| Power system stability is becoming increasingly serious with connection of regional power grid and development of electricity market, traditional methods of power system stability can not meet the requirements of the modern power grid. In order to analyze power system stability reliably and quickly, new method of stability analysis need to be research, and the existing methods also need to continuously improve. Application of direct method in power system small signal stability and transient stability has been studied. Major results are as follow:The direct method has been introduced to power system small signal stability, three problems has been solved:(1) method for solving the lyapunov equation of high order system has been studied, several methods has been analyzed and compared, algorithm of command lyap in matlab has been analyzed, this algorithm can meet the requirements of power system small signal stability reliability and rapidity; (2) consistency of direct method and eigenvalue method in stability judgment that between positive definite of lyapnov equation's solution and negative definite of the eigenvalue's real part has been proved from theory and examples; (3) square integral of state deviation indicators has been introduced to evaluate the dynamic process of power system small signal, the formula to calculate the square integral indicators of angle deviation has been derived. Comparison between this method and the minimum damping in eigenvalue method show that they were not consistent in some cases, the square integral indicators of the state deviation in direct method can evaluate the system dynamic performance more comprehensive than the electromechanical mode minimum damping ratio in eigenvalue method.In power system transient stability, qualitative and quantitative analysis of transient stability has been studied:(1) hybrid method which combined simulation method and direct method has been used to judge transient stability, the termination criterion of integral has been given in the simulation process based on the change characteristics of the power-angle state variables and the transient energy, simulation can be terminated quickly to complete the judgment of system stability; (2) the swing information of termination points in hybrid method has been attempted to use in unit grouping, multi-machine system has been equivalence to a single infinite-bus system based on EEAC method, stability index and fault critical clearing time can be obtained by equal area criteria, quantitative analysis of system stability has been achieved, the example shows the effectiveness of the method. |
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