Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Reexamination Certificate
2002-09-05
2004-08-03
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
Reexamination Certificate
active
06771045
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the present invention is generally battery charging, and in particular systems for charging and equalization by shuffling charge between battery packs.
2. Background
Systems of batteries are used as a power source in a variety of applications, such as batteries used in electric and electric-hybrid vehicles to power the motor or accessories. However, the utility of battery power is reduced by factors that decrease the lifetime of individual batteries in the battery power system. Batteries within the same battery power system will charge and discharge at different rates due to different temperatures, construction and materials. As a result, the charge levels of the batteries will differ over time. When the battery power system is charged to bring lower charged batteries to a full charge, the higher charged batteries will be overcharged thereby reducing lifetime. Yet, if the charge to the battery power system is lessened to avoid overcharging the higher charged batteries, the output of the battery power system will be less than full capacity.
More specifically, the following discussion describes batteries or battery packs connected in series. For the purposes of this invention a plurality of batteries connected in parallel are the same as a single battery. Charge equalization devices have been developed to balance charge levels between battery pairs within a battery power system, thereby reducing the risk of overcharging individual batteries when the battery power system is charged. When the voltage of one battery in the pair is higher than the voltage of another battery in the system by a certain amount, a conventional charge equalization device transfers charge from the higher charged battery to the lower charged battery. The charge equalization device can be configured to transfer charge until the difference in charge levels between batteries is below a designated amount. This process of equalizing charge levels between the batteries can be repeated until all batteries within a battery power system have a consistent charge level.
The conventional charge equalization device is not designed, however, to independently charge an individual battery connected within a plurality of batteries to full capacity. Using charge equalization alone, the highest achievable charge level of a battery is always less than the charge level of the other battery in the equalization pair, i.e., the battery is undercharged. After a sufficient period of undercharging, the portion of the battery cell that has not been charged may no longer be available and the lifetime of batteries will be reduced. The lifetime of certain types of batteries can also be diminished by a memory effect. The memory effect occurs when a battery cell is regularly charged such that the charge does not fall below a particular level. After a sufficient period of time, the battery capacity is lessened because only the portion of the battery cell that has been charged will be available for use and the lifetime of the battery cell is thereby diminished.
SUMMARY OF THE INVENTION
A method and system for charging and equalizing battery packs in a battery power system by transferring charge between battery packs. For purposes of this specification and the claims that follow, the term ‘battery pack’ can represent an individual battery cell or a plurality of battery cells in a module or a plurality of modules. The method can comprise determining if a battery pack is a candidate for charging, selecting a battery pack to transfer charge from, transferring charge, discontinuing charge transfer, and equalizing charge level between battery packs in the battery power system. This charge-then-equalize process can be repeated for each battery pack in a plurality of battery packs. The method can also comprise discharging a battery pack prior to charging in order to counter the memory effect.
The system of battery charging and equalization can comprise a battery charging and equalization unit coupled with a plurality of battery packs, wherein the unit comprises any configuration capable of performing the method of battery charging and equalization. In one embodiment, the battery charging and equalization unit comprises a charge shuffler and a processor. Specifically, the processor can be coupled with each battery pack to monitor charge data. The charge shuffler can be embodied as a DC-to-DC converter that is capable of transferring charge between battery packs. The charge shuffler is coupled with each of the plurality of battery packs. The processor is coupled with the charge shuffler to direct the transfer and equalization of charge between battery packs. The processor can also direct the charge shuffler to transfer charge from the first battery pack to one or more other battery packs, thereby draining the first battery pack. Other aspects, features and embodiments are disclosed in the detailed description that follows and are described in relation to the following figures.
REFERENCES:
patent: 5900716 (1999-05-01), Collar et al.
patent: 6114835 (2000-09-01), Price
patent: 6140800 (2000-10-01), Peterson
patent: 6150795 (2000-11-01), Kutkut et al.
patent: 6271645 (2001-08-01), Schneider et al.
Beuerle Stephen C.
ISE Corporation
Tso Edward H.
LandOfFree
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