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Charging system is quite forgiving of air gap, misalignment with charging pad

Utah State University's Wireless Power Transfer team has applied "a mix of modern advances in engineering and Nikola Tesla's principles of induction" to create a unique mass transport electric vehicle, the Aggie Bus.

While the Aggie Bus at first blush is just a battery-electric conversion of a standard passenger bus, it has a pretty unique trick.  Professor Hunter Wu's team of faculty and student researchers, along with engineers at the Utah Science Technology and Research (USTAR) initiative's Advanced Transportation Institute at USU, created wireless power transfer (WPT) pads that charge the bus as it reaches stops.

The pads can deliver up to 5 kilowatts at 90-percent electrical transfer efficiency, over a 10-inch airgap.  The charger also maintains that efficiency even if the bus is "off" (misaligned) with the charging pad by up to six inches.  This helps, by making it far easier for the driver to hit the charging zone.  The system can deliver a peak power of 25 kilowatts, albeit at lower efficiency.
Power schematic
Wave Pad
The inductive charging transformer (bottom) take power from the grid (top) and transfer it to a detached electrical device, e.g. the Aggie Bus via a magnetic field. [Image Source: WAVE Inc.]

A spinoff, WAVE Inc., will deploy the electric bus next year in the real world.  The first commercial demonstration will be placed on the campus of Utah State University, located in the city of Logan in the northern Utah panhandle.  The bus, which will be launched in collaboration with the Utah Transit Authority, will be forty-feet long and will ferry students around campus, powering up from a next-generation 50 kilowatt variant of the WPT pads.

USU Aggie Bus
The Aggie Bus, an EV bus with inductive charging [Image Source: USU]

The bus is being paid for by USU and a $2.7M USD grant from the U.S. Federal Transit Administration (FTA), a subagency of the U.S. Department of Transportation (USDOT).

WAVE CEO Wesley Smith comments, "Current battery limitations prevent an all-electric transit bus from operating all day from an overnight charge.  WAVE solves that problem by charging the bus wirelessly during its daily operations when the bus stops to load and off-load passengers.  This technology makes electric buses competitive with their diesel hybrid and CNG counterparts."

Robert T. Behunin, Ph.D., USU vice president of commercialization and regional development praised the upcoming Aggie Bus and current prototype, commenting, "The unveiling of the Aggie Bus today is a historic achievement and a great leap forward in the science and engineering related to electric vehicles.  As a result of the work done by Utah State engineers, scientists and partners, EV owners and operators will now be able to simply drive over a pad in the ground to recharge their batteries, the benefits of which reach far beyond convenience."

Given the increasing popularity of inductive charging for cell phones and other electronics, it's not surprising to see an urban EV inductive charging scheme floated.  In fact inductive chargers are already be cooked up elsewhere for consumer electric vehicles.  Such a concept could see substantial traction in "green minded" cities like New York City or San Francisco.

However, it could also face some opposition from the WiFi-fearing crowd in such regions, who are already railing against the dangers of more isolated cell phone broadcasting towers.

Source: Utah State on PRNewswire



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RE: Not enough power
By Shadowself on 12/4/2012 8:50:38 AM , Rating: 2
With a 50 kW transfer system, per the article, a 10% loiter time would be a time averaged 5 kW, not 500 W. Also, the article mentions overnight charging is not enough for a full day. If the bus is charged overnight and starts with a full charge that decreases over the day, but decreases less due to intermittent charges at stops, then the average draw for transport could be significantly higher than 5 kW. We don't know the total battery energy nor do we know the total kW-hr reserve assumed necessary at the end of the day.

This might actually work. We just don't know enough details from this article.

Additionally, systems of this nature were pushed for satellite to satellite charging by the Air Force Research Lab as far back as 1993. If I remember correctly the USU Space Dynamics Lab participated in some of those studies and research projects back then.


RE: Not enough power
By PrinceGaz on 12/4/2012 10:46:08 AM , Rating: 2
I reckon that estimate of 10% "loiter" time is somewhat less than that which the average urban bus actually has during its daily duties. Based on one of my own videos filmed on the top-deck of a typical journey in a British city, and some others on the web, a more realistic figure of the time spent stationery at a bus-stop is more like 20% during the actual journey (with a similar amount of time spent stationery due to traffic lights but that doesn't count).

On top of that 20% at bus stops during its journey, once it reaches its terminus a typical city bus will spend at least two or three minutes preparing for and awaiting the departure time for the return run so you can easily add another 5-10% to the overall time spent stationery and charging for that.

I reckon a more realistic worst-case figure would be 20% time available for charging during rush-hours, but generally around 30% for most of the day.


RE: Not enough power
By HoosierEngineer5 on 12/4/2012 1:52:29 PM , Rating: 2
Good point. Urban busses probably spend way more time idling at stop lights than the ones I am used to seeing.


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