Research on high frequency injection technique without filtering for redundant polarity identification of PMSM

To address the challenges of permanent magnet synchronous motors relying on filters for rotor position observation at zero and low speeds, and the susceptibility to misjudging initial magnetic pole polarity, a filter-free square wave high-frequency injection method incorporating a redundant polarity identification strategy was proposed. By establishing a mathematical model for this method, the extraction of high-frequency current signals and the mechanism of rotor position calculation are clarified, and a corresponding redundant polarity identification process is designed. Simulation and experiments were conducted to verify the performance of the proposed method in rotor angle tracking, speed tracking, and polarity identification. The results show that this method effectively integrates filter-free square wave injection and redundant polarity discrimination mechanisms, enabling reliable initial rotor position positioning and magnetic pole polarity discrimination, ensuring accurate acquisition and real-time tracking of rotor position and speed information at low speeds. The scheme proposed in this paper provides an effective solution for the sensorless stable operation of PMSM within the zero and low-speed range, combining theoretical significance with engineering application value.