Research On The LLC Resonant Converter Based On Digital Control

With the rapid development of power electronics technology,the direction of switching power supply gradually toward the high-frequency,miniaturization,high efficiency and high power density.However,with the increase of the switching frequency,the switching loss of the system will restrict the efficiency and power density of the switching power supply.LLC resonant converter can improve the switching frequency of the system without increasing the switching loss.Synchronous rectification can significantly reduce the output side loss and greatly improve the efficiency of the converter.The research on LLC resonant converter and synchronous rectification is necessary.In this paper,the characteristics of series resonant converter,parallel resonant converter and series-parallel resonant converter are compared and analyzed.It is concluded that the LLC resonant converter can realize the Zero Voltage Switching in primary switches and Zero Current Switching in secondary rectification within the range of wide input voltage and full load.Meanwhile,the parasitic parameters of the system can be used to realize the soft-switching technology,which is beneficial to the device integration and decreases the cost.Then a brief introduction of the key technologies of LLC resonant converter is given.Secondly,this paper introduces the fundamental equivalent model of LLC resonant converter,and derives the expression of gain characteristic of the system.The gain characteristic curve of the system is used to analyze the influence of different inductance ratios,quality factors and parasitic parameters on the system.It can also determine the ZVS conditions of the system and the design process of the resonant parameters.Then,the selection of the power devices in the main circuit is described in detail,such as the resonant parameters and transformers of the system.Next,the hardware and software design of the control system are introduced.At the same time,the advantages and disadvantages of the current driving mode and the voltage driving mode of synchronous rectifier are analyzed and compared.The principle of the synchronous rectifier driving circuit used in this paper is introduced.The interlock structure is adopted to prevent the two synchronous rectifiers from being turned on at the same time.Finally,it’s verified the correction of the theoretical analysis through the system simulation.In order to further verify the correction of the analysis results,a 53.5V/50A power supply module was made using TMS320F28035 as the core controller.The experimental results fully verify the correction of the theoretical analysis.