Analysis and Active Damping of Multiple High Frequency Resonances in DFIG System

Abstract

As the wind power generation develops, the Doubly Fed Induction Generator (DFIG) based wind power system are more and more likely to operate in the emerging weak network rather than the conventional stiff network. Due to the comparatively large impedance of the weak network than the stiff grid, the DFIG system may be subject to the resonances due to the impedance interaction between the DFIG system and the weak network. Especially, when connected to a series π sections weak network, the Multiple High Frequency Resonances (MHFR) may occur and require careful studies. The impedance modeling of the DFIG system and the series π sections weak network is firstly demonstrated in this paper. Then, due to the multiple magnitude peaks of the series π sections of the weak network, the MHFR will be produced and can be theoretically explained based on the impedance modeling results. For the purpose of mitigating the MHFR, an active damping strategy which introduces a virtual impedance, including a phase leading compensation unit and a virtual positive resistance, is proposed and demonstrated. Simulations are conducted to validate the DFIG system MHFR as well as the proposed active damping strategy.Index Terms -DFIG system; series π sections weak network; multiple high frequency resonances; virtual impedance; active damping.The authors are with the

Analysis of High-Frequency Resonance in DFIG-Based Offshore Wind Farm via Long Transmission Cable

“…The impedance modeling of the single DFIG unit is established first in this section. Note that the impedance modeling of the single DFIG unit, including both the RSC and the DFIG generator, as well as the GSC and the output LCL filter, has been obtained as done in [12]- [15]. Here for the sake of simplicity, the impedances of the two parts are mentioned here as the following.…”

“…As investigated in previous works [10]- [12], the impedance modeling of the long transmission cable is in this paper assumed to be a series connection of several Π units, which contain a cable resistance and cable inductance in series connection and cable shunt capacitance between the cable and the ground at both ends [10]- [12].…”

“…On the other hand, the DFIG based wind power system consists of the DFIG generator and the Rotor Side Converter (RSC), as well as the Grid Side Converter (GSC) with the output LCL filter. Since the DFIG system behaves mostly inductive in the control frequency range [12]- [15], the DFIG based wind farm with hundreds of DFIG units will also behave inductive under these circumstances.…”

“…Due to the inductive behavior of the DFIG based wind farm and the capacitive behavior of the long transmission cable, a resonance may happen as a consequence of the impedance interaction in certain frequency range. Note that the High Frequency Resonance (HFR) has been investigated in [12]- [15], and the corresponding active damping strategies for the HFR were proposed in [12]- [13], [15]. However, only a single DFIG system, rather than a wind farm with multiple DFIGs in parallel connections, was discussed.…”

“…Compared with the previous studies [12]- [15], the main contribution of this paper is the HFR in DFIG based wind farm containing large numbers of DFIG units, as well as the long transmission cables. Besides, several influencing factors on the HFR, including 1) the length of the cable, 2) the output active power and 3) the rotor speed, will be studied.…”