Published on May 2nd, 2013 | by James Ayre


Greatly Improved EV Charger Design Developed, Faster & Cheaper Charging

May 2nd, 2013 by  

A new, greatly improved electric vehicle charger design has been developed by researchers at the Chalmers University of Technology in Sweden. The unique integrated motor drive and battery charger greatly shorten the charging time, from about 8 hours to 2, and reduce the cost by around $2000, as compared to currently used designs.

"Model of the integrated motor drive and battery charger. The image shows a plug-in hybrid electric vehicle, which also has a fuel tank and a combustion engine, but the technology system works equally well with a purely electric vehicle." Image Credit: Chalmers University of Technology

“Model of the integrated motor drive and battery charger. The image shows a plug-in hybrid electric vehicle, which also has a fuel tank and a combustion engine, but the technology system works equally well with a purely electric vehicle.”
Image Credit: Chalmers University of Technology

The new research was undertaken with the aim of developing the “optimal” electric vehicle charger — which hasn’t yet been achieved, but significant improvements have clearly been made. These improvements include the creation of “a new power transfer method” that involves what is called a “rotating transformer.”

“The ideal scenario would be to have a charger powerful enough to charge a car in five to ten minutes, but this would cost over $100,000, which is more expensive than the car itself,” says Saeid Haghbin, a doctor of electric power engineering, at the Chalmers University of Technology. “The question we posed was: how can we reduce the size, weight and price of the on-board charger.”

Because the electric motor and the inverter aren’t utilized during battery charging, the possibility was there (as the researchers recognized) to integrate them with the charger circuit and create a sort of “integrated motor and battery charger.” To word it a different way, it uses the motor and inverter in the charger circuit to increase the charging power.

Saeid Haghbin and his co-workers have developed unique solutions for isolated and non-isolated integrated electrical vehicle chargers. Photo: Peter Widing

“Saeid Haghbin and his co-workers have developed unique solutions for isolated and non-isolated integrated electrical vehicle chargers.”
Photo Credit: Peter Widing

“Instead of having a separate isolated battery charger, we introduced a new concept for the power transfer, the rotating transformer, which was developed to transfer electric power while rotating,” says Saeid Haghbin. “The battery is charged through the transformer and a split-phase electric motor that was especially designed for this purpose.”

As of now, the ‘Chalmers Integrated Charger’ is still on the laboratory level, still needing further refinements in order to create a more optimal system, according to the researchers. But the design has already attracted the attention of Volvo AB, and both a Swedish and an international patent are pending.

“Electric cars have been discussed as a possible solution to reduce carbon emissions for a long time, but scientists debate whether this mode of transportation is the future or not,” says Saeid Haghbin. “If we manage to solve the main problems with the battery and the battery chargers, I think the electric vehicles will succeed. And in general, I think electric transportation will become more common in the future, for example trains, trams and plug-in hybrids.”

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's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.

  • arne-nl

    dwj, Ronald,

    I have been contemplating on getting a Renault ZOE. It has a charger that can accept 3 phase up to 43 kW. You can choose different home chargers from 1×16 A up to 3x16A.

    Weighing the options, the 3x16A seems pretty compelling. It would make it a lot easier for me to use the car in the evening, after work. If I get home at 17:00 on a near empty battery (it’s a 100 km roundtrip, no charging at work), I can plug it in and have a full battery at 19:00 and go wherever I want without having to hang around a fast charger doing nothing. And with the Renault rental battery, each fast charge costs extra.

    So I think most people will definitely want more than 1x16A charging at home.

    • i assume 100km roundtrip is much more than the avg person & many people wouldn’t need the faster charger. but nonetheless, the point that many people would prefer to have it (and are in a similar situation to you) is a good point worth remembering.

      • pure curiosity: weren’t you previously commenting (several months back) under the name Anne? I’m assuming you’re name is Arne, but I’m guessing you’re the same commenter, and just wanted to check.

  • dwj

    Domestic electricity supplies and local distribution systems are not capable of providing the power necessary for this type of fast charging. To charge a 20 kWh battery in 10 minutes you would need a 400 amp supply (for 80% charge). As Ronald B suggests, an overnight charge using a 15 amp circuit is well matched to domestic use.

  • Ronald Brakels

    A faster charger would be nice, but most people in Europe, Australia, etc. will do just fine without any dedicated charger at all. Provided the car is built for European current, an overnight charge from a normal power socket is all most people will need. If they are driving out of town then they can go to a public fast charger.

    • Omega Centauri

      The pblic fast charger is limited by the vehicles onboard charging system. So without adding cost the max charge rate will be limted. I think this mechanism is proposed to try to bypass that limitation. The home charger would still be limited by the homes wiring, but presumably the public charger would be able to take full advantage of the new pathway.

      I have noticed my plug in Prius can gain charge a lot faster downhill with regenerative braking, then it gets from the charger. I suspect a “fast-charge” could be contrived by pulling the vehicle and using regenerative braking (which would be ridiculous and probably dangerous). I think this method is similar to using the regenerative capability rather than a dedicated charger circuit.

      • Ronald Brakels

        Apparently the batteries on a Prius can accept over 20 kilowatts when using regenerative braking. However, this may be limited to short periods and I don’t know if the batteries could be charged normally at that rate.

        • Omega Centauri

          I’m pretty certain its limited to only a couple of minutes. I have some biggish downhills on my commute, and it is challenging to avoid the car going into engine-braking mode before the bottom (even including putting the AC on full blast to absorb some of the energy). I suspect the BMS monitors battery temp, and throttles regenerative rates once it reaches a certain value. Nevertheless the sustainable rate is probaly at least several KW.

  • arne-nl

    AC propulsion also used a charger design that, as I understood it, incorporated a winding of the electric motor in the dc-dc converter that a charger mostly is. It seems Tesla have used this technology.

    The solution described here seems to use the motor as a simple ac-ac transformer. But in case that is not entirely clear from the text, the ‘rotating’ transformer is litterally the motor rotating during charging (at first I thought the ‘rotating’ had something to do with the rotation of 3 phase ac). That’s why there is a clutch between the motor and drive train.

    That extra clutch adds cost and another (fallible) mechanical component. So while it may be true that currently this will shave $ 2,000 off the cost of the charger, once EV’s are mass produced in the 100,000’s, the cost of the charger may have dropped by more than that already.

  • James Wimberley

    For the record, Chalmers is in Sweden. Swedish researchers are bilingual.

    • we didn’t write otherwise, did we?

      in any case, i added that in right at the top of the post (1st para). 😀

      curiosity: do they tend to just be bilingual, or actually trilingual?

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