Flying Start and Continuous Operation of a Permanent Magnet Wind Generator Based on Discontinuous Currents, Discrete Second-Order Sliding-Mode Observer and Phase-Locked Loop

In wind energy conversion systems of type 4, the critical operating point in permanent-magnet generators (PMGs) is the moment of switching on the generator-side converter (GSC). The induced back-electromotive force (EMF) acting on PMG terminals can cause inrush currents if the synchronisation between PMG and GSC is not done well. The main condition for achieving a satisfying synchronisation is to know the rotor angle, rotating speed and induced back EMF before the GSC is switched on. This synchronisation together with the switching on of the GSC is called the flying start of a PMG. In this study, a novel sensorless PMG flying-start method is proposed to ensure good synchronisation. The flying-start method is based on an extended flux PMG model in a rotating reference frame with a discrete second-order sliding-mode observer and a phase-locked loop controller during the discontinuous operating mode. This is based on discontinuous currents, which are induced because of the PMG rotation caused by wind energy. The proposed method ensures the operation of PMGs in the continuous operating mode as well. The effectiveness of the proposed method is verified on saturable models of low- and high-power surface and interior PMGs through simulations in Simulink and Piecewise Linear Electrical Circuit Simulation (PLECS).