Stability Analysis of PI-Controller-Type Position Estimator for Sensorless PMSM Drives in Flux Weakening Region

This paper analyzes the stability of sensorless permanent-magnet synchronous motor (PMSM) drives, which adopts the proportional-integral (PI) controller-type position estimator. Due to the limited bandwidth of the angle estimation, the sensorless position estimator can cause a transient angle error, leading to a torque discrepancy between the reference and the actual value. This phenomenon can be more severe in the flux weakening region. If this torque error is not damped sufficiently through the shaft inertia, the rotor angle would also oscillate. Unless the position estimator provides a sufficiently fast dynamic performance to follow the trembling rotor shaft, the system may lose stability. This paper calculates the required minimum bandwidth of the position estimator to ensure control stability. The analysis is verified through the simulation and experimental tests.