Frequency-Adaptive MPC of Grid-Forming VSC-HVDC Systems with Optimal Voltage Reference Tracking during Grid Restoration

Grid restoration strategies gain in significance since fundamental changes inside electrical power grids are in progress. The share in volatile energy sources connected through power electronic components increases, whereas the installed power of grid-connected generators and associated inertia decreases. In this context, critical operating states up to system blackouts, that threaten the security of supply and the access to electical energy, might occur. In order to restore the grid after a blackout in an efficient way, this paper proposes an advanced control concept for high voltage direct current (HVDC) systems using voltage source converters (VSC) in gridforming mode. VSC-HVDC systems open new restoration paths and offer the possibility to involve healthy grid areas form a far distance to take part in the restoration process. To benefit from the potential of renewable energy sources and energy storage devices to support the process, established restoration strategies are extended by the consistent integration of power electronics and intelligent control schemes. The presented model predictive controller (MPC) enables precise voltage reference tracking inside the restoration area to ensure a grid compatible voltage ramp-up process by avoiding undesireable effects, e. g. inrush phenomena of transformers. Moreover, the grid frequency is used as a system-wide parameter that is used as a physical information channel between the grid-forming VSC-HVDC station and further power converters inside the restoration area. In that way, renewable energy sources and storage devices can contribute to speed up the restoration process while guaranteeing system stability.