Variable-speed wind turbine with partial-scale power converter and a DFIG

This wind turbine concept is the most adopted solution nowadays and it has been used extensively since 2000s. As shown in Figure, a PEC is adopted in conjunction with the DFIG. The stator windings of DFIG are directly connected to the power grid, whereas the rotor windings are connected to the power grid by the converter with normally 30% capacity of the wind turbine. In this concept, the frequency and the current in the rotor can be flexibly regulated and thus the variable speed range can be extended to a satisfactory level. The smaller converter capacity makes this concept attractive seen from a cost point of view. Its main drawbacks are however, the use of slip rings and the challenging power controllability in the case of grid faults—these disadvantages may comprise the reliability and may be difficult to completely satisfy the future grid requirements

Source:
Frede Blaabjerg and Ke Ma «Future on Power Electronics for Wind Turbine Systems» IEEE Journal of Emerging and Selected Topics in Power Electronics, Vol. 1, No. 3, September 2013