Zero-sequence voltage injected fault tolerant scheme for multiple open circuit faults in reduced switch count-based MLDCL inverter

Abstract

Neutral shifting (NS) is a popular scheme to achieve fault tolerance operation (FTO) of multilevel inverters (MLIs) such as cascaded H-bridge (CHB). This fault tolerance scheme (FTS) can be realised with/without zero-sequence voltage injection. Among these, NS with zero-sequence injection FTS is relatively easier to implement. However, this scheme is not generalised for multiple open-circuit faults. Moreover, NS-FTS schemes are not directly applicable for fault tolerance of reduced switch count (RSC)-MLIs, as these inverters have limited redundancies. Therefore in this study, FTO for RSC-based multilevel dc-link (MLDCL) inverter using NS zero-sequence injection FTS is proposed for simultaneous failure of multiple switch faults. Generalised mathematical equations are derived to calculate the magnitude and phase angle of injected zero-sequence voltage for obtaining balanced line voltages with uniform power sharing among all healthy units. The proposed generalised NS-FTS with zero-sequence injection is implemented on three-phase 15-level MLDCL inverter for various fault conditions. The obtained simulation results are validated experimentally on nine-level MLDCL inverter