Research on Inter-Converter Harmonic Interaction of Multi-feed DC System Filter Switching Condition

The harmonics at the AC side of each converter station in a multi-feed DC transmission system have an interaction effect. The definitions of the AC side harmonic absorption and harmonic amplification in the multi-infeed DC transmission system are respectively given, and their occurrence phenomena are described. Some specific switching methods of AC filter combinations may cause the interaction of harmonic currents between converter stations. Based on the harmonic impedance method, this paper defines the harmonic current interaction coefficient of converter stations, which is used to calculate the interaction degree of harmonic currents between converter stations. Taking the multi-converter station system composed of three converter stations as a study case, a harmonic impedance model with AC filters was built, and the influence coefficient of harmonic current was calculated for the characteristic harmonics. The influence coefficient of harmonic current is calculated, and the influence of AC filter combination switching on the interaction of harmonic current of the corresponding loop inverter station is analyzed. The results show that the interaction effects of the 11th and 13th harmonic currents are small, while the interaction effects of the 23rd and 25th harmonic currents are relatively large, and the switching of specific filters will cause the absorption and amplification of the harmonic currents of the AC busbars of each converter station. The absorption and amplification of the harmonic current are analyzed by the current interaction coefficient, and the harmonic attenuation and gain conditions are obtained. Finally, a PSCAD electromagnetic transient simulation model is established to verify the above analysis results.