An Improved Grid Synchronization Control of Doubly-Fed Induction Generator

The dynamic performance of Doubly-Fed Induction Generator (DFIG) before and after connection is analyzed based on corresponding mathematical models and transfer functions in decoupled vector control. The parameter tuning methods of rotor current regulator before and after connection are given. To reach same dynamic performance the parameters should take different values and be switched before and after connection. However on one hand the closing moment of stator contactor is difficult to get as the feedback signal is usually twenty millisecond delay or so. The delay in parameter switching will affect rotor current and torque dynamics after connection. On the other hand parameter switching is troublesome. Hence a synchronization control strategy without parameter switching is proposed and analyzed in detail, which has linear rising exciting current to avoid current overshooting. The dynamic performance of the proposed strategy is analyzed in frequency domain and implemented on a DFIG experimental platform subsequently. The proposed synchronization strategy in the paper is validated by experimental results.