Cascade motion control with synchronised saturation

Abstract

This paper introduces an innovative motion control scheme tailored for traction systems, employing a cascade PI controller architecture. The internal loop regulates speed, and the external loop generates the necessary speed setpoint for position control. Two feedforward actions are strategically implemented in each loop to address potential disturbances and optimise overall performance. An inherent challenge in cascade control systems is the phenomenon known as windup, where integral components accumulate errors due to persistent disturbances or sudden changes in position reference. In order to mitigate this phenomenon, a control approach which integrates corresponding saturations for each loop and ensures synchronisation between them is developed. In this way, the external loop does not generate speed setpoints beyond physical thresholds during internal loop saturation. This strategic limitation prevents overly aggressive responses and eliminates undesired traction demands during saturation events. The proposed control scheme is validated through simulations that incorporate various disturbances, and the analysis of results confirms its suitability, showcasing improvements in the performance of such control schemes, especially in scenarios prone to windup.