Research On DC Voltage Fluctuation And Suppression Strategy Of Cascaded Power Electronic Transformer

Power Electronic Transformer(PET)is a new-generation power transformer based on power electronic power conversion technology and high-frequency transformer technology.It has obvious advantages in applications such as smart grid and energy internet,and it has receive.d numerous experts and scholars at home and abroad.s concern.Different from traditional power transformers,PET not only has functions such as transformer,electrical isolation and energy transfer,but also has the advantages of power quality isolation,control fault isolation,active AC/DC energy management and panoramic condition monitoring.Therefore,PET has broad application prospects and value in the fields of new energy access,smart grid,energy internet,and locomotive traction systems.Power electronic transformers serve as an important hub for power cornversion.Reliability,stability,efficiency,size and cost are all important indicators for evaluation.For the power electronic transformer itself,the presence of power module parameter differences and net side ripple power will cause problems such as DC voltage DC component instability and excessive ripple voltage component voltage in PET.These problems will have an adverse effect on the stability of PET,reduce the power quality of the network side,at the same time will reduce the operating efficiency of PET,is not conducive to the optimization of the whole volume and reduce the cost.Therefore,.it is of great significance to carry out suppression of DC voltage fluctuations for PET.In this paper,the DC voltage stability and ripple suppression of PET as the main research content,through the in-depth analysis of the mechanism of DC voltage fluctuations,proposed control and operation strategies for each issue.The main tasks include two aspects:(1)DC voltage equalization:In view of the DC voltage fluctuation caused by inconsistent parameters of cascaded PET modules at various levels,the intrinsic mechanism of the DC voltage fluctuation is analyzed in depth and the difference is pointed out.Duty cycle control can avoid the fluctuation of DC voltage.Based on a brief description and comparison of existing researches,a power equalization control strategy based on low-voltage DC bus power feed forward is proposed.Simulation analysis validates the proposed control strategy.Correctness and effectiveness in suppressing DC voltage fluctuations.(2)DC ripple voltage suppression:In view of the DC ripple voltage problem that occurs in the power transmission process of power electronic transformers,the generation mechanism of DC ripple voltage in single-phase systems and three-phase systems is analyzed in depth,and different The system structure features a targeted ripple suppression strategy.The simulation analysis verifies the correctness and effectiveness of the proposed control strategy in suppressing ripple ripple of DC voltage.At the end of this paper,aiming at the research object of the dissertation,RT_LAB system is used to construct a semi-physical experimental platform,and the main controller is drawn and debugged.The cascaded PET control strategy proposed in the paper is digitally designed and experimentally verified.The experimental results show the feasibility of the digital implementation of cascaded PET DC voltage fluctuation suppression strategy and its effectiveness in suppressing DC voltage fluctuations.