基于实际通带特性的EMI接收机精确模型

A Precise EMI Receiver Model Based on Practical Band-pass Characteristics

电磁干扰(electromagnetic interference,EMI)接收机建模是全电路时域传导EMI仿真技术的重要组成部分。对不同控制策略的开关电源的EMI频谱进行深入的分析,指出采用变频和/或变占空比控制策略时,其EMI噪声频谱会存在边带效应,明确了边带效应和EMI接收机的测量带宽是导致用快速傅里叶变换(fast Fourier transform,FFT)得到的噪声频谱与EMI接收机测量结果产生差异的本质原因。提出一种通过测量获得EMI接收机中频(intermediate frequency,IF)滤波器真实通带特性的方法,建立基于高斯函数的数学模型。对中频滤波器的相对相位偏移特性进行实验测量和分析,其对输出信号相位的影响可以忽略。通过对开关电源中典型的信号进行分析,确定EMI接收机模型的合理通带带宽,从而获得精确的EMI接收机模型。最后,通过实验验证所建立的模型的正确性和有效性。

The model of electromagnetic interference (EMI) receiver is critical for conductive EMI simulation technique with full circuit time-domain simulation. The EMI spectrum characteristics with different control strategies has been analyzed which points out that sideband effects in the EMI noise spectrums would exist with variable frequency and/or variable duty cycle controls. The sideband effects and the bandwidth of the EMI receiver are the key reasons for the spectrum differences between fast Fourier transform (FFT) analysis and results of EMI receiver. A method was proposed, via experiments, to get the practical band-pass characteristics of IF (intermediate frequency) filter of the EMI receiver, and mathematical model based on Gaussian function was then induced. Phase-frequency characteristics of IF filter of the EMI receiver was analyzed by an experiment and it has little impact on the output of IF filter. Thus the influence of phase-frequency characteristics of IF filter can be neglected. Based on analysis of the common waveform of the switch-mode power supply, the suitable bandwidth of the EMI receiver was determined to get the precise EMI receiver model. At last, the noise tests had been performed to verify the effectiveness and the accuracy of the model.