| Two group 12-pulse converters in series are adopted in this paper on the basis of comparison on three proposed ultra-high voltage d.c (UHVDC) converter linetype. The UHVDC converter harmonics model is constructed when 3-pulse model theory is introduced to HVDC transmission. After deeply analysis on the 3-pulse model theory, the current circle of harmonics produced by the UHVDC converter is displayed in the UHVDC transmission line and stray capacitor of converter transformer. UHVDC transmission d.c. side filter system including smoothing reactor, DC filter and neutral capacitor is simply stated and selected. The UVDC transmission system modeled with 3-pulse theory is simulated under various combinations of DC filter i.e. 12/24 filter, 12/24/36 filter and 12/36 filter. The equivalent disturbing current is calculated under these conditions. By comparison of 3-pulse converter model and classic converter model, the correctness of 3-pulse is validated, and proved by the values on different conditions. The introduction of 12/24/36 filter brings about its advantage by contrast with 12/24, 12/36 filter.
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