Nonlinear hybrid flatness control for suppressing overcurrent of DFIG during high voltage ride through

With the rapid development of the wind power penetration, the suppression of wind turbine overcurrent becomes a significant challenge for high-voltage ride-through. A nonlinear hybrid flatness control (NHFC) strategy is proposed to reduce overcurrent, shorten overcurrent duration time and provide reactive power support. The control strategy consists of the following three parts: 1) a differentiate flatness control (DFC) strategy is designed for improving the duration time of the overcurrent. 2) a time-based virtual resistance control (TBVRC) strategy, where the resistance is varied with the fault voltage occurrence time, is employed to regulate and suppress the stator and rotor overcurrent. 3) a coefficient backpropagation droop control (CBDC) strategy, obtained by optimum droop coefficient calculation, is developed to provide outstanding reactive power injection for voltage support. Simulation results indicate that the proposed control strategy can effectively suppress overcurrent with less duration time while providing effective reactive power support.