Control of voltage source converter based multi-terminal DC grid under DC fault operating condition

Recently, Voltage Source Converter (VSC) based Multi-Terminal DC (MTDC) transmission systems have gained more attention. Compared to current source converter technology, voltage source converters have several benefits including higher power quality, lower power transmission losses, and higher voltage capability. Flexibility in bidirectional power flow control is the main advantage of voltage source converters in large scale MTDC power transmission systems. However, VSC based MTDC transmission systems are vulnerable to DC side fault, and expensive DC circuit breakers are required to protect them against DC fault. This paper proposes a control method of a dc fault resilient voltage source converter that has ultra-fast electronic isolation capability following dc fault which can be protected against dc fault without using expensive DC circuit breakers. In this paper, the control scheme of MTDC grid based on droop control method with dead-band controller is proposed. The appropriate control algorithm of VSC based MTDC transmission system for DC fault operation and recovery after DC fault is also proposed. Finally, PSCAD simulation results are presented to evaluate the dynamic performance of VSC based MTDC grid with the proposed control algorithm under DC fault operating condition.