The Application Of Nonlinear Circuit Dynamic Analysis Method To Quickly Calculate The Limit Current Of Power System

With the rapid development of the modern power industry,the power system has gradually entered the development stage of large-scale,heavy-duty,long-distance and ultra-high-voltage transmission.The addition of AC and DC interconnection and distributed power supply increases the complexity of the power system network structure and the number of power users and power demand,which leads to bigger difficulty of maintaining safe and stable operation of the power system.Therefore,as for the study of voltage stability,it is of great practical siginificance to figure out the power system voltage stability limit point and ultimate power flow.In the method of calculating the voltage stability limit point,the continuous power flow calculation is generally based on the power flow equation and its extended equation.Using the continuous power flow method,after the parameterization of the equation,the prediction step,the step size control,and the iterative calculation of the correction step reach the region near the system voltage stability limit point,there is a problem of the singularity of the Jacobian matrix,which shows like a slow calculation convergence speed.In order to speed up the calculation,how to choose the appropriate step size is the main research content of the continuous power flow calculation method.Using the dynamic analysis method of nonlinear circuit,the injection power load model is linearized to obtain the dynamic equivalent impedance model of the load branch.In the load node of the system network,by adding the load dynamic equivalent impedance grounding branch,the network dynamic impedance matrix network reflecting the nonlinear characteristics of the system is proposed.The dynamic impedance matrix has the following characteristics: dynamic self-impedance is the system dynamic equivalent impedance of the load node.(ie,the system's Thevenin equivalent impedance)and the parallel value of the load branch impedance,which can quickly calculate the system dynamic equivalent impedance of each load node;by comparing the dynamic equivalent impedance mode of the system with the dynamic impedance mode of the load,the distance at which the load power reaches the limit state can be determined,thereby selecting the appropriate step size for the increase in load power.A method for quickly calculating the ultimate power flow of power systems using nonlinear dynamic analysis methods is proposed.It is proved that when the loadpower reaches the limit state,the load dynamic impedance and the system dynamic equivalent impedance are inverse to each other in the complex domain.Based on this,an iterative calculation method of the network dynamic impedance matrix parameters is proposed.By comparing the dynamic equivalent impedance mode of the system with the dynamic impedance mode of the load,the static equivalent impedance of the load is corrected,and the linear network equation is solved to quickly determine the appropriate load power increase step size.When the load reaches the voltage stability limit state,the self-impedance of the network dynamic matrix tends to infinity,and the criterion for the end of the extreme power flow iterative calculation is proposed.The feasibility of applying the non-linear circuit dynamic analysis method to quickly calculate the limit power flow is verified by the 3-node system and IEEE14-node system simulation.That this method can effectively reduce the calculation amount verifies the correctness and validity of the criterion.