Contents I. INTRODUCTION
POWER systems are typical stiff systems. The solutions of such systems require a suitable numerical integration method. Conventional integration methods are generally classified as implicit or explicit methods depending on whether or not only past values are required to compute new values of the state variables. Unfortunately, most of the explicit methods are conditional stabile, and usually they are unsuitable for stiff systems. On the other hand, the implicit methods have the danger of calculation; namely, the region of absolute stability for an algorithm is not equal to the region stability of the system, though they may be A-stability.
