Multi-MHz IPT Systems for Variable Coupling

Abstract

This paper proposes solutions for an IPT system to operate efficiently when large changes in coupling take place. To achieve high power-efficiency independent of coupling, we utilise inherent regulation properties of resonant converters to avoid losing soft switching for any coupling value, and present the optimal load to the IPT-link at the maximum energy-throughput coupling. A probability-based model is introduced to assess and optimise the IPT system by analysing coupling as a distribution in time, which depends on the dynamic behaviour of the wireless charging system. The proposed circuits are a Class D rectifier with a resistance compression network (RCN) in the receiving-end and a load-independent Class EF inverter in the transmitting-end. Experiments were performed at 6.78 and 13.56 MHz verifying high efficiency for dynamic coupling and variable load resistance. End-to-end efficiencies of up to 88% are achieved at a coil separation larger than one coil-radius for a system capable of supplying 150 W to the load, and the energy-efficiency was measured at 80% when performing a uniformly-distributed linear-misalignment of 0-12.5 cm, corresponding to a receiver moving at constant velocity over a transmitter without power throughput control

Dynamic Capabilities of Multi-MHz Inductive Power Transfer Systems Demonstrated With Batteryless Drones

“…Various techniques to optimise the link were then formulated in [8], and by implementing this theory at multi-MHz frequencies significant improvements in end to end efficiencies have been achieved. For example in [9] a dc-ac efficiency of 77 % was reported at 6 MHz and 3.5 % coupling, and most recently in our previous work [10] we achieved 88 % dc-dc efficiency at 6.78 MHz and 10.5 % coupling. The introduction of wide bandgap devices has also pushed the capabilities and end-toend efficiency of these systems forward.…”

“…8 describes the distribution of k as a histogram with equal size bins of 0.5 % coupling, when the drone is at maximum throttle and has no external flight control. Characterising motion as a probability distribution is useful because it allows optimising for the link and the circuits at both ends of the system for maximum overall energy efficiency as proposed in [10].…”

“…Hence, when employing resonant converters power throughput control is often performed by additional power conversion stages, either at the transmittingend before the inverter or at the receiving-end after the rectifier. Solutions for variable coupling using multi-MHz resonant power converters can be found in [10], [17].…”

A 100W 6.78MHz Inductive Power Transfer System for Drones

“…Class EF inverter circuit topology pad dictate the range of coupling for the drone to land and recharge. As this system relies on variable coupling, it was designed considering the spatial distribution of coupling as in [7] from simulations but also from measurements.…”

“…A crucial feature of using high frequency IPT systems for wireless charging of autonomous drones is that these can be designed for a wide range of misalignment and independent of angular orientation [7]. Thus, the drones to be charged do not require a millimetre-precise landing system.…”