A Secondary-Side-Parallel CLLC Coreless Transformer with Load-Independent Voltage Ratio

In this article, a novel coreless transformer (CLT) with a secondary-side-parallel CLLC tank is proposed. Different from existing CLTs, the proposed CLT needs no superconductor or very-high-frequency technologies. Due to proper tuning, the proposed CLT can achieve a load-independent voltage ratio, which is an important characteristic of conventional magnetic core transformers. Moreover, the proposed CLT can normally operate at a relatively low frequency, reducing the requirements for switching devices. Characteristics under sinusoidal and square wave excitations are analyzed, especially the influence of harmonics. Finally, a 1-kW prototype of the proposed CLT is built for experimental verification. Experimental results show that the peak efficiency reaches 97.6% and the gravimetric power density reaches 6.7 W/g .