Application Of Nonlinear Control Theoretic In HVDC System

In our country, the distributing of resources and loads is asymmetrical. With the development of electric power industry, it is a challenge for long distance power transmission. "Interconnection in the whole country, transmission electric power from West to East and exchange electric power between South and North" is the developmental stratagem in whole grid in future. High voltage direct current (HVDC) transmission systems, which are fit for transmission electric power in long distance and large capability, can be widely applied in our country.HVDC is high controllable. The control system is the core of DC transmission system. The performance of its basic controller decides the operation condition of HVDC system. For improving the system stability in AC/DC system, the additional controller is very important. This paper focuses on the applying of the nonlinear control theory in HVDC control system. The main method is feedback linearization in the nonlinear systems, combined with the control theory in linear system. New basic controller and additional controller are designed in this paper.In chapter 4, a basic controller of HVDC is designed. For the voltage problem at the inverter, this paper adopts the constant reactive current control at the inverter, which is different from the traditional control method. The constant reactive current control can adjust reactive power consume at the inverter and improve the voltage stability. Based on feedback linearization in the nonlinear systems and Variable-Structure control theory in the linear system, a new nonlinear basic controller is designed. The effectiveness and superiorities of new controller have been testified through simulation.In chapter 5, considering an AC/DC system that includes two DC lines. Based on feedback linearization in the nonlinear systems and linear quadratic optimization control theory in the linear system, two new nonlinear additional controllers are designed in the same time. Simulation results show that the controllers can improve the stability of AC/DC system.