Feature: Power
New technologies for wireless power transfer Satisfying this demand will require innovative new technologies that can deliver increased performance and very high efficiency over greater distances than have been possible with legacy wireless charging topology. Figure 1 shows a block diagram
of a conventional inductive charging design that will charge a mobile device based on the Qi standard. In this case an external AC/DC adapter converts the mains voltage to DC to supply the wireless charger transmitter coil section through an external DC cable. Te coil then transfers the energy to the wireless receiver built into the device to be charged. In such a design the typical maximum charging distance is around 5 mm and the maximum power is around 30 W. As we can see, from a system perspective it takes at least three
different blocks, comprising five distinct stages in cascade, to realise this design. And, as a result a traditional wireless charging system
has between 12 and 16 active devices, at least two magnetic components, two coils, an AC cable and a DC cable. Tis number of elements not only contributes to a high bill of material (BoM) cost but also impacts on overall system efficiency, with typical efficiency being in the region of 70 per cent. Recent advances in architectures and the widespread adoption
of wide bandgap technologies have enabled much more efficient wireless charging systems that facilitate higher power densities with larger distances than previous wireless charging designs. Te latest of these architectures supports efficiency levels comparable with the best conventional wired adapters. For example, Eggtronic’s E2WATT topology reduces the total
number of stages required to implement a complete end-to-end wireless charging system from five to two, merging multiple stages into a multi-functional single-stage ZVS-ZCS (zero voltage switching, zero current switching) wireless power supply. As figure 2 illustrates, this topology encompasses an AC/AC
transmitter, with power supplied from the mains. Tis is modelled as a bridgeless AC converter to drive the coil using a half-bridge architecture based on two gallium nitride (GaN) power ICs and two diodes. Tis allows fine control of energy transmitted through the coils with good voltage regulation and can support power factor control. Additionally, this then uses a single-stage AC/DC receiver
half-bridge with two active devices, acting as both secondary side rectifier and non-dissipative output regulator. In the transmitter stage, thanks to a combination of ZVS and
near-ZCS conditions and robustness to input and load variations, the switching power losses are close to zero. And because the transmitter stage is not resonant, ZVS operation can be reached for any load condition. As a result, transmitter efficiency remains high
Figure 3: Stage efficiency vs output power – data from Eggtronic E2WATT transmitter
over a wide range of output powers. Te single-stage receiver commutes always in ZVS conditions
and incorporates a low-latency data exchange scheme that reduces receiver temperatures when compared to conventional designs by up to 30°C at 30 W. By controlling the ratio between the active power delivered to the load and the reactive power reflected to the primary, the receiver stage provides a fast control loop that enables output voltages to be finely regulated without the need for additional buck converters or LDOs in series. A second control loop further improves efficiency (to over 96
per cent at 300 W) by minimising reactive power across the whole transmitter and receiver system, for a significant improvement of efficiency. When higher power and higher efficiency are required, the TX
EPIC controller provided by Eggtronic also works as an input boost-PFC (to ensure power factor corrected input) or totem pole PFC (for further reduction of power loss). With the capability of ensuring high power (up to tens of
kilowatts) and extreme efficiency, Eggtronic proprietary wireless technologies and IC controllers enable the replacement of not only legacy wireless charging but also wired systems for every autonomous vehicle, from small robots and drones, to electric vehicles.
Conclusion Initiatives to reduce the number of cars and trucks on city streets, reduce emissions and improve quality of life are driving the growth in everything to EV and bike sharing fleets to autonomous service robots and drones. Tese technologies require power – power that can be delivered with as little human intervention as possible in the shortest possible times, and with the highest possible reliability. Wireless power transfer is critical to achieving these goals,
but legacy wireless power architectures have limited efficiency and are unable to provide energy over extended distances. New architectures, such as E2WATT, however, are changing this, laying the foundation to take wireless charging from a few watts to tens of kilowatts.
www.Eggtronic.com
www.electronicsworld.co.uk November 2024 21
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