基于虚拟阻抗的LLC谐振变换器并联均流控制

Parallel Current Sharing Control of LLC Resonant Converter Based on Virtual Impedance

近年来,LLC谐振变换器因其优越的性能得到了广泛的应用。LLC谐振变换器并联结构对于低压大电流的场合十分适用。但是难点在于模块间的均流,谐振网络参数的微小差异就可能引起较大的模块电流不平衡。从阻抗的角度出发,利用虚拟阻抗来模拟谐振网络串联阻抗,通过该串联阻抗来调整等效输出阻抗,从而获得均流特性的改善。以两路并联LLC模块为例,给出基于虚拟阻抗的控制框图和实现方法。最后,利用DSP数字控制,搭建一台400V输入、12V/80A输出的两路并联LLC谐振变换器原理样机,实验结果表明,所提控制方法可在全负载范围内将输出电流不平衡度减小在5%之内,验证了该方法的有效性。

In recent years,LLC resonant converter has been widely used because of its superior performance.The structure of parallel LLC resonant converter is very suitable for low voltage and large current applications,but it has the difficulty of current sharing between modules.A small difference in the parameters of the resonant network may cause large module current imbalance.In this paper,the virtual impedance is used to simulate the series impedance of the resonant network from the point of impedance.To improve the current sharing characteristics,the equivalent output impedance is adjusted by the series impedance.Taking two-parallel LLC module as an example,the control block diagram and the realization method based on the virtual impedance are given.Finally,using DSP digital control,a prototype of a two-phase parallel LLC resonant converter with 400V input and 12V/80A output is built.The experimental results show that the proposed control method can reduce the output current imbalance to 5%within the full load range,which verifies the proposed method.