| The UHVDC (Ultra-High Voltage Direct Current) converter can be considered as harmonic source because of its nonlinear characteristics. Harmonics will propagate both at AC side and DC side when UHVDC put into operation. Effects of power dissipation, temperature rising and acoustical noise caused by the converter harmonics will be given after quantity analysis. The results will be helpful to UHVDC project design. During the studies of the origin of the UHVDC harmonics, the non- characteristic harmonics in UHVDC have been analyzed based on modulation theory by considering three non-ideal conditions: the unbalance of ac voltage supply, the unbalanced three-phase impedances of the transformer and the unequal intervals of the triggering pulses. New models for simulating the double 12-pulse series converters have been developed for modulation analysis. In order to study the harmonic transferring process in AC power grid, a network model containing all the voltage levels is formed according to the practical circumstances of the power network in China. And the UHVDC harmonic current source is supposed to be connected to 500kV side and propagating down to low level voltage networks. The mechanism of harmonics propagating is analyzed and the recommend total harmonic distortion standard at the AC side of UHVDC is proposed. |
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