Electromagnetic Emissions Mechanisms below 30 MHz in High Voltage Power Switching

This study investigates electromagnetic emissions mechanisms below 30 MHz due to high voltage switching of power devices. The relationship between conducted and radiated emissions is discussed. A prototype buck converter with a 300 A / 1200 V IGBT module is used to analyze switching behavior at switching speeds from 1.5 kV/μs to 28 kV/μs, using time-domain measurement methods. It is found that switching behavior affects both conducted and radiated emissions, particularly from 10 MHz to 30 MHz. Furthermore, radiation mechanisms of the buck converter are experimentally analyzed by changing its configurations. The results show that the buck converter exhibits an incidental radiated emission mechanism involving the protective earth cable, which acts as a monopole antenna due to potential fluctuations relative to the ground. The mechanism, which bypasses the conventional common mode emission path, degrades the effectiveness of choke coils and filters.