Analysis And Calculation Of Extreme Power Of Multi-machine System Based On Flexible Equivalence

The actual power system is usually operated under normal conditions.As the system's current operating point gradually approaches the critical point,the overall safety and stability of the system gradually declines.Therefore,from the perspective of safe and stable operation of the system,it is of practical significance to monitor the change of the stability margin over the instability criterion,which also provides quantitative indicators for determining the static power angle stability level of the power system.However,the actual power system is a multi-machine system,and its power-angle characteristic curve is a multivariable function.Theoretically,it is impossible to accurately determine the limit power of a multi-machine system.Therefore,the static power angle stability margin cannot be obtained.At present,a practical calculation method for calculating the limit power of the static power angle of a complex system is based on different assumptions.There are two kinds of calculation methods,namely the constant angle method and the constant active power method.However,these two algorithms all use the constant impedance model.The load power under this model is smaller than the expected value when the system is under small disturbance,and the structural characteristics of the system are not completely preserved.The calculation results may be biased.Based on the principle of flexible equivalence,this paper adopts a constant power load model to simplify the equivalence of systems viewed by PV nodes.By analyzing the extremum conditions of the PV nodes active power in the simplified system,the critical state criterion for the static power angle stability of the power system is proposed,and the resistance margin for evaluating the static power angle stability of the PV nodes is obtained.According to the system power flow equation,the resistance margin of the PV node is obtained.The voltage static characteristics of the nonlinear components in the system are fully considered.The structural characteristics of the system are completely preserved,and the static power angle stability state of the system can be accurately determined.The resistance margin is equivalent to the full-step power factor of the single-machine infinite system,and has a sine function variation law.It can intuitively reflect the distance that the current operating point of the system reaches the critical point,and provides quantitative indicators for the safe and stable operation of the power system.According to the above critical state criterion for static power angle stability,a method for calculating the static power limit stability power system power system is proposed.Based on the convergence of high-order Taylor series and the system flow network equation,the third-order Taylor series non-linear equivalent model of node voltage mode,node voltage phase angle and power factor angle is established.According to the criterion of the critical state of the static power angle,the unique maximum of the Taylor series is determined in the critical state of the system,and the Taylor series non-linear equivalent model is applied to obtain the critical power angle and the limit power of the complex system.This overcomes the difficulty of solving the limit power of complex systems.IEEE standard system simulation results show that compared with the traditional practical calculation method,the proposed method preserves the nonlinearity of the system components,and the calculation speed and calculation accuracy are greatly improved,which verifies the accuracy and rapidity of the model built in this paper.