Research On Current Sharing Strategy Of LLC Resonant Converter In Parallel

LLC resonant converters usually need to run multiple LLC modules in parallel in low-voltage and high-current applications.The LLC module adopts a combination of input and output in parallel,which can effectively reduce the current stress of each module’s input and output power tubes.This article mainly studies the control strategy of load current even distribution when multiple LLC modules are operated in parallel.This paper analyzes the working principle of LLC,establishes the fundamental wave equivalent model to derive the steady-state gain function,establishes the small signal model,and obtains the expressions of the transfer function and the input impedance.The main circuit parameter design and closed-loop feedback controller design of LLC resonant converter are carried out,and simulation verification is carried out.In low-voltage and high-current applications,LLC parallel operation is required,and the load current of each LLC module is evenly distributed.However,the deviation of resonance parameters between LLC modules will cause serious uneven load current distribution.This paper analyzes the influence of the difference of Lr,Cr and Lm parameters between modules on load current sharing in LLC parallel system,especially the deviation of voltage gain curve,the influence of voltage gain and the compensation of corresponding quality factor,which cause the difference of load current.The principle.The impedance characteristics of the LLC voltage closed-loop control system and the circulating current impedance characteristics of the LLC parallel system are deduced,and the compensation strategy of the virtual impedance is proposed.Then a closed-loop controller is built to realize the virtual impedance,and finally the simulation verification is carried out.An experimental platform was built in the laboratory to test the steady-state experimental waveforms under different loads when the LLC is running in a single machine and the current sharing effect waveforms when the LLC is running in parallel.The experimental results verify the current sharing strategy proposed in this paper.