Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-06-26
2001-03-20
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S162000, C320S164000
Reexamination Certificate
active
06204634
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of batteries and electrical storage devices. More particularly, the present invention relates to optimum charging of battery cells.
BACKGROUND OF THE INVENTION
Existing charge control systems for lithium-ion or lithium polymer battery cells typically utilize voltage-limited constant current charging of individual cells to maintain an adequate battery charge while also limiting cell degradation rates. This kind of a charge control system, while adequate for commercial applications that do not have large cycle life requirements, is not capable of optimizing the cycle life capability of lithium-ion and lithium polymer battery cells. Ultimate cycle life has a strong inverse correlation with the cumulative amount of overcharge put into the cells by the charge control system. The optimum cycle life is achieved when unnecessary overcharge is exactly zero. In addition, degradation rates can change significantly as the electrodes transition among several charge states. Also, the recharge voltage limit shifts as the cell temperature changes and as the cells degrade over life. Charge control devices or algorithms that automatically optimize the recharge process and that adapt to changes in the environment or to internal cell degradation are not presently available for lithium-ion and lithium polymer battery cells. These and other disadvantages are solved or reduced using the invention.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method for adaptively charging battery cells.
Another object of the invention is to provide a method for adaptively charging battery having time varying charge capacities.
Yet another object of the invention is to provide a method for adaptively charging of lithium ion battery cells that have time averaging charge capacities.
A further object of the invention is to provide a method for adaptively charging battery cells by adjusting a recharge fraction parameter that is the amount of charging divided by the amount of discharging over a charging cycle.
The present invention provides an algorithm that meters the correct amount of recharge into a battery cell such as a lithium-ion or a lithium-polymer battery cell, to optimize cycle life, while maintaining the cell at a high state-of-charge. The algorithm automatically adapts to any changes in the thermal environment or any internal cell degradation to maintain the minimum stress condition needed to optimize cycle life. Subtle adaptive changes in the charge control parameters provide an order of magnitude variation in cycle life.
The adaptive algorithm eliminates unnecessary overcharging by metering a charge into each cell and exactly balances the input charge capacity to the discharged capacity. This balance point is adaptively maintained over repetitive cycling by adaptively changing the control parameters reducing cell degradation. Capacity degradation relates to the cell charge and discharge voltages. The adaptive algorithm uses a plurality of control parameters to adaptively adjust the recharge fraction. For example, a low discharge voltage due to capacity degradation is compensated by a slight upward adjustment to the charge into the cell during recharge. This assures minimum degradation rates while keeping each cell at the maximum state-of-charge consistent with optimum cycle life. The recharge algorithm firstly locates the optimum charge control point for each cell in a battery, and secondly adapts the charge control parameters as the cell degrades or the thermal environment changes so as to maintain the optimum condition for best cycle life. These and other advantages will become more apparent from the following detailed description of the preferred embodiment.
REFERENCES:
patent: 4709202 (1987-11-01), Koenck et al.
patent: 5561360 (1996-10-01), Ayres et al.
Quinzio Michael V.
Zimmerman Albert H.
Reid Derrick Michael
The Aerospace Corporation
Tso Edward H.
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