The Research On HVDC And SVC Nonlinear Control For Improving Power System Stability

In recent years,more and more regional power grid using high-voltage AC and DC lines for large-scale interconnection,and the stability of power grid becomes more and more important.High Voltage Direct Current(HVDC)and Static Var Compensator(SVC),as important parts of the large-scale interconnected power grid,can be used to design suitable controllers to improve the power grid stability.The power system is a nonlinear system.The additional controller designed by the traditional linearization method is based on the approximate linearization model near the equilibrium point.It has unavoidable limitations when the deviation is far away from the equilibrium point.Therefore,it is of great theoretical and practical significance to study the nonlinear control of HVDC,the nonlinear control of SVC,and the coordinated nonlinear control of HVDC and SVC to improve the stability of power system under disturbance.In this thesis,a HVDC nonlinear controller based on synergetic control theory is designed for the difficult modeling and strong nonlinearity of large-scale AC-DC hybrid networks firstly.A multi-machine system that contains HVDC detailed model is built in PSCAD.Compared with the traditional HVDC controller based on pole-placement method and sliding mode control,the simulation results show that the proposed controller can restore stable operation of the power system faster under disturbance,which verifies the effectiveness and superiority of the controller.Secondly,as for the traditional SVC can only improve the voltage stability of the installation point but lack of effective damping for the system characteristics,a nonlinear controller is designed based on synergetic control to improve the system damping and voltage stability.The multi-machine system model that contains SVC is built in PSCAD,and the simulation results show that the controller can quickly suppress the oscillation of the system after the fault,and the voltage can also be restored more quickly,which verifies its superiority in maintaining voltage stability and damping interval oscillation.At last,as for there are interactions between HVDC and HVDC,SVC and HVDC.A coordinated damping controller for HVDC and SVC is designed based on synergetic control theory.A multi-HVDC feed system model with SVC is built in PSCAD,and the simulation results show that the controller can effectively coordinate the control between HVDC and HVDC,SVC and HVDC to improve the stability of the system.