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.

No abstract

No abstract

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

No abstract

In view of smooth trajectory generation for a 3-axis machine tool, many methods have been presented. Among them, the optimal control based method is increasingly concerned, because it is considered to be able to make full use of kinematic abilities of machine tools. Under the unified framework of optimal control, the feedrate can be adjusted flexibly by adding or removing axial constraints and tangential constraints. But the problem of smooth trajectory generation (PSTG) based on optimal control for a machine tool is not easily to be solved. In this paper, to efficiently solve the PSTG, it is divided into two sub-problems: the problem of minimum time trajectory planning (PMTTP) and the pseudo problem of smooth trajectory generation (PPSTG). Since both sub-problems are convex, the existence of unique solutions can be guaranteed. Then, the PMTTP and the PPSTG are transformed into nonlinear programming (NLP) problems with radau-pseudo-spectral (RPM) method successively. Due to convexity, the two NLP problems can be efficiently solved with mature optimization methods. In addition, the RPM method allows two sub-problems to have different Legendre-Gauss-Radau (LGR) points, thereby further saving computational costs. Finally, three different predefined paths are employed to test the proposed method, and simulation results show the effectiveness of proposed method.

No abstract

No abstract