Design and Control of the Adjustable Turn-ratio LLC Converter for High-Efficiency Operation of Wired/Wireless Integrated EV Charging System

This paper proposes an LLC resonant converter with an adjustable turn-ratio of the transformer to replace phase-shift (PS) control for high-efficiency operation in a wired/wireless integrated EV charging system (ICS) for electric vehicles (EVs). To design the LLC converter of the ICS, the range of the dc-link voltage by the characteristics of inductive power transfer (IPT) converter and the design specification are derived by simulation. Considering the voltage gain of the LLC converter by each parameter, the parameters of the LLC converter are determined and a multi-tap transformer is manufactured. After that, the LLC converter is operated in ICS, by PS control and the adjustable turn-ratio transformer. The feasibility of the adjustable turn-ratio transformer is verified by comparing the efficiency of the LLC converter.