A Stability Condition on Nominal System Recovery of PMSM Against Mixed Uncertainties Using a Full-Order Load Torque Observer

Abstract

Since the feedforward compensation using a load torque observer for permanent magnet synchronous motor (PMSM) has been widely used so that an outer feedback loop controller can be designed independently by considering only the nominal plant model, this paper presents an explicit theoretical analysis on the robust performance based on the singular perturbation theory. Unlike the previous result on a reduced-order load torque observer, a stability condition as well as a new coordinate transformation for the boundary-layer system is found out to obtain the desired quasi-steady-state model that equals to the nominal PMSM equation. When the observer gains satisfy the stability condition for the boundary-layer system, as the observer poles are placed sufficiently left of the complex plane, the disturbance observer-based compensation can recover the nominal system characteristics without accounting for model uncertainties that include external disturbances as well as some model parameter uncertainties. Computer simulations verify the disturbance estimation performance against variations of parameters and the disturbance.