Research On Interleaved Parallel Technology Of LLC Resonant Converters

LLC resonant converters are widely used due to their natural soft switching characteristics,which can ensure high efficiency under high-frequency operating conditions.However,due to the large output current ripple of a single LLC resonant converter,in order to improve the quality of the output current,two LLC resonant converters are usually connected in parallel,with the phase difference of 90° between the two drives,forming a interleaved parallel connection form.However,the two parallel circuits will inevitably result in unbalance output current due to differences in resonant tank parameters.In severe cases,it can cause one circuit to bear all the load current while the other circuit has almost no current output,affecting the safe and reliable operation of the circuit.To achieve current sharing between two interleaved parallel LLC resonant converters,this dissertation proposes a structure of interleaved parallel LLC resonant converters with automatic current sharing capability.By utilizing the series-parallel connection relationship on the secondary side and the introduction of decoupling capacitors,automatic current sharing between the two interleaved parallel converters is achieved.The structure is simple and easy to implement,and the control method is the same as traditional two interleaved parallel LLC,which not only has the advantages of traditional LLC,it also has the advantages of reducing the number of primary side turns of the transformer,reducing secondary side voltage stress,and automatically balancing power between the two transformers in each converter.After analyzing the working principle and designing the main circuit parameters of the LLC interleaved parallel converter with automatic current sharing capability proposed in this dissertation,a time-domain model of this circuit was established based on Floquet theory,the derivation of Jacobian determinant,determination of steady-state large signal equation,determination of steady-state operating point,and calculation of eigenvalues of Jacobian determinant under different PI parameters were also carried out,finally,the range of PI parameters that can stabilize the closed-loop system is determined by using the stability criterion,and comparative simulation is carried out under different PI parameters,which verifies the effectiveness of closed-loop stability analysis based on Floquet theory and the correctness of the range of PI parameters derived.We have made an experimental prototype with a rated input voltage of 400 V,an output voltage of 120 V,and a rated power of 2k W,and completed the experiment of the interleaved parallel LLC resonant converter.The experimental results verify that the converter has ZVS characteristics;When there are differences in the parameters of the two resonant tanks,it has the ability to automatically balance the output currents of the two channels under different input voltages and load conditions;The output current ripple is significantly reduced;Within the range of 20% rated load to full load,the efficiency of the converter is greater than 96%,and the peak efficiency is close to 97.3%.