Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Reexamination Certificate
2000-06-22
2001-10-16
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
06304059
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to power plants and, more specifically, to a battery management system, method of operation therefor, and a battery plant employing 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 connected in strings (battery strings) and coupled directly to the output of the rectifiers to 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. However, because all the battery strings in battery plants found in the prior art are charged simultaneously and for the same duration, the individual battery strings are typically not charged to their optimum potentials.
The batteries are typically float charged in multiple battery strings, with each battery string having multiple batteries or monoblocks. For example, four 12V monoblocks may be connected in series to form a 48V battery string. The battery strings are coupled across the output of the rectifiers and are charged by drawing current from the output bus of the rectifiers. As the batteries charge, the amount of current drawn from the rectifiers is reduced, until only a small float current, sufficient to keep the batteries fully charged, is drawn. A float voltage may be adjusted based on battery temperature. With multiple battery strings, however, the temperature of the battery strings may be different. However, since the voltage of the rectifiers' output bus is common to all the battery strings, the float voltage of an individual battery string cannot be set at an optimal level.
Furthermore, the prior art methods of determining the individual capacities of each battery remain crude and imprecise. Current battery plants test the capacity of all the battery strings as a whole. Specifically, to determine the charge capacity of a battery string, the controller adjusts the overall battery plant voltage to allow the batteries in the battery string to discharge at a constant and desired current level. During this process the voltage of the battery string may be monitored to assess its capacity.
A problem occurs when multiple battery strings are employed in a single battery plant. In this situation, while the controller can still adjust the battery plant voltage to provide battery discharge at a constant desired current level, it is necessary to assess the capacities of all the battery strings at the same time. A defective battery string may, therefore, not be detectable.
Accordingly, what is needed in the art is a battery management system, and related method, employable with a battery plant having at least one battery string and, in many instances, a plurality of battery strings, that can individually assess and improve the performance of each battery string in the battery plant.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides, for use with a battery plant coupled to a source of electrical power and having a power bus coupled to a load, the battery plant including a battery string coupled across a pair of rails of said power bus, a battery management system, method of operation therefor and battery plant employing the battery management system or the method. In one embodiment, the battery management system includes a DC/DC converter, couplable in series with the battery string, adapted to condition a voltage provided to the battery string as a function of a characteristic of the battery string. The battery management system also includes a switching circuit, coupled across the DC/DC converter, adapted to selectively decouple the DC/DC converter from the battery string thereby allowing the battery string to power the load.
The present invention, in one aspect, introduces a battery management system for a battery string located in a battery plant. The battery management system is designed to be series-coupled to the battery string and adapted to condition a voltage to the battery string as a function of a characteristic thereof. The charging of the battery string can be customized by taking into account various parameters, such as the environment (e.g., temperature), state of charge of the battery and electrical characteristics (e.g., a voltage) of the battery string. The battery management system, therefore, provides additional functionality to the battery plant such as charging control and state of health assessment of the battery string.
In one embodiment of the present invention, the battery plant further includes at least one AC/DC rectifier coupled to the source of electrical power. The AC/DC rectifier transforms AC power from the source of electrical power to a substantially equivalent DC component to power the battery plant and, ultimately, the load.
In one embodiment of the present invention, the DC/DC converter is a bi-directional DC/DC converter. Of course, other power converter topologies may be used in accordance with the requirements of a particular application.
In one embodiment of the present invention, the battery plant further includes a controller that monitors the characteristic of said battery string. The controller is adapted to monitor any condition of the battery string such as a voltage, state of charge or environmental conditions. The controller then employs that information to regulate the battery management system.
In one embodiment of the present invention, the battery plant further includes a plurality of battery strings coupled across the rails of the power bus. A battery plant often includes a plurality of battery strings to accommodate higher load requirements or for backup protection. The battery management system is especially useful in such applications to customize the treatment of each battery string when there are multiple battery strings. In a battery plant including multiple battery strings, it is preferable to include a plurality of DC/DC converters and switching circuits adapted to be coupled to corresponding battery strings.
In one embodiment of the present invention, the battery string includes a battery selected from the group consisting of: (1) a valve-regulated lead-acid (VRLA) battery; (2) a flooded lead-acid battery; (3) a nickel-cadmium battery; and (4) a lithium battery. Such batteries are often employed in battery plants to power telecommunications systems such as transmission and switching systems, and in wireless base stations as the energy rese
Chalasani Subhas C.
Davis Roy J.
Steeves Michael C.
Thottuvelil Vijayan J.
Toatley , Jr. Gregory J.
Wong Peter S.
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