Fault Diagnosis And Tolerant Control For Power Converter In Switched Reluctance Motor Drives

Switched reluctance motors(SRMs)have been recognized for their robust configuration and fault tolerant capabilities.In addition,SRMs are fabricated from rare-earth-free materials.These peculiar characteristics make SRM a competitive candidate for many critical applications such as EV/HEV and more electric aircraft industry.However,due to harsh operational environment and repetitive duty cycles,power switching devices in traction drives are susceptible to failure particularly in transient of speed up and braking.In such applications,high system reliability and fault tolerance is of paramount importance.In addition,one major drawback of SRM drive is relatively high-torque ripple compared to the conventional AC machines.Torque ripple in an SRM drive results from highly saturated magnetic circuit and discrete excitation of phase winding for torque production,and its fluctuation is severe during commutation between two adjacent phases.Therefore,in this thesis,torque ripple is minimized using two strategies namely torque sharing function(TSF)and direct instantaneous torque control(DITC).Moreover,novel strategies for fault diagnosis and tolerant control in SRM drives are investigated.Two real time fault diagnosis methods for power converter are proposed based on high-frequency(HF)signal injection.In addition,two fault tolerant topologies are also developed to sustain the driving operation after occurrence of faults.The first diagnostic strategy is based on high-frequency(HF)voltage injection,in which the fault signatures are extracted from the fundamental current by injecting a high-frequency(HF)voltage signal into the upper switches of the asymmetric converter.The injected HF voltage introduces HF currents to the phase current which is then filtered using band-pass filters.Open-circuit and short-circuit of the power switches are analysed by monitoring the frequency and amplitude of the filtered HF current along with the variation in fundamental current with the occurrence of fault.The second diagnostic approach is based on high-frequency current signal injection.In this method,a sinusoidal HF current signal is injected into the power switches of the converter and likewise HF voltage signal injection method,the frequency and amplitude of the HF current along with the fundamental current are analysed to monitor the health condition of the power switches.However,in this method open-circuit fault in both switches exhibits same fault features.Therefore,another PWM pulse is injected into the lower switch to locate the faulty switch when an open-circuit fault is detected.Moreover,some new fault tolerant topologies are developed based on the standard asymmetrical topology.The developed topologies are composed of two or four additional switching devices with a relay network that can ensure the continuity of machine operation when a fault occurs in one phase or faults occur in two phases.The effectiveness of the proposed strategy is verified though thorough simulation results based on a three–phase 12/8 SRM drive system.The presented simulation results demonstrate the effectiveness of the proposed scheme under wide range of mechanical operating conditions,which may enhance the reliability and cost efficiency of the SRM drive system for automotive applications.