The Research On Control Scheme For High Voltage Direct Current System Based On VSC

The technology of HVDC power transmission based on VSC which could be highly controlled had some successful applications in the power systems. But as a new technology, study in this field is not mature in our country. So the study in this field especially the immature control scheme is of great meaning in both theory and experience.Starting from the structure of single-phase circuit of VCS, this article briefly analyzed both the principle and control method of VSC-HVDC power transmission system. On that basis stable math model of the VSC-HVDC power system under given control scheme was deduced. Then the model is converted to a fully controllable linear model using state feedback and coordinate transformation in nonlinear system control theory. Last a nonlinear optimal control strategy is derived based on the optimal control theory of linear systems. Finally a new nonlinear controller is designed for VSC-HVDC systems.The state equation and output equation are obtained using linearization method on the basis of analyzing the hybrid transmission systems. Then an optimal control strategy is derived based on the structure restriction control theory of linear systems. Finally a new decentralized and coordinated controller is designed for hybrid transmission systems.Numerical simulations of the newly designed nonlinear controller and decentralized and coordinated controller are carried out by using the electromagnetic transient simulation software PSCAD/EMTDC. Simulation results show that the models using in the paper are feasible and the linearization method are efficient. Controllers can restore the system subjected to a disturbance or fault to normal state faster and better than the system with the existing controllers. It improves efficiently the dynamic performance of the hybrid transmission systems.