AC/DC Harmonic Interaction in HVDC Systems

The harmonic interaction between AC- and DC-systems has been discussed in various publications with respect to both charactcristic and non-characteristic harmonic phenomenon injected into ac-power transmission systems by HVDC converters. However, in recent convener stations different magnitudes of harmonic currents than the theoretical predicted values have been measured. This paper describes a mathematical circuit analysis to determine the transfer of harmonics from the supplying ac-grid to the receiving ac-system and vice versa connected by HVDC links. In general there are mathematical rules, which type and magnitude of harmonics (dependent on the positive or negative sequence system components) will be transferred through the dc-circuit and injected into the receiving power grid. A mathematical model is represented to describe the transfer of harmonics (harmonic voltage distortion from the sending ac-system) through the HVDC link and its impact on the receiving ac-side. The contribution of these harmonic voltages has been analyzed and will be considered for modelling the harmonic current source for the inverter terminal. The model is valid for power flow in both directions.