LLC Resonant Converter Interleaved Parallel Uneven Current Problem Research

LLC resonant converter has excellent performance of high transmission efficiency and high power density due to its soft switching characteristics and high frequency operating conditions.However,for the further application of the output current ripple and the stress limiting LLC resonant converter of circuit devices,the application mode of interleaving and parallel can effectively solve the ripple problem and the problem of excessive stress of components in the application scenario of low voltage and high current,so the interleaving and parallel multi-channel LLC resonant converter has a good application prospect.Because the parameters of the resonant element have a great influence on the voltage gain of the LLC resonant converter,the minor parameter deviation of the resonant element will lead to the serious current imbalance of each LLC resonant converter.In order to solve this problem,this paper mainly carries out the following research work:(1)The circuit topology and working state of the single-loop LLC resonant converter are analyzed.Based on this,the fundamental wave equivalent model and converter frequency-output voltage transfer function model are derived,and the circuit gain analysis and circuit parameter design of the LLC resonant converter are carried out,which serve as the basis for the staggered parallel analysis of the two-channel LLC resonant converter.(2)The causes of uneven alternating parallel current in multi-channel LLC resonant converter are analyzed from the principle.The synchronous rectifier on the secondary side of the converter is replaced by controlled rectifier,and the output current of each channel is used as the control signal to carry out pulse width modulation control on the secondary side,so as to provide additional voltage gain and form a current-sharing control loop to ensure the voltage gain of each channel is the same.Thus,the multi-channel LLC resonant converter can operate at the same switching frequency.(3)Based on the electromagnetic transient process,the staggered parallel simulation of the single-loop LLC resonant converter and the two-channel LLC resonant converter is carried out,and the current unbalance degree under different load rates is obtained.An experimental prototype of a 100 W two-channel LLC resonant converter was built in the laboratory,and the feasibility and effectiveness of the current sharing control method were verified under the condition of maximum current unbalance.