Research On Optimal Control Technology Of Asymmetric Half-bridge Flyback

With the development of our social life and the progress of science and technology,the highly efficient portable power sources are more and more demanded in daily life.Researchers are paying increasing attention to how to effectively overcome the problem of energy loss.Conventional flyback inverters have the advantages of low cost,simple construction and are portable,but they cannot fully recover leakage inductance energy and are less efficient.Asymmetric half-bridge flyback inherits the advantages of flyback converter in the cost,and achieves soft switching as asymmetric half-bridge converter,and can recover the leakage inductance energy of the transformer well.Therefore,the AHBF converter topology will be studied in this dissertation.Firstly,due to the introduction of the resonant process in the asymmetric halfbridge flyback circuit,the stability of the circuit will be interfered by the resonant components,the asymmetric half-bridge flyback converter with traditional complementary control and operating in DCM is analyzed in detail and the voltage gain is derived.After that,the circuit parameters are designed out.Secondly,this dissertation has studied the working process of the AHBF converter with primary resonance and conventional complementary control.The resonant current drop problem has been illustrated establishing the equivalent circuit model and relative circuit equations.After that,a secondary resonant AHBF converter is proposed according to secondary resonant active clamped flyback converter.By establishing the equivalent circuit model and relative circuit equations,it has been proved that resonant current drop problem can also been effectively resolved in secondary resonant AHBF converter.Two 20 V / 65 W laboratory prototype based on these two modes were fabricated,and the circuit waveform and experimental data were presented.Finally,considering the two major problems of the asymmetric half-bridge flyback converter with primary resonance and traditional complementary control,i.e.resonant current drop in light load and the large cycle loss,a new complementary/ noncomplementary hybrid mode control strategy based on emulation of the secondary current realized from the primary side has been proposed.This control method can effectively offset the transformer magnetizing current component of in the primary side sampling current,so as to effectively emulate the output rectifier current waveform and accurately obtain the load current information.The converter is controlled to operate in complementary mode under full load and in non-complementary mode under light load.In this way,the problem of resonant current drop under light load can be resolved,and the light load efficiency is also improved.The theory and design considerations of the converter with proposed control scheme are introduced in detail.The theoretical analysis is verified by simulation.A 20 V / 65 W laboratory prototype is made to verify the feasibility of the new control scheme.At the end of this dissertation,the experimental results under three different control schemes are compared.The paper analyzes the relative merits of the three control methods,and also calculate the loss.Proved by the results,the asymmetric halfbridge flyback with the proposed control strategy has the highest average efficiency,and the efficiency improvement is particularly obvious under light load condition.