Study On The Decoupling Control Of Isolated Multiple Active Bridge DC-DC Converter

With the continuous development of the world's productivity and the change of the global energy structure,the proportion of non renewable energy power generation is becoming less and less,while the proportion of new energy power generation is increasing year by year.And more microgrids need to be incorporated into the large power grid.The power system will be electronic,and the traditional power frequency transformer will be replaced by the power electronic transformer(PET)gradually in the specific field.PET can not only realize electrical isolation and change voltage level,but also can be used as energy router of all kinds of power grid.Among them,PET based on multiple active bridge(MAB)DC-DC converter structure contains the characteristics of multiple DC interfaces of MAB,which can be connected to multiple voltage and power levels of energy network.There is energy coupling between the DC interfaces of the MAB,so the decoupling control of the MAB DC-DC converter is studied in this paper.This paper introduces the classification of PET,and analyzes the advantages of bidirectional DC-DC converter as the intermediate DC-DC link by comparing various topologies.The development of bi-directional DC-DC converter in topology,control strategy and mathematical modeling is described.In view of the coupling problem in the power transmission of the MAB converter,the power decoupling of each DC interface of the MAB converter is the main research content of this paper.The topology and working principle of dual active bridge(DAB)converter are introduced.This paper analyzes the working state and soft switching characteristics of the DAB converter under the single phase shift control,deduces the relationship between the transmission power and the shift ratio of the DAB converter,studies the range of the soft switching of the DAB converter,and verifies the voltage and current waveforms of the switch tubes under the balance and unbalance conditions by simulation.The mathematical model of the MAB converter is established,the working mode and switching characteristics of the MAB converter under the SPS control are analyzed,the qualitative and quantitative analysis of the two power transmission states are carried out.And the coupling phenomenon caused by the multi winding transformer is summarized.The simulation model is built to verify the independent characteristics of each port in balanced transmission state and the coupling phenomenon of unbalanced transmission state.An open-loop current decoupling control is analyzed,and its mathematical principle,parameter design conditions,advantages and disadvantages are introduced.In view of the fact that the open-loop current decoupling control can only solve the decoupling problem of one-way power transmission,the zero shift phase linearization decoupling method is adopted,the mathematical formula being derived,the decoupling matrix of the four source bridge converter being summarized.The application of fixed decoupling method and real-time decoupling method is extended for different application scenarios.A simulation model is built to verify the effectiveness of the decoupling method under the power and voltage change scenarios.Finally,the experimental platform of the modular four source bridge converter with the rated power of 10 k W is built to verify the decoupling effect of the zero phaseshifting linear decoupling method.The platform design mainly includes the hardware and software design of the controller,the main circuit design,the drive circuit design and the high frequency transformer design.