Control and Experiment of an H Bridge Based Three Phase Three Stage Modular Power Electronic Transformer
Compared with conventional power transformer, the power electronic transformer (PET) or solid state transformer has many attractive additional features. This paper focuses on an H bridge based three phase three stage modular PET, which consists of an input stage with series connected H bridge converters, an isolation stage with several independent dual active bridge converters, and an output stage with parallel connected H bridge converters. This PET suffers dc link capacitor voltage unbalancing issue, and the parallel connected module current unbalancing sharing issue. In this paper, a system control structure is proposed for the PET to deal with these issues. Different input stage individual module dc link voltage balancing control methods are analyzed and compared. It is found that the one implemented by directly trimming module output voltage amplitude is most suitable for PET. Moreover, a downscaled laboratory prototype is designed, built, and tehsted to verify the control strategy.
IEEE Transactions on Power Electronics