Optimal Design Of Bidirectional CLLC Resonant DC Converter

With the development of new energy and energy storage technology,a large number of unstable distributed power sources are connected to the power grid,which not only brings great challenges to the stable operation of the power grid,but also brings difficulties to the control.Among them,power electronic transformer combines the characteristics of traditional power transformer and power electronic transformation,can realize the flexible access of AC/DC power supply/load,and has the flexible regulation function of electric energy,which has been widely concerned and applied in engineering.As the core of power electronic transformer,the highfrequency isolation link affects the loss and control range and device volume,so the research on its isolation link is particularly important.Among them,bidirectional DC/DC converter,as a common interface converter,can realize electrical isolation,voltage conversion and two-way flow of energy,and is widely used in electric vehicles,renewable energy and power electronic transformers.In this paper,CLLC resonant DC converter is used for DC/DC converter applied in isolation link.Combined with the practical application and characteristics of the converter,a hybrid control mode,namely full-bridge variable-frequency,fixedfrequency phase-shifting and half-bridge variable-frequency control,is proposed.This hybrid control can further increase the gain range and reduce the frequency variation range without increasing the auxiliary circuit and changing the original topology,thus solving the problem that the frequency variation range of the traditional CLLC resonant converter is too large when it is applied to the wide gain situation.At the same time,a parameter design method is given to realize the soft switching characteristics of CLLC resonant converter,calculate the resonant inductance according to the parameters of the MOSFET used in the application scenario,and then analyze the influence of the parasitic parameters of the converter device on the voltage gain of the DC transformer under light load,which can ensure that the relatively simple closedloop feedback control is effective while increasing.the efficiency of the converter.Finally,the CLLC resonant converter in the application scenario is simulated and verified by a design example.The simulation software is used to build the model to verify the effectiveness of the hybrid control,that is,it can achieve the requirements of wide voltage gain.Compared with the traditional design method,the frequency variation range is also small.At the same time,the parameter design is compared with the traditional parameter design method under the frequency conversion control mode,and the magnitude of the resonant current is compared through the waveform diagram.It is concluded that this control method can reduce the current value of the resonant cavity,thus reducing the loss and improving the efficiency,which proves the superiority of this parameter design method.