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Variable-speed pitch-controlled wind turbines with doubly-fed induction generators (DFIG) are modelled for power system dynamic stability. The model is explained and the parts of the model are verified. The model is implemented in the simulation tool PSS/E and created as a modular structure. This means that it is possible easily to add other control loops, as other modules, to the existing model code for ad-hoc investigations. This article is the first part of a large work dealing with investigation of dynamic interaction between the variable-speed wind turbines equipped with DFIG and the power grid.

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Variable-speed wind turbines are a promising concept for large offshore wind farms. The variable-speed concept can be realised with multi-pole synchronous generators (MPSG) excited by permanent magnets. The main advantages of this concept are that (i) the wind turbines are gearless and (ii) the electrical excitation system is replaced by permanent magnets. The electromagnetic construction of the permanent magnet generators (PMG) is, however, more complex than in conventional concept generators. The PMG are grid-connected through and controlled by their frequency converters. The converter control can be used to stabilise the large wind farm at transient events in the grid to complete the grid specifications of the power system controllers. This article gives an overview of the structural concepts of PMG and explains modelling details of the PMG and their frequency converters.

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A model of variable-speed wind turbines equipped with doubly-fed induction generators (DFIG) and controlled by partial-load frequency converters described in [1,2] is applied in power stability investigations. A technical feature of uninterrupted operation at grid disturbances of large wind farms with such variable-speed wind turbines is suggested and discussed. This technical feature is based on fast re-start of the rotor converter, which blocks at grid faults. The main reactive power control is organised by the rotor converter [3]. The new part is that reactive power is controlled by the grid-side converter when the rotor converter blocks. Possible discrepancies between the results reached with the detailed representation of the frequency converter and the representation where only the rotor converter is regarded are notified and explained. The converter representation details influence on the machine current transients modelled at grid disturbances and also on damping characteristics of torsional shaft oscillations.