High-Frequency Resonance of DFIG-Based Wind Generation under Weak Power Network

Abstract

As the mainstream generation devices in the current wind power market, doubly fed induction generators (DFIG) based wind farms in China are always located in the northwest, northeast and north China and other remote areas where DFIG systems have to be connected with the weak grid. In that case, the resonance may occur in the system on account of the interaction between AC and DC system and lead to harmonic amplification. The subsynchronous resonance (SSR) lower than the fundamental frequency and the high-frequency resonance (HFR) are the two main resonance modes in the DFIG grid-connected system. However, researches on HFR characteristics of DFIG connected to grids have been drawn attention. This paper will fill this gap. The DFIG system model under the weak power grid with different kinds of compensations is set up firstly. Then, the grid impedance and the DFIG numbers are changed separately to discuss the influence of them on harmonic characteristics by Bode diagrams. Afterward, a detailed model for DFIG system under weak grid is developed in MATLAB/Simulink. The harmonic characteristics of the system are analyzed by fast Fourier transform (FFT). The study shows that HFR is more serious when the DFIG system is integrated into the parallel compensated weak grid than connected to the series compensated grid. HFR is more possibly to happen with the growth of the system capacity or the DFIG numbers.