Start-up and shut-down strategies of hybrid LCC/VSC DC grids

The line commutated converter based high-voltage direct-current (LCC-HVDC) technology has been widely used for transferring bulk power over long distances in the past decades. In recent years, the voltage level and power capacity of voltage source converter (VSC) based HVDC technology have experienced a great development which provides a possibility of building hybrid LCC/VSC dc systems. In this paper, a four-terminal hybrid LCC/VSC dc grid with two LCCs as the rectifiers and two VSCs as the inverters is proposed. The start-up and shut-down control strategies of this hybrid systems have been proposed with the consideration of the inherent characteristics of the two technologies. The proposed strategies can mitigate the voltage spikes and current surges during the start-up and shut-down processes. The proposed dc grid model and control strategies are developed and validated in PSCAD/EMTDC