A hybrid method and its applications to analyze the low frequency oscillations

In this paper, a hybrid method is proposed to calculate oscillatory parameters and the approximate mode shapes (AMSs) of low frequency oscillation based on the measured signals from power system. This hybrid method not only breaks the limitations of the single technique, but also integrates the advantages of all the techniques which are used. Firstly, , two level decomposition is proposed to decrease the influence of mode mixing in the EMD. Then, the Gibbs phenomenon of traditional Hilbert Transform (THT) is reduced based on the normalized Hilbert Transform (NHT). Next, the relative phase calculation algorithm (RPCA) is introduced to realize the generator grouping and mode identification. Finally, the approximate mode shapes (AMSs) of dominant oscillation at different time ranges and frequency distributions are determined. The EPRI-36 bus simulation model and actual measured signals are used to evaluate the performances and validities of the proposed hybrid method.