反激变换器共模噪声的抑制

Reducing Common Mode Noise in Flyback Converter

随着开关电源高频化和小型化的发展,功率器件快速开关造成的电磁干扰(EMI)问题愈发严重。针对反激变换器,分析共模(CM)噪声源和CM噪声传播路径,建立变换器的CM噪声模型。在变压器分布电容模型的基础上,定量分析通过铁氧体磁心这一路径传播的CM噪声的影响。提出不完全屏蔽层和平衡绕组这两种CM噪声抑制措施的定量分析方法。基于屏蔽层结构参数,不完全屏蔽层可分为宽度不完全和长度不完全屏蔽层。通过建立变压器的xy轴坐标系,得到绕组的电势分布表达式,通过对共模位移电流的推导,基于抵消原理,给出了不完全屏蔽层的宽度或长度以及平衡绕组匝数的计算方法。实验结果验证了所研究方法的有效性和计算方法的准确性。

As the frequency of the switching mode power supply(SMPS) tends to be higher and the size of SMPS tends to be smaller, the electromagnetic interference(EMI), which is caused by the switching of power semiconductor device, has become more serious. The common mode(CM) noise source and CM noise propagation path of flyback converter are analyzed, then the CM noise model of converter is established. Based on the distributed capacitance model of transformer, the influence of the CM noise through the path of the ferrite core is analyzed quantitatively. A quantitative analysis method for two kinds of CM noise suppression measures, incomplete shielding layer and balanced winding, is proposed. The incomplete shielding layer can be further divided into incomplete-width and incomplete-length shielding layer for different structural parameters. The x-y axis coordinate system of the transformer is established, then the expression of electric potential distribution along winding is obtained. Based on the cancellation of common mode displacement current, the calculation method of width or length of the incomplete shielding layer and the turns of the balanced winding is given. Experimental results verify the effectiveness of proposed method and the accuracy of the calculation method.