Economic Power-Sharing and Stability Enhancement for Virtual Synchronous Generators in Islanded MG

Abstract

Dispatchable inverter-based distributed generators can share their power economically in islanded microgrids (MGs) using cost-based droop schemes. However, incorporating cost function into the droop adversely affects the MG stability, and since the main limitation of droop is the lack of inertia provision, a high rate of change of frequency (RoCoF) following a frequency event arises. To address these aspects, this paper proposes a novel control structure for the virtual synchronous generator (VSG) that emulates inertia to mitigate the RoCoF, enhance the MG marginal stability, and preserve decentralized economic power-sharing. The proposed economic dispatch-based VSG (ED-VSG) operates as a cost-based droop during steady-state and a VSG during disturbances. An improved version of ED-VSG is proposed by adding a zero to the transfer function of the ED-VSG to increase the MG stability margin further. A comprehensive evaluation framework has been employed to show the efficacy of the proposed control. Sensitivity analyses have been performed on the MG eigenvalues, considering parameter variations. Consequently, numerical simulations for small and large-scale systems and a lab-scale experimental MG setup show that the proposed controller optimally manages the MG. Furthermore, the results reveal a significant reduction in the maximum RoCoF, highlighting a commendable alignment with stability-oriented techniques.