High-frequency EMI attenuation at source with the auxiliary commutated pole inverter

Fast-switching power converters are a key enabling technology for the More Electric Aircraft (MEA), but the generated Electromagnetic Interference (EMI) poses significant challenges to the electrification effort. To meet the stringent aerospace EMI standards, passive filters are commonly employed, despite the weight and size constraints imposed by the MEA. Alternatively, the EMI source, i.e., the high dv/dt and di/dt slew rates, can be addressed through waveform-shaping techniques. For example, while most soft-switching converters can reduce switching loss, they do so by switching the semiconductor devices in a slower and smoother manner, resulting in the attenuation of high-frequency harmonics. This paper examines the Auxiliary Commutated Pole Inverter (ACPI) topology, and its first contribution is the attenuation of the high-frequency content of its EMI source, that is, the output voltage, in a predictable manner, through the active control of the resonant circuit. This is achieved by firstly discussing the time-domain characteristics of trapezoidal and S-shaped pulse-trains that lead to attenuated high-frequency harmonic content, and secondly, by analysing the equivalent LC circuit of the ACPI. The design of the inverter is then focused on the active control of the resonant parameters, for a predetermined and enhanced output voltage high-frequency response. The second contribution of this paper is the comparison of the EMI performance of hard switching and of three soft-switching modes, fixed-timing control, variable-timing control, and capacitive turn-offs, and how this informs important metrics like power efficiency, current stress, and implementation complexity. Lastly, the third contribution is on the trade-offs that arise when the primary design goal is enhanced EMI performance, as opposed to switching loss reduction. A 5-kW, 3-phase ACPI prototype is used for validating the high-frequency content attenuation at source. It is shown that the ACPI can achieve a 37-dB harmonic attenuation of its output voltage at 4 MHz, compared to a hard-switched inverter.