Method for integrating battery protection function in motor controller of electric vehicle

Abstract

The application discloses a method for integrating battery protection function of an electric vehicle motor controller, including the method for integrating battery protection function of a motor controller of two-wheel, three-wheel and four-wheel vehicles. The neutral point of a three-phase winding of a driving motor of the electric vehicle is led out and connected with the voltage midpoint of a DC bus capacitor of the motor controller and a battery pack, and an inverter circuit of the motor controller is a conventional three-phase inverter bridge. The motor controller has certain battery protection function, the balance state of the battery pack is monitored by collecting the midpoint potential of the battery pack, whether the voltage inconsistency phenomenon occurs in the upper and lower series-connected batteries is judged, and the zero sequence current of the winding middle line is used to protect the battery in a certain capacity balance. The battery protection method is simple, efficient and reliable, reduces the dangerous factors caused by overcharging and overdischarging of the electric vehicle battery, and provides a feasible scheme for solving the unbalanced protection problem of the power battery of a low-speed and low-voltage electric vehicle.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of battery protection technology of electric vehicles, and particularly relates to a method for integrating battery protection function of an electric vehicle motor controller. BACKGROUND

[0002] The vehicle-mounted integrated charging system can realize convenient vehicle-mounted charging with minimized modification of the vehicle drive system, greatly reduces the manufacturing cost of the electric vehicle, has good environmental adaptability, and thus has been increasingly widely applied. However, the integrated system can only charge and discharge the entire battery pack, and cannot realize energy monitoring and equalization protection of each unit battery pack.

[0003] If a battery pack in the battery pack becomes a weak battery due to performance degradation, the voltages of the unit batteries will be inconsistent, resulting in overcharging or over-discharging of the weak battery in the series battery pack. At this time, if the charging and discharging is still performed at the normal battery voltage, the weak battery will be accelerated to degrade, and thus the service life of the entire battery pack will be accelerated to degrade, and in the extreme case, the normal operation of the motor and the battery system will be affected. SUMMARY

[0004] The present application aims to solve the above-mentioned problems in the prior art, and provides a method for integrating battery protection function of an electric vehicle motor controller, so that the motor controller integrates driving capability and certain battery protection function, and reduces the dangerous factors caused by overcharging and over-discharging of the power battery. At the same time, the extraction of the neutral point of the motor winding enables the vehicle drive system to have single-phase fault tolerance operation capability.

[0005] The present application adopts the following technical solutions to solve the above-mentioned technical problems:

[0006] A method for integrating battery protection function of an electric vehicle motor controller, in the battery pack of a low-voltage electric vehicle, in addition to two wires for supplying power to the motor controller from the positive and negative bus lines, the voltage midpoint of the series battery pack is extracted by a wire and connected to the midpoint of two series DC bus capacitors of the electric vehicle motor controller, and then connected to the neutral point of the three-phase winding of the electric vehicle drive motor, so as to use the topological connection relationship among the battery, the motor controller and the electric vehicle drive motor as the topological basis for completing the integrated battery protection function;

[0007] The stator of the electric vehicle drive motor comprises three-phase windings A, B and C which are uniformly distributed in space, three-phase resistors R s , and three-phase inductors L s ;

[0008] The motor controller has a three-phase full-bridge inverter circuit, which includes power tubes T1, T2, T3, T4, T5 and T6 and their anti-parallel diodes D1, D2, D3, D4, D5 and D6, and the motor three-phase winding is connected to the three-phase full-bridge inverter circuit, wherein the A-phase winding is connected to the midpoint of the power tubes T1 and T2, the B-phase winding is connected to the midpoint of the power tubes T3 and T4, and the C-phase winding is connected to the midpoint of the power tubes T5 and T6.

[0009] The neutral point of the electric vehicle drive motor winding is led out and connected to the midpoint of the series battery pack, and then connected to the midpoint of the two series DC bus capacitors of the motor controller.

[0010] The system structure takes the motor controller as the hub of bidirectional energy flow, and realizes the topology reconstruction of the system charging mode and driving mode through the input / output part function modules:

[0011] In the charging mode, the DC charger is input into the system, and the DC-DC converter composed of the three-phase inverter bridge and the motor winding supplies power to the load battery; in the driving mode, the DC charger is cut out of the system, and the series battery pack serves as the DC power supply, and supplies power to the load motor through the three-phase inverter bridge.

[0012] Further, the zero-sequence current of the three-phase motor is synthesized from the motor winding neutral point, and the equivalent reconstruction of the motor zero-sequence inductance and the three-phase full-bridge inverter circuit is used as a Buck, Boost and Buck-Boost converter for controlling the size and direction of the balancing current, i.e. adjusting the amount of power flowing into or out of the battery midpoint, to balance and protect the battery.

[0013] The topology structure for battery charging and discharging protection synthesizes a parallel three-phase inductor and a three-phase bridge arm into a one-phase equivalent circuit, including the following processes:

[0014] If the system works in the charging state, the external DC charger provides energy to the load battery, and when there is a weak battery in the series battery unit above the midpoint, the reconstructed Buck circuit is used to implement step-down operation on the upper battery pack; when there is a weak battery in the series battery unit below the midpoint, the reconstructed Buck circuit is used to implement step-down operation on the lower battery pack.

[0015] If the system works in the discharging state, the series battery pack provides energy to the load motor, and when there is a weak battery in the series battery unit above the midpoint, the reconstructed Boost circuit is used to implement step-up operation on the upper battery pack; when there is a weak battery in the series battery unit below the midpoint, the reconstructed Buck-Boost circuit is used to implement step-up operation on the lower battery pack.

[0016] Further, the midpoint voltage of the introduced series battery pack is detected by the internal MCU of the electric vehicle motor controller, whether the midpoint potential deviates is monitored, so as to judge whether the voltage inconsistency phenomenon caused by the performance degradation of a certain series battery unit to become a weak battery occurs in the upper and lower series battery packs, if the performance of the series battery units in the series battery pack is consistent, the midpoint voltage is half of the bus voltage, if the performance difference of the series battery units in the series battery pack occurs, the midpoint voltage deviates from half of the bus voltage, different imbalance forms are shown during charging and discharging, and a corresponding balancing control method needs to be designed, including the following processes:

[0017] In the parking charging state, if the midpoint potential rises, it indicates that there is a weak battery in the series battery unit below the midpoint, the battery reaches the critical voltage requiring trickle charging early due to capacity decline, at this time, the battery midpoint current should be controlled to flow out, that is, the motor zero sequence current is controlled to flow in;

[0018] In the parking charging state, if the midpoint potential drops, it indicates that there is a weak battery in the series battery unit above the midpoint, the battery reaches the critical voltage requiring trickle charging early due to capacity decline, at this time, the battery midpoint current should be controlled to flow in, that is, the motor zero sequence current is controlled to flow out;

[0019] In the driving discharging state, if the midpoint potential rises, it indicates that there is a weak battery in the series battery unit above the midpoint, the battery reaches the critical voltage requiring trickle charging early due to capacity decline, at this time, the battery midpoint current should be controlled to flow out, that is, the motor zero sequence current is controlled to flow in;

[0020] In the driving discharging state, if the midpoint potential drops, it indicates that there is a weak battery in the series battery unit below the midpoint, the battery reaches the critical voltage requiring trickle charging early due to capacity decline, at this time, the battery midpoint current should be controlled to flow in, that is, the motor zero sequence current is controlled to flow out.

[0021] Further, on the basis of the topology integrated with the battery protection function, the motor winding neutral point is connected with the series battery pack midpoint, so that the low-speed and low-voltage electric vehicle has the fault-tolerant operation ability that the remaining two phases continue to work normally when a single-phase fault occurs.

[0022] The technical scheme adopted by the present application has the following beneficial effects compared with the prior art:

[0023] 1. The present application provides a method for integrating battery protection function of electric vehicle motor controller, by time-sharing multiplexing and reasonable reconstruction of drive motor winding and inverter to realize the switching of system charging and driving function, which greatly reduces the cost, quality and volume of electric vehicle;

[0024] 2. This invention provides a method for integrating battery protection function into an electric vehicle motor controller. The topology for integrating battery protection function is achieved by adding a zero-sequence current path to the conventional controller. The zero-sequence current is fully utilized to protect the weak battery during charging and discharging, extending the battery life without affecting the motor's output torque, and ensuring the stable and safe operation of the electric vehicle during balanced protection charging and discharging.

[0025] 3. The present invention also provides a method for integrating battery protection function into electric vehicle motor controller. The controller uses an internal MCU to quickly detect the voltage balance of the battery pack midpoint. For four different imbalance forms during charging and discharging, the magnitude and direction of the balancing current are controlled by software programming. The battery balance judgment is simple and the charging and discharging protection response is rapid.

[0026] 4. This invention provides a method for integrating battery protection function into electric vehicle motor controller. When a single-phase fault occurs in an electric vehicle, the remaining two phases continue to operate normally, providing a fault-tolerant operation function. When reconfiguring the circuit, one phase is reserved as a backup. When a certain working phase fails, it is used to form a charging and discharging circuit with another normal phase to obtain continuous charging capability, thereby reducing the risk of system downtime caused by the fault.

[0027] In summary, this invention has the advantages of simple circuit topology, fast response speed, simple control method, and strong fault tolerance, and is suitable for low-speed, low-voltage electric vehicles, including electric two-wheeled, three-wheeled and four-wheeled vehicles, where the requirement is to extend the life of the power battery. Attached Figure Description

[0028] Figure 1 This is an external structural diagram of an electric vehicle motor controller that integrates battery protection functions according to the present invention.

[0029] Figure 2 This is a topology diagram of an electric vehicle motor controller that integrates battery protection function according to the present invention;

[0030] Figure 3 The Buck equivalent circuit for system reconfiguration during charging in this invention;

[0031] Figure 4 This is the equivalent circuit of Boost and Buck-Boost for system reconfiguration during discharge in this invention. Detailed Implementation

[0032] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings:

[0033] This invention can be implemented in many different forms and should not be considered limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully express the scope of the invention to those skilled in the art. In the drawings, components are enlarged for clarity.

[0034] like Figure 1 As shown, the external structure of the electric vehicle motor controller with integrated battery protection function is as follows: In the battery pack of a conventional low-voltage electric vehicle, in addition to the two wires that lead out the positive and negative buses to supply power to the motor controller, the voltage midpoint of the series-connected battery pack is led out with a wire and connected to the midpoint of the two series-connected DC bus capacitors of the electric vehicle motor controller, and then connected to the neutral point of the three-phase winding of the electric vehicle drive motor. This topological connection relationship between the battery, motor controller, and drive motor forms the topological basis for completing the integrated battery protection function.

[0035] like Figure 2 As shown, the stator of the electric vehicle drive motor contains three-phase windings A, B, and C that are spatially evenly distributed, and three-phase resistors R s Three-phase inductor L s ;

[0036] The inverter circuit includes power transistors T1, T2, T3, T4, T5 and T6 and their anti-parallel diodes D1, D2, D3, D4, D5 and D6. The three-phase windings of the motor are connected to the three-phase inverter bridge, wherein the A-phase winding is connected to the midpoint of power transistors T1 and T2, the B-phase winding is connected to the midpoint of power transistors T3 and T4, and the C-phase winding is connected to the midpoint of power transistors T5 and T6.

[0037] The neutral point of the motor winding is led out and connected to the midpoint of the series-connected battery pack, and then connected to the midpoint of the two series-connected DC bus capacitors of the motor controller.

[0038] The system architecture uses the motor controller as the hub for bidirectional energy flow, and achieves topology reconfiguration of the system's charging and driving modes by adding / switching in certain functional modules:

[0039] In charging mode, the DC charger is put into the system, and the load battery is powered through the DC-DC converter composed of the three-phase inverter bridge and the motor windings. In driving mode, the DC charger is disconnected from the system, and the series-connected battery pack is used as a DC power source to power the load motor through the three-phase inverter bridge.

[0040] Based on the above topology, this invention proposes a method for integrating battery protection functions into an electric vehicle motor controller. Utilizing the characteristic that the zero-sequence current of a three-phase motor has the same magnitude and phase and does not affect the output torque, it is synthesized and output from the neutral point of the motor windings to form the battery's balancing current. Simultaneously, the motor's zero-sequence inductance and the three-phase inverter are equivalently reconstructed into Buck, Boost, and Buck-Boost converters to control the magnitude and direction of the balancing current, i.e., adjusting the amount of electricity flowing into or out of the battery's neutral point, thus providing a certain level of balancing protection for the battery. To simplify the system structure, the stator winding resistance and the back electromotive force generated by the stator winding cutting the rotor magnetic field under driving mode are ignored. The parallel three-phase inductors and three-phase bridge arms are combined into a single equivalent circuit for battery balancing principle analysis.

[0041] like Figure 3 As shown, if the system is operating in charging mode, the external DC charger provides energy to the load battery. The working principle of the reconfigured Buck step-down circuit during equalization charging of the weaker battery by the DC power supply is as follows:

[0042] When a weak battery exists in the series-connected battery cell below the midpoint, a Buck circuit is used to step down the voltage of the lower battery pack. Let the switching period be Ts and the duty cycle be D. During the time interval 0 to DTs, power transistor T2 is turned on, forming a current path of "DC power supply positive terminal - battery B1 positive terminal - battery B1 negative terminal - zero-sequence inductor L0 - power transistor T2 - DC power supply negative terminal". During the time interval DTs to Ts, power transistor T2 is turned off, and the current in the zero-sequence inductor L0 cannot immediately change direction. At this time, freewheeling diode D1 is turned on, forming a current path of "zero-sequence inductor L0 - diode D1 - battery B1 positive terminal - battery B1 negative terminal".

[0043] When a weak battery exists in the series-connected battery cell above the midpoint, a Buck circuit is used to step down the voltage of the upper battery pack. Let the switching period be Ts and the duty cycle be D. During the time interval 0 to DTs, power transistor T1 is turned on, forming a current path of "DC power supply positive terminal - power transistor T1 - L0 - battery B2 positive terminal - battery B2 negative terminal - DC power supply negative terminal". During the time interval DTs to Ts, power transistor T1 is turned off, and the current in the zero-sequence inductor L0 cannot immediately change direction. At this time, freewheeling diode D2 is turned on, forming a current path of "zero-sequence inductor L0 - battery B2 positive terminal - battery B2 negative terminal - diode D2".

[0044] like Figure 4 As shown, if the system is operating in a discharge state, the battery pack provides energy to the load motor. The operating principle of the reconfigured Boost and Buck-Boost buck-boost circuits during the equalization charging of weaker batteries by normal battery cells is as follows:

[0045] When a weak battery exists in the series-connected battery cell above the midpoint, a Boost circuit is used to boost the voltage of the upper battery pack. Let the switching period be Ts and the duty cycle be D. During the time interval 0 to DTs, power transistor T2 is turned on, forming a current path of "battery B2 positive terminal - zero-sequence inductor L0 - power transistor T2 - battery B2 negative terminal". During the time interval DTs to Ts, power transistor T2 is turned off, and the current in the zero-sequence inductor L0 cannot immediately change direction. At this time, freewheeling diode D1 is turned on, forming a current path of "zero-sequence inductor L0 - diode D1 - battery B1 positive terminal - battery B1 negative terminal".

[0046] When a weak battery exists in the series-connected battery cell below the midpoint, a Buck-Boost circuit is used to boost the voltage of the lower battery pack. Assuming the switching period is Ts and the duty cycle is D, with the duty cycle adjusted to D>0.5, during the time interval 0 to DTs, power transistor T1 is turned on, forming a current path of "battery B1 positive terminal - power transistor T1 - zero-sequence inductor L0 - battery B1 negative terminal"; during the time interval DTs to Ts, power transistor T1 is turned off, and the current in the zero-sequence inductor L0 cannot immediately change direction. At this time, freewheeling diode D2 is turned on, forming a current path of "zero-sequence inductor L0 - battery B2 positive terminal - battery B2 negative terminal - D2".

[0047] This invention also discloses a control algorithm for controlling the magnitude and direction of the battery balancing current (motor zero-sequence current) based on midpoint potential imbalance information:

[0048] The electric vehicle motor controller's internal MCU detects the increased midpoint voltage of the battery pack, monitoring any deviation in the midpoint potential. This helps determine if voltage inconsistencies are caused by performance degradation in one battery cell, resulting in a weaker cell. If the battery cells in the pack have consistent performance, the midpoint voltage is half the bus voltage. If the battery cells exhibit performance differences, the midpoint voltage will deviate from half the bus voltage, displaying different imbalances during charging and discharging, requiring the design of appropriate balancing control methods.

[0049] If the midpoint potential rises while the battery is parked and charging, it indicates that there is a weak battery in the series battery cell below the midpoint. The battery reaches the critical voltage that requires trickle charging earlier due to the decrease in capacity. At this time, the outflow of the battery midpoint current should be controlled, that is, the inflow of the motor zero-sequence current should be controlled.

[0050] If the midpoint potential drops while the battery is parked and charging, it indicates that there is a weak battery in the series battery cell above the midpoint. The battery reaches the critical voltage that requires trickle charging earlier due to the decrease in capacity. At this time, the inflow of the battery midpoint current should be controlled, that is, the outflow of the zero-sequence current of the motor should be controlled.

[0051] If the midpoint potential rises during driving and discharging, it indicates that there is a weak battery in the series battery cell above the midpoint. The battery reaches the critical voltage that requires trickle charging earlier due to the decrease in capacity. At this time, the outflow of the battery midpoint current should be controlled, that is, the inflow of the motor zero-sequence current should be controlled.

[0052] If the midpoint potential drops during driving and discharging, it indicates that there is a weak battery in the series battery cell below the midpoint. The battery reaches the critical voltage that requires trickle charging earlier due to the decrease in capacity. At this time, the inflow of the battery midpoint current should be controlled, that is, the outflow of the motor zero-sequence current should be controlled.

[0053] In addition, connecting the neutral point of the motor winding to the midpoint of the battery pack enables the low-speed, low-voltage electric vehicle motor controller to have the fault-tolerant operation capability that allows the remaining two phases to continue to operate normally when a single-phase fault occurs.

[0054] When an electric vehicle is in a parked charging state, the motor drive system is reconfigured into a Buck circuit. When the three-phase windings are operating normally, only one phase needs to participate to achieve voltage reduction, with the other two phases serving as backups. If any phase fails, the backup phase and the normal phase can still combine to form a Buck converter, preventing overcharging of the weak battery and providing balanced charging capability in the event of a single-phase motor failure. For example, if phases A and B are operating normally and phase A fails, the backup phase C is activated, combining with the normal phase B to form a Buck converter and continue controlling the balancing current.

[0055] When an electric vehicle is in a driving discharge state, the motor drive system is reconfigured into a Boost and Buck-Boost circuit. When the three-phase windings are working normally, only two phases are needed to achieve the boost operation, with the remaining phase as a backup. If any phase fails, the backup phase and the normal phase can still be combined to form a Boost and Buck-Boost converter, preventing over-discharge of the weak battery and achieving balanced charging capability in the event of a single-phase motor failure. For example, if phases A and B are working normally, and phase A fails, the backup phase C is activated, combining with the normal phase B to form a Boost and Buck-Boost converter, continuing to control the balancing current.

[0056] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0057] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for integrating battery protection function into an electric vehicle motor controller, characterized in that: In the series battery pack configured in the electric vehicle, in addition to the two wires that lead out the positive and negative bus to supply power to the motor controller, the voltage midpoint of the series battery pack is led out with a wire and connected to the midpoint of the two series DC bus capacitors of the electric vehicle motor controller, and then connected to the neutral point of the three-phase winding of the electric vehicle drive motor. This topological connection relationship between the series battery pack, the motor controller, and the electric vehicle drive motor forms the topological basis for completing the integrated battery protection function. The stator of the electric vehicle drive motor includes three-phase windings A, B, and C that are spatially evenly distributed, and three-phase resistors R. s Three-phase inductor L s ; The motor controller contains a three-phase full-bridge inverter circuit, which includes power transistors T1, T2, T3, T4, T5 and T6 and their anti-parallel diodes D1, D2, D3, D4, D5 and D6. The three-phase windings of the motor are connected to the three-phase full-bridge inverter circuit, wherein the A-phase winding is connected to the midpoint of power transistors T1 and T2, the B-phase winding is connected to the midpoint of power transistors T3 and T4, and the C-phase winding is connected to the midpoint of power transistors T5 and T6. The neutral point of the electric vehicle drive motor winding is led out and connected to the midpoint of the series battery pack, and then connected to the midpoint of the two series DC bus capacitors of the motor controller.

2. The method for integrating battery protection function into an electric vehicle motor controller according to claim 1, characterized in that: Taking advantage of the fact that the zero-sequence current of a three-phase motor has the same magnitude and phase and does not affect the output torque, it is synthesized and output from the neutral point of the motor winding to form the battery's equalization current. At the same time, the zero-sequence inductance of the motor and the three-phase full-bridge inverter circuit are equivalently reconstructed into Buck, Boost and Buck-Boost converters to control the magnitude and direction of the equalization current, that is, to adjust the amount of electricity flowing into or out of the battery's midpoint and to provide equalization protection for the battery. The topology used for battery charge and discharge protection combines three-phase inductors and three-phase bridge arms in parallel into a single-phase equivalent circuit, including the following processes: If the system is in charging mode, the external DC charger provides energy to the load battery. When there is a weak battery in the series battery cell above the midpoint, the reconfigured Buck circuit is used to perform a step-down operation on the upper battery pack. When there is a weak battery in the series battery cell below the midpoint, the reconfigured Buck circuit is used to perform a step-down operation on the lower battery pack. If the system is operating in a discharge state, the series battery pack provides energy to the load motor. When there is a weak battery in the series battery cell above the midpoint, the reconfigured Boost circuit is used to boost the voltage of the upper battery pack. When there is a weak battery in the series battery cell below the midpoint, the reconfigured Buck-Boost circuit is used to boost the voltage of the lower battery pack.

3. The method for integrating battery protection function into an electric vehicle motor controller according to claim 1, characterized in that: The electric vehicle motor controller's internal MCU detects the added midpoint voltage of the series-connected battery pack and monitors whether the midpoint potential deviates. This helps determine if the voltage inconsistency between the upper and lower sections of the series-connected battery pack is caused by the performance degradation of a particular battery cell, resulting in a weak battery. If the performance of the series-connected battery cells is consistent, the midpoint voltage is half the bus voltage. If the performance of the series-connected battery cells differs, the midpoint voltage will deviate from half the bus voltage, exhibiting different imbalances during charging and discharging. A corresponding equalization control method needs to be designed, including the following process: If the midpoint potential rises while the battery is parked and charging, it indicates that there is a weak battery in the series battery cell below the midpoint. The battery reaches the critical voltage that requires trickle charging earlier due to the decrease in capacity. At this time, the outflow of the battery midpoint current should be controlled, that is, the inflow of the motor zero-sequence current should be controlled. If the midpoint potential drops while the battery is parked and charging, it indicates that there is a weak battery in the series battery cell above the midpoint. The battery reaches the critical voltage that requires trickle charging earlier due to the decrease in capacity. At this time, the inflow of the battery midpoint current should be controlled, that is, the outflow of the zero-sequence current of the motor should be controlled. If the midpoint potential rises during driving and discharging, it indicates that there is a weak battery in the series battery cell above the midpoint. The battery reaches the critical voltage that requires trickle charging earlier due to the decrease in capacity. At this time, the outflow of the battery midpoint current should be controlled, that is, the inflow of the motor zero-sequence current should be controlled. If the midpoint potential drops during driving and discharging, it indicates that there is a weak battery in the series battery cell below the midpoint. The battery reaches the critical voltage that requires trickle charging earlier due to the decrease in capacity. At this time, the inflow of the battery midpoint current should be controlled, that is, the outflow of the motor zero-sequence current should be controlled.

4. The method for integrating battery protection function into an electric vehicle motor controller according to claim 1, characterized in that: Based on the topology of integrated battery protection function, the neutral point of the motor winding is connected to the midpoint of the series battery pack, so that the electric vehicle has the fault-tolerant operation capability that the remaining two phases can continue to work normally when a single-phase fault occurs.

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