Research On Fault Diagnosis And Fault Tolerant Technology Of Open Winding Permanent Magnet Synchronous Motor System For Electric Vehicle

Safety and reliability are important indicators of electric vehicles,and motor and its driving system are important components of electric vehicles.The fault diagnosis research and fault-tolerant operation methods of motor and its drive system is an important means to improve the safe and reliable operation of electric vehicles.Permanent magnet synchronous motor has become the most widely used model in the field of motor drive because of its advantages of high power density and high efficiency.As an important branch of permanent magnet synchronous motor,open winding permanent magnet synchronous motor has great advantages over traditional three-phase permanent magnet synchronous motor in terms of power device capacity demand,fault tolerance ability and control performance.Based on the application of open-winding permanent magnet synchronous motor in electric vehicles,and on the premise of ensuring that the vehicle can still safely drive to the safe area or maintenance point after the fault,this thesis studies some possible fault diagnosis and operation problems after the fault in the application process.A diagnosis method based on fault current characteristics is established for the possible open circuit faults of power devices in the drive system of open winding permanent magnet synchronous motor.This method consists of two parts:preliminary diagnosis and fault location of power devices.According to the current characteristics of power devices after open circuit fault,the preliminary diagnosis transforms the judgment of fault characteristic value and threshold value into positive,negative and zero sign judgment of fault characteristic value by introducing new variables on the basis of the traditional fault diagnosis method,which simplifies the setting of threshold value.The system structure of open-winding permanent magnet synchronous motor determines the preliminary diagnosis method based on the current characteristics after the fault,which can only judge that the fault occurs in a pair of power devices of H-bridge.For the open-circuit fault location of power devices,on the premise that the open-winding permanent magnet synchronous motor switches to two-phase fault-tolerant operation after preliminary diagnosis,combined with the induced EMF generated by the permanent magnet,single power device modulation is carried out on the H-bridge where the faulty power device is located,and the open-circuit fault location of power devices is completed according to the current characteristics after modulation.Aiming at the possible short-circuit fault between turns of phase winding in the operation of open winding permanent magnet synchronous motor,a diagnosis method is proposed to identify the degree of short-circuit fault between turns of phase winding.This method can locate the fault phase of the inter-turn short circuit by judging the current unbalance degree.Based on the established mathematical model of inter-turn short circuit of open-winding permanent magnet synchronous motor,the fault diagnosis is transformed into the optimization problem of inter-turn short circuit turn ratio,and the identification of fault degree is realized by combining the improved particle swarm optimization algorithm.The results show that the improved particle swarm optimization algorithm has better convergence speed and optimization accuracy.A low switching frequency fault-tolerant operation scheme is proposed for the fault-tolerant operation of a single power device in the open-winding permanent magnet synchronous motor drive system.In this scheme,the phase winding connected to the power device after open circuit failure is connected to the midpoint of two capacitors parallel with DC voltage by solid-state switch as the hardware topology.In order to solve the problem of difficult sector selection in the modulation process caused by capacitor voltage fluctuation,the reference voltage modulation considering capacitor voltage fluctuation is converted to a three-phase stationary coordinate system.In addition,in order to reduce the switching frequency,the reference voltage is adjusted synchronously according to the polarity of the reference voltage,so that the switching times of the power devices of the whole system are only 4 times in a single control cycle.Aiming at the possible phase break fault of open winding permanent magnet synchronous motor,a control strategy under phase break fault of common DC bus open winding permanent magnet synchronous motor system is proposed.By establishing the mathematical model between the current component in the synchronous coordinate system and the current component in the static coordinate system and the zero sequence current,and analyzing the relationship between the double frequency component and the four frequency component in the synchronous coordinate system and ZSC,the method of using the proportional integral resonant controller to suppress ZSC in the synchronous coordinate system is proposed.In addition,according to the distribution law of the voltage vector of the open-winding PMSM system under the phase break fault of the winding,a scheme is proposed to generate the reference voltage vector by unified modulation using a group of mutually perpendicular voltage vectors.Aiming at the energy balance problem of two independent battery packs of open-winding permanent magnet synchronous motor,an energy distribution method based on model predictive control is proposed.The value function is established based on the mathematical model of capacity loss,temperature and state of charge of lithium battery.According to the demand of energy in the motor running,the current of two battery packs is predicted with the control objective of minimizing the state of charge error,battery temperature difference and capacity loss error of the two battery packs,and according to the prediction of the battery current,calculate the open winding permanent magnet synchronous motor drive system in the two reference voltage vector converter,and achieve the optimal allocation of the reference voltage vector.Compared with the traditional voltage vector distribution method,this method can effectively improve the balancing ability of the two battery packs,so as to ensure the safe and reliable operation of the vehicle.