Modular DC/AC Microgrid

A microgrid was developed as a modular "plug and play" system to accommodate both AC and DC loads up to a combined 125kVA total system power with a grid tie. A common DC bus configuration forms the backbone of the system, with bi-directional DC/DC and AC/DC power converters, allowing for a variety of renewable energy sources including PV arrays, battery energy storage, and an AC grid connection - both AC and DC loads can be seamlessly connected and powered. Converter control systems maintain a constant DC voltage on this common bus within a predetermined voltage band limit. All DC bus control was localized to the converters. Control decisions are determined by preset converter setpoints maintained in each converter. The state and availability of various sources determine power flows. By segregating loads into critical and essential, a programmable logic controller (PLC), with a specified algorithm, is used for load shedding. Upon the loss of grid power, essential loads are automatically shed if sufficient power was not available from other sources. This work describes the microgrid architecture and our experience testing the microgrid including the use of a generator source, battery power, PV array power, and utility power sources. Grounding and protection, efficiency, overload, EMI and THD are discussed including measurements made over a range of operating and load conditions. Based on these results, recommendations are made for future product development needs.