Current Sharing Control For Resonant Converters In Parallel Operation

Modular parallel technique is an effective way to increase the capacity of DC power systems,enhance system redundancy and reliability.Multi-module interleaved can effectively reduce the input and output current ripples and improve the efficiency of the power system.However,unlike PWM converters,resonant converters using PFM are difficult to realize staggered parallel.Because the resonant elements of each module inevitably deviate.At the same switching frequency,slight differences in the resonant cavity will cause serious imbalance in output currents.To solve the problem,this paper studies current sharing methods of interleaved LLC converters.In order to eliminate the influence caused by the inconsistency of resonant cavities and enable interleaved LLC converters to realize current sharing,this paper studies hybrid rectifiers.By introducing a switch in the rectifier,the LLC converter can fine-tune the output voltage and current through hybrid rectifiers.By adding a degree of control freedom for LLC converters,current sharing of interleaved resonant converters can be realized.Using the state plane method,the working principles and characteristics of the LLC converter with hybrid rectifier in PFM and PWM control are analyzed.An interleaved LLC converter based on LLC converters with hybrid rectifier is presented.Its current sharing mechanism and control strategy are analyzed.A parameter design method is given and a 1000 W prototype is built.The test results show that by adjusting the duty cycle of the secondary side switch,the interleaved LLC converter can realize a wonderful current sharing performance.Considering that active current sharing methods require extra switches and controls,resulting in more complex control and higher cost,this paper studies three-phase interleaved LLC converters with automatic current sharing capability.By building a star-connected structure,the three-phase interleaved LLC converter can realize current sharing without extra sampling and control circuits.The effect of multiple connection methods on the parallel LLC converter’s current sharing is analyzed.The primary-side star-connected three-phase interleaved LLC converters are selected.Its working principles is analyzed and the equivalent circuit model is derived.Based on this model,the influence of parameter design on the automatic current sharing characteristics of the presented converter is analyzed,which can be used to optimiz the parameter design.Finally,a 1500 W prototype is built for verification.The test results show that the presented converter can achieve automatic current sharing.