Postfault Zero-Sequence Current Injection for Open-Circuit Diode/Switch Failure in Open-End Winding PMSM Machines

Abstract

This paper proposes and experimentally assesses two zero-sequence current control strategies that allow continuous operation of the three-phase dual-inverter drive using an open-end winding permanent magnet synchronous machine (PMSM) when freewheel diodes (or semiconductor switches) in either inverters fail open circuit. With an identified failure present, the proposed control strategies inject zero-sequence current to bias the phase current(s) of the faulted phase(s) such that the phase current(s) are unipolar, thereby eliminating current flow in the device(s) that have failed. Two possible injection modes are proposed. The first mode injects the minimum required zero-sequence current to bias the current in the phase that has a semiconductor open-circuit failure(s). The injected zero-sequence current varies over a fundamental cycle. This minimizes the increase in total rms currents in the phases yielding higher torque capability in fault conditions. The second mode injects a zero-sequence current that has a constant value over a fundamental cycle to bias all three-phase currents appropriately. This mode is used if more than one phase has suffered a fault. Additional thermal and current stresses resulting from both techniques were assessed and compared. A detailed electromagnetic torque model was also developed to demonstrate that the zero-sequence current does not affect the average torque output. Experimental results verify the theoretical treatment and are used to examine the advantages of techniques and show the improvement in the maximum available torque under fault conditions.