New System Delivers Power Wirelessly to Multiple Devices

Novel repeater units and a clever layout of ferrite plates helps this new wireless-power-transfer system simultaneously deliver power to 10 devices

3 min read
10 repeater units spaced six centimeters apart are able to transfer power from one unit to another, while delivering power to loads that are connected to each unit.
In experiments, 10 repeater units spaced 6 centimeters apart were able to transfer power from one unit to another, while also delivering power to loads connected to each unit. This setup allows for different amounts of power to be delivered to each load.
Photo: San Diego State University/IEEE

Many of us are ready to throw our collection of tangled charging cables in the garbage and replace it with technology that relies on wireless power transfer. So far, though, wireless power transfer (WPT) systems have mostly been limited to supplying power to a single load, such as an individual phone. The few systems that support multiple loads do not currently allow for independent control over each one, making it a challenge to simultaneously charge devices that require different amounts of power.

This may change in the near future, thanks to a new design developed by Chris Mi at San Diego State University and his colleagues that allows for independent control over 10 loads. Their work is described in a recent study in IEEE Transactions on Power Electronics.

Supplying different amounts of power to individual devices could be useful in a number of scenarios, such as for charging stations that serve various types of vehicles (including electric cars, bicycles, and scooters). But it has been hard to customize the delivery of power in this way due to a fundamental constraint of conventional circuits: If the resistance for one load changes, that changes the power passing through every other load connected to the same WPT system.

This new wireless power transfer system can support multiple loads, thanks to the unique design of its repeater units, which contain two perpendicular coils. This new wireless-power-transfer system can support multiple loads, thanks to the unique design of its repeater units, which contain two perpendicular coils. Photo: San Diego State University/IEEE

To address this issue, Mi and his team developed a novel WPT system. They started with a typical near-field WPT system that uses magnetic induction to transfer power between a sequence of repeater units. These units are unique, however, in the sense that they harbor two repeater coils perpendicular to one another. The first coil is responsible for receiving power from the previous unit, while the second coil supplies wireless power directly to the load, and transfers power to the next unit in line. “Thus, multiple loads can be powered at the same time with isolation between each other,” explains Mi.

Another key factor that makes this system successful is the strategic layout of ferrite plates, which are used to boost magnetic induction between units. Here, the ferrite plates are laid out in such a way that they increase the magnetic coupling between adjacent units—while sparing unwanted coupling between the perpendicular coils inside each unit. This enhances the flow of power between units and to each load.

Tests of their system reveal that, in terms of efficiency, it outperforms two other existing multiple load systems. “The maximum efficiency of the designed system can reach 83.9 percent, which is very high considering there are a total of 10 loads,” says Mi. One other system compared in this study can reach roughly 90 percent efficiency, but it only supports three loads.

In their current experimental setup, the units were spaced 6 centimeters apart, but Mi says his team is working on increasing that distance to up to 50 cm. As well, the system is intended to deliver power to receiving circuits, which have not yet been designed. In this study, resistors were used as a load.

Mi says, “In the future, we will design the receiving circuit to transform the received power to constant DC output for the driver circuit and use the proposed technology in real driver circuits, which will [bring] our research one step closer to industrial applications.”

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Smokey the AI

Smart image analysis algorithms, fed by cameras carried by drones and ground vehicles, can help power companies prevent forest fires

7 min read
Smokey the AI

The 2021 Dixie Fire in northern California is suspected of being caused by Pacific Gas & Electric's equipment. The fire is the second-largest in California history.

Robyn Beck/AFP/Getty Images

The 2020 fire season in the United States was the worst in at least 70 years, with some 4 million hectares burned on the west coast alone. These West Coast fires killed at least 37 people, destroyed hundreds of structures, caused nearly US $20 billion in damage, and filled the air with smoke that threatened the health of millions of people. And this was on top of a 2018 fire season that burned more than 700,000 hectares of land in California, and a 2019-to-2020 wildfire season in Australia that torched nearly 18 million hectares.

While some of these fires started from human carelessness—or arson—far too many were sparked and spread by the electrical power infrastructure and power lines. The California Department of Forestry and Fire Protection (Cal Fire) calculates that nearly 100,000 burned hectares of those 2018 California fires were the fault of the electric power infrastructure, including the devastating Camp Fire, which wiped out most of the town of Paradise. And in July of this year, Pacific Gas & Electric indicated that blown fuses on one of its utility poles may have sparked the Dixie Fire, which burned nearly 400,000 hectares.

Until these recent disasters, most people, even those living in vulnerable areas, didn't give much thought to the fire risk from the electrical infrastructure. Power companies trim trees and inspect lines on a regular—if not particularly frequent—basis.

However, the frequency of these inspections has changed little over the years, even though climate change is causing drier and hotter weather conditions that lead up to more intense wildfires. In addition, many key electrical components are beyond their shelf lives, including insulators, transformers, arrestors, and splices that are more than 40 years old. Many transmission towers, most built for a 40-year lifespan, are entering their final decade.

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