Back EMF Harmonics and DC Components Rejection for Improvement in Sensorless FTC for Multiphase PMSM Based on SMO With Enhanced Cross-Coupling Second-Order Sequence Filter

This article presents a new sensorless fault-tolerant control approach for five-phase permanent magnet synchronous motor (PMSM) using a sliding mode observer (SMO) due to its strong robustness and stability. Asymmetric operations under open-circuit faults (OCFs) cause high harmonics and dc components in back EMFs, making it challenging to estimate speed and position. Thus, in this article, a cross-coupling second-order sequence filter (CC-SOSF) works for extracting the symmetrical sequence components of back EMFs by eliminating the harmonic. In addition, a dc mitigation circuit is added to this filter to eliminate dc bias. To ensure frequency adaptation and avoid the issue of the estimated frequency feedback, an open-loop frequency estimator (OLFE) is adopted. Finally, a phase-locked loop calculates the estimated rotor position and speed. Simulations and experimental tests confirm the effective elimination of both harmonics and dc components, leading to accurate position and speed estimation in the presence of OCFs.