Full-Speed-Range Sensorless Control for PMSM with VVVF Start-up and Sliding Mode Observer

Sensorless control technology for permanent magnet synchronous motors (PMSMs) has become a research focus due to its advantages of low cost, high reliability, and environmental adaptability. Among various sensorless methods, the sliding mode observer (SMO) has garnered significant attention for its fast response and simple structure. However, it suffers from inaccuracies in position estimation at low speeds, limiting its applicability in low-speed operations. In contrast, Variable voltage variable frequency (VVVF) control, as an open-loop strategy, enables low-speed startup without requiring rotor position information. This study presents a comprehensive sensorless control strategy for PMSMs across their entire operating range. The strategy comprises three key stages: First, initial reliable startup from standstill, achieved through an open-loop variable voltage variable frequency scheme. Second, a proposed smooth mode-switching strategy enabling low-chattering transition from VVVF operation to a sensorless vector control mode; Third, high-performance sensorless closed-loop operation in the vector control stage, utilizing the sliding mode observer for precise estimation of back-electromotive force (back-EMF) to extract accurate rotor position and speed information. Simulated results demonstrate that the proposed strategy facilitates smooth startup and stable sensorless operation for PMSM from zero to high speeds, validating its effectiveness and practicality.