An intentionally seamless transfer strategy between grid-connected and islanding operation in micro-grid

Micro-grid is a regional power system, which contains several distributed energy resources (DERs). It can effectively respond to the dispatching from the utility grid. Generally, micro-grid can operate in parallel with the utility grid or operate in islanding mode. In this paper, the intentionally seamless transfer strategy is studied in a grid-connected micro-grid in PSCAD/EMTDC, which contains PV system, microturbine generation system (MTGS) and battery system. In grid-connected operation mode, power flow following control system is adopted to keep the active power of the point of common coupling (PCC) at a constant level. In this control mode, the inverter system for each controllable distributed generation (DG) usually works in P/Q control mode. When PCC in micro-grid is cut off, state tracking control strategy is adopted and battery system in micro-grid must switch to V/f control mode to stabilize voltage and frequency. Due to the power transient fluctuations caused by the unbalanced demands form local loads, the power following control system with the state tracking strategy is employed to minimize the transient fluctuations of voltage and frequency during the transferring process of the operation mode. Effectiveness of the control strategy is validated by simulations.