A Novel Wind Energy Conversion System with DFIG DC-Side Connected to SST for Medium-Voltage DC Grid Integration

This paper investigates a novel DFIG Low-Voltage DC connected to SST type wind energy conversion system for direct medium-voltage AC grid integration. The novel DFIG-based wind turbine can support active power to DC bus through both SSC and RSC, and the active power through these two converters can be adjusted by changing the rotor speed. The DC side of the generator is combined with the medium-voltage grid through solid state transformer (SST) instead of the fundamental frequency transformer. In this paper, an improved independent phase current control is adopted. The unified mathematical model of high voltage stage and isolation stage is reduced from (n+1) to 1 order by using CLLC resonant converter structure, which greatly reduces the number of signals acquisition and simplifies the control structure. What’s more, the proposed configuration can not only realize reactive power compensation without a reactive power compensator, but also can maintain stable operation even when the voltage of the grid is unbalanced. A detailed simulation study in PSCAD is conducted to verify the performance of the proposed structure.