Transformer-Integrated Series-Series (TISS) Resonant Tank for EV Wireless Charging application: Analysis and Comparative Study Against SS and LCC Topologies

This paper proposes a novel Transformer-Integrated Series-Series (TISS) topology for Electric Vehicle (EV) wireless charging applications, and compares it with two other resonant compensation topologies widely used in this application: the Series-Series (SS) and the double-sided LCC resonant tanks. The analysis is carried out under the recommendations defined by the SAE J2954 standard for WPT2Z2 chargers. While the SS topology offers simplicity and nearly sinusoidal current waveforms, it becomes impractical at high power levels and low coupling factors because the low inductance values recommended by the standard for the coils lead to excessively high circulating currents. The LCC topology provides improved performance across wide coupling ranges but requires more components, a more complex design, and suffers from pronounced third-harmonic content. To address these limitations, this work introduces the TISS topology, which retains the simplicity of the SS while significantly reducing the primary-side current through voltage balancing. A unified analytical derivation of the input impedance for all three topologies is provided, enabling a consistent comparison of their frequency responses. Experimental validation confirms that the TISS achieves a balanced current distribution, reduced conduction losses, and efficiencies close to those of the LCC topology. Overall, the study demonstrates that the proposed topology constitutes a strong candidate for EV wireless chargers operating in the 5–10 kW range and subject to wide coupling variability.