When calculating noncharacteristic harmonics generated by an HVDC converter, unbalance in the AC system at fundamental frequency and all harmonics must be taken into account. This entails that a full three-phase load flow be part of the solution, as there is considerable distortion interaction between the load flow and the converter. To date, this has been achieved by iterating sequentially between the load flow and a harmonic converter model, in a type of decoupled method which is likely to suffer poor convergence. The decoupled method is implemented here, and convergence compared with a unified Newton solution of the load flow and converter models. Finally, the effect of not modelling the distortion interaction between the two systems is investigated.
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