Three-phase electric driving system integrating bus boosting and open-circuit fault tolerance functions

Abstract

The invention discloses a three-phase electric driving system integrating bus boosting and fault-tolerant functions, which comprises three phase bridge arms and a fourth bridge arm F. Each phase bridge arm consists of an upper switch tube and a lower switch tube which are in complementary conduction, DC bus voltage is converted into AC voltage to drive a motor, a negative electrode of a DC power supply is connected with a neutral point of the motor, and a negative electrode of the DC power supply is connected with a positive electrode of the motor. The fourth bridge arm F is connected to the middle point of the fourth bridge arm after being connected in series with a filter inductor, required direct-current voltage is provided for an inverter, the bus boosting function is achieved, and when an open-circuit fault occurs to the motor, the fourth bridge arm F can quickly respond, conduct fault-tolerant control and ensure stable operation of the system. According to the invention, faults can be detected, current given values of a d axis, a q axis and a 0 axis can be automatically switched, effective torque is output through residual normal phases, torque balance is maintained, bus boost and open-circuit fault tolerance functions are integrated by sharing a zero-sequence channel of a three-phase electric driving system, the integration level of the system is improved, and the cost of the system is reduced.

Description

Technical Field

[0001] The present invention relates to power electronics and motor drive technology, and in particular to a three-phase electric drive system topology structure and a control method that integrates busbar boosting and open-circuit fault tolerance functions. Background Art

[0002] With the widespread popularity of new energy electric vehicles, people are paying close attention to the range, safety and reliability of electric vehicles. The size and weight of electric vehicles affect the range of the entire vehicle. The current connection method between the energy storage system and the drive device of new energy vehicles is mainly a two-stage configuration, that is, the front stage is a boost converter and the back stage is a drive inverter. The purpose of the boost converter is to raise the inverter DC bus voltage and improve the motor operating efficiency.

[0003] As an important component of new energy electric vehicles, the reliability of the permanent magnet synchronous motor drive system is of vital importance. If the drive system fails, the motor will generate torque pulsation, which will cause severe mechanical vibration, leading to more serious secondary injuries, greatly increasing the safety risks of drivers and passengers. Therefore, the electric drive system needs to have a certain fault tolerance capability to improve the reliability of the system. The faults of the electric drive system mainly include inter-turn short circuit, inter-phase short circuit, winding open circuit, and short circuit and open circuit faults of the inverter circuit. Among them, the short circuit and open circuit faults of the inverter and the short circuit faults of the motor winding can ultimately be equivalent to open circuit faults. Therefore, an electric drive topology with open circuit fault tolerance is of great significance to improving the reliability of electric vehicles.

[0004] At present, a three-phase electric drive system that can realize bus boost and open circuit fault tolerance functions usually needs to be equipped with a boost converter and an additional auxiliary bridge arm. However, the auxiliary bridge arm does not participate in the work when the motor is in normal operation, resulting in a low utilization rate of power devices. Therefore, there is an urgent need for a new three-phase electric drive topology structure in this field, which can effectively integrate bus boost and open circuit fault tolerance functions while reducing the use of power devices, thereby improving the integration and reliability of the electric drive system. Summary of the invention

[0005] The purpose of the present invention is to address the problems of the prior art and propose a three-phase electric drive topology structure and a control method thereof that integrates bus boosting and open circuit fault tolerance functions, so that the three-phase electric drive system has bus boosting and open circuit fault tolerance capabilities under the condition of using less hardware.

[0006] In order to achieve the above purpose, the technical solution of the present invention is as follows:

[0007] A three-phase electric drive system integrating busbar boosting and open circuit fault tolerance functions, which is characterized by including:

[0008] An inverter, comprising four parallel bridge arms connected to a DC bus capacitor; wherein the bridge arms are respectively an A-phase bridge arm, a B-phase bridge arm, a C-phase bridge arm and a fourth bridge arm F, each phase bridge arm is composed of an upper switch tube and a lower switch tube that are complementary, and the fourth bridge arm F is composed of an upper switch tube and a lower switch tube that are complementary;

[0009] A permanent magnet synchronous motor, wherein the three-phase windings are connected to the midpoints of the A-phase bridge arm, the B-phase bridge arm and the C-phase bridge arm respectively;

[0010] DC power supply in Its negative pole is connected to the neutral point N of the permanent magnet synchronous motor, and its positive pole is connected in series with the filter inductor L b Then connected to the midpoint of the fourth bridge arm F;

[0011] The control system is used to generate PWM signals for controlling the three-phase inverter and the fourth bridge arm F. When an open circuit fault is detected, fault-tolerant control is achieved by switching the current settings of the d-axis, q-axis, and 0-axis.

[0012] The three-phase electric drive system of the present invention with integrated busbar boosting and open circuit fault tolerance functions comprises the following steps:

[0013] Step 1: Establish a mathematical model for the three-phase electric drive system with integrated busbar boost and open circuit fault tolerance functions.

[0014] The topology of the three-phase electric drive system with integrated busbar boost and open circuit fault tolerance is as follows: Figure 1 The whole system consists of a three-phase two-level inverter, a permanent magnet synchronous motor, and a DC power supply u in , DC bus capacitor C bus , filter inductor L b and auxiliary bridge arm F. Each phase bridge arm contains two power devices, marked as S x , S′ x , where x = A, B, C, F.

[0015] According to Kirchhoff's law and time average equivalent modeling method, the mathematical model of the electric drive system in the abc coordinate system is established, and its average voltage equation is:

[0016]

[0017] The average current equation is:

[0018]

[0019] where u invABC =[u AO u BO u CO ] T is the terminal voltage of the inverter; αABC =[α A α B α C ] T is the duty cycle of the A, B, and C phase bridge arms; u bus is the DC bus voltage; u ABC =[u AN u BN u CN ] τ is the three-phase voltage of the motor; u in is the DC power supply voltage; L b is the filter inductor; i N is the neutral point current, which is also the input current of the entire system; α F is the duty cycle of the fourth bridge arm; i bus is the DC bus current; C bus is the DC bus capacitor.

[0020] Transform the equation in the abc coordinate system to the dq0 coordinate system and obtain:

[0021]

[0022] where α d , α q , α0 is the duty cycle of the inverter in the dq0 coordinate system; u d 、u q , u0 is the voltage of the inverter in the dq0 coordinate system; R is the stator resistance; L d , L q and L0 are the d-axis, q-axis and zero-sequence inductances respectively; i d 、i q are the d-axis and q-axis currents respectively; ω e is the electrical angular velocity; ψ f is the permanent magnet flux linkage; is the average duty cycle of the inverter; α E , L E 、i o These are variables introduced to facilitate analysis.

[0023] Step 2: According to the power conservation principle, analyze the neutral point current and boost ratio in steady state.

[0024] Ignoring the loss of the entire system, in steady state:

[0025]

[0026] Where P i is the input power; P o is the output power (mechanical power of the motor); T eis the electromagnetic torque; n p is the number of pole pairs of the motor.

[0027] Under steady-state conditions, the input current of the entire system, that is, the neutral point current i N is constant. Therefore, the derivative term di in the voltage equation N / dt is equal to 0, ignoring the voltage drop on the resistor, that is:

[0028]

[0029] As long as α F -(α A +α B +α C ) / 3 is less than 1, the bus voltage boost effect can be achieved, that is, u bus Greater than u in .

[0030] Step 3: Taking the torque consistency before and after the fault as the constraint condition, obtain the reference of the motor q-axis current after the fault.

[0031] When an open-circuit fault occurs in the motor, the torque before and after should be consistent. For a surface-mounted three-phase permanent magnet synchronous motor, the torque after the fault remains unchanged, and the q-axis current after the fault should be consistent with that before the fault. q_f =i q_h , where the subscript _f represents the variable after the fault, and the subscript _h represents the variable under healthy conditions.

[0032] Step 4: Based on the constraint that the current is zero after an open circuit fault occurs in one phase of the motor, obtain the relationship between the motor dq0 current after the fault.

[0033] After the motor has an open circuit fault, taking phase A as an example, there is i A_f =0, according to the relationship between the current in the abc coordinate system after the fault and the current in the dq0 coordinate system after the equal power transformation, we have where θ e is the electrical angle of the motor.

[0034] Step 5: According to the power conservation constraints under healthy conditions and fault conditions, the constraints of the neutral point current after the fault are obtained.

[0035] In healthy conditions, i d_h =0,i q_h with i 0_h Determined by the motor load and speed. From step 4, we can see that after an open circuit fault, i N_f is not a constant, but is related to the electrical angle θ e Therefore, the instantaneous input power of the electric drive system will change with the electrical angle θ after the fault. echanges with the changes of.

[0036] To achieve the goal of open-circuit fault tolerance, the output power of the motor remains unchanged. In order to keep the average input power and output power of the system equal, Where T f is an electrical cycle, <>_T f An operator that represents the average value of a variable over one electrical cycle.

[0037] Step 6: According to the constraints of step 3, step 4, and step 5, the current reference after the fault is obtained:

[0038]

[0039] Step 7: Design a three-phase electric drive system control strategy with integrated bus boost and open circuit fault tolerance functions.

[0040] The control objectives of the three-phase electric drive system with integrated bus boost and open circuit fault tolerance are to control the motor and the DC bus voltage. The motor is controlled by the classic vector control technology. The DC bus voltage is controlled by the dual closed-loop control strategy of voltage outer loop and current inner loop.

[0041] Classical vector control is achieved through i d 、i q To adjust the torque and flux, for surface mounted permanent magnet synchronous motors, i d =0 control. q The reference value is obtained through the speed loop PI controller. N The reference value of is obtained through the bus voltage outer loop PI controller, which is designed to control the DC bus voltage u bus The average value of u bus The average value needs to be obtained through a low-pass filter.

[0042] When no fault occurs, the current given in normal condition is selected and input into the current loop controller for control. When a fault is detected, all current givens are switched from the given in normal condition to the current given after the fault and input into the current controller for control.

[0043] Step 8: Obtain the duty cycle of the three-phase inverter and the fourth bridge arm for modulation.

[0044] The duty cycle α is obtained according to the current controller output d , α q and α F , for α d , α q Perform Park inverse transformation to obtain the three-phase duty cycle α A , α B and α C αF As the duty cycle of the fourth bridge arm. After the duty cycle of each bridge arm is obtained, it is input into the PWM module to generate a control signal to drive the power device.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1) By introducing the fourth bridge arm F, the system can realize the bus boost function, ensure the provision of stable DC voltage during motor operation, and improve the voltage adaptability and stability of the system. It can help reduce the impact of voltage fluctuations on motor performance, thereby improving the operating efficiency and reliability of the motor. A four-bridge-arm inverter structure is adopted, and the traditional three-phase bridge arm is expanded into four bridge arms, in which the fourth bridge arm F is used to realize the bus boost and fault-tolerant control functions, solving the shortcomings of the traditional three-phase electric drive system in bus boost and fault-tolerant control.

[0047] 2) When an open-circuit fault occurs in the motor, the system can perform fault-tolerant control through the fourth bridge arm F to ensure that the remaining normal phases can continue to output effective torque and maintain torque balance.

[0048] 3) By optimizing the control strategy, including motor speed control and bus voltage control, as well as fault-tolerant control after a fault, the system can achieve precise control of motor speed, bus voltage, and fault-tolerant control after a fault, improving the flexibility and adaptability of the system. Through the nested control of the outer speed loop and the inner current loop, the system can achieve precise control of motor speed and current. In terms of fault-tolerant control, the system achieves fault-tolerant control by switching the current set values ​​of the d-axis, q-axis, and 0-axis to ensure that the remaining normal phases can continue to output effective torque. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 The topological structure of the three-phase electric drive system of the present invention integrates bus voltage boosting and fault tolerance functions.

[0050] Figure 2 This is a control block diagram of a three-phase electric drive system integrating busbar boosting and fault tolerance functions according to the present invention.

[0051] Figure 3 This is a structural diagram of the three-phase electric drive with integrated busbar boosting and fault tolerance functions after an open circuit fault occurs in phase A of the present invention. DETAILED DESCRIPTION

[0052] The present invention is further explained below in combination with examples and drawings, but the protection scope of the present invention should not be limited thereto.

[0053] See also Figure 1 , Figure 1The topological structure of the three-phase electric drive system with integrated bus boost and fault tolerance functions of the present invention is shown in the figure. The system includes three phase bridge arms (A phase bridge arm, B phase bridge arm, C phase bridge arm) and a fourth bridge arm F. After the four bridge arms are connected in parallel, they are connected to the DC bus capacitor to form a four-bridge arm inverter.

[0054] The A phase bridge arm consists of the upper switch tube S A With the lower switch tube S' A The two switch tubes are complementary, that is, when one switch tube is turned on, the other switch tube is turned off. The midpoint of the bridge arm is connected to the motor A to provide electrical energy to the motor;

[0055] The B phase bridge arm consists of the upper switch tube S B With the lower switch tube S' B The two switch tubes are complementary and turned on, and the midpoint of the bridge arm is connected to the motor B;

[0056] The C phase bridge arm consists of the upper switch tube S C With the lower switch tube S' C The two switching tubes are complementary and turned on, and the midpoint of the bridge arm is connected to the motor C.

[0057] These switches convert the DC bus voltage into AC voltage to drive the motor by turning on and off the control signals.

[0058] Fourth bridge arm, DC power supply u in The negative pole is connected to the neutral point N of the motor, and the DC power supply u in Series filter inductor L b Then it is connected to the midpoint of the fourth bridge arm F to provide the required DC voltage for the inverter, ensuring that the system can realize the bus voltage boost function and can perform fault-tolerant control through the fourth bridge arm when an open-circuit fault occurs in the motor.

[0059] Current detection point i A 、i B 、i C and i N , used to monitor the current of each phase in real time to ensure the safety and efficiency of the motor operation.

[0060] Figure 2 The control block diagram of the three-phase electric drive system with integrated busbar boost and fault tolerance functions of the present invention is as follows: Figure 2 As shown, the control strategy of the present invention includes motor speed control and bus voltage control, as well as fault-tolerant control after a fault.

[0061] Motor control: The motor control includes an outer speed loop and an inner current loop. The output of the PI controller of the speed loop is the given value of the q-axis current as the reference value of the inner current controller. The voltage reference value is obtained through the current loop controller, and then a d 、a q , the three-phase voltage duty ratio a is obtained by Park inverse transformation a 、a b 、a c .

[0062] Bus voltage control: The bus voltage control is composed of the outer loop voltage control and the inner loop current controller, and finally outputs the duty cycle a of the fourth bridge arm. F .

[0063] PWM signal generation: The duty cycle is compared with the triangular carrier to generate a PWM signal, which controls the inverter operation.

[0064] Fault-tolerant control: When a fault is detected, the system switches the current set values ​​of the d-axis, q-axis, and 0-axis to achieve fault-tolerant control, output effective torque through the remaining normal phases, and maintain torque balance.

[0065] The specific implementation steps of the multifunctional system integrating busbar boosting and open-phase fault tolerance of the present invention include:

[0066] Step 1: Establish a mathematical model of a multifunctional system integrating busbar boosting and open-phase fault tolerance

[0067] According to Kirchhoff's law and time average equivalent modeling method, the multifunctional electric drive system is modeled in the abc coordinate system, and its average voltage equation is:

[0068]

[0069] The average current equation is:

[0070]

[0071] where u invABC =[u AO u BO u CO ] T is the terminal voltage; α ABC =[α A α B α C ] T is the duty cycle of each phase bridge arm; u bus is the DC bus voltage; u ABC =[u AN u BN u CN ] T is the voltage of each phase; u in is the DC power supply; L b is the filter inductor; iN is the neutral point current, which is also the input current of the entire system; α F is the duty cycle of the fourth bridge arm; where i bus is the DC bus current; C bus is the DC bus capacitor.

[0072] Transform the equations in the abc coordinate system to the dq0 coordinate system:

[0073]

[0074] where α d , α q , α0 is the duty cycle in the dq0 coordinate system; u d 、u q , u0 is the voltage in the dq0 coordinate system; R is the stator resistance; L d , L q and L0 are the d-axis, q-axis and zero-sequence inductances respectively; i d 、i q are the currents of the d-axis and q-axis respectively; ω e is the electrical angular velocity; ψ f is the flux linkage of the permanent magnet; Represents the average duty cycle of the inverter; α E , L E 、i o These are variables introduced to facilitate analysis.

[0075] Step 2: Analyze the neutral point current and steady-state boost ratio in steady state

[0076] In steady state, ignoring the loss of the entire system, the power conservation equation is

[0077]

[0078] Where P i is the input power; P o is the output power (mechanical power of the motor); T e is the electromagnetic torque; n p is the number of pole pairs of the motor.

[0079] From (4), we can see that i N The theoretical value is

[0080]

[0081] where γ is i N and i q A coefficient in .

[0082] In steady state, assuming that the power of the motor is constant, according to the law of conservation of power, the input current of the entire system, that is, the neutral point current i N is constant. Therefore, the derivative term di in equation (3) N / dt is equal to 0, ignoring the voltage drop on the resistor, that is,

[0083]

[0084] It can be observed that as long as α F -(α A +α B +α C ) / 3 is less than 1, the DC bus voltage u bus can achieve a DC voltage source u in Higher value.

[0085] Step 3: Taking the torque consistency before and after the fault as the constraint condition, obtain the q-axis current reference after the fault.

[0086] When an open-circuit fault occurs in the motor, the torque before and after should be consistent, so the magnetomotive force generated by the current of the remaining normal phase should be the same as that under healthy conditions. For a three-phase surface-mounted permanent magnet synchronous motor, in order to maintain the torque after the fault consistent with that before the fault, the q-axis current after the fault must be kept consistent with the q-axis current before the fault, as shown in (7), where the following table h represents the variables under healthy conditions, and the subscript f represents the variables after the fault.

[0087] i q_f =i q_h (7)

[0088] Step 4: Obtain the relationship between the dq0 current after the fault

[0089] When an open circuit fault occurs in the motor, the fault phase branch should be disconnected immediately. Taking the open circuit fault of phase A as an example, the branch where phase A of the motor is located should be disconnected immediately. Figure 3 As shown, there is i A_f =0, according to the relationship between the current in the abc coordinate system after the fault and the current in the dq0 coordinate system after the equal power transformation, we have

[0090]

[0091] where θ e is the electrical angle of the motor.

[0092] Step 5: Based on the power conservation constraints under healthy conditions and fault conditions, obtain the constraints of the neutral point current after the fault

[0093] In healthy conditions, i d_h =0,i q_h with i0_h It is a constant determined by the motor load and speed. N_f is not a constant, but is related to the electrical angle θ e Then the instantaneous input power of the electric drive system will change with the electrical angle θ after the fault. e changes with the changes of.

[0094] To achieve fault tolerance, the output power of the entire system needs to remain constant. Therefore, in order to keep the average input power equal to the output power,

[0095]

[0096] T f is an electrical cycle, <>_T f Represents the average operator within one electrical cycle.

[0097] Step 6: According to the constraints of step 3, step 4, and step 5, obtain the current reference after the fault:

[0098]

[0099] Step 7: Design the controller for the multifunctional three-phase electric drive system

[0100] The multifunctional electric drive system combines bus boost and open-phase fault tolerance functions, so the controller of the system should include a vector controller and a boost controller. The boost converter is a typical nonlinear system, and a nonlinear control strategy can be used to control the boost converter. The current reference value after the fault is a non-constant value, and a current controller with good tracking performance can be designed to track it, such as a controller with a resonant term.

[0101] The traditional PI controller can only perform steady-state error-free regulation on DC signals, but cannot achieve error-free regulation on AC signals. The PR controller can be used to perform error-free control on AC quantities. Since the control object of the PR controller is a current with AC harmonic components, in which the harmonic current is related to the angular velocity, the PR controller will be affected by the speed of the motor. The bandwidth of the ideal PR controller is small. When there is a measurement error in the speed, the gain at the control frequency will be significantly reduced, and the control effect will also deteriorate. Therefore, it is necessary to increase the bandwidth of the PR controller to achieve enhanced control effect. At this time, the transfer function can be expressed as:

[0102]

[0103] Where K P is the proportionality coefficient, K R is the resonance coefficient, ω c is the cut-off frequency, and ω0 is the angular frequency of the AC that needs to be controlled.

[0104] A PIR controller with a resonant term is used to control the current given after a fault. The PIR controller is a resonant controller connected in parallel with a PI controller. In this way, the PI controller can be used to accurately control the DC given quantity and ensure dynamic performance while tracking the AC quantity. The transfer function of the PIR controller is shown in (12), where K i is the integration coefficient.

[0105]

[0106] Classical vector control is achieved through i d 、i q To adjust the torque and flux, for surface mounted permanent magnet synchronous motors, i d =0 control. q The reference value is obtained through the speed loop PI controller. N The reference value of is obtained through the bus voltage outer loop PI controller, which is designed to control the DC bus voltage u bus The average value of u bus The average value needs to be obtained through a low-pass filter.

[0107] When no fault occurs, the current setting under normal conditions is selected for control. After a fault is detected, all current settings are switched from the settings under normal conditions to the current settings after the fault.

[0108] Step 8: Obtain the duty cycle of the three-phase inverter and the fourth bridge arm for modulation.

[0109] The duty cycle α is obtained according to the output of the current controller d , α q and α F , for α d , α q Perform Park inverse transformation to obtain the three-phase duty cycle α A , α B and α C α F As the duty cycle of the fourth bridge arm. After the duty cycle of each bridge arm is obtained, it is input into the PWM module to generate a control signal.

[0110] So far, the control strategy of the multifunctional three-phase electric drive system with integrated bus boost and open-phase fault tolerance has been explained. The multifunctional three-phase electric drive system proposed in the present invention can simultaneously realize the bus boost and open-phase fault tolerance functions. The proposed control method can use the remaining normal phases to output effective torque and maintain torque balance. It has broad application prospects in fields such as aerospace, electric vehicles, etc. that have high requirements for integration and reliability.

[0111] The above content only shows some specific embodiments of the present invention, but the protection scope of the present invention is not limited to these modes. For those skilled in the art, within the technical scope disclosed by the present invention, equivalent replacement or change can be made according to the technical solution and inventive concept of the present invention, and these replacement or changed embodiments should be included in the protection scope of the present invention.

Claims

1. A three-phase electric drive system integrating busbar boost and open circuit fault tolerance functions, characterized in that: include: An inverter, comprising four parallel bridge arms connected to a DC bus capacitor; wherein the bridge arms are respectively an A-phase bridge arm, a B-phase bridge arm, a C-phase bridge arm and a fourth bridge arm F, each phase bridge arm is composed of an upper switch tube and a lower switch tube that are complementary, and the fourth bridge arm F is composed of an upper switch tube and a lower switch tube that are complementary; A permanent magnet synchronous motor, wherein the three-phase windings are connected to the midpoints of the A-phase bridge arm, the B-phase bridge arm and the C-phase bridge arm respectively; DC power supply in Its negative pole is connected to the neutral point N of the permanent magnet synchronous motor, and its positive pole is connected in series with the filter inductor L b Then connected to the midpoint of the fourth bridge arm F; The control system is used to generate PWM signals for controlling the three-phase inverter and the fourth bridge arm F. When an open circuit fault is detected, fault-tolerant control is achieved by switching the current settings of the d-axis, q-axis, and 0-axis.

2. The three-phase electric drive system with integrated busbar boost and open circuit fault tolerance function according to claim 1, characterized in that: The control system further comprises the following steps: Step 1. According to Kirchhoff's law and time average equivalent modeling method, establish the mathematical model of the electric drive system in the coordinate system abc, including the average voltage equation and the average current equation: In the formula, u invABC =[u AO u BO u CO ] T is the inverter terminal voltage; α ABC =[α A α B α C ] T is the duty cycle of the A-phase bridge arm, the B-phase bridge arm, and the C-phase bridge arm; u bus is the DC bus voltage; u ABC =[u AN u BN u CN ] T is the motor phase voltage; u in is the DC power supply voltage; L b is the filter inductor; i N is the neutral point current, which is also the input current of the entire system; α F is the duty cycle of the fourth bridge arm; where i bus is the DC bus current; C bus is the DC bus capacitor; The average model in the abc coordinate system is transformed to the average model in the dq0 coordinate system through equal power Park: where α d , α q , α0 is the duty cycle of the inverter in the dq0 coordinate system; u d 、u q , u0 is the voltage of the inverter in the dq0 coordinate system; R is the stator resistance; L d , L q , L0 are d-axis, q-axis and zero-sequence inductance respectively; i d 、i q are the currents of the d-axis and q-axis respectively; ω e is the electrical angular velocity; ψ f is the permanent magnet flux linkage; is the average duty cycle of the inverter; α E , L E 、i o This is to facilitate the analysis of the derived variables; Step 2. According to the principle of power conservation, analyze the neutral point current and boost ratio in steady state, determine the theoretical value of the neutral point current, and derive the conditions for achieving busbar boost: that is, α F -(α A +α B +α C ) / 3<1, then u bus >u in , where α A α B α C are the duty cycles of the A-phase bridge arm, the B-phase bridge arm, and the C-phase bridge arm respectively; α F is the duty cycle of the fourth bridge arm; u bus is the DC bus voltage, u in is the DC power supply voltage; Step 3. When an open circuit fault occurs, the torque before and after the fault is the same as the constraint condition to obtain the q-axis current reference after the fault, i q-f =i q-h , where subscript _f represents the variable after the fault, and subscript _h represents the variable under healthy conditions; Step 4. When an open circuit fault occurs in the motor, the fault phase branch is immediately disconnected, and the relationship between the dq0 currents after the open circuit fault is obtained based on the current relationship after the fault: where θ e is the electrical angle of the motor; Step 5. According to the power conservation constraints under healthy conditions and fault conditions, obtain the constraints of the neutral point current after the fault: Among them, T f is an electrical cycle, <>_T f represents the average operator; Step 6. Combine the above constraints to get the current reference after the fault: Step 7. Design a control strategy integrating bus voltage boost and open circuit fault tolerance functions, including classic vector control and dual closed-loop control strategy of voltage outer loop and current inner loop; Step 8. When no fault occurs, the current setting under normal conditions is selected for control; after a fault is detected, all current settings are switched from the settings under normal conditions to the current settings after the fault; Step 9. According to the output of the current controller, the duty cycle of the three-phase inverter and the fourth bridge arm is obtained, and modulated to generate a control signal to drive the power device.

3. The three-phase electric drive system with integrated busbar boost and open circuit fault tolerance function according to claim 2, characterized in that: The current controller in the control system adopts a PIR controller with a resonance term to achieve zero-difference control of the AC quantity and improve the control effect.

4. The three-phase electric drive system with integrated busbar boost and open circuit fault tolerance function according to claim 2, characterized in that: The classical vector control adjusts the torque and magnetic flux by adjusting the current of the d-axis and the q-axis. For the surface-mounted permanent magnet synchronous motor, i_d=0 control is adopted.

5. The three-phase electric drive system with integrated busbar boost and open circuit fault tolerance functions according to claim 2, characterized in that: The reference value of the voltage outer loop PI controller is obtained by the average value of the bus voltage, and the average value needs to be filtered by a low-pass filter.

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