Reduced-order model for computing frequency oscillation mode of power systems

Reduced-order model for computing frequency oscillation mode of power systems

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Frequency oscillations with very low oscillation frequencies were observed in several power systems. In frequency oscillations, the speeds of all generators change coherently and the frequencies in the system oscillate together. An equivalent model, which only preserves the governors, turbines, and an equivalent generator, is subsequently built. In the model, the inter-machine rotor-angle oscillation modes are eliminated and only the frequency oscillation mode is preserved. First, a simplified relationship between the total generator output power and frequency is adopted to obtain an original reduced-order model. With the model, an initial estimation of the eigenvalue corresponding to the frequency oscillation mode is obtained. The initial estimation is used to obtain a more accurate relationship between the total output power and frequency, and then an improved reduced-order model is built. With the model, a more accurate eigenvalue estimation can be obtained. Owing to the low order of the proposed model, the computational burden is greatly reduced compared to the direct analysis with fully modelled systems. The test results verify the validity of the proposed method.


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