A Novel Diagnostic Technique for Open-switch Faults of Inverters Based on Operating Mode Analysis

A novel real-time diagnostic and locating technique for open-switch faults in inverters was proposed in this paper.Based on the switching function model and operating modes of the inverter,the method is implemented with simple hardware circuits according to different voltages of the lower switches between faulty and normal conditions,which has advantages of low cost,high reliability,short diagnostic time and good applicability.The operating modes of inverters were researched and the real voltages of the lower switches under both normal condition and the upper and lower switches open-circuit faults were analyzed.The analytic results indicate that different error voltages are derived by the upper and lower switches open-circuit faults respectively,comparing with the estimated voltages of lower switches deduced from the switching function model.Otherwise,error voltages can be developed by switching delay,dead time and measurement noise,which need to be eliminated.Threshold compares and pulse-width limits are used to filter the error voltages coming with switching delay and measurement noise.In addition,in order to eliminate the error voltages during the dead time,the error voltages are modulated with corresponding switching signals.This paper presented a realization scheme using hardware circuits,and simulations and experiments were completed in field-oriented control system of permanent magnet synchronous motor.The results validate the proposed method and indicate that the method is immune to closed loop control strategies.Fault detection can be achieved within 10μm.