Research On Control Of VSC HVDC By Use Of Inverse System Method

With the increasing rating and improved performance of self-commutated semiconductors, Voltage Source Converter (VSC) based on HVDC (VSC-HVDC) has been realized. VSC-HVDC has been attracted more and more attention for its favorable advantages. However, domestic study on VSC-HVDC is just at the beginning.In this dissertation, nonlinear controller of VSC-HVDC is studied. The transient mathematical model for the VSC-HVDC system ind-q synchronous reference frame is developed and a novel controller is designed. It is applied in the inverse system method based on nonlinear feedback linearization theory. An inverse system model of VSC-HVDC system is deduced and a pseudo linear system is constructed for the decouple control system of the active and reactive power. Finally, by synthesizing the pseudo linear system, the controller with Sliding mode variable structure control and limiting point disposition is proposed. Furthermore, as an essential problem in nonlinear feedback linearization, the implicit dynamics is researched in detail so that the stability of the control system is guaranteed.In this paper, the popular direct feedback decoupling control is introduced, and the double closed-loop controller based on the direct current control is designed. Then, it is compared to the controller by use of inverse system method. The simulation results show that dynamic response characteristics of the controller by use of inverse system method are significantly better than the double closed-loop controller. The model of VSC-HVDC system is mandatorily linearized by use of inverse system method in the former, in order to achieve the global linearization and ensure the system stability in a wide area. The controller can quickly and accurately make the system return to the desired steady-state operating point with the large disturbance.