Diagnosis And Fault-tolerant Control Strategies Of Inverters In Six-phase Permanent Magnet Synchronous Motor Drive Systems

The six-phase permanent magnet synchronous motor has the advantages of low voltage,high power,high efficiency,fault tolerance,and low noise.It has been used in applications with high reliability requirements such as ship propulsion and aviation actuators.In the motor drive system,the power switch tube and the drive circuit in the power converter have a high failure rate,and problems related to maintaining the reliability of the inverter have not been effectively dealt with.Identify the faults of the inverter quickly and accurately,and adopt appropriate fault-tolerant control strategies to ensure the stability of the system,restore the original performance of the system,and ensure that the system still has a high execution power after the fault is repaired.Therefore,research on fault diagnosis and fault-tolerant control strategies of inverters in motor drive systems has important theoretical significance and engineering application value.Diagnosing the faults that occur in the inverter is a prerequisite for implementing a fault-tolerant control strategy for the motor drive system.The speed and accuracy of fault diagnosis are often proportional to the fault-tolerant effect.Traditional motor modeling methods generally model motors and inverters separately,and cannot well reveal the common operating state information of motors and inverters.In this paper,the hybrid system theory is introduced into the fault diagnosis process of multi-phase motors.The discrete voltage model of the inverter is combined with the steady-state equation of the motor to establish a mixed logic dynamic model of the motor drive system.The strategy provides a theoretical basis.Based on the mixed logic dynamic model of the six-phase motor drive system,a current residual error diagnosis method based on fundamental wave subspace and harmonic wave subspace is proposed.By deducing the current dynamic model of the multi-phase inverter switch tube after the fault,the current residual equation of the multi-phase motor system is constructed,and the current residual is used to diagnose and locate the fault,and the fault diagnosis of the multi-phase motor system is improved.Robust fundamental current and harmonic subspace threshold current determination methods.This method can greatly reduce the impact of the closed-loop control algorithm on the diagnosis effect in the fault state,and can shorten the diagnosis time to within one quarter of the fundamental wave period.Based on the mixed logic dynamic model of six-phase motor drive system,a fault diagnosis method for multi-phase inverter based on error voltage is proposed,that is,the fault is diagnosed by the error between the measured value and estimated value of the bridge arm midpoint-to-ground voltage.In order to simulate the actual working situation as much as possible,it is proposed to double judge the amplitude and time width of the error voltage,so as to eliminate the influence of the power tube switching delay and the dead zone.While ensuring the reliability and robustness of the diagnosis strategy,this method can also lock the diagnosis time within a few switching cycles.The above two diagnostic method have been verified by simulation.Finally,two fault-tolerant control schemes are proposed for one phase open circuit fault which is common in multiphase motor system.The two fault-tolerant control schemes based on the minimum stator copper loss and the maximum output torque are proposed to realize the fault-tolerant operation of the motor.At the same time,the two control strategies are compared in the efficiency and loss of the motor.The fault operation of the control system is simulated,and the current response curve and torque fluctuation curve after fault-tolerant control are analyzed to verify the reliability of the fault-tolerant control strategy.