Determining modes of low frequency oscillations based on power oscillation flows in the tie lines

This paper proposed a new algorithm to perform the online determination of the low frequency oscillation modes in large interconnected power system. First, the generator´s active power and its speed deviation were represented in the form of generalized phasor and the relationship between their phase angles was deduced. Then a simple system was constructed to illustrate the correspondence between the power oscillation flows in the tie lines and the low frequency oscillation modes. Theoretical analysis indicates that different oscillation modes correspond to different phase angle combinations, and vice versa. The small signal stability of the SE Australian power system was analyzed by PSS/E. The analysis reveals that both of the operating point and modeling deepness have essentially no effect on the correspondence between oscillation modes and phase angle combinations. Finally the procedure to use the algorithm in practical power system was given, and it was applied to the Eastern China power grid. Results indicate that the algorithm proposed by this paper is able to determine the low frequency oscillation modes online and is helpful for the monitoring of low frequency oscillation.