Research on control method for avoiding transformer magnetic biasing in cascaded H-Bridge multilevel inverters

Cascaded H-bridge (CHB) multilevel inverter has gained more and more focus due to its adaptability to high-power, high-voltage applications and capability of fault tolerant. Under the circumstance of instantaneous value feedback control, the magnetic biasing of the transformer is a problem of great significance. This paper shows the circumstances under which a transformer has to be used for the CHB multilevel inverter, and the adverse impact of the magnetic biasing of the transformer. Also, it analyses the mechanism of the occurrence of the DC component in output voltage which causes the magnetic biasing, then the carrier phase shifted modulation strategy of the CHB multilevel inverter is discussed. Finally, this paper proposes a novel control scheme with several advantages compared with other control schemes which can eliminate the magnetic biasing of the transformer. The experiment results are carried out which verifies the advantages and feasibility of the proposed control scheme.