A Synergetic Control Scheme for HVDC Transmission System

HVDC power transmission system is a typical time varying system with many nonlinear relationships among different variables, it is difficult for the conventional PI controller to work effectively for large changes in the operation. In this paper, the synergetic control theory is discussed, and a nonlinear controller based on such theory is proposed for the HVDC power transmission system, in which a constant DC current controller for the rectifier and a constant extinction angle controller for the inverter are designed respectively. Details of design for such control scheme are also given in the paper. In order to verify the effectiveness of the proposed control, the performance the proposed control scheme in the CIGRE benchmark DC transmission system is simulated with PSCAD/EMTDC. The simulation results show that the proposed control works effectively in the start-up process as well as in the conditions when the operation mode shifts for the HVDC system.