Coordination of virtual inertia control and frequency damping in PV systems for optimal frequency support

The photovoltaic (PV) systems are being required to support the grid more flexibly than ever before. One of the emerging demands is the frequency regulation, including the virtual inertia control (VIC) and the frequency damping control (FDC). To achieve the full-range frequency regulation, i.e., to deal with under-frequency and over-frequency issues, power reserve is necessary for PV systems, which should be properly utilized to realize optimal frequency support. In this context, a novel coordination strategy for the VIC and the FDC in PV systems is proposed in this paper. According to relevant grid codes, the key indices to evaluate the frequency quality are identified at first, i.e., the rate of change of frequency (RoCoF), the frequency nadir, and the recovery frequency. Then, the impact of the inertia constant and damping gain on the frequency quality is explored. Accordingly, the coordination strategy of the VIC and the FDC is designed to achieve optimal frequency support with a certain amount of power reserve. Simulations are performed to validate the performance of the proposed control strategy.