Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Reexamination Certificate
2000-02-11
2001-08-07
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
C320S119000
Reexamination Certificate
active
06271645
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and a circuit for balancing energy levels among batteries in a battery pack.
2. Disclosure of Related Art
As shown in U.S. Pat. No. 5,631,534, a conventional system for powering an electric or hybrid vehicle may include a battery pack having a plurality of batteries connected in series across a first current bus. The first current bus may be used to provide power to an electric motor in the vehicle. The power provided across the first current bus is limited by the energy level of the weakest battery in the group of series connected batteries. Accordingly, also as shown in U.S. Pat. No. 5,631,534, it is conventional to provide a circuit for balancing the energy levels among the series connected batteries. It is also conventional for the battery pack to include an additional battery coupled across a second, accessory current bus that provides power for lighting, starting, and other electrical systems in the vehicle. The use of an additional battery to power vehicle electrical systems increases the cost and size of the battery pack and vehicle, however.
There is thus a need for a method and circuit for balancing energy levels in a battery pack that will minimize or eliminate one or more of the above-mentioned deficiencies.
SUMMARY OF THE INVENTION
The present invention provides a method and a circuit for balancing energy levels among batteries in a battery pack. In particular, the present invention provides a method and circuit for balancing energy levels between a first battery group and a second battery group in a battery pack wherein the first and second battery groups are connected across a first current bus and the first battery group is further connected across a second current bus. The first current bus may be used, for example, to provide power to an electric motor in a vehicle while the second current bus may be used, for example, to power vehicular electrical systems including lighting, and other systems. The starting function may be performed by the electrical machine on the first current bus (i.e., the higher voltage bus).
A method in accordance with the present invention may include the step of generating a first state of charge value indicative of a first energy level of the first battery group. The method may also include the step of generating a second state of charge value indicative of a second energy level of the second battery group. Finally, the method may include the step of controlling the first energy level responsive to the first state of charge value and the second state of charge value.
A circuit in accordance with the present invention may include means, such as current sensors and a controller operating under the control of software, for generating first and second state of charge values indicative of a first energy level of the first battery group and a second energy level of the second battery group, respectively. The circuit may also include means, such as the above-identified controller and a converter, for controlling the first energy level in said first battery group responsive to the first and second state of charge values.
One advantage of a method and circuit in accordance with the present invention is that the inventive method and circuit are able to maintain a balance in energy levels among batteries within a battery pack wherein the pack is used to provide power to two current buses having different loads. The inventive method and circuit therefore eliminate the need for a separate, additional battery to provide power to the second current bus.
These and other advantages of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.
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Fattic Gerald Thomas
Schneider Eric Duane
Delphi Technologies Inc.
Dobrowitsky Margaret A.
Tibbits Qa
Wong Peter S.
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