Droopless Active and Reactive Power Sharing in Parallel Operated Inverters in Islanded Microgrids

Microgrids have emerged as viable alternatives for supporting the utility grid, reducing feeder losses and improving power quality by enabling integration of growing deployments of distributed energy resources (DERs) with local loads. They can operate in both grid-tied as well as islanded modes. There are two primary objectives in the islanded mode - (a) ensuring system stability by regulating the voltage and frequency at the point-of-common-coupling (PCC), and (b) load power sharing among multiple DERs connected in parallel. While droop based schemes enjoy the advantages of fully decentralized implementation (no communication) and plug-and-play capabilities, such schemes often fail to address the issue of precise active and reactive power sharing, primarily due to unmatched impedances. In this paper, we overcome this limitation by proposing a novel, droopless control scheme for accurate active and reactive power sharing among DERs in an islanded microgrid, while simultaneously regulating output voltage and frequency at the PCC. Similar to droop based schemes, the proposed method too facilitates fully decentralized implementation. This is achieved by smart choice of control design enabled by - (a) disturbance rejection viewpoint, (b) decoupling of $d-q$ control loops through appropriate feedforward blocks, and (c) extension of the network control scheme proposed in our prior work [1]. A system consisting of three parallel inverters is simulated in MATLAB Simscape for various challenging scenarios and the results corroborate the effectiveness of the proposed approach.