To solve the problem of the slow convergence rate of the reaching law and the chattering problems in the dynamic response in the sliding mode control, an improved double-power sliding mode reaching law is proposed. The reaching law is adjusted by changing the magnitude of the power terms adaptively at different stages of the system approach process, and the convergence speed of the dynamic response process is greatly improved. Its existence, accessibility and stability are proven by theory. The simulation results show that the improved double-power reaching law is faster than the double-power reaching law and the fast power reaching law. When there is uncertainty in the system, the system state and its derivatives can rapidly converge to the neighborhood of the equilibrium zeros. In the presence of time-varying perturbations of the two-order system, the sliding mode control system based on the improved double-power sliding mode reaching law has higher tracking precision of the given signal and differential signal and effectively reduces the high-frequency chattering phenomenon of the control input signal.

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This paper proposes a generalized design procedure for the extended state observer (ESO) based sliding mode control for voltage source converter (VSC) station. In this work, the non-linear loads and external disturbances and parameter perturbations of converter station is considered as an external disturbances which are bounded. The ESO is designed to reject the external disturbances which include not only the unmeasured system states but also the modeling uncertainties. At the same time, the nonsingular terminal sliding mode (NTSM) control method based on ESO is proposed to solve the problems of slow dynamic response of output voltage and high waveform distortion rate in converter station. The proposed control method is validated through numerical simulations shows a closed-loop dynamics and better transient performance, and the controller can effectively suppress the differential peak values of active power, reactive power and DC voltage in the initial stage of system start-up. Under the conditions of non-singularity of the controller, the influence of system disturbances on the chattering of the controller is effectively eliminated and the robust performance of the system is enhanced.. INDEX TERMSExtended state observer (ESO), Converter station, Nonsingular terminal sliding-mode control (NTSMC), Uncertain disturbances