Research on steady state control strategies of wind farm integration by VSC-LCC hybrid HVDC transmission

Abstract

Wind farm is integrated by a hybrid high voltage direct current (HVDC) system with line commutated converter (LCC) and modular multilevel converter (MMC). Power sources at the sending end include wind farm and AC system, which can complement each other. Basic control strategies of each converter of the system are proposed. Considering the capacity limitation of MMC, basic control strategy under fluctuating wind power is made and the system is not able to transmit rated power under the strategy when the wind power is low. In order to enlarge the range of wind power when the system can transmit the rated power, an improved control strategy that lower the voltage of MMC is devised. Under the improved strategy, performance of the system is improved. Operation characteristics are compared under different short circuit ratio (SCR) of AC system at the sending end, and additional control is introduced when SCR is low.