The Analysis Of Power System Static Voltage Stability Based On Comprehensive Dynamic Equivalent Method

In recent decades,many countries including our country have occurred quite serious voltage collapse accidents,which hinders the safe and stable operation of power system,causes enormous economic losses,so the voltage stability problem draws more and more attention to people.With the increasing scale of power grid,the rapid development of distributed generation and the popularity of electric cars,how to quickly assess the voltage stability of power grid and make corresponding defensive measures to avoid blackouts is always the research focus of electricity workers.Aiming at the problem that Thevenin equivalent method requires at least two power flow operation point data and it exists parameter drift problem,etc.,in this essay,a comprehensive dynamic equivalent method suitable for nonlinear complex system was presented.Concrete steps:power parameter was introduced,Lagrange function was constructed,considering the load power factor changes,it was proved the necessary condition of the maximum transmission active power of nonlinear analytic ancd non-analytic complex power system that load static equivalent impedance mode is equal to dynamic equivalent impedance mode of load node looking into the system;Based on the relationship between the dynamic equivalent impedance of system and static equivalent impedance of load,the corresponding impedance modulus margin index was put forward to assess static voltage stability of power network and judge the weakest node of power system voltage stability,focusing on monitoring the weak nodes.The calculation speed is fast,the theory is simple and intuitive.Through simulation on IEEE30 nodes standard test system under different disturbance ways,the effectiveness of the proposed method is verified.In order to obtain power system voltage stability bifurcation saddle node point,a new mixed method was proposed based on continuous power flow method and local curve fitting method.Concrete steps:by use of comprehensive dynamic equivalence theory,the static voltage stability weakest node of power system was determined by impedance modulus margin values;The increasing step length was obtained by next operating point power flow state predicted by impedance modules of current operating point,so it was realized automatic variable step size,approaching quickly and was not over saddle node bifurcation point;When impedance modulus margin value was satisfied with local curve fitting setting value,namely,to meet impedance modulus margin criterion,the saddle node bifurcation point was accurately fitting and the quite accurate saddle node bifurcation point value was obtained.For this proposed method,the algorithm is simple,the calculation result is accurate,the speed is fast,and it can be used in large scale power network.Through simulation on several IEEE standard test systems,the feasibility of the proposed method is tested.