Voltage control in an HVDC system to share primary frequency reserves between non-synchronous areas

This paper addresses the problem of frequency control for non-synchronous AC areas connected by a multi-terminal HVDC grid. It proposes a decentralized control scheme for the DC voltages of the HVDC converters aimed to make the AC areas collectively react to power imbalances. A theoretical study shows that, by using local information only, the control scheme allows to significantly reduce the impact of a power imbalance by distributing the associated frequency deviation over all areas. A secondary frequency control strategy that can be combined with this control scheme is also proposed so as to restore the frequencies and the power exchanges to their nominal values in the aftermath of a power imbalance. Simulation results on a benchmark system with five AC areas illustrate the good performance of the control scheme.