Uncertain Nonlinear System Higher-order Sliding Mode Control And Its Application In Power System

It is widely regarded as a prospective field to study sliding mode control for uncertain nonlinear system.However,the problems of chattering and relative degree restrict the development and application of conventional first-order sliding mode.Higher-order sliding mode is suitable for system with arbitrary relative degree,and the sliding accuracy is high and chattering is small.Higher-order sliding mode is a research focus of sliding mode control in recent years.It is of great theoretical significance to study higher-order sliding mode algorithm to solve finite time control problem of SISO and MIMO uncertain nonlinear system.Simultaneously,with rapid development of modern power system and explosive growth of wind power generation in new energy power system,there are some important application values to enhance power system stability,achieve maximum wind power tracking of wind power system and improve the efficiency of wind power by designing advanced control method.Therefore,this paper studies novel higher-order sliding mode algorithms for several classes of uncertain nonlinear systems,designs higher-order sliding mode excitation control strategy and maximum wind power tracking method based on existing research results of higher-order sliding mode algorithm,power system stability control and maximum wind power tracking of wind power system.The achievements of this paper further extend higher-order sliding mode control method for uncertain nonlinear system;enrich the application range of higher-order sliding mode control and provide new methods for improving power system stability and maximum wind power tracking.In this paper,the innovative achievements mainly include the following aspects:(1)For the finite time stability problem of a class of higher-order SISO uncertain nonlinear system,a novel adaptive gain continuous higher-order sliding mode control method is proposed.Homogeneous continuous control law is employed to achieve finite time convergence of nominal part.Super-twisting algorithm with adaptive switching control gain is designed to conquer uncertainty for the condition when first derivative upper bound of system uncertainty is unknown.The possible minimum switching control amplitude is achieved.The system control effect is continuous and chattering phenomenon is greatly weakened.(2)Continuous higher-order sliding mode control method with adaptive control gain is proposed for a class of SISO uncertain nonlinear system.Sliding mode control problem for uncertain system is converted to finite time stability problem of higher-order uncertain integrator chain.The designed virtual control law is composed of two parts after imposed state feedback.One part realizes finite time stability of nominal system and the other part achieves system robustness by super-twisting second-order sliding mode.The adaptive laws are designed for the two control parameters of super-twisting algorithm to deal with the case without the knowledge of upper bound of system uncertainty.The higher-order sliding mode control for the uncertain system is finally achieved.(3)A continuous higher-order sliding mode control method for a class of MIMO uncertain nonlinear system is proposed.The MIMO system higher-order sliding mode control is accomplished via the conversion to finite time stability problem of multivariable uncertain systems.A finite time continuous control law is employed to achieve states convergence rapidly and a non-decoupled super-twisting algorithm is proposed to overcome uncertainty and achieve system robustness.The control inputs for the MIMO system are continuous and chattering is greatly restrained.(4)For enhancing power system stability,excitation control strategies based on continuous higher-order sliding mode are proposed.A continuous higher-order sliding mode excitation controller for single machine infinite bus power system is designed to improve stability under small perturbation and large perturbation.Considering system uncertainty of multi-machine power system,interconnection between each generator is viewed as the disturbance to specific sub-system.The decentralized higher-order sliding mode excitation strategy for multi-machine system is proposed.Adaptive control parameters are also designed to handle system uncertainty with unknown upper bound.Multi-machine system transient stability is substantially improved.The continuous effective of excitation voltage and power system robustness are achieved.(5)A control scheme for maximum wind power tracking and reactive power regulation of double-fed wind power system is proposed based on variable gain high-order sliding mode.The reduced-order model of double-fed wind power system is deduced.Optimal torque tracking and reactive power regulation are achieved by controlling rotor voltage in dq axis based on second-order sliding mode.The adaptive laws for rotor voltage control parameters are constructed to solve the case when the uncertain parameters such as network voltage,frequency,rotor resistance and coefficient of mutual induction have unknown upper bound.