Double-iterative algorithm for the analysis of power and harmonic flows at AC/DC convertor terminals

The accuracy of the formulation of the convertor models normally used in single-phase and three-phase AC/DC loadflows is restricted by the assumptions of perfectly smooth direct currents and of perfectly sinusoidal commutating voltages. Conversely, the harmonic current injections from convertor plant are calculated from nominal and generally symmetrical conditions and are thus unreliable. An algorithm integrating loadflow and harmonic analysis is proposed in which these assumptions are not made, thus allowing evaluation of their effect on the fundamental and harmonic flow solutions. It is shown that the interaction between the harmonic and load flows cannot be ignored even in the presence of filters, particularly when the convertor plant or AC system parameters are unbalanced.