Strategies for Independent Deployment and Autonomous Control of PV and Battery Units in Islanded Microgrids

In this paper, autonomous control strategies are proposed for Photovoltaic (PV) and battery units operating in a droop-controlled islanded microgrid. Based on the proposed strategies, the PV and battery units can be deployed independently in any droop-controlled microgrid. Both the PV unit and the battery unit are controlled as voltage sources that follow multisegment adaptive power/frequency (P/f) characteristic curves. These P/f characteristic curves are adjusted locally in real time based on the available PV power, load demand, and the state of charge of the battery to autonomously coordinate the operation of these units and maintain the power balance in the microgrid. The strategy proposed for the battery unit enables it to autonomously supply power only during peak load periods, to support the droop-controlled units and maintain the power balance in the islanded microgrid. The control strategies are implemented in each unit using multi-loop controllers, without relying on communication, a central management algorithm, or switching logic. Small signal models of the proposed control loops are presented, and the performance of the proposed strategy is validated using simulation and also through experiments on a 3-kVA prototype microgrid.