Research On The Characteristics Of DFIG-based Wind Turbine With The Ability Of Inertia And Primary Frequency Response

The large-scale development of wind power is one of the core objectives to promote Smart Grid construction in China. Based on the characteristics of the wind resource distribution, large-scale wind power development mode with high concentration and long-distance transmission by HVDC/EHVDC is widely used, which poses a severe challenge for the operation stability and reliability of power system, so does the issues arising from fast-developing distributed generation. Meanwhile, due to the continued expansion of offshore wind and high wind power generation proportions, low inertia and power system frequency stability is inevitable to be the significant scientific and technical challenges for the wind power development.This paper focuses on the realization mechanism of short-term dynamic power support and island operation for DFIG-based wind turbines generation system. Then the mechanism of interaction between the machine itself and the dynamic characteristics of DFIG-based wind turbine(DFIG WT), with the ability of inertia and primary frequency response, is explored. Additionally, the outcome possesses important theory and practice significance for the large-scale development of wind power and power system operation security.First, this paper outlines the basic control of DFIG WT and the principles of inertia and primary frequency control. In this paper, the rotor side control(RSC) and grid side control(GSC) are both based on the orientation of the stator terminal voltage with phase lock loop(PLL) synchronization control. In this case, the principles of inertia control is explained from the perspective of internal voltage dynamics, i.e., altering power angle which is determined by active power and reactive power, adjusting PLL bandwidth, or adopting slow synchronous control. Analogizing conventional synchronous generator(SG), primary frequency control of DFIG WT is achieved by adjusting the pitch angle, which is to maintain the pre-set reserved mechanical power. On the basis, this paper reviews the DFIG WT inertia and primary frequency control, besides proposes some associated design principles.Then, the electromechanical characteristics of DFIG WT is elaborated with the phase movement equation of DFIG WT’s internal voltage, meanwhile the equivalent inertia and damping coefficients are derived. In this sense, the coupling effects between DFIG WT’s electromechanical behaviors and its machine components &electrical control dynamics are hence revealed.Lastly, the research suggests that DFIG WT, with additional inertia and primary frequency control, has the similar structure form and dynamic power transmission process with SG. In this sense, DFIG WT has the ability to operate in island mode like SG. It should be noted that the frequency feedback control(like droop control) need to be introduced to keep frequency stability and synchronization stability for DFIG WT’s stand-alone operation. In addition, the analysis and verifications about the island system stability mechanism, by taking DFIG WT operating under different wind speeds into consideration, are finally presented in this paper.