Simulation of convertor performance under unbalanced conditions

The paper is devoted to the development of mathematical models for the analysis of the behaviour of h.v.d.c. convertors during unbalanced a.c. faults. A current-source simulation is used for the convertor in either 3-phase or sequence components representation. The analysis using these models can be adapted for digital/analogue simulation. Using the digital approach, results were obtained for systems with varying degrees of unbalance, and limits of normal operation were established. For normal operation, the degrees of unbalance of the convertor currents were determined. This provides both the pattern and the limits of variation of these currents, which form a valuable basis for the assessment of overall performance of a.c./d.c. interconnected systems.