A 9 kW 3.47 MHz Wireless Power Transfer System with a Parallel Differential Class E Inverter for Industrial Applications

Wireless power transfer in the low kW power range can have numerous applications in industrial settings, such as powering machinery and charging automated guided vehicles. High frequency inductive power transfer combines lightweight and compact coils with efficient resonant converters resulting in high power density. However, combining multi-MHz operating frequency with multi-kW level power output using conventional half-bridge or multi-resonant Class E type topologies and wide band-gap devices is challenging. In this paper we demonstrate a 9 kW, 3.47 MHz dc to three-phase wireless system that is capable of reliably providing 50 Hz, 400 V mains supply to industrial units that cannot be physically plugged in, over an air-gap of 12 cm. The system is robust over the entire load range, providing a stable output voltage to the load, with 95% dc-dc efficiency over most of the load range. The power density of the inverter is 4.8 W/cm
³
and it can produce over 70 A peak current in the primary coil. This performance is achieved using power-combining Class E type converters with the secondary operating slightly off-resonance to better accommodate the effects of the highly varying load.