Response Characteristics and Regulation Feasibility of DC Charging Station Controlled by GFM/GFL Virtual Inertia for Grid Frequency Stability

To investigate the feasibility and differences between the grid-forming (GFM) and grid-following (GFL) control strategies for the frequency response (FR) in DC charging stations (CSs), this paper first identifies the characteristics of the virtual inertia of GFM and GFL and establishes an analytical model of the system frequency response considering FR in CSs. Second, the virtual inertia response control model of CSs are proposed under GFM and GFL controls, respectively. And their FR characteristics are analyzed. Finally, the frequency response characteristics of CS FR under variations of time delay, FR capacity, and virtual inertia are analyzed in the improved IEEE 3-machine 9-node and 10-machine 39-node benchmarks. The results show that the frequency response of the GFM CS is less affected by time delay and can affect the grid frequency in the form of inertia when the amount of electric vehicles (EVs) required in the CS groups is about 300-400. Whereas the overcapacity of the GFL CS will cause the system frequency to oscillate. Therefore, the choice of virtual inertia control strategy adopted by the CS is closely related to the number of EVs in the station and its adjustable margin.