High-penetration wind power grid access requires wind turbine generators (WTGs) to provide frequency regulation, and an accurate system frequency response (SFR) model is required for frequency stability analysis. To overcome the limitations of conventional methods, different operational regions of WTGs and wind speed disturbances are fully taken into account and a frequency response model of wind power (WPFR) participating in primary frequency control is developed by employing small signal analysis theory. Then, the WPFR model is integrated into the conventional SFR model to obtain an extended SFR model, which is given in the form of a symbolic transfer function with two input variables and single output variable, and can clearly and intuitively show the specific parameters that determine the system frequency response. Finally, the accuracy and effectiveness of the extended SFR model are verified through comparisons of the detailed model, and the impacts of initial wind speed, wind speed disturbance, and the wind power's penetration level on the system frequency response characteristics are analyzed and discussed. Such extended SFR model significantly avoids the need for modeling complex transient process while preserving the frequency response fidelity in a satisfactory level. INDEX TERMS Wind power, primary frequency control, small signal analysis, frequency response model, operational regions, wind speed disturbance, extended SFR.

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Control mode and control parameters of the excitation system play an important role in the security and stability operation of generator and even power grid. It is shown in some generator oscillation accidents without system fault in industrial enterprises that there have exciter stability problems in industrial power plants. In this paper, an extended Heffron-Philips model considering Var and power factor excitation system was established to analyze such the excitation system stability problem. And then with the system characteristics matrix system characteristics root will be carried out to study the principle factors on excitation system stability. A parameter optimal method for excitation system considering local power system small signal stability was proposed based on system root locus. The mechanism of abnormal oscillation without system fault occurred in actual industrial power grid was analyzed and the excitation control parameter was redesigned using the proposed method, which was verified by simulation results.Index Terms--extended Heffron-Philips model, excitation system, var controller, power factor controller, small signal stability I.

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