Supraharmonics Mitigation Strategy of Rolling Mill Converter Clusters Considering High-frequency Circulating Currents

The integration of fully-controlled rolling mill converter clusters leads to an increase in the supraharmonics content of the distribution networks. Each rolling mill converter operates in different states with inconsistent carrier phases, resulting in serious high-frequency circulating currents(HFCC) between converters. Moreover, existing carrier phase-shifting strategies fail to mitigate supraharmonics and HFCC comprehensively. Within this context, this article proposes a supraharmonics mitigation strategy considering HFCC for rolling mill converter clusters. This strategy is founded on the tenet of random carrier frequency pulsation width modulation. According to the correlation between carrier frequency randomness and supraharmonics amplitude and phase randomness, the supraharmonic emission characteristics are modeled, and the HFCC model is constructed. The interactive coupling mechanism of supraharmonics of converter clusters under random carrier frequency is analyzed. Additionally, the carrier frequency is randomly changed so that switching frequency dominated harmonics are not formed between converters. Consequently, the generation of HFCC is suppressed. Finally, real case studies are conducted to validate the efficacy of the proposed means. The outcomes indicate that the mitigation rates of grid-side supraharmonics and HFCC are more than 88% and 85%, respectively, indicating satisfactory comprehensive mitigation performance.