Variable structure model-following control for a servo motor system

A variable structure model-following controller is proposed in this paper. Only output from the plant is needed in the variable structure system (VSS) control law to enhance the robustness of the control system. The position control of a servo motor system using the proposed control strategy is illustrated. First, an integral-proportional (IP) position controller is systematically designed according to the prescribed specifications of the command tracking. Next, in order to allow the given specifications to be maintained under wide operating conditions, the state-space model of the systematically designed inner IP speed loop in the nominal case is chosen as the reference model. Then, the proposed controller based on VSS theory is designed and augmented to the inner speed loop to preserve the control performance. Simulation results show that the proposed control approach produces an accurate model-following characteristic and is robust with regard to plant parameter variations and external load disturbance.