A Current-Sourced Converter-based HVDC Light transmission system

HVDC Light, which uses fully controllable switches rather than thyristors in its converter stations, has several advantages over standard HVDC. It allows reactive power to be controlled, reduces the size of filter and smoothing components required, and responds faster to changes in reference signals. To date, all HVDC Light implementations have been based on Voltage-Sourced Converters (VSCs). Until the recent invention of non-punch-through IGBTs, IGBT-based Current-Sourced Converters (CSCs) required series diodes to provide reverse voltage blocking, resulting in increased cost and losses. With this problem overcome, there are some advantages to using CSCs in HVDC. As in STATCOMs, the control of reactive power with CSCs is simpler and faster because reactive current can be controlled directly. Also, since the smoothing element and feedback paths of CSC-based HVDC systems are similar to those of conventional (thyristor-based) systems, properly-sized CSCs could be used to replace thyristor converters in existing HVDC implementations. In this paper a CSC-based HVDC system is designed and simulated using PSCAD/EMTDC. It is shown through simulation results that the system operates as desired in various forward and reverse power transfer conditions, as well as during a DC fault.