Abstract：Permanent magnet synchronous linear motor (PMLSM) has excellent control accuracy and response speed. It is widely applied in automatic control systems, automatic precision machine tools, and other occasions. However, due to its structure, PMLSM has thrust ripples, which can cause vibration and noise, greatly affecting the control accuracy of the motor drive at low speeds. The detent force is the main cause of thrust ripples, containing end and cogging forces. This paper proposes a thrust ripple suppression strategy based on the proportional resonant internal model extended state observer (PR-IMESO) to improve system performance and control accuracy. Firstly, thrust ripples are modeled and analyzed, and cogging force and end force models are established. Then, the detent force model, a function of mover position with motor pole distance τ as the period, is obtained. Its frequency is twice the frequency of the primary winding phase current. Aiming at the large detent force in thrust ripples, the internal model expanded state observer is studied, considering the detent force model to compensate for the detent force and other unmodeled thrust ripples in real-time. In addition, a resonant term is introduced into the observer to enhance the compensation ability of the fixed frequency detent force. The observer is designed according to the motion equation of PMLSM considering various thrust disturbances, and parameters are adjusted by the observer bandwidth. Finally, simulation and experiment are carried out. Set the motor running speed to 0.06 m/s and load tension to 10 N. According to the simulation results, the amplitude of velocity fluctuation with the PR-IMESO suppression strategy attenuates to 3.4% of the amplitude of velocity fluctuation, and the suppression rate is 96.6%. It is theoretically verified that the proposed strategy has a significant suppression effect on the detent force with a secondary fluctuation frequency. Further, the experiment is carried out with a 750 W PMLSM experimental platform. The PMLSM thrust ripple suppression strategies based on ESO, IMESO, and PR-IMESO are verified under the motor speed of 0.03 m/s, 0.0 6m/s, no-load, load 2 kg, 3 kg, and 4 kg. The velocity fluctuation significantly decreases with the proposed strategy. The suppression rate can reach up to 73.5%, and the average suppression rate is 68.7%. In addition, the dynamic performance of the PR-IMESO thrust ripple suppression strategy is demonstrated in the sudden loading of 4 kg. Great fluctuations of the mover velocity before and after the sudden loading exist without a suppression strategy. After adding the proposed strategy, the fluctuation of the mover velocity is significantly reduced during the whole motion process. In the process of sudden loading, the transition of the velocity error and Q-axis current is smooth and rapid. The average suppression rate of the mover velocity fluctuation is 68.7%.
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2024, Vol. 39 
