Potential of using DC voltage restoration reserve for HVDC grids

• This paper defines DC grid reserves.
• It shows that the control of DC voltage restoration reserve can be arranged in a similar manner as frequency restoration reserve.
• The general concept and main features are validated using specific test cases.

Any electric power system has to maintain an energy equilibrium at every moment. This is the case for existing AC systems and will be the case for future HVDC grids. Otherwise, the frequency will fluctuate beyond acceptable values, as will the voltage in DC grids. Therefore, energy balancing services are needed to manage both quantities. This paper defines reserve steps for HVDC grids, in analogy to the reserves for AC systems as implemented in Europe. It shows that if the HVDC grid reaches a certain scale, the services can be organised in a similar way as existing AC reserves. In this paper, the focus lies on the DC secondary reserve/DC voltage restoration reserve. The introduction of such reserves will benefit the system through increased stability, damping of small or slow unpredicted fluctuations and the option to organise a DC system in multiple control areas.