Non-overshooting PI control of variable-speed motor drives with sliding perturbation observers

This paper describes the design of a non-overshooting proportional-integral (PI) controller with pre-assigned initial integral state and perturbation compensation for variable-speed motor drives. According to the requirement of non-overshooting output response and the specified settling time in tracking a step reference signal, the PI gains and the initial integral state are determined systematically. The proposed PI controller design provides continuous control signals even when the nominal system is subject to sudden set-point changes, implying smooth system performance. To compensate for the system perturbation resulting from parameter variations and unknown disturbances, a sliding perturbation observer is proposed and integrated into the PI-controlled system. The perturbation-estimation process, consisting of an integral action and a low-pass filtering, does not require a switching gain with its magnitude larger than the absolute value of system perturbation. Moreover, since the sliding mode exists in the observer during an entire response, the estimation process is fast and active from the very beginning of the system operation while the chattering problem in control is alleviated. The usefulness of the proposed design is demonstrated through experimental studies.