Different Switching Positions of On-Load-Tap-Changer of Converter Transformer with Delay Angle Control Harmonic Current Characteristics Analysis

The fundamental components of the UHV DC transmission control system, which are essential to the reliable functioning of the HVDC transmission system, are converter valve delay angle control and converter transformer on-load tap-changer (OLTC) control. However, the converter's harmonic current change rule is directly impacted by the intricate regulatory approach. Thus, using the line commutated converter (LCC) type conventional DC transmission system as an example, we build a control circuit model of delay angle control coupled with tap control in this paper. Current and minimum α angle are constant for the rectifier side, and current and γ angle are constant for the inverter side. The current waveform of the converter transformer network and valve side during the voltage boost and buck process is examined by turning the tap. The findings of the simulation demonstrate that the current waveform's degree of distortion varies with various tapping, with the most severe waveform distortion occurring during the boost operation, which has localized sharp waves and a high harmonic content. Conversely, there is less harmonic content and the waveform tends to be more regular.