Open-Transistor Fault Diagnostics in Voltage-Source Inverters by Analyzing the Load Currents

A novel method is presented for the detection and isolation of open-transistor faults in voltage-source inverters feeding ac motors. The method is an extension of the normalized dc-components method. The normalized average currents are combined with additional diagnostic variables which convey information about the percentage of time spent by the phase currents in the near-zero zone. The combined diagnostic signals permit much more robust diagnostics of single-transistor faults and make feasible the diagnostics of multiple-transistor faults. Suggested in this paper is also an alternative solution for the normalization of dc components, which is easier interpreted and simpler to implement.