Sensorless Six-Phase Permanent Magnet Synchronous Motor Drive Assisted by High-Order Back-EMF Harmonics

This paper presents a robust sensorless control strategy for wide-speed-range operation of a six-phase permanent magnet synchronous machine. The proposed approach exploits multi-harmonic back-EMF estimation combined with rotor permanent magnet flux synchronization to achieve accurate rotor position estimation under dynamic load conditions and in the presence of parameter uncertainties. Back-EMF components are extracted in both the fundamental and higher-order harmonic subspaces, and a dedicated harmonic synchronization strategy is introduced to guarantee correct position estimation. A smooth transition from open-loop I–f control to sensorless closed-loop operation is implemented, ensuring stable and continuous operation over the entire speed range. The control system architecture is presented in detail, and its effectiveness is validated through an extensive set of experimental results. The experimental analysis includes full-range speed operation, synchronization and lock-in performance, dynamic response to speed and torque transients, and robustness against parameter mismatches. The impact of position estimation errors caused by parameter variations on current magnitude and Joule losses is also analyzed.