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In this research we present a short distance capacitively coupled wireless power transfer (WPT) system with a self-oscillating half-bridge converter, which uses a positive feedback signal from the WPT system. By this novel implementation we find additional features of the system compared to linear amplifier based systems. With the DC bias voltage supplying the power converter, we achieve a controllable output power, tunable self-oscillation frequency and extension of the self-oscillation range. We present the analytical expressions for the converter waveforms. The theoretical analysis is confirmed by circuit simulation results and measurements on a prototype featuring a half-bridge converter with Gallium-Nitide (GaN) HEMTs. We achieve a system efficiency of 93% at a load power of 83W and 150kHz switching frequency.
We present the design of a half-bridge converter
for a capacitively coupled wireless power transfer
system. The load signal acts as a positive feedback
signal for a self-oscillation circuit which generates the
driving gate signals for the converter. Our research
reveals a robust wireless operation for a large range
of load resistors and coupling capacitors. Based on an
electric network analysis we obtain design criteria for
self-oscillation and for the power transfer. The theoretical
predictions are confirmed by circuit simulation
and measurement results on a converter prototype with
GaN-HEMTs. We report on a transfer efficiency of 92%
for a power greater than 50W at a switching frequency
of 300kHz and 200V DC link voltage.