JP7734709B2 - Electric vehicle control device - Google Patents

Description

The present invention relates to a control device for an electric vehicle.

In electric vehicles equipped with an engine and a drive motor driven by electricity generated by the engine, a fail-safe control technique is known that stops inverter operation in the event of a malfunction in the motor drive device equipped with an inverter.

Patent No. 6296169

However, with the above-mentioned conventional technology, when the inverter operation is stopped by fail-safe control, the drive motor enters an uncontrolled state with its output released. At this time, the capacitance element used to smooth the DC power input to the inverter is charged by the back electromotive force of the drive motor. This can result in an overvoltage being applied to the capacitance element, potentially leading to its destruction.

The object of the present invention is to provide a control device for an electric vehicle that can prevent damage to inverter capacitance elements that occurs during fail-safe control.

In order to achieve the above object, the present invention provides a control device for an electric vehicle including an engine, a battery for storing electric power obtained by converting power of the engine, an inverter for converting DC power output from the battery into AC power, and a drive motor for supplying driving power for running drive wheels using the AC power output from the inverter, the control device including a withstand voltage map acquisition unit for acquiring a withstand voltage map showing the relationship between a voltage of a capacitance element for smoothing the DC power input to the inverter and a durable time, a voltage information acquisition unit for acquiring voltage information showing the voltage of the capacitance element, a temperature information acquisition unit for acquiring temperature information showing the temperature of the drive motor, and a rotation speed information acquisition unit for acquiring a rotation speed of the drive motor. The inverter includes a rotation speed information acquisition unit that acquires information, a timing unit that measures time, and a short-circuit control unit that performs winding short-circuit control to short-circuit the windings of the drive motor when the operation of the inverter is stopped by fail-safe and the capacitance element is not durable based on the withstand voltage map, the voltage information, and the time measured by the timing unit for which the voltage indicated by the voltage information has continued, and the short-circuit control unit cancels the winding short-circuit control during the winding short-circuit control if the voltage of the capacitance element acquired by the voltage information acquisition unit is equal to or lower than a first threshold, the temperature of the drive motor acquired by the temperature information acquisition unit is equal to or higher than a second threshold, and the rotation speed of the drive motor acquired by the rotation speed information acquisition unit is equal to or lower than a third threshold.

With this configuration, it is possible to determine whether the inverter's capacitive elements are in an unsustainable state based on the breakdown voltage map, the voltage of the capacitive elements, and the duration of the capacitive element voltage. If the capacitive elements are in an unsustainable state, winding short-circuit control can be performed to stop the application of the drive motor's back electromotive force to the capacitive elements. This prevents damage to the inverter's capacitive elements due to fail-safe control.

This invention can prevent damage to inverter capacitance elements caused by fail-safe control.

FIG. 1 is a block diagram showing an example of a main configuration of a hybrid vehicle. FIG. 2 is a diagram illustrating an example of a schematic configuration of the second inverter. FIG. 3 is a diagram showing an example of the relationship between the three-phase voltage of the drive motor and the voltage of the smoothing capacitor. FIG. 4 is a diagram showing an example of the relationship between the vehicle speed and the voltage of the back electromotive force of the drive motor at the time of shutdown. FIG. 5 is a diagram showing an example of a withstand voltage map. FIG. 6 is a diagram showing an example of functions of the MG-ECU. FIG. 7 is a timing chart showing an example of the operation of the HEV-ECU and the MG-ECU when an internal failure occurs in the PCU. FIG. 8 is a flowchart showing an example of the operation of the MG-ECU.

Below, an embodiment of a hybrid vehicle control device of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiment.

Figure 1 shows an example of the main configuration of a hybrid vehicle 1 according to this embodiment. The hybrid vehicle 1 is equipped with a series hybrid system 10. The hybrid system 10 includes an engine 11, a generator motor (MG1) 12, a drive motor (MG2) 13, a battery 14, and a PCU (Power Control Unit) 15.

The engine 11 is, for example, a gasoline engine.

The generator motor 12 is, for example, a permanent magnet synchronous motor. The rotating shaft of the generator motor 12 is mechanically connected to the crankshaft of the engine 11 via a gear (not shown). For example, an output gear of the engine 11 is supported on the crankshaft of the engine 11 so as not to rotate relative to the crankshaft, and an output gear of the engine 11 is supported on the rotating shaft of the generator motor 12 so as not to rotate relative to the crankshaft, and the output gear of the engine 11 and the motor gear are meshed.

The drive motor 13 is, for example, a permanent magnet synchronous motor that is larger than the generator motor 12. The rotating shaft of the drive motor 13 is connected to the drive system 16 of the hybrid vehicle 1. The drive system 16 includes a differential gear, and the power of the drive motor 13 is transmitted to the differential gear, and then distributed and transmitted from the differential gear to drive wheels 17, which consist of the left and right front or rear wheels. This causes the left and right drive wheels 17 to rotate, causing the hybrid vehicle 1 to move forward or backward.

The battery 14 stores the electric power obtained by converting the power of the engine 11. For example, the battery 14 is a battery pack made up of multiple secondary batteries. The secondary batteries are, for example, lithium-ion batteries. The battery 14 outputs, for example, DC power of approximately 200 to 350 V.

The PCU 15 is a unit for controlling the operation of the generator motor 12 and the drive motor 13, and is equipped with a first inverter 21, a second inverter 22, and a converter 23.

When starting the engine 11, the DC power output from the battery 14 is boosted by the converter 23, the boosted DC power is converted to AC power by the first inverter 21, and the AC power is supplied to the generator motor 12. This causes the generator motor 12 to operate in powered mode, and the engine 11 is motored (cranked) by the generator motor 12. When the rotation speed of the crankshaft of the engine 11 has increased to the rotation speed required for starting due to motoring, the engine 11 starts when the spark plug of the engine 11 is fired.

When the hybrid vehicle 1 is running, the drive motor 13 is powered and generates power.

When the output required of the drive motor 13 is less than the output of the battery 14, the hybrid vehicle 1 runs in EV mode. That is, the engine 11 is stopped, no power is generated by the generator motor 12, and power is supplied from the battery 14 to the drive motor 13, which then drives the drive motor 13.

Furthermore, when the remaining capacity of the battery 14 falls below a predetermined level, the generator motor 12 operates to generate electricity while the engine 11 is running, regardless of whether the drive motor 13 is running or stopped. At this time, the AC power from the generator motor 12 is converted to DC power by the first inverter 21, and the DC power output from the first inverter 21 is stepped down by the converter 23. The stepped-down DC power is then supplied to the battery 14, thereby charging the battery 14.

When the hybrid vehicle 1 decelerates, the drive motor 13 operates in regenerative mode, and the power transmitted from the drive wheels 17 to the drive motor 13 is converted into AC power. At this time, the drive motor 13 acts as a resistor in the driving system, and this resistance acts as a braking force (regenerative braking force) that brakes the hybrid vehicle 1. At this time, in the PCU 15, the AC power supplied from the drive motor 13 to the second inverter 22 is converted into DC power by the second inverter 22, and the DC power output from the second inverter 22 is stepped down by the converter 23. The stepped-down DC power is then supplied to the battery 14, charging the battery 14.

The ECU 31 is a control device that controls the hybrid vehicle 1. The ECU 31 includes multiple ECUs, such as the HEV-ECU 100, which controls the hybrid system 10, and the MG-ECU 200, which controls the motor system, including the generator motor 11, drive motor 13, and PCU 15. The ECUs are interconnected via electrical communication lines such as a CAN (Controller Area Network) so that they can communicate with each other.

Next, we will explain the fail-safe control performed in the event of a failure of the PCU 15 in this embodiment. In this embodiment, the MG-ECU 200 stops (shuts down) the operation of the second inverter 22 as fail-safe control in the event of an internal failure of the PCU 15. Figure 2 is a diagram showing an example of the schematic configuration of the second inverter 22. As shown in Figure 2, the second inverter 22 includes a smoothing capacitor C (corresponding to a "capacitance element") for smoothing the input DC power, six transistors S1 to S6, and six diodes D1 to D6 that correspond one-to-one to the six transistors and are connected in parallel in the reverse direction of their corresponding transistors. The combination of the six transistors and the six diodes D1 to D6 forms a full-bridge circuit.

In this example, the three upper transistors S1 to S3 are referred to as the first upper arm transistor S1, the second upper arm transistor S2, and the third upper arm transistor S3, respectively. The three lower transistors S4 to S6 are referred to as the first lower arm transistor S4, the second lower arm transistor S5, and the sixth lower arm transistor S6, respectively. The first upper arm transistor S1 and the first lower arm transistor S4 are paired and connected in series, with their connection point (node) connected to one of the three phases (u, v, w) of the drive motor 13. The second upper arm transistor S2 and the second lower arm transistor S5 are paired and connected in series, with their connection point (node) connected to one of the three phases (u, v, w) of the drive motor 13. The third upper arm transistor S3 and the sixth lower arm transistor S6 are paired and connected in series, with their connection point (node) connected to one of the three phases (u, v, w) of the drive motor 13.

The six diodes D1 to D6 are referred to as the first diode D1, second diode D2, third diode D3, fourth diode D4, fifth diode D5, and sixth diode D6, respectively. The first diode D1 is connected in parallel in the reverse direction with the first upper arm transistor S1. The second diode D2 is connected in parallel in the reverse direction with the second upper arm transistor S2. The third diode D3 is connected in parallel in the reverse direction with the third upper arm transistor S3. The fourth diode D4 is connected in parallel in the reverse direction with the first lower arm transistor S4. The fifth diode D5 is connected in parallel in the reverse direction with the second lower arm transistor S5. The sixth diode D6 is connected in parallel in the reverse direction with the third lower arm transistor S6.

If an internal failure occurs in the PCU 15, the MG-ECU 200 performs fail-safe control by stopping the operation of transistors S1 to S6 (stopping the operation of the second inverter 22). This causes the drive motor 13 to enter an uncontrolled (output-disconnected) state, and smoothing capacitor C is charged by the back electromotive force of the drive motor 13 via the full-bridge circuit. Figure 3 shows an example of the relationship between the three-phase voltage and the voltage VH of smoothing capacitor C (voltage applied between the electrodes). The direction of the current indicated by the arrow in Figure 2 corresponds to the state at time t shown in Figure 3.

Figure 4 shows an example of the relationship between vehicle speed and the voltage of the back electromotive force (back voltage) of the drive motor 13 during shutdown due to the PCU 15 fail-safe. As shown in Figure 4, the back electromotive force of the drive motor 13 during shutdown is proportional to the vehicle speed. Figure 5 shows an example of a withstand voltage map showing the relationship between the voltage of smoothing capacitor C and the endurance time. As shown in Figure 5, when the voltage exceeds V1, the endurance time shortens proportionally. For example, when the voltage of smoothing capacitor C is V2 (700 V, for example), the endurance time is approximately 60 seconds. This means that if the voltage applied to smoothing capacitor C continues for 60 seconds or more, the withstand voltage limit may be exceeded, resulting in overvoltage breakdown (meaning the capacitor will not be able to withstand the voltage).

In this embodiment, the MG-ECU 200 determines whether the smoothing capacitor C is unsustainable based on the above-mentioned withstand voltage map, the voltage VH of the smoothing capacitor C, and the time that the voltage VH is continuously applied to the smoothing capacitor C. If the smoothing capacitor C is unsustainable, it performs winding short-circuit control to short-circuit the windings of the drive motor 13, thereby preventing overvoltage breakdown of the smoothing capacitor C. The specific configuration of the MG-ECU 200 is described below.

Figure 6 is a diagram showing an example of the functions of MG-ECU 200. As shown in Figure 6, MG-ECU 200 has a fail-safe control unit 210, a withstand voltage map acquisition unit 220, a voltage information acquisition unit 230, a timer unit 240, a temperature information acquisition unit 250, a rotation speed information acquisition unit 260, a short-circuit control unit 270, and a discharge control unit 280. In this example, the functions illustrated in Figure 7 are realized by a processor executing a program stored in non-volatile memory, but this is not limiting, and for example, some or all of these functions may be realized by dedicated hardware circuits (e.g., semiconductor integrated circuits).

Note that the example in Figure 6 illustrates only the functions necessary to explain the main parts of this embodiment, but the functions possessed by the MG-ECU 200 are not limited to these.

When an internal failure occurs in the PCU 15, the fail-safe control unit 210 performs fail-safe control to shut down the second inverter 22. More specifically, the fail-safe control unit 210 stops the operation of transistors S1 to S6 included in the second inverter 22.

The withstand pressure map acquisition unit 220 acquires the withstand pressure map described above. The withstand pressure map may be stored in any location, and may take various forms depending on design conditions, etc. For example, the withstand pressure map may be stored in ROM 202, in memory external to MG-ECU 200, or in an external device such as a server.

The voltage information acquisition unit 230 acquires the voltage VH of the smoothing capacitor C. The timer unit 240 has a timer function. The temperature information acquisition unit 250 acquires temperature information indicating the temperature of the drive motor 13. The rotation speed information acquisition unit 260 acquires rotation speed information indicating the rotation speed of the drive motor 13.

When the operation of the second inverter 22 is stopped by the fail-safe control unit 210, the short-circuit control unit 170 performs winding short-circuit control to short-circuit the windings of the drive motor 13 if the smoothing capacitor C is not durable, based on the withstand voltage map acquired by the withstand voltage map acquisition unit 220, the voltage information acquired by the voltage information acquisition unit 230, and the duration of the voltage VH indicated by the voltage information measured by the timing unit 240. For example, in the withstand voltage map of Figure 5, if the voltage VH of the smoothing capacitor C remains at V2 for 60 seconds, it is determined that the smoothing capacitor C is not durable. In this case, the short-circuit control unit 170 performs winding short-circuit control. The winding short-circuit control may be any control that short-circuits the three phases of the drive motor 13, and may be, for example, control that simultaneously transitions the first upper arm transistor S1, the second upper arm transistor S2, and the third upper arm transistor S3 to the ON state, or control that simultaneously transitions the first lower arm transistor S4, the second lower arm transistor S5, and the third lower arm transistor S6 to the ON state.

Furthermore, during winding short-circuit control, if the voltage VH of the smoothing capacitor C is equal to or lower than the first threshold and the temperature of the drive motor 13 acquired by the temperature information acquisition unit 250 is equal to or higher than the second threshold, the short-circuit control unit 270 cancels the winding short-circuit control. When the drive motor 13 is short-circuited, the drive motor 13 heats up due to the short-circuit current, which may result in demagnetization or winding burnout due to overheating. Therefore, if the voltage VH of the smoothing capacitor C is equal to or lower than the first threshold, which indicates a voltage that does not pose a risk of overvoltage breakdown (e.g., a voltage equal to or lower than voltage V1 in Figure 5), and the temperature of the drive motor 13 is equal to or higher than the second threshold, which indicates a temperature that may result in winding burnout, the winding short-circuit control is canceled, thereby protecting the drive motor 13.

Furthermore, the short-circuit control unit 270 cancels the winding short-circuit control when the rotation speed of the drive motor 13 acquired by the rotation speed information acquisition unit 260 is equal to or less than a third threshold value.

Continuing with the explanation of Figure 6, the discharge control unit 280 controls the discharge of the smoothing capacitor C. For example, the discharge control unit 280 can promote the discharge of the smoothing capacitor C by powering the generator motor 11 (active discharge). The smoothing capacitor C can also be discharged via a discharge resistor (not shown) (passive discharge).

Figure 7 is a timing chart showing an example of the operation of the HEV-ECU 100 and MG-ECU 200 when an internal failure occurs in the PCU 15. In Figure 7, the IGCT activation signal, one of the internal signals of the HEV-ECU 100, is a signal that indicates whether the ignition switch is on or off. SMRB and SMRG are signals that indicate whether power is being supplied from the battery 14 to the converter 23. When SMRB and SMRG are on, this indicates that power is being supplied from the battery 14 to the converter 23, and when they are off, this indicates that power supply from the battery 14 to the converter 23 is being cut off.

In addition, the "system voltage" shown in Figure 7 refers to the voltage VH of smoothing capacitor C. In the example of Figure 7, when an internal failure occurs in PCU 15, system voltage VH rises and exceeds the first threshold, and the time indicated by the withstand voltage map as reaching overvoltage breakdown has elapsed, MG-ECU 200 performs winding short-circuit control. Thereafter, the temperature of drive motor 13 rises and reaches the second threshold (≦critical temperature), and if the rotation speed falls below the third threshold and system voltage VH falls below the first threshold, winding short-circuit control is released.

After the winding short-circuit control is released, the system voltage rises again and exceeds the first threshold. When the time has passed until the voltage resistance map indicates overvoltage breakdown, the MG-ECU 200 performs winding short-circuit control again. The state of the drive motor 13 is then monitored, and if the temperature of the drive motor 13 again reaches the second threshold, the rotation speed is below the third threshold, and the system voltage VH has fallen below the first threshold, the winding short-circuit control is released. If the system voltage does not show an increasing trend after the winding short-circuit control is released, the motor short-circuit necessity determination flag, which indicates whether or not a determination is required to short-circuit the drive motor 13, is turned off.

Figure 8 is a flowchart showing an example of the operation of the MG-ECU 200 when an internal failure occurs in the PCU 15. Explanations of portions that overlap with the functional description above will be omitted where appropriate. As shown in Figure 8, first, when the second inverter 22 is shut down by the fail-safe control unit 210 (step S1: Yes), the voltage information acquisition unit 230 acquires voltage information (step S2).

The short-circuit control unit 270 determines whether the voltage VH (voltage VH of smoothing capacitor C) indicated by the voltage information acquired in step S2 exceeds the first threshold (step S3). If the result of step S3 is positive (step S3: Yes), the timer unit 240 starts timing (step S4), and the voltage information acquisition unit 230 acquires voltage information (step S5).

The short-circuit control unit 270 determines whether the voltage VH indicated by the voltage information acquired in step S5 exceeds the first threshold (step S6). If the result of step S6 is positive (step S6: Yes), the short-circuit control unit 270 determines whether there is a possibility that the component withstand voltage of the smoothing capacitor C will be exceeded (whether it will be unable to withstand the voltage) based on the withstand voltage map and the elapsed time (step S7).

If the result of step S7 is positive (step S7: Yes), the short-circuit control unit 270 performs winding short-circuit control, and the discharge control unit 280 performs discharge control of the smoothing capacitor C (control related to passive discharge and active discharge) (step S8). After step S8, the temperature information acquisition unit 250 acquires temperature information (step S9). Then, the short-circuit control unit 270 determines whether the temperature indicated by the temperature information acquired in step S8 is equal to or greater than the second threshold (step S10). If the result of step S10 is positive (step S10: Yes), the voltage information acquisition unit 230 acquires voltage information (step S11). Then, the short-circuit control unit 270 determines whether the voltage VH indicated by the voltage information acquired in step S11 is equal to or less than the first threshold (step S12).

If the result of step S12 is positive (step S12: Yes), the rotation speed information acquisition unit 260 acquires rotation speed information (step S13). Then, the short circuit control unit 270 determines whether the rotation speed indicated by the rotation speed information acquired in step S13 is equal to or less than a third threshold value (step S14).

If the result of step S14 is positive (step S14: Yes), the discharge control unit 280 stops the discharge control, and the short-circuit control unit 270 releases the winding short-circuit control (step S15).

As described above, when the MG-EU 200 of this embodiment stops operation of the second inverter 22 due to a fail-safe caused by an internal fault in the PCU 15, the MG-EU 200 uses a withstand voltage map showing the relationship between the voltage VH of the smoothing capacitor C and the endurance time to monitor the voltage VH of the smoothing capacitor C and the application time of the voltage VH to determine whether the smoothing capacitor C is beyond its endurance. If the smoothing capacitor C is beyond its endurance, winding short-circuit control is performed to short-circuit the windings of the drive motor 13. This makes it possible to prevent damage to the smoothing capacitor C of the second inverter 22 that would otherwise be caused by the fail-safe control caused by an internal fault in the PCU 15.

Furthermore, if the drive motor 13 is short-circuited by the above-mentioned winding short-circuit control, the drive motor 13 will heat up due to the short-circuit current, which could result in demagnetization or winding burnout due to overheating. Therefore, as described above, the MG-EU 200 of this embodiment can protect the drive motor 13 by canceling the winding short-circuit control when the voltage VH of the smoothing capacitor C is equal to or lower than the first threshold value indicating a voltage that does not pose a risk of overvoltage breakdown, and the temperature of the drive motor 13 is equal to or higher than the second threshold value indicating a temperature that could result in winding burnout, etc.

The above describes an embodiment of the present invention, but the above-described embodiment is presented as an example and is not intended to limit the scope of the present invention. This novel embodiment can be embodied in a variety of other forms. Furthermore, various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. Furthermore, this embodiment is included within the scope and spirit of the invention, as well as the invention and its equivalents as set forth in the claims.

1 Hybrid vehicle 10 Hybrid system 11 Engine 12 Generator motor (MG1)
13 Drive motor (MG2)
14 Battery 15 PCU
16 Drive system 17 Drive wheels 21 First inverter 22 Second inverter 23 Converter 31 ECU
100 HEV-ECU
200 MG-ECU
201 Processor 202 ROM
203 RAM
204 I/F unit 210 Fail-safe control unit 220 Withstand voltage map acquisition unit 230 Voltage information acquisition unit 240 Timer unit 250 Temperature information acquisition unit 260 Rotational speed information acquisition unit 270 Short-circuit control unit 280 Discharge control unit

Claims (1)

A control device for an electric vehicle including an engine, a battery that stores electric power obtained by converting power of the engine, an inverter that converts DC power output from the battery into AC power, and a drive motor that uses the AC power output from the inverter to supply drive power for driving drive wheels,
a withstand voltage map acquisition unit that acquires a withstand voltage map that indicates a relationship between a voltage of a capacitance element for smoothing DC power input to the inverter and a durable time;
a voltage information acquiring unit that acquires voltage information indicating a voltage of the capacitive element;
a temperature information acquisition unit that acquires temperature information indicating the temperature of the drive motor;
a rotation speed information acquisition unit that acquires rotation speed information indicating the rotation speed of the drive motor;
a timing unit that measures time;
a short-circuit control unit that performs winding short-circuit control to short-circuit a winding of the drive motor if the capacitance element is not durable, based on the withstand voltage map, the voltage information, and the duration of the voltage indicated by the voltage information measured by the timer unit , when the operation of the inverter is stopped by a fail-safe function;
Equipped with
the short-circuit control unit cancels the winding short-circuit control when, during the winding short-circuit control, the voltage of the capacitive element acquired by the voltage information acquisition unit is equal to or lower than a first threshold, the temperature of the drive motor acquired by the temperature information acquisition unit is equal to or higher than a second threshold, and the rotation speed of the drive motor acquired by the rotation speed information acquisition unit is equal to or lower than a third threshold.
Control device for electric vehicles.