An Improved Sliding Mode Observer for Sensorless Control of Open-Winding Permanent Magnet Synchronous Motor

To address zero-sequence current interference and parameter sensitivity in sensorless control systems of open-winding permanent magnet synchronous motor (OW-PMSM) with a common DC bus, this paper proposes an improved sliding mode observer-based sensorless control strategy. First, in the sliding mode observer (SMO), a novel continuous function replaces the traditional signum function. The SMO dynamically adjusts the reaching law via adaptive weight coefficients to suppress chattering, eliminating the need for low-pass filters. Second, the improved SMO estimates fundamental and third-harmonic back electromotive force (EMF), using the third-harmonic back-EMF estimate directly as compensation voltage to mitigate zero-sequence currents. Finally, a fusion-weighted algorithm enhances the robustness of rotor position estimation across the full speed range. Simulation results validate that the proposed improved SMO effectively reduces chattering in conventional SMO and provides accurate rotor position estimation for OW-PMSM over the entire speed range.