Overview of DFIG-Based Wind Power System Resonances Under Weak Networks

The wind power generation techniques are continuing to develop and increasing numbers of doubly fed induction generator (DFIG)-based wind power systems are connecting to the on-shore and off-shore grids, local standalone weak networks, and microgrid applications. The impedances of the weak networks are too large to be neglected and require careful attention. Due to the impedance interaction between the weak network and the DFIG system, both subsynchronous resonance (SSR) and high-frequency resonance (HFR) may occur when the DFIG system is connected to the series or parallel compensated weak network. This paper will discuss the SSR and the HFR phenomena based on the impedance modeling of the DFIG system and the weak networks, and the cause of these two resonances will be explained in details. The following factors will be discussed in this paper: 1) transformer configuration; 2) different power scale of DFIG system with different parameters; 3) L or LCL filter adopted in the grid side converter (GSC); 4) rotor speed; 5) current closed-loop controller parameters; and 6) digital control delay. On the basis of the analysis, active damping strategies for HFR using virtual impedance concept will be proposed.