Method to Maximise Utilisation Rate of Flux Linkage in Coreless Transformer

ABSTRACT In this article, a coreless transformer (CLT) with a maximum utilisation rate of flux linkage is proposed. By adding a proper capacitor to the secondary side, the phase difference between the self‐generated flux linkages of the primary winding and the secondary winding can be minimised, which maximises the utilisation rate of the flux linkages. Therefore, the proposed CLT can normally operate without a magnetic core, and the magnetising current is relatively low. Compared to existing CLTs, the proposed CLT operates at a significantly lower frequency of 100 kHz, and there is no need for superconductors. Compared with the magnetic‐core transformer (MCT), the proposed CLT has almost the same efficiency, while the gravimetric power density is about two times that of the MCT. Characteristics of the proposed CLT, including flux linkage, input impedance, and transfer ratio, under the excitation of sinusoidal and square‐wave voltage are analysed in detail. The gravimetric power density of the 1‐kW prototype of the proposed CLT reaches 6.11 W/g, the maximum efficiency reaches 97.6%, and the full‐load efficiency is 97.3%.