Observer Pre-Synchronization for Smooth Transition in Wide-Speed-Range Sensorless Control of IPMSM Drives

To reduce transition disturbances in wide-speed-range sensorless control of interior permanent magnet synchronous motor (IPMSM) drives, this paper proposes an observer pre-synchronization method for the transition between a low-speed high-frequency-injection (HFI) estimator and an active-flux observer used in the medium- and high-speed regions. The HFI estimator maintains position observability at standstill and low speeds, whereas the active-flux observer estimates rotor position and speed at higher speeds while accounting for IPMSM saliency. However, when the active-flux observer runs in the background at low speed, its estimated angle may not be sufficiently aligned with the HFI-estimated angle before the transition, which can cause angle discontinuities and speed fluctuations. To reduce this initial angular mismatch, the HFI-estimated rotor position is used to construct a reference active-flux vector and correct the observer state before the transition interval. A speed-dependent sigmoid weighting factor is then introduced to smoothly blend the two estimated angle vectors and scale the HFI voltage amplitude during the transition. The paper first establishes the HFI and active-flux estimation models, then formulates the observer pre-synchronization and smooth-transition strategy, and finally validates the proposed method experimentally. Experimental results show that the proposed method improves the alignment between the two estimators before the transition and reduces angle and speed transients, thereby improving transition smoothness in the IPMSM sensorless drive.