Forming a microgrid to islanded operation as a mean to improve quality of supply in low voltage networks with distributed generation

In this paper a novel concept of improving power quality (PQ) in low voltage networks with distributed generation (DG) is proposed. In contrast to traditional methods which require the application of dedicated resources to compensate for power quality disturbances, the proposed idea is simply to form a microgrid (MG) capable to isolate from the utility grid and operate islanded when a disturbance occur. In the paper conditions for island creation are discussed and a control strategy is presented for a small-scale active network with microturbine, renewable energy sources, loads and storage system. The strategy assumes using energy storage unit as a grid forming unit for islanded operation and a central controller for supervising the network operation in grid-connected and islanded modes. The part of strategy is islanding condition detection method which is based on immunity curve defined for the considered network. Performance of the proposed strategy is presented as a reaction of the network on voltage dips, however the idea is applicable to any PQ disturbance of unacceptable level occurring in the utility grid. For the considered network a simulation model has been developed using PSCAD/EMTDC platform. Simulation results are presented in the paper which illustrate the operation of the control system and show the microgrid behavior after transition from grid-connected to islanded operation mode.