The Nonlinear And Variable Structure Control Of Converts In HVDC System

High voltage and Direct Current Transmission (HVDC) system is controllable highly, and a set of control system is the core technology of HVDC. Whether or not HVDC system can run normally is relative closely with the basic controller. Moreover, the additional controller also is the important guarantee to improve the stability of running in HVDC/AC.Firstly, 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.Secondly, when the big disturbance happens in HVDC system, the linear system after accurate linearization couldn't ensure the robustness of system. However the variable structure control 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 variable structure 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. The simulating results show: that basic controller can enhance effectively the stability of system at the big disturbance and exert the active action of HVDC between two AC systems in different frequency. Additional controller has stronger adaptability and robustness on the change of system parameters and the structure of power grid. Moreover, additional controller can regulate largely the transmission power on the HVDC lines and guarantee validly the stability of HVDC/AC. Comparing with nonlinear optimization controller in reference [16] by simulations, when the big disturbance happens, two nonlinear variable structure controllers, including basic controller and additional controller, can make the trajectory return the steady state more quickly.