An Optimal Active Short-Circuit Strategy for Permanent Magnet Synchronous Machines

Active short-circuits (ASC) serve as a fail-safe protective measure for permanent magnet synchronous machines (PMSMs) during certain faults and operating conditions. However, large stationary and transient fault currents pose critical challenges to the design and reliability of PMSMs. This article introduces an optimal ASC strategy aimed at minimizing the steady-state stress on individual power switches and suppressing the transient current overshoots. Moreover, we expand the traditional ASC technique, originally developed for two-level three-phase systems, to encompass three-level converters for various multiphase systems and topologies. The concept was validated numerically and experimentally for three-phase and six-phase configurations. The results show that, for low-attenuation PMSMs operating at high speed, the proposed asynchronous ASC (AASC) method achieves nearly 50% transient current reduction. Additionally, the active neutral-point-clamped converter is shown to significantly enhance performance, increasing the steady-state short-circuit withstand level by 91% while also allowing the flexible implementation of AASC.