Seamless Transitions of Variable-Speed Wind Generator in Standalone Microgrid

Control of a standalone microgrid during steady-state and transitions of constituent wind generator (WG) is presented. At PCC, a battery energy storage (BES) is connected via a bidirectional VSC, and a variable speed WG is connected directly. The PCC voltage and frequency are typically controlled by the VSC operating in grid-following (GF(o)) mode in presence of the WG and in grid-forming (GF) mode in absence of the WG. During every plug-in or plug-out operation of the WG, the operating mode of the VSC would switch aptly from one to another. A simple technique is presented in this paper, which allows to operate the VSC always in the GF mode, thus avoiding its mode switching. A pre-synchronizing loop handles the WG transitions. The principle of control scheme is presented and its efficacy is shown with help of simulation studies.