A distributed DC voltage control method for VSC MTDC systems

With the development of VSC HVDC transmission, the realization of the first VSC MTDC grid is coming within reach. An outstanding issue is DC voltage control in MTDC systems. The easiest way to maintain stable operation is to assign the task of DC voltage regulation to one converter. This paper discusses a control strategy for an extended VSC MTDC grid using a typical DC voltage control on one DC bus, combined with a DC voltage droop characteristic on the other DC buses. The impact of the proposed control structure on the stability of the AC and DC grid is investigated by numeric simulations using the MatDyn software package.

► The DC grid voltage can be controlled by a single converter or by a distributed control.
► A distributed voltage control can relieve the pressure of the otherwise centralized voltage controlling converter.
► We combined a PI-controller on the main voltage controlling converter with a voltage droop characteristic in other converters.
► The combined approach reduces DC voltage transients.