Electricity: battery or capacitor charging or discharging – One cell or battery charges another – Vehicle battery charging
Reexamination Certificate
2000-02-04
2001-03-20
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
One cell or battery charges another
Vehicle battery charging
Reexamination Certificate
active
06204630
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to battery chargers, and in particular, this invention relates to a lightweight, onboard, isolated, electric vehicle battery charger which corrects for power factor and can be constructed to include a built-in DC to DC Converter.
BACKGROUND OF THE INVENTION
Electric vehicles include battery packs which supply the electricity for their motors. These battery packs require frequent charging. The longest range which such vehicles have achieved with available battery packs is approximately 80 miles. One method however of recharging batteries is through stations with large, stationary chargers. This method ties vehicle owners to a relatively small geographic area near an available charging station. The better solution is to utilize an onboard charger so that the vehicle's battery pack can be charged wherever there is an electric outlet.
Onboard battery chargers require solutions to specific problems before they achieve practicality. The first problem is safety. Unless the battery charger isolates the power source from the battery pack, there is an unacceptable risk of fatal electric shock during charging. Chargers which do not include such isolation cannot be integrated into vehicles or utilized for any other purposes by the public.
The engineering solution must result in sufficient isolation for safety, while providing adequate charging power to charge vehicle battery packs quickly and at thesame time keep charger size and weight to a minimum. The ratio of charging power to charger weight is known as “power density.”
The second problem is correction for power factor and total harmonic distortion (THD). Power factor must be corrected to prevent large amounts of power which do not register on electric meters from being converted into second, third, fifth and higher order harmonics which reflect back into the power grid causing large amounts of THD. See PG&E.
The Impact of Electric Vehicle Battery Charging on the PG&E Distribution System,
1994.
Third, sixth, ninth, etc. harmonics heat neutral conductors in wiring and electrical panels, and the primary windings of utility pole or vault transformers and, over time, damage this costly equipment. Second, fifth, eighth, etc. harmonics cause counter-rotating magnetic fields in electric motors so they draw more power to do less work, again leading eventually to costly equipment failures.
The power factor/THD problem therefore is a major, emerging priority for utility companies. The International Electrical and Electronic Engineers (IEEE) are currently discussing standards which will be mandated for all equipment which uses the power grid. See
IEEE Proposed Standard
519. With thousands of electric vehicles anticipated by the end of this decade, imposition of this standard will require substantial improvement in power factor correction and THD for electric vehicle battery chargers.
A third problem is that constant current control schemes lead to rising power throughout, especially during the initial bulk charge step, during which most of the total charge energy is returned to the batteries. As a result power throughput reaches 100% of the charger's capability only in the last moment before bulk charge termination, and charging time is much longer than with constant power throughput as achieved in this invention.
The optimum number of charging steps varies with each battery management scheme chosen by each manufacturer. Usually these consist of several bulk charge steps followed by several equalization steps. The problem that must be addressed is to provide a sufficient number of programmable steps with programmable power levels to satisfy the charge algorithms of each battery manufacturer.
A fourth problem is the charge termination criterion used by a charger, that is, how a charger decides when to terminate each step of the charging process, and when to start each step. Most chargers use voltage leveling detection. This method is not as precise and is therefore inferior to “temperature compensated absolute voltage threshold detection.” Absolute voltage threshold detection uses a temperature compensated absolute voltage reference so that the correct voltage threshold can be precisely established for charge termination. This is very important because the correct voltage to which a battery should be charged varies with the temperature of the battery.
A fifth problem is compatibility of the charger with the different voltages required for specific battery packs. Most chargers are designed to charge at a specific voltage level and cannot be used for charging when a battery pack with a different voltage level is installed.
Sixth and finally, electric vehicles require converters so that their high-voltage battery pack can be utilized to power the peripheral electrical systems of the vehicle, such as the radio, the cooling system and the windows. Vehicle manufacturers currently incorporate a separate DC to DC converter into their vehicles which adds an increment of cost to the vehicle's manufacture.
DESCRIPTION OF PRIOR ART
First, other small, lightweight chargers, even though they may be usable in terms of size or offer isolation between the battery pack and the input power source, lack the charging capacity or weigh considerably more than the charger achieved with the present invention. For example, Lester Electrical's 2.5 KVA chargers weigh 43.18 Kg and have a power density of 58 watts per kilogram. American Monarch's 2 KVA chargers weigh 22 Kg and have a power density of 90 watts per kilogram. American Monarch's 7.2 KVA charger weighs 54 kilograms and has a power density of 132 watts per kilogram. Applicant's invention produces 5 KVA in throughput and weighs 15 kilograms, producing a power density of 333 watts per kilogram, an improvement in power density of nearly three times.
Weight is a critical consideration for electric vehicles which must include large heavy battery packs and are limited to low horsepower motors in order to achieve adequate cruising range. Because low horsepower ratings are needed to achieve a practical range, small increments of extra weight can have a material impact on vehicle speed and range. This invention weighs less than 15 kilograms, substantially less than any other onboard charger currently available.
Second, because correction for power factor and THD is of increasing importance, this invention contains circuitry which corrects power factor fully (99.9+%) and reduces THD to between 2% and 3%, meeting the requirements of IEEE Proposed Standard 519, and the standards (5% max. for THD) set by EV America, explained below.
Many electric chargers small enough to mount on board vehicles offer no power factor correction (for instance the Soleq 2400 and the ZIVAN chargers). Both Lester Electric's chargers and American Monarch's chargers are also in this category. All these non-corrected chargers have power factors of 65% to 75% and THD figures between 90% and 105%. These are all grossly unacceptable to the utility companies and will not meet the standards of IEEE Proposed Standard 519, or the standards set by EV America.
The Hughes onboard charger includes a power factor correction circuit which corrects power factor to 89.3% and produces THD of 19.5%, still far short of performance achieved using this invention and the standards of the IEEE. The Hughes power factor correction circuitry is also static in design and unlike this invention cannot optimally correct for power factor and THD at all power levels, resulting in periods of even higher power loss and higher THD.
Third, no other compact, lightweight charger, including those cited above, can charge from 120 VAC, 208 VAC, 240 VAC, or from any other voltage between 200 VAC and 275 VAC, or between 95 VAC and 145 VAC. Each such charger cited, other than this invention, must be custom designed to accommodate different input voltages, while this invention automatically adjusts to whatever input voltage level is supplied.
Fourth, no other compact, lightweight charger inclu
Fish Robert D.
Fish & Associates, LLP
Tso Edward H.
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