is undesirable from the viewpoint of electric vehicle operation. Therefore, measures to suppress overvoltage are being considered.

[0004] Patent Document 1 discusses problems with electric vehicles that rectify AC voltage generated by a generator, convert it with an inverter, and apply AC voltage to a motor. It points out that if the motor rolls back while outputting torque in the forward direction and generates electricity through regenerative operation, the DC link voltage to the inverter increases, and the inverter switching elements may be damaged by overvoltage. As a measure against this, it describes that a d-axis current that does not contribute to torque is set to flow together with a q-axis current that generates torque in the AC current, triggered by the vehicle body rolling back, and the power generated by regenerative operation is consumed by this d-axis current, suppressing the increase in DC link voltage and suppressing damage to the inverter switching elements. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2009-219189 A Summary of the Invention [Problem to be solved by the invention]

[0006] In a four-wheel electric vehicle with separate motors for driving the front and rear wheels, when one of the front or rear motors slips, it is considered desirable from the viewpoint of driving stability to maintain the driving force of the vehicle by compensating for the torque with the other motor. Figure 6 shows the ideal behavior of the power consumption of each motor.

[0007] However, even if the power consumption, which is directly linked to the torque of each motor, is constantly monitored, and a sudden decrease in torque (i.e., power consumption) that indicates that one of the front or rear wheels has slipped is detected, and the power consumption of the other motor is increased to compensate for the torque, a time lag is unavoidable. This realistic behavior of the power consumption of each motor is shown in Figure 7. As a result, the total power consumption of both motors will inevitably temporarily decrease significantly due to the delay in the increase in the power consumption of the other motor. On the other hand, as mentioned above, it is difficult to suddenly change the power output by the power generation device. Therefore, while the generated power remains the same, the total power consumption decreases, resulting in a power surplus, and a large current will flow to the large-capacity battery to cover the surplus, which may cause an overvoltage.

[0008] However, even if excessive current was passed through the motor on the slipping side, the q-axis current that contributes to torque was trying to produce high output at the slipping stage, and passing a current greater than the rated current could have led to deterioration of the device.

[0009] Therefore, an object of the present invention is to prevent overvoltage from being applied to the battery even when the front or rear wheels of a four-wheel electric vehicle slip. [Means for solving the problem]

[0010] The present invention relates to A power generation device; a first motor that rotates one of the front wheels or the rear wheels by AC power generated by the power generation device, and a second motor that rotates the other of the front wheels or the rear wheels; A battery that can store surplus power; An electric vehicle comprising: a power monitoring means for monitoring the power consumption of each of the first motor and the second motor; a torque compensation means for increasing the power to the other motor when the power consumption of one of the motors shows a rapid decrease state that satisfies a predetermined condition, thereby suppressing a torque decrease in the entire vehicle; an overvoltage prevention means for consuming the difference in power by changing the phase of a current to one of the first motor and the second motor (A), which has a smaller power consumption, and controlling the current to flow to a d-axis when a difference between an upper limit current of the battery and an effective charging current charged to the battery becomes equal to or smaller than a predetermined value when the torque compensation means is executed; The above problem is solved by a first solution, which is an electric vehicle having the above-mentioned features.

[0011] In addition to the first solving means, the electric vehicle according to the present invention has the following features: A second solution can be adopted, which has a charge limit adjusting means for adjusting the predetermined value according to the SOC of the battery.

[0012] In addition to the second solution, the electric vehicle according to the present invention has the following features: When the power consumption of one of the first motor and the second motor (A) that has a current flowing through the d-axis exceeds the power consumption of the other motor (B), Stop the current flow to the d-axis of one of the motors (A), A third solution can be adopted, which has a first overvoltage prevention switching means for consuming the differential power by passing a current through the d-axis of the other motor (B).

[0013] Furthermore, the electric vehicle according to the present invention has, in addition to the second solving means, When the power consumption of one of the first motor and the second motor (A) through which a current flows to the d-axis reaches a predetermined allowable value, Stop the current flow to the d-axis of one of the motors (A), A fourth solution can be adopted, which has a second overvoltage prevention switching means for consuming the differential power by passing a current through the d-axis of the other motor (B).

[0014] In addition to the second to fourth solving means, the electric vehicle according to the present invention has the following features: A driving mode switching means for switching to a driving mode having a different wheel spin rate; A fifth solution can be adopted, which has a slip response means for adjusting the predetermined value to be increased when the wheel spin rate is switched to a high slip occurrence mode in which the wheel spin rate is lowered than normal. Effect of the Invention

[0015] With the electric vehicle of the present invention, even if either the front or rear wheels slip and torque compensation by the other wheel is not completed in time, a d-axis current of a different phase is passed to the motor, which has a margin in current rating compared to ideal torque compensation, to prevent overvoltage from being applied to the battery due to excess power. If too much current is simply discarded to avoid overvoltage, the battery voltage will drop and the motor will not be able to produce torque. However, by using the d-axis current to carry the excess power, the battery voltage does not drop and a significant drop in torque is avoided, while overvoltage is prevented from being applied to the battery. This reduces the possibility of breakdowns in the electric vehicle's mechanisms. [Brief description of the drawings]

[0016] [Figure 1] A wiring diagram showing an embodiment of an electric vehicle according to the present invention. [Diagram 2] FIG. 1 is a functional block diagram showing an embodiment of an electric vehicle according to the present invention; [Diagram 3] Comparison of battery capacity depending on SOC for each driving mode [Figure 4] FIG. 2 is a flow chart showing an example of an embodiment of controlling an electric vehicle according to the present invention. [Diagram 5] A transition diagram showing a state in which the first overvoltage prevention switching means is executed. [Figure 6] A diagram showing the power consumption during torque compensation desired when one of the front or rear wheels is slipping in an electric vehicle. [Figure 7] A diagram showing the actual power consumption when trying to put Figure 6 into practice DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the wiring diagram shown in FIG. 1 and the functional block diagram shown in FIG. The electric vehicle 1 according to the present invention has a power generation device 11 that generates AC power for propelling the vehicle. Examples of this power generation device 11 include a generator using an engine 10 and a fuel cell. That is, the electric vehicle 1 according to the present invention may be a hybrid engine vehicle or a fuel cell vehicle. In the case of a hybrid engine vehicle, the electric vehicle may not only be charged by the power generated by the engine, but may also be a plug-in hybrid vehicle (PHEV) equipped with an external charger that allows charging of power from the outside and an external power supply that allows power to be supplied to the outside.

[0018] 1 and 2, a generator using an engine 10 is described as an example of the power generation device 11, but is not limited to this. It is difficult to increase or decrease the output of these power generation devices 11 in real time, and it is desirable to continue stable output. This invention solves the problems faced due to the difficulty in increasing or decreasing the output.

[0019] The electric vehicle 1 according to the present invention has a first motor 21 and a second motor 22 driven by AC power generated by a power generation device 11. Note that the terms "first" and "second" are merely used to distinguish between the two and do not particularly limit the order of priority. The first motor 21 and the second motor 22 each rotate one of the front wheels 23 and the rear wheels 24. Here, as an example, a configuration in which the first motor 21 rotates the front wheels 23 and the second motor 22 rotates the rear wheels 24 will be described.

[0020] The electric vehicle 1 according to the present invention has a battery 16 capable of storing surplus power. This battery 16 is not only a so-called 12V battery or 24V battery based on a lead-acid battery and used for starting the engine, driving electrical components and the ECU, etc., but also includes a large-capacity battery such as a lithium-ion battery or a sodium-ion battery capable of supplying power to drive the motors (21, 22) as necessary.

[0021] The electric vehicle 1 according to the present invention has a control unit 31 that executes each of the means described below as control including the power introduced to these motors. The control unit 31 has a semiconductor arithmetic unit and a storage device, receives signals from sensors attached to each unit and transmitted data, and sends instructions to each unit such as the engine 10, the power generation unit 11, the first motor 21, and the second motor 22 in response to an operation from the driver. Each of the means described below is realized as a function realized by executing a recorded program or a function by a dedicated circuit. It is preferable that the control unit 31 is implemented as an additional function by introducing and executing a program that realizes this invention into an ECU (Electronic Control Unit) mounted on the electric vehicle 1 for driving control, rather than providing a separate arithmetic unit specifically for the means specified in this invention, because this is easy to introduce.

[0022] The relationship between power and voltage in the electric vehicle 1 according to the present invention in normal operation will be described with reference to FIG. GIt is difficult to suddenly increase or decrease this AC power. This AC power is the power (current: i 1 ) and the power (current: i 2 ) and the remaining power (current: i G -i 1 -i 2 ) is supplied to the battery 16. At this time, the voltage V applied to the battery batt is the potential of battery 16, V 0 From the internal resistance R of the battery 16, the following equation (1) is obtained. V batt =V 0 +(i G -i 1 -i 2 ) × R... (1)

[0023] The electric vehicle 1 according to the present invention is effective in a situation where the torque of one of the motors suddenly decreases, such as when either the front wheel 23 or the rear wheel 24 slips. When the torque suddenly decreases, the power consumption of the motors also suddenly decreases accordingly, so by monitoring the power consumption of each motor, it is possible to detect this sudden decrease in motor torque. The electric vehicle according to the present invention executes a power monitoring means 41 that monitors the power consumption of each of the first motor 21 and the second motor 22. As an environment for executing this, it is preferable to install a voltmeter that measures the voltage applied to these motors and transmit the voltage value from this voltmeter to the control unit 31, but there is no particular restriction on the implementation form as long as similar monitoring and data reception can be performed using an ammeter or other sensor. The control unit 31 executes the power monitoring means 41 to constantly monitor the transmitted voltage value, and is able to detect a case where the voltage value falls below a predetermined value even though the vehicle continues to travel. This makes it possible to detect a situation where a slip has occurred and execute the processing according to the present invention.

[0024] As an example, a case will be described in which the front wheels 23 slip and the torque applied by the first motor 21 suddenly decreases. 1becomes close to 0. On the other hand, the AC current i G It is difficult to reduce it rapidly, and basically, G It remains as it is. If i 1 ≒0, the voltage V applied to the battery 16 during this sudden decrease in motor torque is batt The value of i is as shown in the following formula (2). 1 If this voltage is applied to the battery 16 as is, it will become an overvoltage, which may lead to deterioration or damage to the battery 16 and its control circuit, etc. At the same time, the torque from the first motor 21 is suddenly reduced, and the torque used to run the electric vehicle 1 is accordingly reduced. V batt =V 0 +(i G -i 2 ) × R ··· (2)

[0025] The torque reduction is achieved by increasing the current (+i 2 By controlling the current to the motor that has not experienced a torque reduction (second motor 22 in this case), a certain degree of torque compensation becomes possible. When the control unit 31 detects the torque reduction with the power monitoring means 41, it executes the torque compensation means 42, which increases the current to the motor that has not experienced a torque reduction (second motor 22 in this case) to suppress the reduction in torque in the entire electric vehicle 1. However, in an environment where slippage occurs, the torque originally borne by the second motor 22 is often large, and it is not possible to pass a current large enough to add torque unlimitedly. At this time, V batt The value of i is as shown in the following formula (3). 2 ' is i 1 If this voltage is applied to the battery 16, an overvoltage will inevitably occur. V batt =V 0 +{i G -(i 2 +i 2 ')}×R ···(3)

[0026] When the torque compensation means 42 is executed, the control unit 31 of the electric vehicle 1 according to the present invention calculates the upper limit current of the battery 16 and the effective charging current (here, i G -i 1 -i 2 -i 2 When the difference between the q-axis current and the d-axis current becomes equal to or smaller than a predetermined value T, the overvoltage prevention means 43 is executed, which changes the phase of the current to one of the first motor 21 and the second motor 22, which consumes less power (the first motor 21 in the above example), and controls the current to flow on the d-axis. Of the three-axis AC currents, the q-axis current is directly connected to the torque, so the allowable range in which it can be increased beyond the current that originally flowed is limited. On the other hand, the d-axis current is not directly connected to the torque, so there is almost no current flowing originally, and so the allowable range in which it can flow is secured. By changing the phase from the original current phase to such an extent that the d-axis component is increased within the range in which the amount of current required for the q-axis component can be secured, the differential power can be consumed. In the above example, the current of the d-axis component of the first motor 21 is changed to i 1d Then, V shown in the following formula (4) batt The phase is changed so that the voltage Vout becomes equal to or lower than a predetermined threshold value that indicates an overvoltage. V batt =V 0 +(i G -i 2 -i 2 '-i 1d ) × R · · · (4)

[0027] The control unit 31 of the electric vehicle 1 according to the present invention preferably appropriately executes a charging limit adjustment means 44 that adjusts the above-mentioned predetermined value according to the state of charge (SoC) of the battery 16. If the SOC is low, that is, if the power acceptance is high, energy loss is reduced by using the differential power for charging rather than consuming it in the d-axis component. In this case, the above-mentioned predetermined value T is lowered to change the conditions so that the phase is less likely to be changed by the overvoltage prevention means 43. Conversely, if the SOC is high, that is, if the power acceptance is low, even accepting a small amount of differential power makes it easier to fall into an overvoltage, so it is preferable to prioritize the phase change to the d-axis component. In this case, the above-mentioned predetermined value T is raised to change the conditions so that the phase is more likely to be changed by the overvoltage prevention means 43.

[0028] In order to execute the charge limit adjustment means at an appropriate timing, the control unit 31 may execute the SOC monitoring means 45 that acquires the SOC value periodically or according to conditions. The acquired SOC value may be stored in the memory so that the control unit 31 can refer to it as needed.

[0029] In addition, the control unit 31 of the electric vehicle 1 according to the present invention may be capable of executing a driving mode switching means 53 for switching between driving modes with different wheel spin rates. Examples of such driving modes include a normal mode for general paved roads and an off-road mode for gravel roads where slippage is likely to occur, or a rainy / snowy road mode. Various driving modes may be set depending on the purpose and model of the electric vehicle 1. The high slip generation mode, such as the off-road mode and the rainy / snowy road mode, is a mode that is switched when traveling in an environment where the front wheels 23 and the rear wheels 24 are likely to spin, and switching to the high slip generation mode makes it difficult for the vehicle to spin in terms of controlling the torque of the vehicle. The method of switching the mode may be by the driver, such as turning a switch on and off, switching a lever, or operating a touch panel, or may be automatic switching according to map information, and is not particularly limited. However, switching to such an off-road mode or the like means that the driver is aware that he or she is about to travel in an environment where slippage is likely to occur. Therefore, when the high slip generation mode is switched to, the environment is one in which torque reduction due to slippage is likely to occur. For this reason, if the same judgment as in the normal mode is made, overvoltage is likely to occur. In order to deal with this, when switching to the high slip occurrence mode, the control unit 31 may also execute the slip response means 54 that increases the predetermined value T and changes the conditions to make it easier for a phase change to occur in the d-axis component.

[0030] FIG. 3 shows a graph that shows the amount of power that the battery 16 can accept relative to the SOC in the normal mode and the high slip mode. Basically, the lower the SOC (right side in the figure), the more power the battery 16 can accept. Therefore, in the normal mode, the power that the battery 16 can accept is determined based on a standard that is proportional to the SOC or similar. On the other hand, in the high slip mode, in preparation for the occurrence of a sudden overvoltage in a limited area of ​​high SOC, charging the battery 16 is not performed, and priority is given to a process in which power is consumed with a current having a d-axis component. The line that is the standard for this high SOC may be changed for each mode. For example, if slippage is more likely to occur in the off-road mode than in the rainy / snowy road mode, a lower SOC is determined as a high SOC, making it easier to switch to a current having a d-axis component.

[0031] An example of a flow of an embodiment of controlling the electric vehicle 1 according to the present invention taking into account the difference between SOC and modes as described above will be described with reference to Fig. 4. First (S101), the control unit 31 executes the SOC monitoring means 45 to periodically acquire the SOC of the battery 16 after start-up (S102). If the SOC is lower than a predetermined threshold L (S103→Yes), the charge limit adjustment means 44 is executed to decrease the predetermined value T (S104). This makes it difficult to satisfy a condition (S111) described later, and power consumption by charging the battery 16 progresses instead of power consumption by the d-axis current. On the other hand, if the SOC is higher than the predetermined threshold L (S103→No), the predetermined value T is left unchanged.

[0032] The control unit 31 also detects a subsequent change in the driving mode. If the driving mode is the normal mode (S105→No), the process proceeds to the determination process in this state (S111 onward). If the driving mode is a high slip occurrence mode such as a rainy / snowy road mode or an off-road mode (S105→Yes), the control unit 31 increases the predetermined value T (S106) and executes the slip response means 54 that makes it easier for power consumption to occur in the d-axis current.

[0033] Up to this point, this is a preparation stage, and the control unit 31 continues traveling while adjusting the predetermined value T as necessary. At some point during traveling, the current flowing through the battery continues to be detected. In other words, the power monitoring means 41 continues to be executed.

[0034] To simplify the description in the figure, the battery is abbreviated to "cell". It is determined whether the difference between the "upper limit current", which is the maximum value of the current that can be passed through the battery 16, and the effective charging current ("battery current" in the figure) actually introduced into the battery 16 exceeds a predetermined value T (S111). In other words, when the front wheels 23 or the rear wheels 24 slip, the torque decreases, the current that can be consumed by the motor becomes small, and it becomes necessary to pass the difference current to the battery 16, it is determined how close the effective charging current to the upper limit current is. The degree to which it is determined that an overvoltage has occurred is adjusted by adjusting the above-mentioned predetermined value T. If the difference is greater than the predetermined value T (S111→No), the battery 16 still has some margin, so it is acceptable to use the current as charging power for the battery 16, and the vehicle continues running with the q-axis current being applied to both motors (S121).

[0035] On the other hand, when the effective charging current approaches the upper limit current, if the difference is smaller than the predetermined value T (S111→Yes), if the difference current continues to flow to the battery 16, it is likely to cause an overvoltage, so the d-axis current is flowed to one of the motors to consume it. Here, the current of the first motor 21 is compared with the current of the second motor 22 (S112). If the current of the first motor 21 is smaller (S112→Yes), it is determined whether the d-axis current of the first motor 21 has a margin (S113), and if there is a margin (S113→Yes), the overvoltage prevention means 43 is executed (S114), which flows a current to the d-axis current of the first motor 21 to consume the difference power. If there is no margin in the d-axis current of the first motor 21 either (S113→No), there is no choice but to supply it to the battery 16 as it is (S121).

[0036] On the other hand, if the current of the second motor 22 is smaller (S112→No), it is determined whether or not there is a margin in the d-axis current of the second motor 22 (S115), and if there is a margin (S115→Yes), the overvoltage prevention means 43 is executed to supply a current to the d-axis current of the second motor 22 to consume the difference power (S116). If there is no margin in the d-axis current of the second motor 22 either (S115→No), there is no choice but to supply it directly to the battery 16 (S121).

[0037] It is more preferable that after steps S114 and S116, the control unit 31 continues to obtain and compare the magnitudes of the currents of the first motor 21 and the second motor 22. When the magnitudes are reversed, the flow returns to S112 and proceeds to the opposite option.

[0038] As one embodiment, the control unit 31 of the electric vehicle 1 according to the present invention can select a mode in which, when the actual power consumption of one of the first and second motors, which has current flowing through its d-axis, exceeds the actual power consumption of the other motor, the control unit 31 executes the first overvoltage prevention switching means 51, which stops flowing current through the d-axis of one motor and flows current through the d-axis of the other motor, thereby consuming the differential power.

[0039] The situation in which the overvoltage prevention first switching means 51 is executed will be described with reference to the transition diagram of FIG. 5. The horizontal axis indicates time t, and the vertical axis indicates power W. At timing t1, the front wheels 23 slip, and the torque of the first motor 21 and the power generating the torque begin to decrease rapidly. The power monitoring means 41 detects this sudden decrease in power W. The control unit 31 executes the torque compensation means 42, and increases the current flowing to the second motor 22 at timing t2 to suppress the torque decrease in the entire vehicle. Also, since the amount of current flowing in the first motor 21 is lower than that of the second motor 22 at this stage of t2, the overvoltage prevention means 43 causes the first motor 21, which has a larger allowable upper limit, to pass a current to the d-axis. That is, the second motor 22 is caused to increase the q-axis current to compensate for the torque decrease, and the phase is changed so that the d-axis current that does not contribute to the torque also flows.

[0040] As this situation progresses, the actual power consumption of the first motor 21 decreases, and the actual power consumption of the second motor 22 increases. When the actual power consumption of the second motor 22 (one of the motors mentioned above) exceeds the actual power consumption of the first motor 21 (the other motor mentioned above), it is the first motor 21 that has a margin of tolerance up to the upper limit. However, the actual power consumption compared here is a comparison of values ​​excluding the d-axis current. At this timing t3, the phase is returned to stop the d-axis current flowing to the second motor 22, and the phase is changed to flow the d-axis current to the first motor 21. This allows the motor with a margin of tolerance to bear the d-axis current, making it possible to avoid operation close to the limit of the power consumption of each motor.

[0041] Furthermore, as another embodiment, the control unit 31 of the electric vehicle 1 according to the present invention can select a mode in which, when the power consumption of one of the first motor 21 and the second motor 22, which has a current flowing through its d-axis, reaches a predetermined allowable value, the current flowing through the d-axis of the one motor (A) is stopped and a current is flowing through the d-axis of the other motor (B), thereby consuming the differential power. Unlike the above embodiment, this is a mode in which the motor through which the d-axis current flows is switched according to the allowable amount of d-axis current that each motor can consume, not based on the reversal of actual power consumption. When the actual operating environments of the first motor 21 and the second motor 22 are different, it is not judged simply based on the reversal of actual power consumption, but rather that the motor with the surplus should bear the d-axis current, which reduces the load on the vehicle as a whole and contributes to stable operation. [Explanation of symbols]

[0042] 1. Electric vehicles 10 Engine 11 Power generation equipment 16 Battery 21 First Motor 22 Second motor 23 Front wheel 24 Rear wheel 31 Control Unit 41 Power monitoring means 42 Torque compensation means 43 Overvoltage protection measures 44 Charge limit adjustment means 45 SOC monitoring measures 51 First overvoltage protection switching means 52 Second overvoltage protection switching means 53 Driving mode switching means 54 Slip prevention measures

Claims

1. A power generation device; a first motor that rotates one of the front wheels or the rear wheels by AC power generated by the power generation device, and a second motor that rotates the other of the front wheels or the rear wheels; A battery that can store surplus power; An electric vehicle comprising: a power monitoring means for monitoring the power consumption of each of the first motor and the second motor; a torque compensation means for increasing the power to the other motor when the power consumption of one of the motors shows a rapid decrease state that satisfies a predetermined condition, thereby suppressing a torque decrease in the entire vehicle; an overvoltage prevention means for consuming the difference in power by changing the phase of a current to one of the first motor and the second motor (A), which has a smaller power consumption, and controlling the current to flow to a d-axis when a difference between an upper limit current of the battery and an effective charging current charged to the battery becomes equal to or smaller than a predetermined value when the torque compensation means is executed; An electric vehicle having the above configuration.

2. a charging limit adjusting means for adjusting the predetermined value in accordance with an SOC of the battery; The electric vehicle of claim 1 .

3. When the power consumption of one of the first motor and the second motor (A) that has a current flowing through the d-axis exceeds the power consumption of the other motor (B), Stop the current flow to the d-axis of one of the motors (A), The differential power is consumed by passing a current through the d-axis of the other motor (B).

3. The electric vehicle according to claim 2, further comprising a first overvoltage protection switching means.

4. When the power consumption of one of the first motor and the second motor (A) through which a current flows to the d-axis reaches a predetermined allowable value, Stop the current flow to the d-axis of one of the motors (A), The differential power is consumed by passing a current through the d-axis of the other motor (B).

3. The electric vehicle according to claim 2, further comprising a second overvoltage protection switching means.

5. A driving mode switching means for switching to a driving mode having a different wheel spin rate; A slip response means is provided for adjusting the predetermined value to be increased when the wheel rotation rate is changed to a high slip generation mode in which the wheel rotation rate is lower than normal. The electric vehicle according to any one of claims 2 to 4.

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