7. Operating principle of an HVDC-VSC connection connected to the transmission grid

In an HVDC-VSC link connected to the transmission grid, one station controls the power through the link; this station controls the active power, while the station on the other side maintains a constant DC voltage on the DC bus; it controls the DC voltage. The choice of which station controls the power and which controls the DC voltage does not depend on the direction of power flow, and it is possible to reverse their roles.

From an energy perspective, the DC system can be considered as an equivalent capacitor, comprising the capacitors at each station as well as the line shunt capacitance of the underground cables or overhead lines. This equivalent capacitor will tend to charge if the power entering the DC system is greater than the power leaving it, including losses, and vice versa. Thus, by controlling the DC voltage at a constant value, the DC voltage control...