Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells
Reexamination Certificate
2000-10-03
2001-07-24
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
Reexamination Certificate
active
06265846
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to power supplies and, in particular, to a battery pack having a number of individual series-connected cells that combine to produce a particular supply voltage. More specifically, the present invention relates to an active bypass circuit for extending energy capacity and operational life of a multi-cell battery.
2. Description of the Related Art
A battery is typically an electrochemical device that converts chemical energy into electrical current utilizing one or more galvanic cells. A galvanic cell is a fairly simple device that consists of two electrodes, i.e., an anode and a cathode, typically immersed in an electrolyte solution. The amount of energy, i.e., voltage and current, that a galvanic cell generates is directly related to the types of materials employed in the electrodes and electrolyte. The length of time that the cell can maintain a particular voltage and current is related to the amount of active material utilized in the cell and the cell's design.
A key parameter for a battery cell is its capacity, generally stated in ampere hours, or milliampere hours. The capacity of the battery cell is a variable that changes depending on discharge rate, charge rate, temperature, age and number of charge/discharge hours. Cell voltage also varies as a function of temperature, discharge rate and discharge status, i.e., percent of discharge.
A battery cell's voltage profile is the relationship of its output voltage to the amount of time that the battery cell has been discharging, e.g., when connected to a load device, or charging. Generally, in most battery cells, the voltage will reduce steadily as the chemical reactions in the cell are diminished. In the case of nickel-cadmium (Ni—Cd) cells, the output voltage is a relatively flat voltage profile. A Ni—Cd cell's voltages will typically remain constant over approximately two-thirds of the cell's discharge cycle. At some point near the end of the cell's discharge cycle, the cell's voltage will drop sharply to nearly zero volts. This requires that the cell will have to be replaced, or recharged, almost immediately after a drop in voltage. If the battery cell is not replaced, or charged, immediately, the cell will quickly cease to provide any useful energy. Additionally, a cell's voltage that has dropped to zero and is continuing to be used may result in the failure in the cell itself.
In either event, a voltage drop, due to a discharged cell or a failure in the cell, may also adversely impact the rest of the cells in multi-cell battery, contributing to additional failures. Additionally, current energy systems utilizing multi-cell battery packs consider the battery pack as the lowest level field replaceable unit. Thus a failure in one or more (but not all) of the cells in the battery pack will necessitate a replacement of the entire battery pack even if the remaining “good” cells may still have sufficient energy capacity to continue providing power to a load.
Accordingly, what is needed in the art is an improved multi-cell battery system that mitigates the above-discussed limitations in the prior art. More specifically, what is needed in the art is a multi-cell battery system with improved reliability and longer life cycle.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improved multi-cell battery.
It is another object of the invention to provide an active bypass circuit for use with a multi-cell battery and a method of operation thereof.
To achieve the foregoing objects, and in accordance with the invention as embodied and broadly described herein, an active bypass circuit for use with a battery pack having a plurality of cells is disclosed. The active bypass circuit includes a first switching device that is series-coupled with a cell in the battery pack (a separate active bypass circuit is utilized for each cell in the battery pack). A second switching device is parallel-coupled across the first switching device and the cell. The first and second switching devices are switched, i.e., turned ON and OFF, in a complementary fashion. The active bypass circuit also includes a monitoring circuit for monitoring an electrical characteristic of the cell and generating a switching control signal, in response to the monitored electrical characteristic, to selectively control the operation of the first and second switching devices. In an advantageous embodiment, the electrical characteristic is a voltage across the cell. In a related embodiment, the active bypass circuit also includes a switching driver circuit that receives the switching control signal from the monitoring circuit and generates, in response thereto, complementary first and second switching signals to the first and second switching devices, respectively.
The present invention discloses a novel active management circuit for use in batteries utilizing multiple series-couple energy cells to increase the overall operational lifetime of the batteries. The utilization of the novel active bypass circuit of the present invention results in shifting the basic, or lowest level, failure point from the first failure of a cell to the overall composite energy stored in the battery. This results in extending the energy providing capacity and improving the overall operational lifetime of the multi-cell battery. By analogy, the present invention is similar to the concept of redundant arrays of inexpensive disks (RAID) utilized in computer server systems. By shifting the lowest identified replacement, or failure, module away from the individual cell, the device with the highest failure rate is no longer the limiting factor. This results in significantly improving the reliability and, ultimately, lowering the cost of operation of a multi-cell battery.
In another embodiment of the present invention, the monitoring circuit includes an operational amplifier (op-amp), configured as a comparator, and a voltage reference. The switching control signal generated by the monitoring circuit is utilized, in an advantageous embodiment, to control the operation of the first and second switching devices that are n-channel and p-channel metal-oxide-semiconductor field effect transistors (MOSFETs), respectively. Those skilled in the art should readily appreciate that, in other advantageous embodiments, the switching devices may be insulated gate bipolar transistors (IGBTs) or relay-type devices. The present invention does not contemplate limiting its practice to any one type of switching device.
In yet another embodiment of the present invention, the switching driver circuit utilizes an inverter to generate the complementary switching signals. Alternatively, in other advantageous embodiments, a flip-flop device, such as a D-type flip-flop, may be employed to generate the complementary switching signals for the first and second switching devices. In a related embodiment, the first and second switching devices are metal-oxide-semiconductor field effect transistors (MOSFETs).
The foregoing description has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject matter of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
REFERENCES:
patent: 3315140 (1967-04-01), Dadin
patent: 4316185 (1982-02-01), Watrous et al.
patent: 4823086 (1989-04-01), Whitmire et al.
patent: 4931738 (1990-06-01), MacIntyre et al.
patent: 5349535 (1994-09-01), Gupta
patent: 5543245 (1996-08-0
Flechsig Karl A.
Gillis Donald Ray
Bracewell & Patterson L.L.P.
International Business Machines - Corporation
Martin Robert B.
Tso Edward H.
LandOfFree
Active bypass circuit for extending energy capacity and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Active bypass circuit for extending energy capacity and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Active bypass circuit for extending energy capacity and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2497550