Practical robust stabilization of PMAC servo drive based on continuous variable structure control

In the paper, the two stage control design of a high performance PM AC servo drive is described. In the first stage, the nominal PM AC motor model is discussed as an analytical nonlinear system, transformed into the controllable canonical Brunovsky´s form on the basis of input-output linearization. The influence of the load torque is considered implicitly by introducing the disturbance observer. Due to the sensitivity of the nominal model-based control to parameter perturbations the linear tracking control is extended in the second stage by a continuous variable structure stabilizing control derived from Lyapunov´s function of the augmented feedback system. The design of the variable structure control requires no knowledge of the upper bounds of the perturbation function; instead, it considers the variable bounds of the available control signal. Undesired chattering of states and controlled variables are excluded. The introduced two stage control design assures practical robust stabilization for the class of bounded nonlinear perturbations satisfying the matching conditions without affecting the relative degree of the feedback system. Experimental results of the proposed PM AC servo drive control are also presented.