Microgrids are emerging to meet the growing demand for reliability and resiliency in the electricity market. Similar to the utility grid, microgrids face challenges of the intermittency associated with a high-penetration of renewable power generation (e.g., PV) and randomly occurring loads associated with electric vehicle charging. Characterizing and understanding the dynamics of these challenges are required in order to establish the smart controls and other distributed energy resources that will be required for microgrids to remain stable.
At UCI, a unique next-generation DER has been established as part of a U.S. Department of Energy “Irvine Smart Grid Demonstration” project. On the roof of a parking structure, 48kW of PV panels have been deployed. On the first floor of the structure, 20 monitored Chargepoint EV chargers have been installed. Outside but immediately adjacent to the parking structure, a 100kW battery energy storage system (BESS) has been integrated into a combined system. The system has an internal inverter that converts the photovoltaic as well as the battery power outputs from direct current (DC) to alternating current (AC). A site controller switches the inverter between two control modes: the demand response mode and the distributed generation mode. The modes determine to which control signals the inverter responds while the other modes contain the algorithms for overall system behavior.
The demand response mode allows the control of the BESS minimum state of charge. This means that if the battery is at or below this set-point, no further discharge can occur. The distributed generation mode allows the use of PV power without curtailment. The BESS is immediately charged using either PV or grid power.