Research On Soft Switching DC/DC Converter Based On Coupled Inductors

The constant pursuit of miniaturization,high frequency,high efficiency of switching power supply has prompted resonant-switch technology to be widely used in DC/DC converters.The resonant-switch converters overcome the defect that the resonant elements participate in energy transfer during the whole switching period while keeping the natural soft switching and low electromagnetic interference of the resonant converters,and is favored in the process of high frequency conversion of the DC/DC converters.Based on the study of current research results,the paper proposes a novel zero current switching(ZCS)resonant-switch converter based on coupled inductors.In this converter,a single closely coupled inductor is used as the resonant element,avoiding the problem of large volume caused by multiple resonant inductors,and the energy in the leakage inductance is fully absorbed by the resonant capacitor,which can weaken the impact of current and voltage.The converter adopts a pulse frequency modulation(PFM)strategy with constant conduction time.The switches can realize natural commutation according to the output voltage,and the switches can realize stable ZCS turn-on in a wide range of input voltage and switching frequency.With the voltage clamping effect of coupled inductors,the voltage stress of the switches is further limited on the basis of realizing zero voltage and zero current switching(ZVZCS)turn-off,and the output diode is turned off naturally,which overcomes the problem of reverse recovery.In order to improve the limitations such as narrow regulation range of output voltage and relatively low power level,an isolated ZCS resonant-switch converter based on three-winding coupled inductors is constructed,which by replacing the position of the coupled inductors and switches and increasing another inductor on the output side.In this converter,the primary and the secondary side share the coupled inductors and switches,the resonant mode provides a soft switching environment for the switches on the primary side,and the coupled inductors realize magnetic reset automatically by transferring energy to the output.In addition,by reasonably configuring the turn ratio of the primary and secondary coupled inductors,the degree of freedom for controlling the output voltage is increased,thus realizing the two-degree-of-freedom regulation of the output voltage,widening the regulation range and making its application more diversified.By analyzing the steady-state operation principle of the proposed converter,the equivalent circuit of each operating modes is divided,the mathematical model of each modes is derived,and the steady-state characteristics including output voltage characteristics,ZCS critical condition,voltage and current stress are analyzed in detail,especially the leakage inductance and its influence is discussed.According to the results of theoretical analysis,the principles of parameter designing and loss analysis are carried out.Finally,the simulation model of the converter is built with Pspice,and the simulation results prove the accuracy of theoretical analysis as well as the superior performance of the converter.