A controller for the smooth transition from grid-connected to autonomous operation mode

In this paper, a local controller for inverter of Distributed Energy Resources (DERs) is presented to manage a microgrid during grid-connected and autonomous operation modes and also during the transition. It is based on the P-f and Q-V droop control: during grid-connected operation, the controller tracks active and reactive power references and, during islanded mode, it exploits the droop control properties to share the load among the DERs. The peculiarity of this regulator is that it does not need to identify the particular operation mode and so a smooth transition from grid-connected to islanded mode can be achieved with no communication within the power grid or among the disconnecting switch and DERs. This controller has been implemented in a FPGA platform and its operation has been tested via an Hardware-In-the-Loop (HIL) and Real-Time (RT) simulation approach.