Hybrid control of DFIGs for short-term and long-term frequency regulation support in power systems

This paper proposes a new hybrid frequency control strategy for doubly fed induction generator (DFIG)-based wind turbines (WTs) to simultaneously provide short-term and long-term frequency regulation support to the connected power system. The kinetic energy stored in the rotating mass and the mechanical power reserve of the WT are coordinately configured to participate in frequency recovery at both primary and secondary stages. A frequency response model (FRM) is also derived to analyse the mutual interactions between WTs and the power system. Based on the FRM, the impacts of relevant parameter variations on the overall system stability can be investigated through Nyquist criterion and modal analyses and the stable operation range of proposed strategy could be easily identified. Theoretical and numerical results have both verified the effectiveness of the proposed control strategy and its advantages over existing methods.