An improved equivalent-input-disturbance approach for PMSM drive with demagnetization fault

Closed-loop torque control system of permanent magnet synchronous motor (PMSM) drive is highly applied in industrial applications. However, high temperature and other external factors lead to permanent magnet (PM) demagnetization fault of the motor, which inevitably brings barriers to precise torque control. This paper presents a rejection method for demagnetization based on an improved equivalent-input-disturbance (EID) approach. A system model, which contains demagnetization fault, is first constructed. Then, an equivalent-input-demagnetization on the control input channel is used to describe the model. An improved EID approach is designed to reject the effect of the demagnetization fault. In particular, an improved sliding-mode observer rather than the Luenberger observer in a conventional EID theory is designed to estimate the equivalent-input-demagnetization. This greatly enhances the response speed and accuracy of the estimation and rejection, and then effectively improves the accuracy of torque tracking. Finally, the step change and the ramp change of a demagnetization are introduced into a hardware-in-the-loop experiment, separately. Comparisons with other methods show the effectiveness of the method.