Patent Publication Number: US-2022216817-A1

Title: Power supply system of motor control module and vehicle

Description:
TECHNICAL FIELD 
     This application relates to the field of power supply technologies, and in particular, to a power supply system of a motor control module and a vehicle. 
     BACKGROUND 
       FIG. 1  is a diagram of partial architecture of a motor control module in the conventional technologies. As shown in  FIG. 1 , the motor control module includes a pulse width modulation (PWM) generator and an inverter. The PWM generator outputs a PWM wave to the inverter. Based on the PWM wave, the inverter converts a direct current into an alternating current and outputs the alternating current to a motor, to control the motor to rotate/stop. 
     It may be understood that a prerequisite for normal operation of the PWM generator is that power is supplied to the PWM generator. If a power supply system of the motor control module is suddenly faulty, for example, any power supply loop in the power supply system has an excessively large current, the power supply system cannot normally supply power to the PWM generator. As a result, the motor is uncontrollable, the motor suddenly stops, and the like. In addition, this may further cause an irreversible damage to the motor. Therefore, a requirement of the motor control module for the power supply system is that, even when any power supply loop in the power supply system has an excessively large current, the power supply system can still supply power to the motor control module, so that the motor control module can actively control a short circuit of the motor when power is supplied, to avoid a sudden stop of the motor. 
     SUMMARY 
     This application provides a power supply system of a motor control module and a vehicle. Even when any power supply loop has an excessively large current, the power supply system can still supply power to the motor control module, so that the motor control module can actively control a short circuit of a motor when power is supplied, to avoid a sudden stop of the motor. 
     According to a first aspect, an embodiment of this application provides a power supply system of a motor control module. The power supply system is disposed between the motor control module and at least two direct current power supplies. The at least two direct current power supplies include a first direct current power supply and a second direct current power supply. The power supply system includes a first current limiting unit and an isolation unit. The isolation unit is configured to output a voltage to the motor control module. 
     An output end of the first direct current power supply is coupled to a first input end of the isolation unit to form a first power supply loop. 
     A first output end of the second direct current power supply is coupled to one end of the first current limiting unit. The other end of the first current limiting unit is coupled to a second input end of the isolation unit to form a second power supply loop. The second power supply loop is connected in parallel to the first power supply loop. The first current limiting unit is configured to disconnect the second power supply loop when a loop current of the first power supply loop is greater than a first preset current threshold. 
     A second output end of the second direct current power supply is coupled to the motor control module. When the second power supply loop is disconnected, the second direct current power supply is configured to supply power to the motor control module to form a third power supply loop. 
     In this embodiment of this application, when the loop current of the first power supply loop is greater than the first preset current threshold, the first current limiting unit may disconnect the second power supply loop, to avoid that the second direct current power supply is affected by the loop current of the first power supply loop. In addition, the second direct current power supply may supply power to the motor control module by using the third power supply loop. In this embodiment of this application, even when the first power supply loop in the power supply system has an excessively large current (for example, greater than the first preset current threshold), the power supply system can still supply power to the motor control module (that is, the second direct current power supply supplies power to the motor control module by using the third power supply loop), so that the motor control module can actively control a short circuit of the motor when power is supplied, to avoid a sudden stop of the motor, which is highly secure. 
     With reference to the first aspect, in a first possible implementation, the power supply system further includes an alternating current conversion unit, a first transformer, a second transformer, and a second current limiting unit. 
     An output end of the isolation unit is coupled to an input end of the alternating current conversion unit. 
     An output end of the alternating current conversion unit is separately coupled to an input end of the first transformer and an input end of the second transformer, and is configured to: convert a direct current voltage output by the isolation unit into an alternating current voltage, and transmit the alternating current voltage separately to the first transformer and the second transformer. The first transformer and the second transformer are configured to separately transmit a voltage to the motor control module. 
     The input end of the second transformer is further coupled to the second current limiting unit. The second current limiting unit is configured to disconnect the second transformer from the alternating current conversion unit when a loop current of the third power supply loop is greater than a second preset current threshold. 
     In this embodiment of this application, even if the third power supply loop has an excessively large current (for example, greater than the second preset current threshold), the first direct current power supply supplies power to the first PWM generator by using the first power supply loop. When power is supplied, the first PWM generator can control all three IGBTs connected in parallel in a second part of an inverter to be conducted. 
     With reference to the first possible implementation of the first aspect, in a second possible implementation, the motor control module includes a first pulse width modulation (PWM) generator, a second PWM generator, and an inverter. The inverter includes a first part and a second part. Each part includes three insulated gate bipolar transistors IGBTs connected in parallel. The three IGBTs connected in parallel in the first part are respectively connected in series to the three IGBTs connected in parallel in the second part to form a three-phase full-bridge converter. 
     The first PWM generator is configured to control all the three IGBTs connected in parallel in the first part to be conducted. The second PWM generator is configured to control all the three IGBTs connected in parallel in the second part to be conducted. 
     With reference to any possible implementation of the first aspect, in a third possible implementation, the power supply system further includes a rectifier unit. An output end of the first transformer and an output end of the second transformer are separately coupled to the motor control module by using the rectifier unit. 
     With reference to any possible implementation of the first aspect, in a fourth possible implementation, the power supply system further includes an alternating current conversion controller, configured to control a voltage amplitude of the alternating current voltage obtained through conversion performed by the alternating current conversion unit. 
     With reference to the first aspect or any possible implementation of the first aspect, in a fifth possible implementation, the isolation unit includes a first diode and a second diode. A cathode of the first diode is connected to a cathode of the second diode to form an output end of the isolation unit. The first input end of the isolation unit is an anode of the first diode. The second input end of the isolation unit is the cathode of the second diode. 
     In this embodiment of this application, the first direct current power supply and the second direct current power supply are isolated by using unidirectional conductivity of a diode. In this way, the costs are relatively low. 
     With reference to the first aspect or any possible implementation of the first aspect, in a sixth possible implementation, the isolation unit includes a first field effect transistor and a second field effect transistor. A source of the first field effect transistor is connected to a source of the second field effect transistor to form the output end of the isolation unit. The first input end of the isolation unit is a drain of the first field effect transistor. The second input end of the isolation unit is a drain of the second field effect transistor. 
     With reference to the first aspect or any possible implementation of the first aspect, in a seventh possible implementation, the first direct current power supply is a battery. The second direct current power supply includes a step-down unit and a power battery. The power battery is coupled to an input end of the step-down unit. A first output end of the step-down unit is coupled to the first output end of the second direct current power supply. A second output end of the step-down unit is coupled to the second output end of the second direct current power supply. 
     With reference to the first aspect or any possible implementation of the first aspect, in an eighth possible implementation, the power supply system further includes a voltage regulator unit. The voltage regulator unit is configured to regulate an output voltage of the isolation unit. 
     According to a second aspect, an embodiment of this application provides a vehicle. The vehicle includes a power battery, a battery, a motor control module, a motor, and the power supply system according to the first aspect or any possible implementation of the first aspect. A first direct current power supply includes the battery. A second direct current power supply includes the power battery. 
     It should be understood that implementation and beneficial effects of the foregoing aspects of this application may be referred to each other. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram of partial architecture of a motor control module in the conventional technologies; 
         FIG. 2  is a block diagram of application of a power supply system of a motor control module according to an embodiment of this application; 
         FIG. 3  is a block diagram of a structure of a power supply system of a motor control module according to an embodiment of this application; 
         FIG. 4  is another block diagram of a structure of a power supply system of a motor control module according to an embodiment of this application; 
         FIG. 5  is a circuit diagram of an isolation unit according to an embodiment of this application; 
         FIG. 6  is a circuit diagram of a first current limiting unit according to an embodiment of this application; and 
         FIG. 7  is a circuit diagram of a second current limiting unit according to an embodiment of this application. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following clearly describes the technical solutions in embodiments of this application with reference to the accompanying drawings in embodiments of this application. Clearly, the described embodiments are some but not all of embodiments of this application. All other embodiments obtained by a person of ordinary skill in the art based on embodiments of this application without creative efforts shall fall within the protection scope of this application. 
     The technical solutions of this application are further described below in detail with reference to the accompanying drawings. 
     This embodiment of this application may be applied to a use scenario of a motor.  FIG. 2  is a block diagram of application of a power supply system of a motor control module according to an embodiment of this application. As shown in  FIG. 2 , a power supply system  23  is disposed between a motor control module  24  and at least two direct current power supplies. The at least two direct current power supplies include a first direct current power supply  21  and a second direct current power supply  22 . In other words, an output end of the first direct current power supply  21  and an output end of the second direct current power supply  22  are coupled to one side of the power supply system  23 . The other side of the power supply system  23  is coupled to the motor control module  24 . The motor control module  24  may control a motor to rotate/stop. 
     It should be noted that “coupling” described in this application indicates direct or indirect connection. For example, coupling between A and B may be direct connection between A and B, or may be indirect connection between A and B by using one or more other electronic components. For example, A is directly connected to C, and C is directly connected to B, so that A is connected to B by using C. 
     The first direct current power supply  21  and/or the second direct current power supply  22  may be, for example, a power battery (such as a Ni—Cd battery, a Ni-MH battery, a lithium-ion battery, or a lithium polymer battery) or a battery. For example, the first direct current power supply  21  is a battery, and the second direct current power supply  22  is a power battery. A battery voltage of the battery is lower than a battery voltage of the power battery. Optionally, the first direct current power supply  21  and/or the second direct current power supply  22  may be configured to couple an upper-level circuit such as an AC/DC converter (Alternating Current/Direct-Current converter) or another DC/DC converter (such as a BUCK converter, a BOOST converter, or a BUCK-BOOST converter). In other words, the first direct current power supply  21  and/or the second direct current power supply  22  may be a direct power supply, or may be an indirect power supply after transmission by using a circuit. 
     The power supply system  23  may supply power to the motor control module  24 . Power input of the power supply system  23  comes from the first direct current power supply  21  or the second direct current power supply  22 . Optionally, the power supply system  23  may amplify a voltage output by the first direct current power supply  21  or the second direct current power supply  22 , and transmit the amplified voltage to the motor control module  24 . 
     For details of the motor control module  24 , refer to  FIG. 1 . The motor control module  24  includes a PWM generator and an inverter shown in  FIG. 1 . The inverter may convert a direct current into an alternating current, and transmit the alternating current to the motor to control the motor to rotate. For example, the motor may be located in a vehicle. Therefore, the power supply system  23  in this embodiment of this application may be understood as a power supply system of the vehicle. 
     The following describes a specific structure of the power supply system provided in this embodiment of this application with reference to the accompanying drawings. 
       FIG. 3  is a block diagram of a structure of a power supply system of a motor control module according to an embodiment of this application. As shown in  FIG. 3 , a power supply system  34  is disposed between a motor control module  33  and at least two direct current power supplies. The at least two direct current power supplies include a first direct current power supply  31  and a second direct current power supply  32 . The power supply system  34  includes an isolation unit  341  and a first current limiting unit  342 . The isolation unit  341  may output a voltage to the motor control module  33 . 
     The isolation unit  341  includes a first input end and a second input end. An output end of the first direct current power supply  31  is coupled to the first input end of the isolation unit  341  to form a first power supply loop. A first output end of the second direct current power supply  32  is coupled to one end of the first current limiting unit  342 . The other end of the first current limiting unit  342  is coupled to the second input end of the isolation unit  341  to form a second power supply loop. The second power supply loop is connected in parallel to the foregoing first power supply loop. 
     In some feasible implementations, an output voltage of the first direct current power supply  31  is higher than an output voltage of the second direct current power supply  32 . For example, the first direct current power supply  31  is a battery, and the second direct current power supply  32  may include a power battery and a step-down unit. The power battery is coupled to an input end of the step-down unit. A first output end of the step-down unit is coupled to the first output end of the second direct current power supply  32 . In specific implementation, if the output voltage of the first direct current power supply  31  is not higher than the output voltage of the first output end of the second direct current power supply  32 , the second direct current power supply  32  supplies power to the motor control module  33  by using the second power supply loop. Otherwise, the first direct current power supply  31  supplies power to the motor control module  33  by using the first power supply loop. In other words, the second direct current power supply  32  may be understood as a backup power supply of the first direct current power supply  31 . 
     If a loop current of the first power supply loop is greater than a first preset current threshold, the first direct current power supply  31  cannot supply power to the motor control module  33  by using the first power supply loop, and the loop current of the first power supply loop may cause a damage to the second direct current power supply  32 . In this case, the first current limiting unit  342  may disconnect the second power supply loop, to avoid an impact of the loop current of the first power supply loop on the second direct current power supply  32 . Optionally, that the loop current of the first power supply loop is greater than the first preset current threshold may be caused due to a short circuit of any electronic component (such as a capacitor or a resistor) in the first power supply loop. The first preset current threshold may be a preset fixed value, and is related to a component parameter of an electronic component used in the first power supply loop and/or a system temperature of a power supply system. 
     The second output end of the second direct current power supply  32  is coupled to the motor control module  33 . When the second power supply loop is disconnected, the second direct current power supply  32  may supply power to the motor control module  33  to form a third power supply loop. 
     In this embodiment of this application, when the loop current of the first power supply loop is greater than the first preset current threshold, the first current limiting unit may disconnect the second power supply loop, to avoid that the second direct current power supply is affected by the loop current of the first power supply loop. In addition, the second direct current power supply may supply power to the motor control module by using the third power supply loop. In this embodiment of this application, even when the first power supply loop in the power supply system has an excessively large current (for example, greater than the first preset current threshold), the power supply system can still supply power to the motor control module (that is, the second direct current power supply supplies power to the motor control module by using the third power supply loop), so that the motor control module can actively control a short circuit of the motor when power is supplied, to avoid a sudden stop of the motor, which is highly secure. 
       FIG. 4  is another block diagram of a structure of a power supply system of a motor control module according to an embodiment of this application. As shown in  FIG. 4 , a power supply system  44  is disposed between a motor control module  43  and at least two direct current power supplies. The at least two direct current power supplies include a first direct current power supply  41  and a second direct current power supply  42 . In addition to an isolation unit  441   a  and a first current limiting unit  442 , the power supply system  44  further includes an alternating current conversion unit  443 , a first transformer  444 , a second transformer  445 , and a second current limiting unit  446 . 
     To better understand this embodiment of this application, an example of the motor control module  43  is first described. The motor control module  43  includes an inverter  430 , a first PWM generator  431 , and a second PWM generator  432  shown in  FIG. 4 . The inverter  430  includes a first part  430   a  and a second part  430   b.  Each part includes three insulated gate bipolar transistors IGBTs connected in parallel. The three IGBTs connected in parallel in the first part  430   a  are respectively connected in series to the three IGBTs connected in parallel in the second part  430   b  to form three phase circuits (that is, three bridge arms). 
     In this embodiment of this application, for example, an upper bridge arm of each phase circuit is the first part  430   a,  and a lower bridge arm of each phase circuit is the second part  430   b.  An output end of the first PWM generator  431  is coupled to the first part  430   a  of the inverter  430 , and an output end of the second PWM generator  432  is coupled to the second part  430   b  of the inverter  430 . An output end of the motor control module  43  is coupled to a motor. That the motor control module  43  actively controls a short circuit of the motor may be understood as follows: The first PWM generator  431  controls all the three IGBTs connected in parallel in the first part  430   a  to be conducted, or the second PWM generator  432  controls all the three IGBTs connected in parallel in the second part  430   b  to be conducted. 
     Optionally, a lower bridge arm of each phase circuit may be used as a first part, and an upper bridge arm of each phase circuit may be used as a second part (not shown in the figure). 
     The two parts in the inverter  430  respectively correspond to two PWM generators. One PWM generator corresponds to one transformer. In this embodiment of this application, when any power supply loop in the power supply system  44  has an excessively large current, any one of the two transformers may have voltage output. If the first transformer  444  may have voltage output, the first PWM generator  431  may control all the three IGBTs connected in parallel in the first part  430   a  to be conducted, and actively control a short circuit of the motor. If the second transformer  445  may have voltage output, the second PWM generator  432  may control all the three IGBTs connected in parallel in the second part  430   b  to be conducted, and actively control a short circuit of the motor. 
     In some feasible implementations, the isolation unit  441   a  includes a first input end and a second input end. An output end of the first direct current power supply  41  is coupled to the first input end of the isolation unit  441   a  to form a first power supply loop with the isolation unit  441   a.  A first output end of the second direct current power supply  42  is coupled to one end of the first current limiting unit  442 . The other end of the first current limiting unit  442  is coupled to the second input end of the isolation unit  441   a  to form a second power supply loop with the isolation unit  441   a.  The first current limiting unit  442  may disconnect the isolation unit  441   a  from the second direct current power supply  42  when a loop current of the first power supply loop is greater than a first preset current threshold, to avoid a damage caused by the loop current of the first power supply loop to the second direct current power supply  32 . In this case, the second direct current power supply  42  may supply power to the second PWM generator  432  by using the third power supply loop. 
     For example, the first direct current power supply  41  is a battery, and the second direct current power supply  42  may include a power battery and a step-down unit. The step-down unit reduces a battery voltage of the power battery, and transmits the reduced voltage to the first output end/the second output end of the second direct current power supply  42 . A first output end of the step-down unit is coupled to the first output end of the second direct current power supply  42 . A second output end of the step-down unit is coupled to the second output end of the second direct current power supply  42 . The first output end and the second output end of the step-down unit may be, for example, two output ends in a multi-winding transformer. The two output ends output different magnitudes of voltages. The first output end of the second direct current power supply  42  is coupled to the isolation unit  441   a,  and the second output end of the second direct current power supply  42  is coupled to a power end of the second PWM generator  432 . For example, a voltage output by the second output end of the second direct current power supply  42  is greater than a voltage output by the first output end of the second direct current power supply  42 . 
     Optionally, the step-down unit may be coupled to the second output end of the second direct current power supply  42  by using a fifth diode D 5 . The fifth diode D 5  has unidirectional conductivity, so that the step-down unit can output a voltage to the second direct current power supply  42 , to prevent another current from flowing back to the second direct current power supply  42 . Likewise, the step-down unit may be coupled to the first output end of the second direct current power supply  42  by using a diode D 12 , so that the step-down unit can output a voltage to the second direct current power supply  42 , to prevent a current from flowing back to the second direct current power supply  42  from the first current limiting unit  442 . 
     In this embodiment of this application, even if the first power supply loop has an excessively large current (for example, greater than the first preset current threshold), the second direct current power supply supplies power to the second PWM generator by using the third power supply loop. When power is supplied, the second PWM generator can control all the three IGBTs connected in parallel in the second part of the inverter to be conducted. 
     Optionally, in some feasible implementations, an output end of the isolation unit  441   a  is coupled to an input end of the alternating current conversion unit  443 , an output end of the alternating current conversion unit  443  is separately coupled to an input end of the first transformer  444  and an input end of the second transformer  445 , and the alternating current conversion unit  443  converts a direct current voltage of the isolation unit  441   a  into an alternating current voltage, and transmits the alternating current voltage separately to the first transformer  444  and the second transformer  445 . 
     For example, the power supply system  44  may further include a rectifier unit  448 . An output end of the first transformer  444  and an output end of the second transformer  445  are separately coupled to the motor control module  43  by using the rectifier unit  448 . For example, the rectifier unit  448  is a half-wave rectifier. The rectifier unit  448  includes a third diode D 3  and a fourth diode D 4 . An anode of the third diode D 3  is coupled to the output end of the first transformer  444 , and a cathode of the third diode D 3  is coupled to a power end of the first PWM generator  431 , to rectify an output voltage of the first transformer  444  and transmit the rectified direct current to the first PWM generator  431 . An anode of the fourth diode D 4  is coupled to the output end of the second transformer  445 , and a cathode of the fourth diode D 4  is coupled to a power end of the second PWM generator  432 , to rectify an output voltage of the second transformer  445  and transmit the rectified direct current to the second PWM generator  432 . Optionally, the rectifier unit  448  may further include a first capacitor C 1  and a second capacitor C 2 . The first capacitor C 1  may filter a rectified voltage of the third diode D 3 . Likewise, the second capacitor C 2  may filter a rectified voltage of the fourth diode D 4 . 
     Further, the input end of the second transformer  445  is further coupled to the second current limiting unit  446 . When the loop current of the third power supply loop is greater than a second preset current threshold, the second direct current power supply  42  cannot supply power to the second PWM generator  432  by using the third power supply loop, and the loop current of the third power supply loop may cause a damage to the second direct current power supply  42 . In this case, the second current limiting unit  446  may disconnect the second transformer  445  from the alternating current conversion unit  443 , to avoid an impact of the loop current of the third power supply loop on the alternating current conversion unit  443  and ensure that the first direct current power supply  41  can supply power to the first PWM generator  431  by using the isolation unit  441   a,  the alternating current conversion unit  443 , and the first transformer  444 . 
     In this embodiment of this application, even if the third power supply loop has an excessively large current (for example, greater than the second preset current threshold), the first direct current power supply supplies power to the first PWM generator by using the first power supply loop. When power is supplied, the first PWM generator can control all the three IGBTs connected in parallel in the second part of the inverter to be conducted. 
     Optionally, that the loop current of the third power supply loop is greater than the second preset current threshold may be caused due to a short circuit of any electronic component (such as a capacitor or a resistor) in the third power supply loop. The second preset current threshold may be a preset fixed value, and is related to a component parameter of an electronic component used in the third power supply loop and/or a system temperature of a power supply system. 
     In some feasible implementations, the power supply system  44  further includes an alternating current conversion controller  447 , configured to control a voltage amplitude of the alternating current voltage obtained through conversion performed by the alternating current conversion unit  443 . In this case, the alternating current conversion unit  443  may convert a direct current into an alternating current, and may further perform power amplification on the direct current. The alternating current conversion unit  443  includes at least one switch transistor. The alternating current conversion controller  447  controls conduction duration of the switch transistor in the alternating current conversion unit  443 , to control the voltage amplitude of the alternating current voltage output by the alternating current conversion unit  443 . 
     For example, the alternating current conversion controller  447  may be a central processing unit (CPU), another general purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), another programmable logic device, a discrete gate, a transistor logic device, a discrete hardware component, or the like. 
     In some feasible implementations, the power supply system  44  further includes a voltage regulator unit  449 , configured to regulate an output voltage of the isolation unit  441   a . The voltage regulator unit  449  may be a circuit module formed through connection among individual electronic components, or the voltage regulator unit  449  may be an integrated voltage regulator. This embodiment of this application sets no limitation on a specific representation form of the voltage regulator unit  449 . In this embodiment of this application, power provided by the first direct current power supply  41  or the second direct current power supply  42  to the motor control module  43  can be regulated, to facilitate stable operation of the power supply system and further improve reliability of the power supply system. 
     In conclusion, in this embodiment of this application, when the loop current of the first power supply loop in the power supply system is greater than the first preset current threshold, the second direct current power supply supplies power to the second PWM generator by using the third power supply loop. In this case, a capability that the second PWM generator controls all the three IGBTs connected in parallel in the second part of the inverter to be conducted is reserved. When the loop current of the third power supply loop in the power supply system is greater than the second preset current threshold, the first direct current power supply supplies power to the first PWM generator by using the first power supply loop. In this case, a capability that the first PWM generator controls all the three IGBTs connected in parallel in the first part of the inverter to be conducted is reserved. It should be noted that this embodiment of this application may resolve a case in which the loop current of the first power supply loop is greater than the first preset current threshold or the loop current of the second power supply loop is greater than the second preset current threshold. In other words, it may be understood that this embodiment of this application may resolve a case in which a single point of failure occurs in the power supply system. When any single point of failure occurs in the power supply system, the power supply system provided in this embodiment of this application may reserve the capability that any generator controls all the three IGBTs connected in parallel in any part of the inverter to be conducted, to actively control a short circuit of the motor and avoid a sudden stop of the motor, which is highly secure. 
     In some feasible implementations, the isolation unit  441   a  may be shown in  FIG. 4  and include a first diode D 1  and a second diode D 2 . A cathode of the first diode D 1  is connected to a cathode of the second diode D 2  to form an output end of the isolation unit  441   a.  The first input end of the isolation unit  441   a  is an anode of the first diode D 1 . The second input end of the isolation unit  441   a  is the cathode of the second diode D 2 . In this embodiment of this application, the first direct current power supply  41  and the second direct current power supply  42  are isolated by using unidirectional conductivity of a diode. In this way, the costs are relatively low. 
     Optionally, in some feasible implementations,  FIG. 5  is a circuit diagram of an isolation unit according to an embodiment of this application. As shown in  FIG. 5 , the isolation unit  441   a  shown in  FIG. 4  may be replaced with an isolation unit  441   b  shown in  FIG. 5 . In specific implementation, the isolation unit  441   b  includes a first field effect transistor Q 1  and a second field effect transistor Q 2 . A source of the first field effect transistor Q 1  is connected to a source of the second field effect transistor Q 2  to form an output end of the isolation unit  441   b.  A first input end of the isolation unit  441   b  is a drain of the first field effect transistor Q 1 . A second input end of the isolation unit  441   b  is a drain of the second field effect transistor Q 2 . Further, a gate of the first field effect transistor Q 1  and that of the second field effect transistor Q 2  may be further coupled to a controller. The controller may be an alternating current conversion controller, or may be another controller, provided that the controller can control conduction of the field effect transistor. The first field effect transistor Q 1  may be conducted when the first direct current power supply supplies power to the motor control module by using the first power supply loop. The second field effect transistor may be conducted when the second direct current power supply supplies power to the motor control module by using the second power supply loop. A component loss caused when the field effect transistor is conducted is less than a component loss caused when a diode is conducted. In this embodiment of this application, a system loss may be reduced. 
     With reference to  FIG. 6  and  FIG. 7 , the following describes an example of a specific circuit diagram of a first current limiting unit provided in embodiments of this application. 
       FIG. 6  is a circuit diagram of a first current limiting unit according to an embodiment of this application. As shown in  FIG. 6 , the first current limiting unit includes a first resistor R 1 , a first triode Q 3 , and a third field effect transistor Q 4 . One end of the first resistor R 1  is coupled to an output end of an isolation unit, a collector of the first triode Q 3 , and a source of the third field effect transistor Q 4 . The other end of the first resistor R 1  is coupled to a base of the first triode Q 3 . An emitter of the first triode Q 3  is coupled to a gate of the third field effect transistor Q 4 . A drain of the third field effect transistor Q 4  is coupled to a first output end of a second direct current power supply. An implementation principle of current limiting is as follows: When a loop current of a first power supply loop is greater than a first preset threshold, if the isolation unit is damaged, the loop current of the first power supply loop flows through the first resistor R 1 . When a terminal potential of the first resistor R 1  reaches a threshold voltage of the first triode Q 3 , the first triode Q 3  is conducted, so that a voltage at the gate and a voltage at the source of the third field effect transistor Q 4  are the same. The third field effect transistor Q 4  is disconnected, to disconnect the second direct current power supply from the isolation unit (that is, disconnect the second power supply loop). Further, the first current limiting unit may further include a sixth diode D 6  and a seventh diode D 7 . A cathode of the sixth diode D 6 , an anode of the sixth diode D 6 , and an anode of the seventh diode D 7  are all coupled to the base of the first transistor Q 3 . A cathode of the seventh diode D 7  is coupled to the emitter of the first transistor Q 3 . The sixth diode D 6  and the seventh diode D 7  are used to jointly protect the first transistor Q 3  from a damage from the loop current of the first power supply loop, to improve reliability of the first current limiting unit. 
       FIG. 7  is a circuit diagram of a second current limiting unit according to an embodiment of this application. As shown in  FIG. 7 , the second current limiting unit includes a fourth field effect transistor Q 5 , a second resistor R 2 , a first comparator U 1 , a third resistor R 3 , and a ninth diode D 9 . A drain of the fourth field effect transistor Q 5  is coupled to an input end of a second transformer. A source of the fourth field effect transistor Q 5  is coupled to one end of the second resistor R 2  and a negative input end of the first comparator U 1 . The other end of the second resistor R 2  is grounded. A positive input end of the first comparator U 1  is coupled to a voltage source, for example, a 5 V voltage source. An output end of the first comparator U 1  is coupled to a cathode of the ninth diode D 9 . An anode of the ninth diode D 9  is coupled to one end of the third resistor R 3 . The other end of the third resistor R 3  is coupled to a gate of the fourth field effect transistor Q 5 . A specific implementation principle of current limiting is as follows: When the loop current of the third power supply loop is greater than the second preset threshold, if the second transformer is damaged, the loop current of the third power supply loop flows through the fourth resistor Q 5  and the second resistor R 2 . When the second resistor R 2  has a greater terminal potential than the positive input end of the first comparator U 1 , the first comparator U 1  outputs a negative voltage, and the ninth diode D 9  is conducted. A voltage at the gate of the fourth field effect transistor Q 5  is pulled down to a negative voltage. In this case, the source of the fourth field effect transistor Q 5  has a positive voltage, the fourth field effect transistor Q 5  is disconnected, and the second transformer cannot work. The alternating current conversion unit is indirectly disconnected from the second transformer. Further, the second current limiting unit further includes a second triode Q 6  and a fourth resistor R 6 . A base of the second triode Q 6  is coupled to a controller. The controller may be an alternating current conversion controller, or may be another controller, provided that the controller can control conduction of the triode. One end of the fourth resistor R 6  is coupled to the base of the second triode Q 6 . The other end of the fourth resistor R 6  is coupled to an emitter of the second triode Q 6 . A collector of the second triode Q 6  is coupled to the gate of the fourth field effect transistor Q 5 . A specific implementation principle is as follows: When the first comparator U 1  outputs a negative voltage, the controller coupled to the base of the second triode Q 6  controls the second triode Q 6  to be conducted, a voltage at the gate of the fourth field effect transistor Q 5  is zero, and the fourth field effect transistor Q 5  is disconnected. In this way, it can be further ensured that the alternating current conversion unit is disconnected from the second transformer. Therefore, the following case is avoided: Voltage output of the first comparator U 1  changes with a terminal potential of the second resistor R 2 , which causes the fourth field effect transistor Q 5  to be switched between off and on. It may be understood that the second current limiting unit may further include another component, for example, a tenth diode D 10 , an eleventh diode D 11 , and a seventh resistor R 7 . These components are disposed for a more reliable function of the second current limiting unit, and have no impact on a specific implementation principle of the second current limiting unit. Details are not described herein. 
     It should be noted that, the foregoing describes representation forms of the first current limiting unit and the second current limiting unit in an example manner instead of an exhaustive manner. It should be understood that any circuit that can implement current detection and disconnect a corresponding connection relationship may be used. This is not limited in this embodiment of this application. 
     In addition, an embodiment of this application further provides a vehicle. The vehicle includes a power battery, a battery, a motor control module, a motor, and any power supply system described above. It may be understood that the first direct current power supply described above is the battery in the vehicle, and the second direct current power supply is the power battery in the vehicle. 
     It should be noted that the terms “first” and “second” are merely intended for a purpose of description, and shall not be understood as an indication or implication of relative importance. 
     The foregoing descriptions are merely specific implementations of this application, but are not intended to limit the protection scope of this application. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in this application shall fall within the protection scope of this application. Therefore, the protection scope of this application shall be subject to the protection scope of the claims.