Feedforward current reference control for DFIG during grid faults
For doubly fed induction generation (DFIG) based wind turbine, large electromotive force will be induced in the rotor circuit under severe grid faults, and it usually far exceeds the DC-bus voltage. In that case, it is necessary to inject transient and negative-sequence components into rotor current reference to fulfill controllable low-voltage ride through (LVRT). On the synchronous reference frame of vector control system, such current references are 50 Hz and 100 Hz AC items, respectively. Thus, the classical proportional-integral (PI) controller cannot accurately track this AC reference. To solve this problem, a feedforward current reference (FFCR) control scheme is proposed to improve the tracking capability of AC reference. Hence, it unearths the characteristics of such reference. The proposed FFCR control scheme will not alter the stability of original current loop. Furthermore, it has strong robustness for frequency fluctuations of grid voltage and DFIG parameters drift. Finally, simulation and experimental results are presented to demonstrate the effectiveness of the proposed control scheme.