An Optimal Control Strategy for Permanent Magnet Synchronous Motor-driven Three-cylinder Reciprocating Pump

Abstract

Three-cylinder reciprocating pumps present typical periodic load characteristics, which result in obvious speed fluctuation, current distortion, and poor operation stability of the driven Permanent Magnet Synchronous Motor (PMSM). Conventional PI control is incapable of handling periodic disturbances effectively. This study aims to propose a high-performance composite control strategy to improve the speed control performance and system stability of the PMSM drive system. This paper proposes a composite control strategy that integrates a disturbance observer (DOB) with fuzzy PID. The novelty of this method lies in the introduction of the RLS algorithm to perform online identification of key motor parameters (such as magnetic flux), with the identification results fed back into the DOB in real time, thereby significantly improving the observation accuracy of time-varying load torque. Second, feedforward compensation is implemented based on the observed load torque; simultaneously, fuzzy PID is employed for online adaptive tuning of the speedloop parameters. This forms a coordinated control system comprising online parameter identification, precise disturbance observation, rapid feedforward compensation, and fuzzy online control, thereby fundamentally resolving the issue of speed instability under periodic loads. The proposed composite control strategy effectively suppresses speed fluctuation caused by periodic load torque ripple. Compared with traditional PI control, the amplitude of speed fluctuation is reduced by more than 92%. The system exhibits faster dynamic response, smaller overshoot, and higher steady-state control accuracy under various speeds and load conditions. Periodic load torque causes motor speed fluctuation. DOB provides accurate disturbance compensation, and fuzzy PID enables adaptive parameter tuning. Their combination delivers better control performance than single methods alone. The composite control strategy combining DOB and fuzzy PID significantly improves speed control performance and operation stability of PMSM driven by three-cylinder reciprocating pumps. It provides a reliable and practical control scheme for high-performance drive systems of reciprocating pumps and can be extended to other industrial applications with periodic load disturbances.