Improved load-flow techniques for integrated a.c.-d.c. systems

The investigation presented in this paper refers to the development of load-flow techniques in order to improve the accuracy and convergence rates of the standard a.c. programs, when the system contains h.v.d.c. links. In the first part of the paper, an improved simulation of the d.c. link is described. The improvement includes routines for constant-power, as well as constant-current control, checks of control instability, direct interpolation of optimum tap-change positions, and the use of matrix algebra for the interface between the d.c. and a.c. load conditions. In the second part, a program is developed which uses the d.c. routines in conjunction with several standard a.c. load-flow methods, and includes several alternative iterative loops. The program is finally applied to a practical system, and the results of the different combinations are compared.