The Static Voltage Stability Analysis Based On Thevenin Equivalent

With the rapid development of China's economy,the scale of the power system is continuously expanding,and the new energy is connected to the grid on a large scale.The voltage stability problem of the power system is becoming more and more serious.The accurate calculation of the Thevenin equivalent parameter calculation method and the load margin calculation method is of great significance for the static voltage stability analysis of the power system.In the voltage stability analysis of the power system,different equivalent methods are used to determine the network's Thevenin equivalent circuit,and the values of Thevenin equivalent impedance obtained are not the same.When the impedance modulus index is used to judge the voltage stability,the conclusion is inconsistent.Three representative calculation methods were selected to determine the Thevenin equivalent parameters.The simulation was carried out in the IEEE standard system,and the effect of using the impedance modulus index to judge the voltage stability of the power system was analyzed.Through the IEEE standard system simulation analysis,it can be obtained that when the established equivalent network and the original network voltage-to-power sensitivity change trend are consistent,the impedance modulus index can accurately determine the static voltage stability limit point of the system,and its impedance ratio index It can also better reflect the static voltage stability of the system.According to the simulation analysis of three kinds of Thevenin equivalent parameters calculation method,a new calculation method of the Thevenin equivalent parameter is proposed.In the current operating state of the system,the proposed method is used to obtain the Thevenin equivalent circuit of the power network,and the tidal current state and the sensitivity of the voltage to the power are consistent with the original network.The method utilizes the tidal current solution of the equivalent node and the voltage-to-power sensitivity value of the equivalent node.Through simulations in IEEE9 node system and IEEE39 node system,it is proved that the static voltage stability limit point can be accurately obtained by using the impedance modulus index index under different load models and fluctuations.The impedance modulus index can better reflect the static voltage stability,and the calculation amount is small.The impedance modulus index can reflect the voltage stability of the system,but it is difficult to accurately and clearly give the margin level of the load.Combined with the power system's Thevenin equivalent circuit and the continuous power flow method,a method for calculating the voltage stability margin quickly and accurately is proposed.The method of predicting the voltage stability limit point based on the Thevenin equivalent circuit is studied.According to the estimation result,the adaptive variable step size control method is proposed to improve the calculation efficiency.In order to improve the computational efficiency,the selection method of the equivalent nodes and the step correction method are proposed.A prediction method combining the equivalent circuit and the linear method is proposed.A more accurate prediction is achieved without increasing the amount of calculation.The simulation is carried out in the IEEE9 node system,the IEEE39 node system and the IEEE2736 node system.Under the same simulation conditions,compared with the conventional variable step size method,the proposed method can reduce the amount of calculation.The proposed method solves the problem that the conventional continuous power flow method is too large,and can quickly calculate the voltage stability limit point of the power system and obtain an accurate load margin.