A Low-Order System Frequency Response Model for DFIG Distributed Wind Power Generation Systems Based on Small Signal Analysis
Abstract
:1. Introduction
2. Frequency Control Strategy and Response Characteristic of DFIG
- (A)
- Low wind condition: As the available reserve capacity provided by the DFIG is very low, maintaining the DFIG in a stable condition is the first priority. In other words, the DFIG will provide no frequency control during system frequency fluctuations. Furthermore, due to the fact that the rotor speed of a DFIG is decoupled from the dynamic system frequency, DFIG could hardly release or absorb rotor kinetic energy, like the inertia response from synchronous generators. Hence, under low wind conditions, the extra active power provided from a DFIG is almost zero during a frequency disturbance.
- (B)
- Medium wind condition: In this wind region, DFIG can provide sufficient reserve capacity to participate in frequency control just by rotor over-speed regulation, and the pitch angle need not take an action (fixed at minimum angle ) just because the rotor speed could not exceed the upper limit . In order to make the novel SFR model derived in next section more representative, the original primary frequency control strategy in [8] is replaced by the combined inertia and primary control strategy [13,14,15,16,17] (shown in Figure 1) which is now more widely used. In addition, the reserve capacity command sent to the DFIG is set as a deloading rate d% [17] substituting for a fixed command . Once a frequency deviation happens in the system, the AFC will provide extra active power. Therefore, during the whole process of the frequency control, the output active power of DFIG can be expressed as:As seen in Equation (1), it is important to note that the deloading power will be changed along with the actual rotor speed during the process of frequency control. More precisely, the changing amplitude is , but the key point is that the direction of the change is contrary to the extra active power provided by the AFC, causing an adverse effect on frequency control ability of the DFIG.
- (C)
- High wind condition: Above the rated wind speed, the DFIG should keep the torque and rotor speed less than the upper limit by pitch angle control. Therefore, unlike the medium wind condition, the output active power of the DFIG should be expressed as Equation (2) during the process of frequency control:
3. A Novel Low-Order SFR Model for DWPGS
3.1. Novel SFR Model under Low Wind Conditions
3.2. Novel SFR Model under Medium Wind Conditions
3.2.1. Impact of the Initial Operating Point on System Frequency Dynamics Based on the Novel SFR Model
3.2.2. Impact of Parameters of the AFC on System Frequency Dynamics Based on the Novel SFR Model
3.3. Novel SFR Model under High Wind Conditions
4. Validation of the Novel Low-Order SFR Model
4.1. Validation of the Novel SFR Model under Low Wind Condition
4.2. Validation of the Novel SFR Model under Medium Wind Conditions
4.2.1. Validation of the Accuracy of the Novel SFR Model by Comparison with the Detailed Model
4.2.2. Validation of the Impact of the Initial Operation Point on the DFRC
4.2.3. Validation of the Impact of the Control Parameters , of the AFC on the DFRC
4.3. Validation of the Novel SFR Model under High Wind Conditions
5. Conclusions
Acknowledgments
Author Contributions
Conflicts of Interest
Appendix A
Appendix B
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Quan, R.; Pan, W. A Low-Order System Frequency Response Model for DFIG Distributed Wind Power Generation Systems Based on Small Signal Analysis. Energies 2017, 10, 657. https://doi.org/10.3390/en10050657
Quan R, Pan W. A Low-Order System Frequency Response Model for DFIG Distributed Wind Power Generation Systems Based on Small Signal Analysis. Energies. 2017; 10(5):657. https://doi.org/10.3390/en10050657
Chicago/Turabian StyleQuan, Rui, and Wenxia Pan. 2017. "A Low-Order System Frequency Response Model for DFIG Distributed Wind Power Generation Systems Based on Small Signal Analysis" Energies 10, no. 5: 657. https://doi.org/10.3390/en10050657
APA StyleQuan, R., & Pan, W. (2017). A Low-Order System Frequency Response Model for DFIG Distributed Wind Power Generation Systems Based on Small Signal Analysis. Energies, 10(5), 657. https://doi.org/10.3390/en10050657