Abstract
Dynamic stability calculations in power system have been mainly analyzed by the time span in the order of second and many researches in this area have been carried out. But today we need long-term calculations in the order of minute because of the complicated bulk system analysis. In Japan, gnerally, dynamic stability is .analyzed by the so-called alternating solution, which uses the 4th order Runge-Kutta method and the Y-method (for circuit calculations) alternatively. This method has high accuracy and is very simple in programming, but in the case of long-term analysis the Runge-Kutta method becomes unstable, and we can not obtain correct solutions. Today, especially in the U. S. A., the trapezoidal method instead of the Runge-Kutta method is widely being used. In the trapezoidal method the differential equations are solved simultaneously with the circuit equations. However this trapezoidal method tends to lead oscillatory trajectories. Because this property is critical for long-term calculations, the acurracy of the trapezoidal method becomes a problem. In this paper a number of numerical analysis methods are tested for finding the best method for the long-term stability calculation, and a suitable scheme for this purpose has been found.
