Optimal Superconducting Coil Integrated Into DFIG Wind Turbine for Fault Ride Through Capability Enhancement and Output Power Fluctuation Suppression

The vital problems of the grid-connected doubly fed induction generator (DFIG) wind turbine are the fault ride through (FRT) capability and the output power fluctuation. To tackle these problems, this paper focuses on the optimization of the superconducting coil (SC) integrated into a dc link of the DFIG wind turbine for an enhancement of the FRT capability and a suppression of the output power fluctuation. The dc-dc converter, which is used to control the exchanged energy between the SC and the system, is additionally connected between the grid side converter (GSC) and the rotor side converter. During normal operation, the SC acts as an energy storage device to exchange energy with the system so that the power fluctuation of the DFIG wind turbine can be alleviated. On the other hand, when severe faults occur in the system, the SC is used as the current limiting inductor to suppress both overcurrent in the rotor and stator, and overvoltage in the dc link of the DFIG. In the optimization, the inductance of the SC, the initial necessary stored energy in the SC, and the proportional integral (PI) parameters of the dc-dc converter are tuned simultaneously so that both objectives can be achieved. Simulation study elucidates the control effect of the DFIG wind turbine with the optimal SC.