Research On Observability Of Power System Low Frequency Oscillation Modes

With the continually expanding scale of power system, transmission network structure is becoming more and more complicated, the low frequency oscillation problem for large-scale interconnected power system is prevalent and increasingly prominent. It’s important for the safety and stability of power system to identify the low frequency oscillation modes fast and accurate, with witch effective control methods could be used. Wide area measurement system (WAMS) provides a new way to analyze and solve the problem of low frequency oscillation in power system. But the phasor measurement unit (PMU) of WAMS needs a large amount of information to be acquired.At the same time, the observability to different oscillation modes varies for PMU in different position.It weighs a lot to figure out how to acquire the low frequency oscillation information more effectively and with less PMU, with witch we could accelerate the speed of analysis and control, thus improving the safety and economy of the power system.This paper studied the observability of the power system low frequency oscillation mode targeting above problems. This paper chooses the generator active power, transmission line active power and the bus voltage as observed variables. With the Newton method in polar coordinates, response expressions of incremental quantity of each observed variable about system oscillation modes were deduced in OMIB system, two area four machine system and multi-machine system respectively in time domain and verified with simulation analysis. Program the proposed theory with MATLAB. With the comprehensive application of MATLAB program, PSD-BPA power system simulation software and PSD-SSAP small signal analysis software, three examples were designed, OMIB area with area oscillation, two area four machine system with area oscillation and two area four machine system with local oscillation. The effect of different observed variables on the power system oscillation modes was studied in the three cases. Summary of the study is expected to provide theoretical support for the PMU distribution and selection of collected information in the future. At last, the effect of load mode, operational condition and electric distance of interconnecting ties on the observability of power system low frequency oscillation modes was studied respectively with two area four machine system cases.