Closed Loop Stability of a PMSM-EKF Controller-Observer Structure

Use of Permanent Magnet Synchronous Motor (PMSM) has found many applications in the last few decades due to the advantages it offers. Speed/position control of PMSM is based on the vector control strategy which requires an accurate knowledge of rotor shaft position and angular speed in order to synchronize the phase excitation pulses with the rotor position. This information about the rotor position and speed is obtained by state estimation using Extended Kalman Filter (EKF) for sensor-less vector control drive. This paper presents the stability analysis of the closed loop controller-observer (PMSM-EKF) structure. To analyse the stability of the closed loop PMSM-EKF structure, the concepts from nonlinear control theory are employed. It is shown that the closed loop (PMSM-EKF) estimation error is within bounds and the system is Lyapunov stable. The simulation studies for a number of load torques are presented.