周期函数频率调制降低EMI水平研究

EMI Reduction by Means of Periodic Frequency Modulation

周期函数频率调制是降低电路EMI水平的一个有效方法,但国内对其研究很少。这里论述了周期函数频率调制的调制波形、调制系数、调制频率的选择与降低电路传导EMI的关系。分析了占空比的选择对电路传导EMI大小的影响,指出当占空比为0.5时,开关电压功率谱达到最大值。此处还讨论了周期函数频率调制在降低电路传导EMI的同时对输出电压纹波的影响。最后通过搭建一个功率为7.5 W、频率为200 kHz的闭环Boost电路对结论进行了验证。从实验和理论两方面对周期频率调制技术进行了全面深入地分析和阐述。

The primary modulation parameters in periodic frequency modulation which have influence on the EMI sup-pressings,uch as modulation profile,modulation index,modulation frequency are discussed and analyzed.The relationship between the selection of duty cycle and EMI mitigation is explored.The experiment and theoretical calculation indicate that when duty cycle is 0.5t,he level of EMI reaches maximum.These analyses provide a theoretical platform for the selection of these parameters.The effectiveness of such methods in terms of EMI reduction is demonstrated theoretically and con-firmed with experimental results obtained from tests carried out on a closed-loop Boost converter whose power is 7.5 W and nominal switching frequency is 200 kHz.Finallys,pecial attention is paid to output voltage ripple.