Research On Robust Control Of HVDC System

High voltage direct current transmission technology (HVDC) is suitable for power transmissions of large capacity and with long distance, in recently years, it gets a rapid development in our country. HVDC power transmission system is a highly controllable nonlinear control system. It's operating conditions change at any time, and the location, type and severity of disturbance is stochastic, besides, the converters have unmodeled dynamics. These factors make the traditional controller for HVDC based on the classical control theory cannot meet the requirements in practice. So, It is of practical significance both at home and abroad how to design a better stability robust controller to improve its performance and enhance the operating stability o f AC system connected as well.Firstly, This paper introduces the structure and mathematical model of HVDC system, on this basis, the paper analyzes both the principle and performance of main control accommodation mode for HVDC system, and then gives the HVDC system the control theory of based control and additional control.Secondly, state-feedback and accurate linearization is adopted for the linearization of the nonlinear mathematic model of HVDC system. This way turns the synthesis problem of the complicated nonlinear system into the synthesis problem of simple linear system. For the nonlinear system, linear system after accurate linearization can reflect the primary nonlinear system truly. Then, this linear system will be transformed to a uncertainty system with unmodeled dynamics and bounded disturbances, and transformed into the standard Hoo problems to design the robust controller. However the Hoo controller has the strong robustness on the perturbation and the disturbance of system. This thesis is based on the work of anterior researchers and combines accurate linearization with H∞robust control to design the basic controller and additional controller.Finally, the new CIGRE HVDC standard model is chose as the simulation model of the basic controller. This thesis Simulates the designed basic controller and additional controller in MATLAB. Comparing to the nonlinear optimization controller, the results of the simulations show that the proposed controller is effective. It has a robust dynamic performance with a strong capability of restraining unmodeled dynamics and bounded disturbances. The transient and static characteristic of HVDC system has been effectively improved with good robustness.