The paper gives two digital-computer methods for the determination of power flow in an a.c.-d.c. interconnected power system. For each of the two methods of computation, three examples are used, in which the waveform of the convertor terminal voltage is assumed to be, respectively, purely sinusoidal, approximately sinusoidal and nonsinusoidal.In the view of the authors the methods advanced, which are applicable to any large, fast digital computer, are an advance in accuracy on the equivalent-network concepts developed to use an a.c.-network analyser for the representation of a d.c. system. The two methods are based on the representation of the d.c. system by an equivalent direct voltage and an equivalent direct current, respectively.Calculated results of power flow in an a.c.-d.c. interconnected system, obtained from the computer used, are given.