Robust Continuous Sliding Mode Control for Manipulator PMSM Trajectory Tracking System Under Time-Varying Uncertain Disturbances

This paper focuses on a robust continuous sliding mode control (RCSMC) method for manipulator PMSM trajectory tracking system under time-varying uncertain disturbances. The main objective of this study is to improve the trajectory tracking dynamic response and disturbances rejection ability of the manipulator PMSM, and then the manipulator itself, by using the RCSMC method. The RCSMC method consists of two key parts: a terminal continuous sliding mode controller (TCSMC), and an extended state observer (ESO). The TCSMC has been demonstrated to have remarkable capabilities to reduce the chattering phenomenon caused by high frequency switching function in the conventional sliding mode control law, and reject the strong time-varying uncertain disturbances for PMSM velocity loops. However, the high control gain, which could lead high velocity steady state fluctuations, is needed. Therefore, an extended state observer is introduced to estimate the disturbances. The estimated disturbances are further used by the velocity loop controller as a kind of feed-forward compensation to reduce the gain of the TCSMC method. The stability of the PMSM trajectory tracking system with the RCSMC algorithm is guaranteed by the Lyapunov stability criteria. Simulations have been conducted to verify the performance of the proposed RCSMC algorithm. Finally, the proposed RCSMC algorithm is applied in a practical 6-DOF manipulator, and the experimental results exhibit the extraordinary robustness and capabilities in dynamic position tracking characteristics, velocity response and disturbances rejection.