Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-04-26
2001-11-13
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
Reexamination Certificate
active
06316913
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to battery backup and management systems and, more specifically, to a low dissipation system and method for determining battery capacity and battery plant incorporating the same.
BACKGROUND OF THE INVENTION
The traditional reliability of telecommunication systems that users have come to expect and rely upon is based, in part, on the reliance on redundant equipment and power supplies. Telecommunication switching systems, for example, route tens of thousands of calls per second. The failure of such systems, due to either equipment breakdown or loss of power, is unacceptable, since such failure may result in the discontinuation of millions of telephone calls and a corresponding loss of revenue.
Power plants, such as battery plants, address the power loss problem by providing the system with an energy reserve (e.g., a battery) in the event of the loss of primary power to the system. A battery plant generally operates as follows. The battery plant includes a number of batteries, rectifiers and other power distribution equipment. The primary power is produced by the rectifiers, which convert an AC main voltage into a DC voltage to power the load equipment and to charge the batteries. The primary power may, however, become unavailable due to an AC power outage or the failure of one or more of the rectifiers. In either case, the batteries then provide power to the load. Redundant rectifiers and batteries may be added to the battery plant as needed to increase the availability of the battery plant.
A battery plant that powers telecommunications systems, such as transmission and switching systems in wireless base stations, commonly employs valve-regulated lead-acid (VRLA) batteries as the energy reserve. The batteries are typically coupled directly to the output of the rectifiers and may instantly provide power to the load in the event an AC power outage occurs. During normal operation, the batteries are usually maintained in a fully charged state to maximize a duration for which the batteries can provide energy to the load equipment.
As a battery ages, however, its capacity or energy-storage capability decreases thereby reducing a duration for which the battery can provide energy, even when fully charged. In many telecommunications applications, the battery is considered to have failed when its actual capacity has fallen below a threshold, such as 80% of its rated capacity. A failed battery should be replaced in an orderly fashion to maintain the availability of the battery plant. It is crucial, therefore, to be able to assess whether the capacity of a particular battery has fallen below it's threshold.
The capacity of a battery may be assessed with the battery on-line or off-line. One straightforward approach is to take the battery off-line and couple it to a dissipative-resistive load. The load can then discharge the battery completely or partially at a constant current, thus providing an indication of the battery's capacity. The off-line method, however, requires that the battery be temporarily removed from the battery plant, decreasing the availability thereof. Therefore, to maintain the battery plant at the desired availability level, the capacity of the battery should be assessed on-line.
Completely discharging the battery to assess the capacity also presents major disadvantages. If an AC power outage occurs during or after the discharge test, but before the battery has been fully recharged, the full energy reserve provided by the battery will not be available. This obviously jeopardizes the availability of the battery plant and the reliability of the telecommunications system powered therefrom. Further, since a battery may only be charged and discharged a finite number of times, each cycle of complete discharge and charge necessarily reduces the overall life span of the battery. Additionally, power is typically wasted and unwanted heat is usually generated through the use of conventional battery capacity testing.
Accordingly, what is needed in the art is a system and method for assessing the capacity of a battery that provides an accurate measurement of the battery's capacity while avoiding additional power loss and heat generation.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a system and method for determining a capacity of a battery in a battery string that provides power to a load. In one embodiment, the system includes: (1) a power converter, having an input couplable across the battery and an output couplable across the battery string, that is adapted to transfer power from the battery to the load over a period of time and (2) a voltage sensor, associated with the power converter, that measures voltages of the battery during the period of time. The voltages are indicative of the capacity of the battery.
The present invention therefore introduces the broad concept of determining the capacity of a battery by discharging the battery in a low to non-dissipative manner by directing the discharge power to the load. The invention thereby avoids the requirement for additional resistive loads, which are typically physically large, to conduct a battery discharge test. Additionally, removal of the converted heat generated by the dissipated energy is also avoided. Removal of the converted heat is often problematic, especially in outdoor equipment cabinet environments where the batteries are kept in closed compartments.
In one embodiment of the present invention, the power converter transfers the power to the load at a constant current. Testing a battery under a constant current condition allows the battery voltage to be the only test variable, thereby yielding an accurate battery discharge characteristic related to battery capacity.
In one embodiment of the present invention, the power converter is a flyback converter. The flyback converter generally affords a low component count. Additionally, the flyback converter provides isolation between the primary and secondary sides through the use of a transformer. Of course, other power converter topologies may be used as an application may dictate.
In one embodiment of the present invention, the battery remains coupled to another battery in the battery string. Under this test situation, a single battery in a battery string may be tested for short periods of time without disconnecting the battery from the string. The voltage of the battery under test diminishes during the test thereby stressing the other batteries in the string as charging currents through the batteries tend to rise to maintain a constant string voltage.
In one embodiment of the present invention, the battery is decoupled from another battery in the battery string. Under this test situation, the battery may be tested for extended periods of time, since disconnecting the battery effectively removes its battery string from contributing power to the load.
In one embodiment of the present invention, the power converter employs an error amplifier. The error amplifier is used to sense one or more critical currents associated with the battery test, develop an error signal based on a reference current therefrom and provide direction to the power converter for maintaining a constant battery current throughout the duration of the test.
In one embodiment of the present invention, the system further includes a switching arrangement that selectively couples the battery to the power converter. The switching arrangement may thus allow the system to selectively test each battery in the battery string.
The foregoing 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 of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception a
Chalasani Subhas C.
Thottuvelil Vijayan J.
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