基于电感比分析的CLLC谐振变换器效率优化

Efficiency Optimization of CLLC Resonant Converter Based on Analysis of the Ratio of Inductances

变压器励磁电感与原边谐振电感之比对CLLC谐振变换器有重要影响,增大电感比可以减小谐振电流,提高效率,但电感比的提升也受其他条件的限制。为了尽可能增大电感比,得到具有最高效率的CLLC变换器,该文首先通过基波分析法(first harmonic approximation,FHA)得到其直流增益表达式,在此基础上,详细分析限制电感比增大的2个主要因素:一是过大的电感比会使增益曲线在工作频率范围内呈现不单调的特性,导致变换器无法实现稳定控制,并失去零电压开关特性;二是电感比增大会使变换器最大增益减小,导致变换器无法满足电压增益要求。通过理论分析与数学推导,得到2个因素限制下的最大电感比,从而最大程度地提升变换器效率。最后,通过仿真和实验验证所提方法的有效性。

The ratio of excitation inductance of the transformer to the primary resonance inductance-k has an important influence on CLLC resonant converter.Increasing k can reduce the resonance current and improve the efficiency,but the increase of k is limited by other factors.In order to increase k as much as possible and get the CLLC converter with the highest efficiency,the DC gain expression of CLLC converter was obtained by first harmonic analysis(FHA)in this paper.On this basis,two main factors that limit the increase of k were analyzed in detail.One was that too large k would make the gain curve non-monotonous in the working frequency range,which would lead to the converter unable to achieve stable control and lose zero voltage switch.The other was that the increase of k would reduce the maximum gain of the converter,which would make the converter unable to meet the voltage gain requirements.Through the mathematical derivation,the maximum ratio of the inductances under the restriction of the above factors was obtained,so as to improve the efficiency of the converter to the maximum extent.Finally,the effectiveness of the method was verified by simulation and experiment.