Vector controlled brushless doubly fed twin stator cascaded induction generator for variable speed wind generation connected to weak grids

Due to continuous concerns about environmental pollution and a possible energy shortage, renewable energy systems, based mainly on wind power, solar energy, small hydro-electric power, etc have been implemented. Wind energy seems certain to play a major part in the world´s energy future. In spite of sudden wind speed variations, wind farm generators should always be capable of extracting the maximum possible mechanical power from the wind and turning it into electrical power. Nowadays, most of the installed wind turbines are based on doubly-fed induction generators (DFIGs), wound rotor synchronous generators (WRSG) and permanent magnet synchronous generators (PMSGs). The DFIG equipped wind turbine has several advantages over others. One of which, the power converter in such wind turbines only deals with rotor power, hence the converter rating can run at reduced power rating. However DFIG has the famous disadvantage of the presence of slip rings which leads to increased maintenance costs and reduced life-time. Hence, brushless doubly fed induction machines (BDFIMs) can be considered as a viable alternative. In this paper, the brushless doubly fed twin stator induction generator (BDFTSIG) is modeled in details. A wind energy conversion system (WECS) utilizing a proposed indirect vector controlled BDFTSIG is presented. The proposed controller performance is investigated under various loading conditions showing enhanced transient and minimal steady state oscillations in addition to complete active/reactive power decoupling.