Prediction of CM Conducted EMI Noise of High Frequency Class E Resonant Flyback Converters Based on Air-core Transformers

With the rapid development of power electronics technology and the significant increase in the switching frequency of power semiconductor devices, high frequency operation has become an important approach to achieving compact and lightweight systems. However, high switching frequencies also exacerbate the problem of electromagnetic interference (EMI). This paper focuses on the EMI characteristics of high frequency converters and conducts an in-depth study on the CM conducted EMI noise model of high frequency flyback converters based on air-core transformers. By precisely designing the flyback converter to operate in resonant mode and achieve soft switching of the switches, it adapts to high frequency application environments. Furthermore, a detailed analysis of the system's CM noise path is conducted, and the corresponding system model is constructed. Considering the characteristics of air-core transformers, a simplified measurement method based on a four-capacitor model is proposed in this paper to overcome the challenge of complex parameter measurement with traditional methods. Experimental results demonstrate that this model can effectively predict the EMI characteristics of high frequency converters, providing important references for the design of high frequency power electronic systems.