Skin Effect-Related AC Resistance Study in Macroscopic Scale Carbon Nanotube Yarn Applicable to High-Power Converter

This paper presents a study on the skin effect-related AC resistance of macroscopic scale carbon nanotube (CNT) yarn. The range of interest frequency in this study is up to 10 MHz which is considered conventional high-frequency power converters operating range. AC resistance of both CNT yarn and copper (Cu) wires are measured by impedance analyzer for the small-signal frequency-response. The 1-turn core-less layout of inductors made of both CNT yarn and Cu wire are implemented to eliminate the proximity effect and magnetic core. The measurement results are compared with the theoretical model results based on Bessel-Kelvin function. The results show that the increasing rate of AC resistance in CNT yarn is lower than in Cu wire as frequency increases so that it causes lower CNT yarn resistance at higher frequencies. It was found that the Cu wire measurement result follows the theoretical model whereas CNT yarn does not. Therefore, a new skin effect related AC resistance correction factor for CNT yarn is introduced. To verify the same trends in large signal level of current, conduction losses for both CNT yarn and Cu wire are tested as an inductor component in a power converter circuit working like a large signal generator. The losses were collected and presented for the same frequency range (between 1 and 10 MHz). The results show less losses with CNT yarn inductor. Finally, another CNT yarn-based inductor was constructed and tested in around 200 W power converter circuit. The results show 91.72% of high efficiency at 3.125 MHz switching frequency. The study shows that, for power converter circuits working in the range higher than 1 MHz, the CNT yarns are reasonable to replace Cu wires due to the lower skin effect- related losses.