Comparative Evaluation of Virtual Inertia and Fast Frequency Reserve Provided by HVDC Terminals

This paper compares the impact on power system frequency transients from virtual inertia and Fast Frequency Reserve (FFR) provided by HVDC converters. Specifically, frequency nadir, Rate-of-Change-of-Frequency (RoCoF), and the required energy during the frequency support are evaluated. Two control schemes for providing virtual inertia are considered, including a current controlled Virtual Synchronous Machine (VSM) and a grid-following control with frequency derivative-based inertia emulation. The studied FFR provides either short or long support according to the guidelines of the Nordic synchronous area. Simulation studies are conducted in DIgSILENT PowerFactory using a 44-bus simplified model of the Nordic power system. With the same peak power, the results show that the different strategies have similar impact on the frequency nadir, while only the virtual inertia improves the RoCoF. Furthermore, the strategies for virtual inertia support can provide improvement of the frequency nadir with significantly less injected energy than the FFR long support.