Evolutionary changes in the regulatory and operational climate of traditional electric utilities and the emergence of smaller generating systems such as microturbines have opened new opportunities for on-site power generation by electricity users. In this context, distributed energy resources (DER) - small power generators typically located at users' sites where the energy (both electric and thermal) they generate is used - have emerged as a promising option to meet growing customer needs for electric power with an emphasis on reliability and power quality.
The portfolio of DER includes generators, energy storage, load control, and, for certain classes of systems, advanced power electronic interfaces between the generators and the bulk power provider. This paper proposes that the significant potential of smaller DER to meet customers' and utilities' needs, can be best captured by organizing these resources into MicroGrids.
MicroGrid concept assumes an aggregation of loads and microsources operating as a single system providing both power and heat. The majority of the microsources must be power electronic based to provide the required flexibility to insure operation as a single aggregated system. This control flexibility allows the MicroGrid to present itself to the bulk power system as a single controlled unit that meets local needs for reliability and security.
The MicroGrid would most likely exist on a small, dense group of contiguous geographic sites that exchange electrical energy through a low voltage (e.g., 480 V) network and heat through exchange of working fluids. In the commercial sector, heat loads may well be absorption cooling. The generators and loads within the cluster are placed and coordinated to minimize the joint cost of serving electricity and heat demand, given prevailing market conditions, while operating safely and maintaining power balance and quality. MicroGrids move the PQR choice closer to the end uses and permits it to match the end user's needs more effectively. MicroGrids can, therefore, improve the overall efficiency of electricity delivery at the point of end use, and, as micrgrids become more prevalent, the PQR standards of the macrogrid can ultimately be matched to the purpose of bulk power delivery.
The MicroGrid structure assumes an aggregation of loads and microsources operating as a single system providing both power and heat. The majority of the microsources must be power electronic based to provide the required flexibility to insure controlled operation as a single aggregated system. This control flexibility allows the MicroGrid to present itself to the bulk power system as a single controlled unit, have plug-and-play simplicity for each microsource, and meet the customers' local needs. These needs include increased local reliability and security.