Comparison of Torque Control in Flux Weakening Region Under Square-Wave Operation for Sensorless PMSM Drives

This paper analyzes the effect of position estimation errors on torque control for permanent magnet synchronous motors (PMSMs) in flux weakening (FW) region. In sensorless control systems, non-ideal factors such as parameter variation, inverter nonlinearity, and signal noise can introduce position estimation errors, which lead to significant deviations between the actual and commanded torque, particularly in high-speed operation where FW control is required. A graphical approach is adopted to evaluate the impact of position errors on various FW control strategies under square-wave operation, which is commonly used at high speeds for its simplicity and efficiency. Furthermore, torque deviation curves for different methods are derived, enabling direct comparison between actual and reference torque. Simulation results confirm the accuracy of the proposed analysis, highlighting the relative robustness and sensitivity of each method to position estimation errors.