Installation of series controllers can be considered as a effective method of controlling an electric power flow. In order to calculate the optimal allocation of series controllers and the optimal capacity, it is necessary to solve an optimal power flow problem in which line reactance is taken as a control variable. This optimal power flow problem may have strong nonlinearity and may not be converged. In this paper, a new method which is a variant of interior point methods is proposed to solve such a problem and it is shown by numerical experiments that the proposed method is effective.
