State-space representation of DFIG-based wind power plants

This study shows a methodology for state-space representation of large wind power plants, through models that include the dynamics of the internal grid. The methodology presented fundamentally separates plant and controls at the stage of formation of the model. It is shown then that most of the plant can be built up from elementary RL branches – with special clarification about the reduction of the induction machine to an RL network – that are put together by means of a incidence matrix. The problems and solutions of reference frame dynamics – complex because of the existence of two control frames for the doubly-fed induction generator and different frames in the grid, one for each generator – are also discussed. The control is separately formulated into a gain matrix, and control and plant are put together by simple matrix algebra. As a result, detailed, large systems can be easily formed. The study shows an example in which ten generators are considered and shows that there may appear particular dynamic features when multi-machine systems (rather than single, aggregated machine systems) are represented.