DC link voltage control of single phase back-to-back converter for medium voltage motor drive

This paper describes DC link voltage control method of single phase back-to-back converter for medium voltage motor drive system. Cascaded H-Bridge (CHB) topology is widely used to achieve medium voltage operation and low harmonic distortion, simultaneously. Each power cell of CHB should have the isolated DC link voltage by using input transformer and rectifier. Instead of three phase Active Front-End (AFE) which is mostly used, using single phase AFE could make the structure of input transformer and power cell be simple. However, even in the same three phase windings of the input transformer, the DC link voltage of each single phase AFE might be different due to the power imbalance of each phase. In this paper, DC link voltage balancing control method that uses the negative sequence voltage of converter is described. The proposed method is verified with experimental results. The DC link voltage of each AFE has been controlled within 1% error of its reference value.