Robust speed tracking of permanent magnet synchronous motor servo systems by equivalent disturbance attenuation

A new robust controller consisting of a nominal controller and a robust compensator is proposed. The controller is applied to a permanent magnet synchronous motors servo system to eliminate speed-tracking error due to time-varying load torque uncertainty and parameter perturbations. It is proved that the speed-tracking error can be made as small as desired if the initial conditions are zeros. For cases where the initial conditions are non-zero but bounded, after a finite transient period, the same speed-tracking error reduction can be achieved. Simulation results are presented to confirm the efficiency of the proposed method.