Doubly Fed Induction Generator System Resonance Active Damping Through Stator Virtual Impedance

High Frequency Resonance Damping Method for Voltage Source Converter Based on Voltage Feedforward Control

“…As indicated by the impedance stability theory [7,8], resonance occurs if the phase angle difference between the grid impedance and the impedance of VSC has insufficient phase margin at the intersection of impedance magnitude. The existing researches have pointed out that, the grid-connected VSC system has the issue of high frequency resonance (HFR) when it connects to the grid with parallel compensation [9][10][11][12], since the impedance of parallel compensation grid behaves as the capacitance characteristic [7,8], while the impedance of VSC system tends to be an inductance in high frequency [11][12][13]. When HFR occurs, voltage of the point of common coupling (PCC) will be deteriorated significantly by the resonance component, thereby the performance of VSC system cannot satisfy the grid connection standard.…”

“…For the grid-connected VSC, according to the different instability mechanisms, the existing damping methods can be achieved by the optimizing of PLL (Phase locked loop) [16,17] and current feedback [18,19]. For the stability issue which caused by PLL, the optimizing of PLL parameters [16] and the improved PLL structure [17] are the effective methods for damping resonance, while it cannot be used for HFR damping, due to the reason that the bandwidth of PLL is much lower than the frequency range of HFR [9][10][11][12][13][14][15]. The damping methods based on current feedback [18,19] introduce a series impedance which can effectively achieve impedance reshaping at a fixed frequency point [18] or in a wide frequency range [19], thus they have been widely employed in the application of HFR damping [12][13][14][15].…”

“…As of now, the researches about HFR have made some process [9][10][11][12][13]22,23]. The simplified impedance model for VSC which can be employed to analyze the mechanism of HFR was derived in [10,11], thereby the HFR damping control based on the resonator was proposed in [12,13]. However, the controller based on resonator has a narrow bandwidth, usually 20 Hz to 50 Hz, so that the damping control is only effective on the condition that the HFR frequency can be detected accurately and provided to the resonator.…”

“…The current feedback control introduces a virtual impedance of which value is fixed [28], the virtual impedance can effectively reshape the output impedance phase of VSC, thereby to provide a sufficient phase margin between the VSC system and the weak grid. However, if the damping controller is not redesigned, the value of the virtual impedance is fixed [28], when the parameters of VSC systems change, the original impedance of VSC system changes as well, the impedance reshaping may not work properly, since the virtual impedance may not match the original impedance of VSC system [9][10][11][12][13]28]. Therefore, the existing damping controller have to be redesigned to obtain the optimal performance when the controlled object changes.…”

An Enhanced Control Strategy for Doubly-Fed Induction Generators Based on a Virtual Harmonic Resistor and Capacitor under Nonlinear Load Conditions

“…In [21], to suppress the high-frequency resonance phenomenon between the DFIG system and a parallel compensated weak network, an active damping control strategy is introduced by inserting a virtual impedance into the stator branch through stator current feedforward control In this paper, an impedance-based mathematical model which contains the DFIG, GSC, RSC, harmonic current sources and the weak grid are established, and harmonic voltage impact factor and harmonic current impact factor are introduced to analyze the impact of harmonic current source on harmonic voltage and total grid current at PCC. Then total grid harmonic current suppression and harmonic voltage suppression are discussed alongside the proposed harmonic impact factor.…”