Effects of dc voltage control strategies of voltage response on multi-terminal HVDC following a disturbance

The advantages of an HVDC grid are the possibility of transporting large amount of power over long distances and the possibility of trading energy among different ac systems. This paper shows the effects of dc Voltage control strategy on the dynamic behavior of bus voltages at multi-terminal HVDC following a system disturbance. Two different dc voltage control method are simulated in this paper: voltage margin method and voltage-droop method. Time-domain simulations on simple test system using DigSILENT ® PowerFactory TM are used to evaluate the response of ac/dc bus voltage considering two disturbances: sudden load increase and sudden converter-station disconnection. Results demonstrate when two converters on the MTDC operate with dc voltage droop characteristic; it appears a "collaborative scheme" for the dc voltage support, sharing the task of controlling the dc voltage. Simulation results demonstrate the voltage margin control is capable to survive a converter outage just if this converter is operating on constant power mode.