Control strategy reconfiguration for a multilevel inverter operating with bypassed cells

This paper analyzes the fault-tolerant operation of a Series Connected H-Bridge inverter topology (SCHB) supplying an induction machine. The standard approach considers a bypass of the faulty cells by means of a contactor and it carries out a reconfiguration of the modulator in order to generate balanced phase output voltages. The price that must be paid for this emergency operating mode is a reduction of the maximum voltage that the inverter can supply to the machine., therefore the limits for the torque and flux controllers must be also changed. In this work a standard stator flux oriented control strategy is modified to permit the operation the machine according to the new voltage limit. Experimental results are discussed, which validate the ideas presented in this work.