In literature (e.g. in [4], [5] and [6]), the Newton-Raphson method is well described and fully
understood. However, not enough space is given to handle the numerical instability. Several different
approaches can be applied to improve its numerical behaviour. Possible algorithms to find suboptimal
value of a relaxation factor for state variable update are introduced in [1] and [2] by Heckmann et al.
and by Koh, Ryu and Fujiwara, respectively. Tate in [9] calls attention to fractal behaviour of the load
flow analysis using the Newton-Raphson method and gives detailed advices, such as r/x ratio
modifications, state update truncations and one-shot fast-decoupled method, to avoid possible
divergence or convergence to non-physical load flow solutions. Several different procedures using
second Taylor series expansion, Jacobian adjustments and Levenberg-Marquardt method are
introduced in [3]. Schmidt in [8] offers several changes in input data files of tested power systems,
which may lead to better numerical stability and convergence.