A novel dq-vector based control for the three phase active rectifier in a power electronic transformer

In recent years, Power Electronic Transformers (PETs) are being used in micro-grids, distribution systems, renewable energy systems, traction applications etc., due to their power quality enhancement capability and reduced weight as well as size. The design and operation principles of a three phase active rectifier based PET are analysed in the paper. The structure of PET consists of three parts: a three phase active front end rectifier, a dual active bridge (DAB) based isolation stage, and an inversion stage. A novel dq-vector based control strategy for the rectification stage is explained that does not require phase locked-loop (PLL) to calculate the phase angle, maintains unity power factor at the input side, and provides constant DC voltage at the rectifier output terminals under variable load conditions. A modest controller is used for DAB to generate a desired DC-link voltage signal for the inverter circuit. In addition to unity power factor and constant voltage characteristics, bidirectional power flow can also be possible using the discussed topology. Simulation results using PSCAD/EMTDC are presented to validate the discussed topology and the controller.