Analysis of Instability in Torque Control of Sensorless PMSM Drives in Flux Weakening Region

This article analyzes the effect of angle estimation error on the sensorless torque control of the permanent-magnet synchronous motor (PMSM). The actual torque of PMSM may differ from the torque reference due to the angle error in sensorless control. Furthermore, this torque discrepancy can cause instability to the control system, especially in the flux weakening region. The instability is highly dependent on the gain setting of the controller and observer in the control loop. To mitigate the adverse effect of the angle error, a torque feedforward method considering the transient angle error is proposed. With the proposed torque feedforward method, the gain margin of the control loop can be enhanced without modifying the gain of the control system. The proposed method is verified through the simulation and experimental results.