A measurement-based model of the electromagnetic emissions from a power inverter

Rapidly switching semiconductors in modern high power inverter/motor-drive systems generate fast changing voltages and currents which may result in unwanted emissions. While models of power inverters have been built in the past to predict emissions, they are typically "black box" models where the cause of and solution to emissions problems is difficult to analyze. To improve inverter system design strategies, a detailed measurement-based SPICE model of a power inverter system was built in which there is a straightforward correlation between system geometry and parasitic circuit elements. This model was validated through measurements. The model was able to predict transfer characteristics between ports of the inverter within 4 dB from 100 kHz to 100 MHz. Once built, this model was used to identify structures responsible for resonances and to determine possible improvements of the power inverter design to reduce emissions. Measurements of S21 and radiated emissions after adding these improvements demonstrated that they were able to reduce emissions by 10-20 dB, thus confirming the accuracy of the model and its ability to improve understanding of emission mechanisms and to guide development of emissions reduction strategies.