Impedance-Based High-Frequency Resonance Analysis of DFIG System in Weak Grids

The impedance-based model of doubly fed induction generator (DFIG) systems, including the rotor part (rotor side converter (RSC) and induction machine), and the grid part (grid side converter (GSC) and its output filter), has been developed for analysis and mitigation of the subsynchronous resonance (SSR). However, the high-frequency resonance (HFR) of DFIG systems due to the impedance interaction between the DFIG system and parallel compensated weak network is often overlooked. This paper, thus, investigates the impedance characteristics of DFIG systems for the analysis of HFR. The influences of the rotor speed variation, the machine mutual inductance and the digital control delay are evaluated. Two resonances phenomena are revealed, i.e., 1) the series HFR between the DFIG system and weak power grid; 2) the parallel HFR between the rotor part and the grid part of DFIG system. The impedance modeling of DFIG system and weak grid network, as well as the series HFR between DFIG system and parallel compensated weak network has been validated by experimental results.