A critical requirement of an advanced microgrid comes into play when reconnection to loads occurs
in the islanded state especially after the microgrid has been inoperable but loads are still connected.
This connection of the microgrid to the loads in the islanded state is called “black start.” Where
conditions on the main grid result in the microgrid being disconnected from the main utility, the
advanced microgrid should transition either seamlessly or as quickly as possible and continue to
operate as connected DG. During the reconnection state, the operating states of reconnecting to the load reclosing must be carefully considered as must the capability of the advanced microgrid to
provide startup surges and voltage regulation.
Developing local controllers in close co-ordination with an advanced microgrid central controller
must be evaluated from the dynamic-operation point of view. Testing and studies will likely need to
be performed in a simulation and in real time. The black-start functionality will help assure power
system operation, power supply reliability, and protection to critical loads.
The restoration procedure in an advanced microgrid is somewhat similar to the approach adopted for
medium-sized power systems. Several sources within the advanced microgrid must have black-start
capabilities. A stand-by power supply and a monitoring and control scheme will likely be embedded
in the microgrid control center, but autonomous inverter functions may suffice. Black-start
functionalities within advanced microgrids will need minor changes in available standards such as
IEEE 519 for harmonics and voltage, with time-dependent or load-dependent specifications called
out for microgrids.
14 Load shedding may be an alternative method to assure an advanced microgrid
power supply that meets today’s interconnection standards requirements.