Research Of Interleaved Half Bridge LLC Resonant Converter

With the higher and higher requirements on power electronic converters of the new energy distributed generation and electric vehicles,due to its advantages such as main switch tube ZVS,post-stage rectifier tube ZCS,high power density and high efficiency,LLC resonant converter has been widely used.However,the large number and size of the electrolytic capacitors that filter the intermittently distributed output current impose various limitations on the power density,lifetime,and application of the converter.In order to solve this problem,the interleaving and paralleling technology between modules is an effective method.However,considering the volume and cost,the number of parallel modules can not be increased without limitation.At the same time,the tolerance of parameters between the parallel modules caused by the manufacturing process will lead to the current imbalance problem in the interleaving parallel.Therefore,the choice of the optimal number of stations and the current sharing control among the modules are the key.In this paper,a new selection scheme of interlaced parallel optimal number is given,through the analysis of the output ripple of different stations output currents and the calculation of electrolytic capacitor capacity of the output filter,and combining the allowable flow of the maximum ripple current of the capacitor,the capacitance change rate of the output filter capacitor when the LLC parallel is greater than four stations is obtained.Finally,it is determined that the interleaving of four LLC converters are the best on the effective reduction of filter capacitor,reducing the cost and volume.In addition,this paper introduces the concept of parameter sensitivity and load current error,analyzes and compares the parameters affecting the current sharing in detail,and proposes a parameter matching and screening scheme to achieve the automatic current sharing of hardware,which can be avoided in the early stage of design.The current sharing phenomenon is simpler and more effective than increasing the current closed-loop control and adding auxiliary components.In this part,the influence of the resonant parameters on the voltage gain,the equivalent impedance and the output current sensitivity is analyzed,especially the effect of the excitation inductor,which provides the basis for the adjustment of the parameters in the wide frequency range.Then,we select the more sensitive resonant inductor,resonant capacitor,the switching frequency and load to analyze the current sharing problem of the optimal number of interleaved,and consider the interactive effects of the parameter differences when multiple units are connected in parallel.At the same time,the analysis of the interleaving angle is added to the current sharing,the analysis to expand the degree of freedom of regulation provided the basis for the successful conduct of the experiment.Finally,a prototype of 360V~420V input and 24V/41.7A output was designed.The hardware design was completed,including the main circuit and the drive circuit.The correctness of the theoretical analysis was verified by experiments.