2-Terminal hybrid HVDC cost effective alternatives for clearing temporary DC line faults

Abstract

2-Terminal Hybrid HVDC consisting of a Line-Commutated Converter (LCC) in the sending end, and a Voltage Source Converter (VSC) in the receiving end, can be seen as a compromise between cost, loss and performance. A Hybrid system has lower cost and somewhat lower losses than a pure VSC HVDC system. Yet it is able to provide reactive power support and black start capability at the receiving end, which a pure LCC system simply cannot. The focus of this paper is DC fault handling. Two ways of clearing DC faults are investigated and compared, namely AC breaker and Diode. Improvements to the AC breaker alternative are made, which lowers transient DC overvoltage. Two control modes are also compared, namely LCC controlling current, and LCC controlling voltage. It is shown that both control modes are feasible, during steady state operation and also during transients.