A Study On Two-stage Cascade Converter With Varying DC Bus Voltage

In recent years,high requirements for the power converters’ efficiency,volume and cost are needed in the fields of data centers,LED lighting,electric vehicles and other applications.Therefore,industry and academia have invested huge manpower and material resources on how to optimize and improve the efficiency of power converters.The two-stage cascade converter is widely used in the above mentioned fields.This thesis takes it as a research object and proposes a dc bus voltage dynamic regulation strategy to optimize its efficiency and track the overall maximum efficiency of the converter.Firstly,the analysis and design,device selection and loss analysis of the single phase PWM rectifier and LLC resonant converter are completed.Next,the two-stage cascade converter composed of above mentioned converters,whose former AC/DC converter works in continuous inductor current mode,is studied.And the comparison experiment is completed between the dynamic regulation strategy of the dc bus voltage and the fixed dc bus voltage strategy through the experimental prototype.Finally,the two-stage cascade converter in which the former AC/DC converter works in discontinuous inductor current mode is studied.And the comparison experiment is completed between the dynamic regulation strategy of the dc bus voltage and the fixed dc bus voltage strategy through the experimental prototype.Therefore,the main contents of this thesis can be summarized as follows:Firstly,the selection of topology structure of the front-end AC/DC converter and the rear-end converter is completed in the two-stage cascade converter according to the specific technical indicators.At the same time,the operating modal analysis,parameter design,device selection,analysis and calculation of the loss are completed for the specific circuit topology.Then,the dynamic regulation strategy of the dc bus voltage proposed in this thesis is explained in detail combined with the two-stage cascaded converter in which the former AC/DC converter works in continuous inductor current mode.And,the control strategy and the voltage dynamic regulation adjustment range of the dc bus are analyzed and designed.The comparative experiment is completed between the dc bus voltage dynamic regulation strategy and the fixed dc bus strategy by making a concrete experimental prototype.The experimental results show that the efficiency of the two-stage cascaded converter using the dynamic regulation strategy proposed in this thesis is improved to varying degree compared with the traditional fixed dc bus voltage.Finally,the dynamic adjustment range of the dc bus voltage is analyzed and designed in combined with the two-stage cascade converter in which the former AC/DC converter works in discontinuous inductor current mode.The comparative experiment is completed between the dc bus voltage dynamic regulation strategy and the fixed dc bus strategy by making a concrete experimental prototype.The experimental results show that the efficiency of the two-stage cascaded converter using the dynamic regulation strategy proposed in this thesis is improved to varying degree compared with the traditional fixed dc bus voltage.