A novel converter system for DFIG based on DC transmission

Power frequency transformer is necessary when doubly fed induction generator (DFIG) connects with high-voltage ac grid. However power frequency transformer possesses many undesirable properties such as bulky size, environmental concerns. Additionally, the wind farms need reactive power compensation, such as static synchronous compensator (STATCOM). In this paper, the DFIG converter system with integrated active power transfer, reactive power compensation and voltage conversion functionality is proposed, which consists of rotor side converter (RSC), stator side converter (SSC) and dc-dc converter (DDC). The proposed converter system is developed by combining the traditional flexible control on DFIG, and the advantages of SST and dc transmission. It allows DFIG to connect high-voltage dc bus directly and easily without power frequency transformer and STACOM, which has small volume and light weight. In this paper, the converter system models and dc transmission are developed firstly. And then its control strategies are illustrated in detail. Finally, simulation studies are carried out to validate the validity and feasibility of the proposed converter system in steady state.