Motor control method and circuit for a vehicle, motor drive system, and vehicle

Abstract

The present invention relates to a method for controlling a vehicle motor. The method includes: determining that a motor control unit (MCU) has a fault; monitoring the output AC frequency of the motor; and based on the output AC frequency, controlling the motor to switch between an active short circuit state and a safe pulse-off state. The present invention also relates to a motor control circuit for a vehicle, a motor drive system, and a vehicle.

Description

Technical Field

[0001] The present invention relates to a motor control strategy for a vehicle, and more particularly, to a motor control method, a motor control circuit, a motor drive system, and a vehicle for a vehicle. Background Art

[0002] As a basic functional safety requirement for the application of a motor drive system, the system should detect events that may violate safety goals and enter a safe state. However, to improve the usability and user experience of a vehicle, a fail operational mode is introduced. For example, in a dual-motor drive system, if it is assumed that a motor drive system of a permanent magnet synchronous motor (PMSM) fails, the other motor drive system continues to operate in a controlled manner. Therefore, the vehicle will still be in a controlled operation mode or a home mode.

[0003] During the fail operational mode, the motor control unit (MCU) should control the inverter of the motor to switch between an active short circuit state (ASC state) and a safe pulse off state (SPO state). However, if the motor control unit itself fails, it may pose a safety hazard to vehicle driving. For example, when the vehicle is running at a high speed, the back electromotive force of the on-vehicle motor will be very large. At this time, if all the switching tubes of its three-phase bridge inverter are directly turned off (i.e., switched or entered the SPO state), the excessive back electromotive force will cause overvoltage of the DC bus and generate a large regenerative braking torque. The overvoltage of the DC bus may damage the switching tubes of the inverter, and the large regenerative braking torque may cause overcharging or even explosion of the battery or increase the risk of rollover. Summary of the Invention

[0004] According to an aspect of the present invention, there is provided a motor control method for a vehicle, the method including: determining that a motor control unit MCU fails; monitoring an output AC frequency of a motor; and based on the output AC frequency, controlling the motor to switch between an active short circuit state and a safe pulse off state.

[0005] As a supplement or replacement to the above solution, in the above motor control method, monitoring the output AC frequency of the motor includes: obtaining an AC current value output by the motor; converting the AC current value into a digital pulse width modulation signal by using a zero-crossing detector; and converting the frequency of the digital pulse width modulation signal into a first voltage value by using a frequency-voltage converter.

[0006] As a supplement or replacement to the above solution, in the above motor control method, the frequency of the digital pulse width modulation signal is equal to or proportional to the frequency of the AC current value.

[0007] As a supplement or replacement to the above solution, in the above motor control method, controlling the motor to switch between the active short - circuit state and the safe pulse - off state based on the output AC frequency includes: when the output AC frequency is lower than a first threshold, switching the inverter connected to the motor to the safe pulse - off state.

[0008] As a supplement or replacement to the above solution, in the above motor control method, controlling the motor to switch between the active short - circuit state and the safe pulse - off state based on the output AC frequency further includes: when the output AC frequency is greater than or equal to the first threshold, switching the inverter to the active short - circuit state.

[0009] As a supplement or replacement to the above solution, in the above motor control method, controlling the motor to switch between the active short - circuit state and the safe pulse - off state based on the output AC frequency includes: if the first voltage value is less than a second threshold, switching the inverter connected to the motor to the safe pulse - off state; and if the first voltage value is greater than or equal to the second threshold, switching the inverter to the active short - circuit state.

[0010] According to another aspect of the present invention, there is provided a motor control circuit for a vehicle, the circuit including: a monitoring circuit for monitoring the output AC frequency of the motor when it is determined that a motor control unit (MCU) fails; and a switching circuit for controlling the motor to switch between the active short - circuit state and the safe pulse - off state based on the output AC frequency.

[0011] As a supplement or replacement to the above solution, in the above motor control circuit, the motor control circuit is connected in parallel with the motor control unit (MCU).

[0012] As a supplement or replacement to the above solution, in the above motor control circuit, the monitoring circuit includes: an AC current sensor for obtaining the AC current value output by the motor; a zero - crossing detector for converting the AC current value into a digital pulse - width modulation signal; and a frequency - to - voltage converter for converting the frequency of the digital pulse - width modulation signal into a first voltage value.

[0013] As a supplement or replacement to the above solution, in the above motor control circuit, the frequency of the digital pulse - width modulation signal is equal to or proportional to the frequency of the AC current value.

[0014] As a supplement or replacement to the above solution, in the above motor control circuit, the switching circuit includes: a comparator for comparing the first voltage value with a reference threshold; and a switching logic for switching the inverter connected to the motor to the safe pulse off state when the first voltage value is less than the reference threshold; the switching logic is further configured to switch the inverter to the active short circuit state when the first voltage value is greater than or equal to the reference threshold.

[0015] According to another aspect of the present invention, there is provided a motor drive system including a motor control unit MCU and the aforementioned motor control circuit connected in parallel with the motor control unit MCU.

[0016] According to another aspect of the present invention, there is provided a vehicle including the motor drive system as described above.

[0017] The motor control solution for a vehicle according to an embodiment of the present invention can reasonably switch between the active short circuit state (ASC state) and the safe pulse off state (SPO state) by monitoring the output AC frequency of the motor when a failure occurs in the motor control unit (e.g., during a fault operation), which can meet the basic functional safety requirements of the motor drive system application, and avoid entering the safe pulse off state (SPO state) when the vehicle is at high speed, improving the availability and user experience of the vehicle during a fault operation. Description of the Drawings

[0018] From the following detailed description in conjunction with the drawings, the above and other objects and advantages of the present invention will become more fully clear, wherein the same or similar elements are denoted by the same reference numerals.

[0019] Figure 1 Shows a topological structure diagram of a three-phase bridge inverter according to an embodiment of the present invention;

[0020] Figure 2 Shows a schematic diagram of a motor control method for a vehicle according to an embodiment of the present invention;

[0021] Figure 3 Shows a logical schematic diagram of a motor drive system according to an embodiment of the present invention; and

[0022] Figure 4 Shows a structural schematic diagram of a motor control circuit for a vehicle according to an embodiment of the present invention. Detailed Description of the Embodiment

[0023] To make the objectives, technical solutions and advantages of the present invention more apparent, the specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining the present invention, rather than limiting the present invention.

[0024] In addition, it should be noted that for the sake of convenience of description, only the parts related to the present invention rather than all the content are shown in the drawings. Before discussing the exemplary embodiments in more detail, it should be mentioned that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although the operations (or steps) in the flowchart are described as sequential processes, many of these operations can be performed in parallel, concurrently or simultaneously. In addition, the order of the operations can be rearranged. When the operations are completed, the process can be terminated, but there can also be additional steps not included in the drawings. The process can correspond to a method, function, procedure, subroutine, subprogram, etc.

[0025] It should be understood that the term "vehicle" or other similar terms used herein include general motor vehicles, such as passenger cars (including sport utility vehicles, buses, trucks, etc.), various commercial vehicles, etc., and include hybrid electric vehicles, electric vehicles, etc. A hybrid electric vehicle is a vehicle with two or more power sources, such as a gasoline-powered and an electric vehicle.

[0026] Although the exemplary embodiments are described as using multiple units to perform the exemplary processes, it should be understood that these exemplary processes can also be performed by one or more modules.

[0027] In a vehicle electric drive system, the normal operation of the motor is extremely important. Once a motor fails, the system will malfunction at least, or even cause the vehicle to be damaged and people to be killed in the worst case. And as the bottom-level actuator, it is difficult for the electric drive system to achieve its own control and diagnosis. Therefore, in the case of a motor failure, it is necessary to actively protect the electric drive system. The two most common active protection measures are SPO (Safety Pulse Off), which can also be called Freewheeling, and ASC (Active Short Circuit). The implementation method of SPO is to disconnect all the switching tubes, thereby achieving the disconnection between the motor and the controller (this isolation is not complete because the body diode has the function of freewheeling). ASC separates the motor and the controller by short-circuiting the upper bridge or the lower bridge.

[0028] The electric drive system further includes an inverter unit, which is widely used to convert DC voltage into single-phase or polyphase AC voltage. For vehicles such as battery electric vehicles (BEVs) or hybrid vehicles, the inverter unit typically converts the DC voltage provided by the battery into three-phase AC voltage to supply power to the motor driving the vehicle. The inverter unit can be controlled by a motor control unit. For example, the motor control unit directly or indirectly supplies a pulse width modulation (PWM) signal to the gates of the switching elements connected to the intermediate circuit. Thus, the alternating current is generated by the switching mode of the switching elements. In the event of a fault (such as overvoltage), the motor control unit can turn on or off the switching transistors in the bridge arms of the three-phase inverter unit to prevent component damage.

[0029] Figure 1 FIG. shows a topological structure diagram of a three-phase bridge inverter 1000 according to an embodiment of the present invention. Among them, the DC side of the three-phase bridge inverter is connected to the battery, and its AC side is connected to the motor M. And, the upper bridge arm of the three-phase bridge inverter includes three switching transistors S1, S3, and S5, and its lower bridge arm includes three switching transistors S2, S4, and S6. When a certain fault occurs, the motor control unit can control the inverter to turn on the switching transistors S2, S4, and S6 (i.e., the switching transistors in the lower bridge arm), and turn off the switching transistors S1, S3, and S5 in the upper bridge arm (i.e., enter the active short-circuit circuit state). When another fault occurs, the motor control unit can control the inverter to turn off all the switching transistors (i.e., enter the safe pulse-off state).

[0030] The motor control unit MCU can monitor the vehicle speed by decoding the resolver signal and control the switching between the active short-circuit circuit state (ASC state) and the safe pulse-off state (SPO state) based on the monitored speed. However, when the motor control unit MCU itself fails, the only possible safe states are either to continue the SPO state (i.e., all the switching transistors in the inverter remain off) or to continue the ASC state (i.e., keep all the switching transistors in the upper or lower bridge arm of the inverter in the three-phase on state). However, continuing the SPO state at high speeds, the high charging current will pose a potential safety threat to the battery pack.

[0031] Based on this problem, the inventors of the present application propose to monitor the frequency of the motor alternating current when the motor control unit fails and switch between the ASC state and the SPO state based on this frequency (estimating the vehicle speed).

[0032] Figure 2 FIG. shows a schematic diagram of a motor control method 2000 for a vehicle according to an embodiment of the present invention. As Figure 2 shown, the method 2000 includes the following steps:

[0033] In step S210, it is determined that a fault occurs in the motor control unit (MCU);

[0034] In step S220, the output AC frequency of the motor is monitored; and

[0035] In step S230, based on the output AC frequency, the motor is controlled to switch between an active short - circuit state and a safety pulse - off state.

[0036] In the context of the present invention, the "motor control unit" is also referred to as MCU, micro - control unit or micro - controller, which is used to control the motor of a vehicle. The MCU is applicable to various types of motor control. Through the internally integrated motor control module, it can simplify the development of motor control for customers. Moreover, compared with DSP (i.e., digital signal processor), the MCU can better implement the servo control and protection functions of the motor.

[0037] The term "active short - circuit", also known as active short - circuit protection or ASC (Active Short Circuit), can be achieved in the following ways: turning off the three IGBTs of the upper bridge arm of the inverter and simultaneously turning on the three IGBTs of the lower bridge arm; or turning on the three IGBTs of the upper bridge arm of the inverter and simultaneously turning off the three IGBTs of the lower bridge arm. For example, in the following situations, the ASC state or mode can be entered: when the whole vehicle is out of control, implementing ASC can generate a reverse torque to slow down the vehicle for safe parking; when the power battery fails, implementing ASC can isolate the motor, the motor control unit from the power battery side to ensure the high - voltage safety of the whole vehicle; when the driving motor speed is too high or abnormal during the driving of the whole vehicle, implementing ASC can avoid damage to the power battery, bus capacitor and other high - voltage devices caused by excessive back electromotive force; when a certain switching tube IGBT in the inverter fails, implementing ASC can avoid damage to other devices or the power battery caused by uncontrollable rectification.

[0038] The term "safety pulse - off" is also known as pulse - off mode or SPO (Safety Pulse Off), which realizes the disconnection of the controller from the motor by turning off all the switching tubes in the inverter. Under this condition, the energy on the motor side can only be passively rectified through the reverse diodes on the inverter bridge. The advantage of SPO is that it will not generate a large "unexpected torque", thus having no impact on the driver's operation. However, if SPO is performed during the high - speed operation of the motor (usually the motor is in the field - weakening state at this time), the d - axis current will disappear, and the enhancement of the d - axis magnetic field will lead to a relatively high back electromotive force. After the passive rectification of this back electromotive force through the diode, its voltage is greater than the battery voltage, thereby charging the battery and causing the bus voltage to rise. Moreover, it will also affect other electronic components such as IGBTs connected to the bus, increasing the risk of controller failure.

[0039] Therefore, in one embodiment, when it is determined that a motor control unit (MCU) fails, based on the monitored output AC frequency of the motor (i.e., the frequency of the AC current), the motor is controlled to switch between the active short - circuit state and the safe pulse - off state. For example, when the output AC frequency is lower than a first threshold (where the first threshold can be preset according to the situation), the inverter connected to the motor is switched to the safe pulse - off (SPO) state. When the output AC frequency is greater than or equal to the first threshold, the inverter is switched to the active short - circuit (ASC) state.

[0040] In another embodiment, when a fault event occurs in the electric drive system, the ASC state is enabled by default. And the output AC frequency of the motor is continuously monitored until the output AC frequency is lower than the first threshold, then the state is switched from the ASC state to the SPO state, thus avoiding the potential risk of charging the high - voltage battery with uncontrolled regenerative current during the fail - operational mode or fail - safe mode.

[0041] In one embodiment of the above - mentioned motor control method 2000, step S220 may include: obtaining the AC current value output by the motor; converting the AC current value into a digital pulse - width modulation signal by using a zero - crossing detector; and converting the frequency of the digital pulse - width modulation signal into a first voltage value by using a frequency - to - voltage converter. In one or more embodiments, the frequency of the digital pulse - width modulation signal may be equal to or proportional to the frequency of the AC current value.

[0042] In one embodiment, step S230 may include: when the output AC frequency is lower than the first threshold, switching the inverter connected to the motor to the safe pulse - off state. This step S230 may also include: when the output AC frequency is greater than or equal to the first threshold, switching the inverter to the active short - circuit state.

[0043] In another embodiment, step S230 may include: when a first voltage value corresponding to the output AC frequency of the motor is less than a second threshold, switching the inverter connected to the motor to the safe pulse - off state; and if the first voltage value is greater than or equal to the second threshold, switching the inverter to the active short - circuit state.

[0044] In yet another embodiment, when it is determined that the motor control unit (MCU) fails, the ASC state is enabled by default. And the motor speed is continuously monitored until the motor speed is lower than a second threshold, then the state is switched from the ASC state to the SPO state, thus avoiding the potential risk of charging the high - voltage battery with uncontrolled regenerative current during the fail - operational mode or fail - safe mode.

[0045] Figure 3A logic schematic diagram of a motor drive system 3000 according to an embodiment of the present invention is shown. As Figure 3 shown, the motor drive system 3000 includes a motor control unit MCU 310, a motor control circuit 320, and an inverter circuit 1000, wherein the motor control unit MCU 310 is connected in parallel with the motor control circuit 320. When the motor control unit MCU 310 operates normally, the MCU 310 drives the inverter circuit 1000 in a fault operation mode by, for example, sending a PWM (pulse width modulation) signal. When a fault occurs in the motor control unit MCU 310, the motor control circuit 320 starts to work. In one embodiment, the motor control circuit 320 avoids entering the SPO state at high vehicle speeds by continuously monitoring the frequency of the motor alternating current (three-phase) and switching between the ASC state and the SPO state based on the monitored alternating current frequency.

[0046] In Figure 3 the shown motor drive system 3000, the motor control unit MCU 310 is connected in parallel with the motor control circuit 320, and both jointly control the inverter circuit 1000. Among them, the control link of the motor control unit MCU 310 is the main control link (also referred to as the main turn-off link), and the control link of the motor control circuit 320 is the auxiliary control link (also referred to as the auxiliary turn-off link). That is to say, in one or more embodiments of the present invention, based on the motor control unit MCU 310, by additionally setting up a motor control circuit 320 (as an auxiliary control link), it is possible to avoid the motor entering the SPO state at high vehicle speeds when a fault occurs in the MCU 310, thus avoiding potential safety hazards. This implementation method does not require an additional MCU, and the implementation is very simple, direct, and the implementation cost is also relatively low.

[0047] In one embodiment of the present invention, a motor control circuit for a vehicle may include a monitoring circuit and a switching circuit, wherein the monitoring circuit is used to monitor the output alternating current frequency of the motor when it is determined that a fault has occurred in the motor control unit MCU, and the switching circuit is used to control the motor to switch between the active short circuit state and the safe pulse turn-off state based on the output alternating current frequency.

[0048] Figure 4 A specific structural schematic diagram of a motor control circuit 320 for a vehicle according to an embodiment of the present invention is shown. In Figure 4 it, the monitoring circuit may include an alternating current sensor 410, a zero-crossing detector 420, and a frequency-voltage converter 430. The alternating current sensor 410 is used to obtain the alternating current value output by the motor, the zero-crossing detector 420 is used to convert the alternating current value into a digital pulse width modulation signal, and the frequency-voltage converter 430 is used to convert the frequency of the digital pulse width modulation signal into a first voltage value.

[0049] In Figure 4 In the motor control circuit 320 shown, the switching circuit may include a comparator 440 and a gate driver 450. Among them, the comparator is used to compare the first voltage value converted by the frequency-voltage converter 430 with a reference threshold, and the gate driver 450 is used to switch the inverter 460 connected to the motor 470 to the safe pulse-off state (that is, turn off all the switching tubes in the inverter 460) when the first voltage value is less than the reference threshold. In one embodiment, the gate driver 450 is further configured to switch the inverter 460 to the active short-circuit circuit state when the first voltage value converted by the frequency-voltage converter 430 is greater than or equal to the reference threshold (for example, turn off the three IGBTs in the upper arm of the inverter and turn on the three IGBTs in the lower arm at the same time; or turn on the three IGBTs in the upper arm of the inverter and turn off the three IGBTs in the lower arm at the same time).

[0050] Since the above first voltage value reflects the speed of the vehicle, by comparing the first voltage value with a pre-determined reference threshold, it can be determined whether the vehicle is running at a high speed. If so, it should be ensured that the vehicle is switched to the active short-circuit circuit state (to avoid entering the SPO state) to avoid violating the safety objectives of the vehicle.

[0051] In summary, the motor control solution for a vehicle according to an embodiment of the present invention can reasonably switch between the active short-circuit circuit state (ASC state) and the safe pulse-off state (SPO state) by monitoring the output AC frequency of the motor when a fault occurs in the motor control unit (for example, during a fault operation), which can meet the basic functional safety requirements of the motor drive system application, and avoid making the motor enter the safe pulse-off state (SPO state) when the vehicle is at a high speed, improving the availability and user experience of the vehicle during a fault operation.

[0052] Although only some embodiments of the present invention have been described in the above specification, those of ordinary skill in the art should understand that the present invention can be implemented in many other forms without departing from its gist and scope. Therefore, the examples and embodiments shown are regarded as illustrative rather than restrictive, and the present invention may cover various modifications and substitutions without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims

1. A method for controlling an electric motor for a vehicle, characterized in that, the method comprises: determining that a motor control unit (MCU) has failed, wherein the motor control unit (MCU) is configured to monitor the speed of the vehicle and control a switch between an active short - circuit state and a safe pulse - off state based on the monitored speed; monitoring the output AC frequency of the motor; and controlling the motor to switch between an active short - circuit state and a safe pulse - off state based on the output AC frequency, wherein monitoring the output AC frequency of the motor comprises: acquiring an AC current value output by the motor; using a zero - crossing detector to convert the AC current value into a digital pulse - width modulation signal; and using a frequency - to - voltage converter to convert the frequency of the digital pulse - width modulation signal into a first voltage value, and wherein controlling the motor to switch between an active short - circuit state and a safe pulse - off state based on the output AC frequency comprises: if the first voltage value is less than a second threshold, switching an inverter connected to the motor to the safe pulse - off state; and if the first voltage value is greater than or equal to the second threshold, switching the inverter to the active short - circuit state.

2. The method according to claim 1, wherein, the frequency of the digital pulse - width modulation signal is equal to or proportional to the frequency of the AC current value.

3. The method according to claim 1, wherein, controlling the motor to switch between an active short - circuit state and a safe pulse - off state based on the output AC frequency comprises: when the output AC frequency is lower than a first threshold, switching an inverter connected to the motor to the safe pulse - off state.

4. The method according to claim 3, wherein, controlling the motor to switch between an active short - circuit state and a safe pulse - off state based on the output AC frequency further comprises: when the output AC frequency is greater than or equal to the first threshold, switching the inverter to the active short - circuit state.

5. An electric - motor control circuit for a vehicle, characterized in that, the circuit comprises: a monitoring circuit for monitoring the output AC frequency of the motor when it is determined that a motor control unit (MCU) has failed; and a switching circuit for controlling the motor to switch between an active short - circuit state and a safe pulse - off state based on the output AC frequency, wherein the motor control unit (MCU) is configured to monitor the speed of the vehicle and control a switch between an active short - circuit state and a safe pulse - off state based on the monitored speed, wherein the monitoring circuit comprises: an AC current sensor for acquiring an AC current value output by the motor; a zero - crossing detector for converting the AC current value into a digital pulse - width modulation signal; and a frequency - to - voltage converter for converting the frequency of the digital pulse - width modulation signal into a first voltage value, and wherein the switching circuit comprises: a comparator for comparing the first voltage value with a reference threshold; and Switching logic for switching an inverter connected to the motor to the safe pulse-off state when the first voltage value is less than the reference threshold; the switching logic is further configured to switch the inverter to the active short-circuit state when the first voltage value is greater than or equal to the reference threshold.

6. The motor control circuit according to claim 5, wherein, the motor control circuit is connected in parallel with the motor control unit MCU.

7. The motor control circuit according to claim 5, wherein, the frequency of the digital pulse width modulation signal is equal to or proportional to the frequency of the alternating current value.

8. A motor drive system, comprising a motor control unit MCU and a motor control circuit according to any one of claims 5 to 7 connected in parallel with the motor control unit MCU.

9. A vehicle, comprising the motor drive system according to claim 8.

Images