Sensorless Control of Permanent Magnet Synchronous Motor Based on Variable Gain Load Torque Observer

The conventional sensorless control strategy based on a sliding mode observer (SMO) leads to considerable deviation between the estimated and actual rotor positions under sudden load changes. The deviation causes instability in the motor. In order to address this issue, a sensorless control strategy for permanent magnet synchronous motors (PMSM) based on variable-gain load torque observer (LTO) is proposed in this paper. The presented method improves rotor position estimation accuracy under sudden load variations while effectively reducing chattering. The first step in this approach is to implement a hyperbolic tangent function with a variable boundary layer. This designed function replaces the switching function in the sliding mode observer. Next, a load torque observer with a variable feedback gain is designed, and the influence of the gain parameter <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> on estimated speed and position error is analyzed to trace the suitable value. Finally, simulations and experimental results confirm the feasibility and effectiveness of the proposed method.