Disturbance Suppression Discrete Integral Sliding Mode Current Control of Experimental Advanced Superconducting Tokamak Fast Control Power Supply

The primary performance of the fast control power supply for the experimental advanced superconducting Tokamak (EAST) is to quickly track the reference signal, realize the excitation of the load coil, and feedback control the vertical displacement of the plasma. The load coil of the EAST fast control power supply is affected by the internal components and the plasma in the vacuum. The coil inductance will fluctuate slowly in a small range, and there will be mutual inductance electromotive force interference on the coil. The traditional proportional-integral (PI) control has shortcomings in the current tracking control process. Sliding mode control has been widely used due to its advantages of simple control and strong robustness. To realize disturbance suppression and cope with load fluctuation, a discrete integral sliding mode control method with disturbance suppression is proposed based on the system state equation of the EAST fast control power supply. The control disturbance caused by inductance fluctuation and mutual inductance electromotive force on the load side is equivalent to lumped disturbance. The observation of lumped disturbance is realized using a sliding mode disturbance observer. In order to compensate for the lumped disturbance on the load side, a discrete integral sliding mode controller and a sliding mode disturbance observer are combined to perform feedforward compensation control. A variable gain observer structure is designed based on the observed current error and the tracking current error to balance the chattering magnitude and convergence speed in the sliding mode control process. Thus, the gain is adaptively adjusted with the observed current error. According to the observer error stability conditions, the adaptive adjustment range of the observer gain is determined. The stability of the designed sliding mode controller is analyzed to ensure sufficient convergence of the sliding mode controller. A novel smooth saturation function is designed to address insufficient chattering suppression of traditional symbolic and linear saturation functions in sliding mode control. By analyzing the gain characteristics and convergence time characteristics of different saturation functions, the designed new smooth saturation function with continuous differentiability in the full definition domain and great switching gain is demonstrated to provide a faster overall convergence rate. Combined with a gain adaptive disturbance observer, the proposed new smooth saturation function can achieve rapid convergence and further chattering suppression of the control system. Simulation and experimental results show that the proposed control method has better current tracking characteristics and faster dynamic response than traditional PI control under small output current overshoot. It has outstanding disturbance rejection performance, current tracking performance, and strong robustness. As a result, accurate excitation of the coil inductance can be achieved to ensure vertical displacement closed-loop feedback control of the plasma, even considering load side disturbance. © 2024 China Machine Press. All rights reserved.