Failure adapted techniques to improve service dependability in systems using fault-tolerant converters

The paper deals with some problems concerning fault analysis in multilevel V.S.I. converters. With reference to cascaded H-bridge topology, first the possible conditions of "single fault" are classified by analyzing the modification of output voltages when a generic power device is damaged ("short-circuited" or "definitely open"). Then a procedure for on-line quick identification of the corrupted device is explained. It is based only on output voltages and currents measurements and does not require additional sensors. The minimum number of measurements allowing fault identification is linked to the number of converter levels. Finally, failure adapted techniques of converter modulation are presented and simulation results are discussed with reference to some significant cases. These techniques have the aim to minimize the influence of the different faults on the service of the whole drive.