Optimal Design And Parallel Current Sharing Control Strategy Of LLC Half-bridge Resonant Converter

With the rapid development of high-frequency power electronic technology in the21 st century,reducing energy consumption is one of the important topics in the development of modern power electronic technology.With the development of LLC resonant converter with good soft-switching characteristics,high power density and high efficiency,resonant power modules are more and more frequently used in high-power occasions,which puts forward higher requirements for the optimal design of converter and multi-module parallel technology.The main contents of this paper are as follows:Firstly,the development process and research status of resonant converter are reviewed,and the performance differences of various resonant converters are compared.The advantages of LLC resonant converter compared with other resonant converters are clarified.On this basis,the equivalent fundamental approximation method is used to analyze the important characteristic parameters of LLC half bridge resonant converter,which provides the theoretical basis for the optimization analysis of device parameters for the later prototype development.Then,the simulation circuit topology of LLC resonant converter is designed and built in the Simplis simulation software,and the operation waveforms of LLC resonant converter under different loads are simulated by using this group of design parameters,which preliminarily confirms the feasibility of the design.The efficiency of LLC resonant converter is further optimized in hardware experiment.Starting from the control mode of LLC resonant converter under light load or no-load starting,the efficiency of LLC resonant converter is optimized by using FAN7688 chip with PWM(pulse width modulation)and PFM(pulse frequency modulation)mixed control mode.FAN7688 is a PFM controller of LLC resonant converter,which has synchronous rectification control function,charge current control,good transient response characteristics and simpler feedback circuit design.The energy saving function of symmetrical PWM control under light load can limit the switching frequency,reduce the switching loss and improve the efficiency of light load.Finally,the power limitation of single module operation leads to the parallel operation mode of two modules.In the process that distributed generation is gradually replaced by more portable,small and efficient resonant switching power supply,it is the development trend that two or more resonant converter modules are operated in parallel to reduce the single-phase current stress,conduction loss,output current ripple and the volume of filter capacitor at the output end under the condition of high power output.The multi module parallel power supply system,which is developing towards higher efficiency,can adopt the modular design scheme,which solves the problems of complicated design of single switching power supply,long development cycle and unable to ensure the stability of the system.However,in practical engineering applications,due to the influence of various factors,there will be differences in power distribution,that is,the current can not be completely evenly distributed in each phase.The current sharing control strategy of the parallel module becomes an important technical support for the resonant converter to achieve high efficiency in parallel operation.The parallel prototype system controlled by droop current sharing method is simulated in Simplis to verify its current sharing effect.