Research On Effects Of The Composite Load Model On Small Signal Stability In Multi-machine System

With the power grids connected, low-frequency oscillation occured in many power grids of china. Low-frequency oscillation has great impact on the power system. At present, domestic and international research on low-frequency oscillation mainly concentrate on power supply side and the theory of the effects of load model on low-frequency oscillation is still not clear. In fact, load model has great influence on power system dynamic analysis and control. Since low-frequency oscillation is subordinate to small signal stability, it has great significance to analyze the effects of load model on small signal stability in power system.The models of power system equipments in small signal stability have been established. The link between the free response of the dynamic system and the sensitivity of the eigenvalue to the system state matrix leads to the concept of sensitivity factor. First analyze the effects of the uncertainty of the load model parameters on system state matrix, and then use the concept of sensitivity factor to analyze the effects on small signal stability of the system. The formulas of sensitivity of damping ratio and oscillation frequency to load model parameters have been derived based on the formula of sensitivity of eigenvalue to model parameters. How the damping and the oscillation frequency of the system change with the parameters can be analyzed. The results of these two aspects have been concluded and a method to analyze the effects of the uncertainty in load model on small signal stability in power system has been proposed in this paper. The method is suit for multi-machine system analysis, as its derivation does not depend on the specific strcture of the system. As it avoids the difficulty in damping analysis of multi-machine system using damping torque method and locates the effects of load model on system oscillation modes at specific parameters, this method has solved the problem that how load model influence oscillation modes in power system and has a practical significance. The effectiveness of the method proposed in this paper has been verified by analyzing the two-area four-machine system.