Modeling of Power Support Capability and Frequency Coordinated Control of DFIG-Based Wind Farm Considering Coupling Constraints of Multi-State Variables

The operational states of wind turbines are different in large-scale wind farms, which presents serious challenges to the frequency control of power systems. The doubly fed induction generator-based wind turbine (DFIG) can be coordinated to participate in frequency control by altering the rotational kinetic energy. The coordinated control of wind farms is usually conditioned by the accurate assessment of the power support capability (PSC) of DFIG. However, the assessment mainly focuses on the influence of single variables such as wind speed and rotor speed. The coupling constraints of rotor speed, pitch angle and rotor current on the PSC are ignored. The PSC of wind farms is still difficult to accurately assess and fully utilize. Therefore, the power characteristics of DFIG under dynamic variations of mechanical power are analyzed. The PSC of DFIG considering the coupling constraints of multi-state variables is modeled. Then the assessment method of PSC considering the coupling constraints of rotor speed, pitch angle and rotor current is proposed. The allocation method of the contribution of DFIG considering different operational states of DFIG is proposed, and the frequency coordinated control method of DFIG-based wind farm is proposed. The effectiveness of the proposed method is verified by case studies.