Improved active disturbance rejection position control for PMSM based on cascade observers

• A cascade extended state observer was designed for motor disturbance. • A new type of nonlinear function was designed. • A cascaded state observer was designed to estimate external disturbances. To address the challenges of low positioning accuracy and poor disturbance rejection capabilities in permanent magnet synchronous motor (PMSM) position servo control systems, this paper proposes an active disturbance rejection control (ADRC) strategy based on cascade observers. The mathematical model of the PMSM is first established. Design a nonlinear function combining polynomial and trigonometric function to improve the nonlinear function, so that the function has continuity and smoothness at piece wise points, and the saturation function is introduced to improve the instability of the system in high error states. Designing cascaded state observers to estimate external perturbations, ESO1 makes an initial observation of the perturbation, and ESO2 observes the perturbation observed by ESO1 as a known part of the remaining perturbation, double estimation is achieved to reduce the observation error. The results prove the effect of the improved nonlinear function and the cascade state observer. At the same time, it is proved by comparison that the proposed control strategy has better control accuracy, response speed and robustness than PI control, ADRC control, MADRC control and NADRC control.