The Design Of LLC Resonant Converters Controled By Bi-frequency

LLC resonant converter can.realize zero current switch and zero voltage switch in wide input voltage range,and LLC resonant converter also can obviously reduce the loss of energy when the converter works at high operating frequency.Therefore,more and more scholars pay attention to LLC resonant converter in the field of high frequency power semiconductor today.And with the development of technology,the demand for dynamic performance of an LLC resonant converter is getting higher and higher,and the control of bi-frequency can greatly improve the dynamic response speed of the converter.So it's significant to research how to apply the bi-frequency control method to the LLC resonant converter.At first,the working principle of the half-bridge LLC resonant converter working in two main working areas is studied,especially the soft switching process of the primary switch transistor' ZVS and secondary rectifier diode' ZCS are analyzed in detail.Then the fundamental wave equivalent(FHA)method is used to simplify the LLC resonant circuit,the equivalent circuit is simulated to analyze the characteristics of steady state in use of Matlab software.Then describes the principle of the traditional bi-frequency control of LLC half-bridge resonant converter and the low frequency oscillation caused by the traditional control mode.And in order to reduce the low frequency oscillation,a new type of bi-frequency control method is proposed.Finally using PSIM software builts the closed loop system of the half-bridge LLC resonant converter controlled by bi-frequency,simulating and analysising the converter' steady state performance and dynamic performance,and verifying the validity and effectiveness of the bi-frequency control design.Simulation shows that: the LLC half-bridge resonance converter controlled by the new type of bi-frequency in rated working condition,the input voltage is 400 V,the load is 4.8 ?,the stable output is24 V,and the output voltage ripple is 0.1 V.The input voltage varies from 360 V to 420 V,the response time is 0.17 ms,and the undershoot voltage is 100 mV.When the input voltage varies from 420 V to 360 V,the response time is 0.1 ms,overshoot voltage is 90 mV.The load varies from full load to 10% load,the response time is 0.6 ms,the undershoot voltage is 100 mV,and when the load varies from 10% load to full load,the response time is 1.3 ms,the overshoot voltage is small than 220 mV.Compared with other control type of the LLC resonant converter,the new designed bi-frequency control has better dynamic performance,and meet the design requirements.