Improved Continuation Method And Tracing PV Curves Based On Extended Thevenin Equivalent Circuit

Power system has got fast development for meeting the electrical user rising demand in recent years, but power system often runs close to limit point, followed by a series of voltage stability safety accidents. Therefore, the voltage stability problem is one of the hot spot in recent studies. To get the voltage stability critical point and PV curves have extremely vital significance in the study of voltage stability. CPF is the important tool of voltage stability analysis, which can get accurate voltage stability limit points and PV curves, but existing methods have large-capacity computing. In the paper, the research direction is the CPF, the improvement of calculating CPF and tracing PV curves quickly are on further research with good effect.The step size controlling is the key to the computation for CPF. An improved continuation method with controlled step size with the predicted limited power flow is presented. First the paper extended Thevenin equivalent theory in linear circuit, and it proved that the maximum power transmission power system is a necessary condition: Thevenin dynamic equivalent impedance mode should be equal to the load equivalent impedance mode; then this algorithm uses predicted limited power flow based on the load impedance changes leaded by Thevenin dynamic equivalent impedance to adjusts step size automatically, which can be proved accurately and effectively to obtain the voltage stability margin in IEEE14,IEEE30,IEEE57,IEEE118standard system.In order to further improve the speed of calculating the PV curve and voltage stability critical point, the paper presents a method based on the current mode for calculating PV curve fast, which from another aspect concisely proved the extended Thevenin dynamic equivalent theory in nonlinear power system. The load power factor can be arbitrarily changed. The theory turned the complex non-linear AC power system into the simple DC power system, and converted the variables to the mathematical equations of current modes for load node. The paper calculated the Bifurcation of the voltage stability and PV curves, also gave the rapid PV curves algorithm process, which can be proved accurately and effectively to in IEEE14, IEEE30standard system of matlab.