Control of multi-terminal DC transmission system based on voltage source converters

These paper discusses the control strategies that may improve the control of the power flow and power dispatch in voltage source converter based multi-terminal dc transmission systems. This is achieved by allowing the converters controlling the dc line voltages to participate in active power control using active power dc voltage droop characteristics. The paper also presents a recovery strategy that allows voltage source converter based multi-terminal dc transmissions to recover from ac faults with minimum voltage and current stresses on the converter switches. This is achieved by matching the power command to the actual power that can be transferred, as the voltage on the ac side collapses due to the fault or any major disturbance. The validity of these strategies are confirmed by simulation.