Study On The Nonlinear Control For Power System Based On Fixed-time Method

In recent years,with the continuous expansion of power system scale,especially the extensive use of large capacity units,as well as the emergence of long-distance,ultra-high voltage and high-power transmission systems,which makes the transmission system become economical and efficient,but at the same time it makes the structure and operation mode of the power system more complicated,which brings many serious problems that affect the safe and stable operation of the system.Therefore,it is necessary to study the subject of stability control of power system.In the thesis,based on the control problem of power system,three sub-problems are studied separately: SVC control,steam turbine valve opening control and and coordinated control of SVC and steam turbine valve opening.Aiming at the control problem of single machine infinite bus system with SVC,the working and control mechanism of SVC is firstly analyzed,and the mathematical model of single machine infinite bus system with SVC is established.Secondly,considering the difficulty of accurate measurement of generator damping parameters,the influence of power system disturbances and the shortcomings of traditional control algorithms in increasingly complex practical production,this paper designs an improved SVC stabilization controller and the adaptive damping parameter replacement law by improve adaptive terminal sliding mode control based on fixed-time control,which is based on adaptive control theory,terminal sliding mode theory and fixed-time control method.Finally,the simulation results show that the designed SVC stability controller has good control performance when the power system is disturbed suddenly,which ensures the stable operation of the power system.In order to solve the control problem of single machine infinite bus system with valve opening control,an adaptive fixed-time terminal controller is proposed in this paper.Firstly,aiming at the non-linearity of power system,the back-stepping method is used to retain the non-linearity of the system.,the Lyapunov function is selected step by step,so that the adaptive damping parameter replacement law is calculated,which has strong robustness to uncertain damping,and in the last step,the control law of valve opening is designed by adding terminal sliding surface with fixed time term.Finally,the simulation results show that the proposed valve opening controller in this paper can quickly return to the stable position when the system is suddenly disturbed,and the overshoot is small,the anti-interference ability is strong,which ensures the safe and stable operation of the power system.Aiming at the problem that the performance of the SVC stability controller and the valve opening controller is not good enough when they are controlled separately,the coordinated controller of SVC and the valve opening based on adaptive fixed-time terminal sliding mode strategy is designed.In order to achieve the coordinated operation of the two controllers and promote each other,the SVC control law is obtained by introducing the virtual control method based on the calculation of valve opening control law.Finally,the simulation results show that the power system can quickly suppress oscillation under the action of SVC and valve opening coordination controller,and has strong robustness to uncertain parameters and external disturbances.It can achieve safe and stable operation.The control objectives are improved compared with those of the two controllers when they act alone.