A Diagnostic Method of Simultaneous Open-Switch Faults in Inverter-Fed Linear Induction Motor Drive for Reliability Enhancement

To enhance the reliability in an inverter-fed linear induction motor (LIM) drive under simultaneous open-switch faults, practical online basis fault detection and localization schemes are presented. The open-switch faults in the inverter incur overcurrent stress to other electric components, resulting in a severe secondary fault in the entire system. As compared with the conventional schemes that the fault detection and faulty switch identification rely on the averaging or current error from the reference value, the proposed algorithms are achieved through signal processing schemes such as harmonic analysis, averaging, and waveform analysis by using only the measured current information. In addition, the proposed scheme classifies the open-switch faults as four faulty groups according to their unique fault signature, which enables the proposed scheme to identify faulty switches effectively. Since the fault detection is accomplished by using the relative magnitude of the second-order harmonic component in phase currents, the influence on steady-state error or dc offset of current is significantly reduced. Once the fault is detected, the operating mode is changed to identify the faulty group which the fault belongs to. By identifying the faulty group, the faulty switches can be found in a much more straightforward way. The entire LIM drive system is implemented using DSP TMS320F28335 to verify the feasibility of the proposed fault detection and faulty switch identification schemes. Without requiring any additional hardware or measuring apparatus, the proposed diagnostic algorithm can effectively detect a fault even under simultaneous open-switch faults by online basis.