Modified Feedforward Control to Suppress DC Voltage Disturbances for Three-Stage MMC-PET

Power electronic transformer (PET) has attracted significant attention from academia and industry because of its excellent function integration, including flexible energy management, adaptable voltage variation, and accurate power quality regulation. The modular multilevel converter based PET (MMC-PET), which is architected as three-stage structure with both low voltage dc bus and high voltage dc bus, gains great popularity due to its adaptability in large-power and high-voltage cases. To achieve an excellent output performance and maintain system stability, the voltage at DC buses in MMC-PET should be well controlled. This paper puts forward an improved control strategy to suppress DC bus fluctuations during the occurrence of some external disturbances. The proposed control introduces the feed-forward power path to outer voltage loop, thus the system power change could be offered to each stage directly, which would help the DC buses of MMC-PET recover with smaller fluctuations and shorter time under abrupt PET power changes. The effectiveness of the proposed control strategy is verified by the simulation results.