Decentralized Inertia Emulation in AC/DC Hybrid Microgrids

Frequency response is an essential issue for normal and effective power system operation and it is degraded by the growing penetration of renewable energy sources (RESs). To solve this problem, inertia emulation can be implemented with dc-link capacitor of grid-tied inverter or distributed generation units (DGUs) in hybrid microgrids. However, the efforts of the former solution is limited by its capacity and the allowable dc-link voltage range, and the rate of change of grid frequency (RoCoF) estimation with DGUs relies on communication between grid-tied inverter and DGUs or central controllers in the latter. For these problems, a decentralized inertia emulation strategy in AC/DC hybrid microgrids is proposed. In this method, the RoCoF information transmission path consists of three parts: the proportional relation between dc-link voltage and grid frequency in grid-tied inverter local controller, inherent physical differential relation between dc-link capacitor voltage and current, and the proportional relation for RoCoF estimation in DGU local controller. On this basis, the DGU power reference is compensated according to the obtained RoCoF for inertia enhancement. Finally, the feasibility of the proposed strategy is validated with simulation results.