Electricity: battery or capacitor charging or discharging – Cell or battery charger structure – Charger inductively coupled to cell or battery
Patent
1998-11-03
2000-08-08
Riley, Shawn
Electricity: battery or capacitor charging or discharging
Cell or battery charger structure
Charger inductively coupled to cell or battery
320119, H02J 700
Patent
active
061006637
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
This invention relates to the field of battery charging apparatus and methods where individual cell charging can be controlled, and to transport, where it relates to electric vehicles using batteries that are charged by inductive power transfer.
BACKGROUND
There is considerable interest in electric vehicles (EVs) as pollution-free transport units, but the public has become so used to the convenience of gasoline as a fuel that the problems of electricity supply and storage still render EVs relatively unacceptable.
Providing power to an EV involves selecting a source. One extreme is where the vehicle carries its own energy on-board--the pure battery approach, with rechargeable batteries charged at a supply depot, and the other extreme is an immediate supply approach without the use of any storage battery at all, perhaps using a pickup brush rubbing on an electrified rail or an overhead wire, or using an inductive power transfer approach. (Some EVs may supplement these methods with solar generated power or occasional use of an on-board generator driven by an engine). Generally it is desirable to provide sufficient charge in a given vehicle to provide for a reasonable distance of travel. It is desirable to provide a convenient, "invisible" charging process so that the user simply gets into the vehicle as and when required, and goes off to a destination. Circumstances determine the most appropriate source selection from this range of choices of supply of power. It may be too expensive to electrify a route. At least some battery storage is preferred for most EVs, so that the vehicle can at least temporarily go off an energised route, and so that peak power levels can be provided at levels which exceed the rate at which power can be transferred from the stationary supply. Some vehicles may return power to the battery during regenerative braking; useful in hilly localities.
EVs supplied from stationary sources of electric power generally remain at a charging site for a period, charge up one or more on-board batteries, and then consume the stored energy during movement. Disadvantages of this process include the extended waiting time at a charging position, and the need to make a deliberate refuelling act from time to time in order to continue to travel. Apart from the disadvantage of relatively frequent refuelling, EVs also have technical problems related to the storage batteries themselves. The lead-acid battery is still by far the most commonly used kind even though novel types such as sodium-based cells have recently been developed--and abandoned--and lithium hydride batteries are now being developed. Lead-acid batteries are marginally acceptable for electric vehicle applications because under existing management regimes they suffer from the disadvantages of high weight, high volume, poor energy storage, poor energy density, poor cycle life, and high cost.
A less well appreciated but significant problem relates to those larger vehicles that employ a number of battery units or monoblocks wired in series. Typically the motors of these vehicles run at 100 or 200 V or more, largely to minimise switching costs and ohmic losses. The deleterious effects of either complete discharge or complete (over) charge of the lead-acid battery are well-known. The problem is further compounded by the inevitably differing coulombmetric efficiencies of a set of battery cells. If a series bank of cells is repeatedly charged then discharged, some cells will tend to drift to a fully charged state while others will tend to drift to a fully discharged state. The prior-art procedure used to equalise the charge in all units of a set is to fully charge the entire set until all batteries starts to `gas`--when every cell in the battery is fully or 100% charged--but most are now overcharged and electrolyte is lost during gassing. For a typical EV, a full charging process is done once per day or overnight, with opportunity charging through the day. It is known that provided a lead-acid battery is maintained a
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Boys John Talbot
Green Andrew William
Auckland UniServices Limited
Riley Shawn
Toatley , Jr. Gregory J.
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