Research On Optimal Control Technology Of Active Clamp Flyback

With the sustained advance of technology and the seriousness of energy loss,we are not only satisfied with the simple charging function,but also put forward higher demands on the use of adapters: it is hoped that while ensuring fast charging,adapters can provide power conversion more efficiently.Taking mobile phone charger as an example,charging protocol controls charger to output different powers at different battery levels,so adapter is required to maintain high efficiency within the full load range.Therefore,improving the conversion efficiency within the full load range is one of the keys to the research of adapters.In this thesis,different topologies applicable to power adapters are compared,then active clamp flyback(ACF)circuit is chosen as the research objectives.By comparing the features of different control strategies of the traditional ACF circuit,this thesis also clearly points out that the cyclic energy generated in the fixed frequency control and complementary mode is the main factor for the low light load efficiency of the ACF circuit.Therefore,taking frequency conversion control and dual-mode operation as the core scheme is the basic mind to lift the efficiency of the ACF circuit both in a full voltage range and a full load range.Aiming at solving the problems of the traditional frequency reduction control scheme that the output feedback error amplification signal voltage is used as the referrence,this thesis proposes a dual-mode active clamp flyback(SCE-DMACF)controller based on secondary-side current emulation to realize the load-adaptive adjustment of the switching frequency.The thesis analyzes SCE-DMACF theoretically from the topology and the control idea,gives the derivation process of parameters design and loss calculation in the power circuit,and analyzes the influence on the resonant current and the on-state loss in the resonant circuit caused by the sampling resistor.Combined with the parameter design process,the calculation of switching frequency curve and gain curve of SCE-DMACF is deduced,and the small signal equivalent model is established to design the control loop compensation.Finally,the circuit simulation is implemented in PSIM,which verifies the preliminary feasibility of the new scheme.By learning from the simulation circuit,a65 W experimental prototype is built,whose full range efficiency curve and switching frequency curve are tested and drawn to verify the authenticity and reliability of the theoretical analysis.At the same time,the circuit performances with both two frequency reduction schemes under the same specification are compared,and the scheme that is more conducive to the smooth operation of the converter is selected.In the end,the experiments verify the effect of SCE-DMACF on improving the conversion efficiency in the wide ranges of both input voltage and load: The maximum full load efficiency of the SCE-DMACF prototype is 96.53% and over 90.71% at 10% load.