Research On Design Of Phase-shifted Full-bridge Converter

With the development of power electronics technology and control theory,power electronic products have been widely applied.As a circuit widely used in medium to high power scenarios,the phase-shift full-bridge converter stands out in many power conversion applications because of its simple structure,convenient control,and the fact that the main switch in the phase-shift full-bridge converter can achieve soft switching compared to general hardswitching circuits,reducing the converter losses.This dissertation first introduces the topology of the phase-shift full-bridge converter,analyzes its detailed operating modes,and solves two problems faced by the converter: First,the limited range of soft switching.On the one hand,it is more difficult to achieve soft switching in the lagging bridge arm of the phase-shift full-bridge converter than in the leading bridge arm.On the other hand,under light load conditions,the primary current decreases,and the resonant inductor can store less energy,making it more difficult for the main switch to meet the soft switching conditions.Second,the problem of parasitic oscillation on the secondary rectifying tube.During the commutation stage,the parasitic capacitance on the rectifying tube resonates with the leakage inductance of the transformer and the resonant inductance on the primary side,producing parasitic oscillations and voltage spikes,which affect the stability and efficiency of the circuit.To address these issues,this dissertation achieves soft switching of the converter through the rational design of circuit parameters and effectively suppresses parasitic oscillations on the rectifying tube by adding clamp diodes and CDD passive buffer circuits.In addition,in order to reduce the losses of the converter,synchronous rectification control is adopted on the secondary side.The losses under two synchronous rectification control timings are compared and analyzed.Finally,the slanting diagonal bridge arm or logical control timing is used to optimize rectification losses.Circuit parameters such as high-frequency transformers,resonant inductors,output filter inductors,and output filter capacitors are calculated,and circuit design and chip selection are carried out to design a main circuit and control circuit that meet the requirements.In the average current control mode,the phase-shift full-bridge converter is modeled for small signal analysis to obtain the voltage-current openloop transfer function of the phase-shift full-bridge converter.By analyzing the Bode plot,a suitable PI compensation network is corrected to obtain the corrected closed-loop control system.A simulation model is established to verify that the system has good stability and dynamic characteristics.Finally,an experimental platform for the phase-shift full-bridge converter was constructed,achieving soft switching of the lagging bridge arm and effectively suppressing the parasitic oscillation on the rectifier tube,thus solving the above problems and achieving the design targets.