Steady-State Characteristics of a Loop-Type Multi-Terminal HVDC Transmission System for Series-Connected Wind Power Plants

A line commutated converter based high voltage direct current (LCC-HVdc) system having a power compensator for series-connected wind power plants has been proposed. The system can control output active power and reactive power independently, and can supply high quality ac power without harmonic ac filters. The system can also be expanded to a multi-terminal system by connecting multiple wind power plants and onshore ac systems in series. The system has the advantages of eliminating dc circuit breakers and offshore substations. In this paper, steady-state characteristics of the loop-type multi-terminal HVdc system are investigated. A simulation model of the system is derived first. The steady-state characteristics of the system are calculated with the model, and experimental studies were carried out using a laboratory-scale experimental setup to confirm the validity of the model. It is shown that the system can properly supply the power from the wind power plants to ac grids by controlling the power flow (magnitude and direction) of the onshore substations.