Fault‐tolerant strategies for open‐circuit switch failures in open‐end winding PMSM drives

Abstract

Abstract Many safety‐critical drive systems require post‐fault operation after an open‐circuit switch failure occurs in the inverter. The open‐end winding inverter topology facilitates the injection of zero‐sequence current such that a faulty switch leg can still be used to generate sufficient voltage states to continue operation. Therefore, only a minimal increase in the post‐fault torque ripple is experienced. However, the injection of this zero‐sequence current results in an increase in the copper loss which de‐rates the maximum post‐fault torque of the machine. Existing post‐fault techniques that inject zero‐sequence current, during an open‐circuit switch fault, do not minimize the copper loss resulting in sub‐optimal post‐fault torque per ampere. A method for reducing copper loss by optimizing the zero‐sequence current waveform to achieve the maximum post‐fault torque per ampere is proposed here. The proposed strategy has been experimentally assessed for both three‐phase and five‐phase drive systems. The experimental results demonstrate the continuous post‐fault operation of the drive system with a more balanced thermal load distribution between phases. A 2.8% and 5.6% improvement in post‐fault torque per ampere for three‐phase and five‐phase systems are demonstrated.