EMI Considerations on MHz Inverters

Inhalt:
In this work, an inverter system operating at 2.44 MHz and 10 A output current and a method to calculate the interference voltage spectrum from oscilloscope measurement data of the LISN signal are introduced. With the inverter and the measurement, a very simple model is tested, whereas the interference voltage in a not earthed system is caused by the voltage drop of the commutating current at the DC-Link impedance. The model matches for the second and fourth peak, but cannot explain every coupling path or noise source, that might be present. According to the model, increasing the switching frequency increases the interference voltage, because the DC-Link impedance is higher at higher frequencies and increases filter effort, because filtering is more complicated at higher frequencies.