Distributed energy resources (DER) are small power generators that are typically located near the customer’s load where energy is used. Small DER produce low emissions can be manufactured at low cost and take advantage of waste heat. These devices which are generally grouped with loads into a microgrid with a single interface to the local utility offer a promising means of meeting the rapidly growing demand for more reliable power across the United States. UW-Madison researchers have developed an improved interface switch that seamlessly and automatically connects and disconnects a DER microgrid from a utility grid. The interface switch disconnects the DER from the utility grid for protection and power quality events allowing the cluster of loads and DER to continue to operate as an island. During island conditions the frequency of the DER microgrid differs from that of the utility. When the conditions that created the islanding are gone the interface switch exploits this frequency difference to rapidly and seamlessly reconnect the microgrid to the utility. Applications: Allows the DER microgrid to quickly and seamlessly switch between island mode and utility mode.
1) Operates automatically using only locally available information 2) May be operated manually 3) Minimizes voltage transients current surges and other undesirable strains on the system