Research And Design Of 3KW Two-phase LLC Resonant Converter

LLC resonant converter with soft switching characteristics can realize zero voltage switching on the primary side of the switch and zero current switching off the secondary side of the rectifier diode in the full load range,with the advantages of low switching loss,high efficiency,high power density,widely used in the design of DC/DC power supply.However,due to the influence of device stress,output ripple and other factors,the application of a single LLC resonant converter in high-power and high-current situations is limited.Parallel connection of multiple power sources is a common method of power capacity expansion.Due to the limitation of technological manufacturing level and the influence of environmental factors,the parameters of each parallel module are inconsistent,which will lead to the unbalanced current of each module.The parallel current sharing of LLC resonant converter is very sensitive to the difference of resonant network parameters,and the small parameter difference will cause the unbalanced load current,resulting in poor load adjustment rate and too wide frequency modulation range.In this paper,a single half-bridge LLC resonant converter is firstly studied,its equivalent model is established by fundamental wave analysis,its working principle and gain characteristics are expounded,and the parameters are calculated according to the design index.Then,the establishment of a bipolar LLC resonant converter parallel equivalent model,introducing the unbalance degree of the reference quantity evaluation of converter output current unbalance degree,according to the model relation imbalance degree is deduced and the resonance parameters,analyzes the three resonant parameters and their combinations on parallel flow of the system,and is verified by simulation.Then,a mean-flow control strategy based on virtual impedance is proposed,in which a virtual impedance is connected in series to the resonant network and the equivalent output impedance of each module is adjusted to improve the mean-flow characteristics of LLC parallel system.The relation between LLC equivalent output impedance and output current is derived by the equivalent transformation of several LLC parallel modules,and the effect of the control method is analyzed by simulation.Finally,according to the design index,a prototype of 3kW dual-phase LLC resonant converter is made,and the effectiveness and feasibility of the proposed control strategy are verified by experiments.