Research On Driving System And Fault Tolerant Control Strategy Of Open-winding Less-Rare-Earth Permanent Magnet Motor

With zero emission and high efficiency,electric vehicles have attracted wide attention and been promoted on a large scale.As the core component of electric vehicle,motor and the control system directly determine the whole performance.Permanent magnet(PM)motor has the advantages of small size and high power density,and has become one of the main electric vehicle drive motors.It is important to realize high power density,high efficiency and high reliability operation of permanent magnet motor.According to the inherent requirements of high efficiency,high power density,fault-tolerant operation ability and high reliability in the potential application field of electric vehicles,a new type of open-winding less-rare-earth PM motor drive system is constructed.The mathematical model of the system is established,and the zero sequence current suppression strategy for the open-winding system of this kind of motor is proposed.The sensorless control strategy and the fault-tolerant control strategy of the inverter are proposed successively,and the theoretical analysis,simulation and experimental verification are presented.The main research contents are as follows:1.The open-winding less-rare-earth PM motor drive system with a single DC power supply is constructed.The traditional modulation will lead to zero sequence voltage in phase voltage,and the hybrid structure of two PM materials used in less-rare-earth PM motors will lead to zero sequence component in back electromotive force(EMF).The zero sequence component in driving voltage and back EMF will both generate zero sequence current in windings.In order to suppress the zero sequence current,the decoupling modulation strategy based on 120 degrees is used to suppress the zero sequence voltage in the phase voltage,and a zero sequence current regulator based on proportional and second order generalized integrator(P+SOGI)is proposed.The control strategy not only effectively improves the utilization of DC bus voltage,but also provided conditions for adopting the fault-tolerant control of inverter.2.In order to improve the reliability of the system,the sensorless control strategy of open-winding motor system is adopted.The position signal is estimated by back EMF.The back EMF estimation contains harmonics due to the dead-time effect of the inverter and the structure of the motor.The harmonics may result in harmonic error in the estimated position.The traditional idea of harmonic suppression is a good solution for the specific harmonic elimination.But the traditional method has the problem of too complex to suppress multiple harmonics.In order to solve this problem,a sensorless control scheme based on synchronous rotating low pass filter(SRLPF)is proposed.The SRLPF can extract the fundamental wave of back EMF.Thus the position estimation harmonics can be suppressed.The experimental results show that the strategy can effectively improve the estimation accuracy.3.In order to improve the estimation accuracy and dynamic performance at the same time,the dual second order generalized integrator(DSOGI)is proposed to extract the fundamental wave of back EMF.In addition,a rotor position observer is designed based on active disturbance rejection control(ADRC)theory to further improve the system performance.Thus the control strategy can suppress the harmonics of back EMF estimation to improve the estimation accuracy and maintain good dynamic performance.4.The open-winding motor driven by dual-inverters is easy to realize fault-tolerant control of switch due to redundancy of switches.Thus the reliability of the drive system can be improved.The driving performance may be decreased due to the traditional fault-tolerant method often add the redundant leg or abandon the fault phase.To solve this problem,this paper proposes a fault-tolerant control strategy which makes full use of redundant bridge legs.When an open-circuit fault occurs in an inverter,the fault-tolerant control of the inverter can be realized without adding redundant bridge legs or abandon the fault phase by connecting the winding terminal connection points to the normal running bridge leg with the same switching state.This method can not only improve the output ability of the fault-tolerant system,but also realize fault-tolerant control of any two bridge legs at the same time,which greatly improves the reliability of the system.