Design of a wireless charging system with a phase-controlled inverter under varying parameters

Class-D full bridge is the most common inverter topology at the primary side for wireless electric vehicles (EVs) charging systems. This study takes a novel topology of a phase-controlled inverter as the power amplifier and puts it in a context of the whole charging system. The proposed inverter topology regulates the charging power through adjusting the phase-shift angle among phases with a constant operating frequency, which alleviates the EMI filter design. For various wireless EVs chargers, the gaps between the primary side and the secondary side are changing, which results in various coupling factors k. The equivalent resistance of the EVs battery Rbattery is also changing during the charging process. Even resonant frequencies at two sides are variable because of the components tolerances and operating environments. This study presents design considerations of a wireless EVs charging system with the proposed technology under variable k, Rbattery, and resonant frequencies. Circuit parameters are designed and the system efficiency is derived. Industrial prototype of an EV charging system is manufactured with the proposed topology at 3.0 kW. Experiments show that these design considerations can reflect the system characteristics, and the proposed system is a good candidate to be used in wireless EV battery chargers.