# Patent

## Title
Battery management circuit and related techniques using MOSFET power switch with intelligent switch control

## Abstract

A circuit includes a power supply configured to generate a supply voltage, an electrical load coupled to receive the supply voltage from the power supply, and a switching circuit. The switching circuit has a first terminal coupled to a first terminal of the electrical load, a second terminal, and a control terminal. The first terminal and the second terminal of the switching circuit correspond to current conducting terminals of the switching circuit. The circuit also includes a current sensing circuit and at least one battery having a first terminal coupled to a corresponding terminal of the current sensing circuit. The circuit additionally includes a battery measurement circuit having a first terminal coupled to the control terminal of the switching circuit and at least a second terminal coupled to the first terminal and a second terminal opposing the first terminal of the at least one battery.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. Provisional Application No. 62/079,237 filed Nov. 13, 2014 under 35 U.S.C. §119(e) which application is hereby incorporated herein by reference in its entirety.


GOVERNMENT RIGHTS
Not Applicable.
FIELD
This disclosure relates generally to circuits, and, more particularly, to battery management circuits and related techniques for managing one or more batteries in a circuit or system.
BACKGROUND
As is known in the art, a battery management circuit is an electronic circuit that manages a battery, such as by protecting the battery from operating outside its safe operating area, monitoring its state, calculating secondary data, reporting that data, controlling its environment, authenticating it and/or balancing it.
SUMMARY
In accordance with the concepts, systems, circuits and techniques sought to be protected, described herein is a battery management circuit having an intelligent switch function.
In particular, described herein is the use of a metal oxide semiconductor field effect transistor (MOSFET) disposed between a power supply (e.g., a direct current (DC) power supply) and at least one battery (e.g., at least one battery in a battery pack) and configured to act as a switch. The MOSFET has electrical characteristics selected such that in a first bias state the MOSFET isolates the at least one battery (e.g., a backup battery, or an array of batteries) from the power supply and a load (e.g., an electrical load) such that battery open circuit (OC) behavior of the at least one battery can be evaluated, while concurrently maintaining an uninterrupted current flow from the at least one battery to the load, in the event the power supply fails to provide sufficient power to the load.
In one aspect of the concepts described herein, in a system including a power supply configured to generate a supply voltage, an electrical load configured to receive the supply voltage, and a battery pack comprising at least one battery, a battery management circuit for managing the battery pack has first and second terminals configured to be coupled to first and second opposing terminals of the power supply and first and second opposing terminals of the electrical load. The battery management circuit also has third and fourth terminals configured to be coupled to first and second opposing terminals of the at least one battery. The battery management circuit includes a switching circuit having a first terminal coupled to the first terminal of the battery management circuit, a second terminal, and a third, control terminal. The first and second terminals of the switching circuit correspond to current conducting terminals of the switching circuit.
The battery management circuit also includes a current sensing circuit having a first terminal coupled to the second terminal of the switching circuit, a second terminal coupled to the control terminal of the switching circuit, and a third terminal coupled to the third terminal of the battery management circuit. The current sensing circuit is configured to receive a current signal from the switching circuit, measure a direction of the current signal, and provide a current sensing signal indicative of the direction of the current signal in response thereto at the second terminal of the current sensing circuit.
The battery management circuit additionally includes a battery measurement circuit having a first terminal coupled to the control terminal of the switching circuit. The battery measurement circuit also has at least a second terminal coupled to the first and second terminals of the at least one battery. The battery measurement circuit is configured to measure one or more characteristics of the at least one battery and provide a battery measurement signal in response thereto at the first terminal of the battery measurement circuit. A switch control signal based upon the current sensing signal and the battery measurement signal is provided to the control terminal of the switching circuit and thus controls current flow through the current conducting terminals of the switching circuit.
The battery management circuit may include one or more of the following features individually or in combination with other features. The one or more characteristics measured by the battery measurement circuit may include open circuit voltage and/or open circuit voltage behavior of the at least one battery. The battery measurement circuit determines state of charge (SOC) and/or state of health (SOH) characteristics of the at least one battery in response the measured open circuit voltage and/or open circuit voltage behavior of the at least one battery.
The battery management circuit includes a logic gate having a first input coupled to the second terminal of the current sensing circuit, a second input coupled to the first terminal of the battery measurement circuit, and an output coupled to the control terminal of the switching circuit. The logic gate is configured to receive the current sensing signal from the current sensing circuit and the battery measurement signal from the battery measurement circuit at the first and second inputs thereof. In response thereto, the logic gate provides a logic gate output signal at the output thereof. The logic gate output signal controls current flow through the current conducting terminals of the switching circuit.
The battery management circuit includes a switch control circuit having an input coupled to the second terminal of the current sensing circuit and an output. The switch control circuit is configured to receive the current sensing signal at the input thereof and in response thereto produce a switched output signal at the output thereof. The battery management circuit includes a logic gate having a first input coupled to the output of the switch control circuit, a second input coupled to the first terminal of the battery measurement circuit, and an output coupled to the control terminal of the switching circuit. The logic gate is configured to receive the switched output signal and the battery measurement signal at the first and second inputs thereof. In response thereto, the logic gate provides a logic gate output signal at the output thereof. The logic gate output signal controls current flow through the current conducting terminals of said switching circuit.
In one embodiment, the switching circuit includes a field-effect transistor (FET) having a source terminal, a drain terminal and a gate terminal. The source terminal corresponds to the first terminal of said switching circuit, the drain terminal corresponds to the second terminal of said switching circuit, and the gate terminal corresponds to the third terminal of said switching circuit so as to provide a configuration which supports negative voltage system configurations.
It should be appreciated that the drain and source terminals must be reversed for positive voltage systems (i.e. the drain terminal corresponds to the first terminal of the switching circuit, the source terminal corresponds to the second terminal of the switching circuit).
It should also be appreciated that the switching circuit can be placed in either a negative or positive power path of the battery management circuit.
The battery management circuit may also include one or more of the following features individually or in combination with other features. The FET of the switching circuit may be provided as a metal-oxide-semiconductor field-effect transistor (MOSFET). The MOSFET may be provided as an enhancement mode MOSFET. The switching circuit may include at least one diode having a positive terminal and a negative terminal. The positive terminal may be coupled to the first terminal of the switching circuit, and the negative terminal may be coupled to the second terminal of the switching circuit. The at least one diode may be provided as a p-n junction diode. The at least one diode may be provided as a parasitic diode integrated into the MOSFET of the switching circuit, a discrete diode or a combination thereof. The battery measurement circuit may be provided as part of a controller. The controller may be configured to provide the battery measurement signal.
In another aspect of the concepts described herein, a circuit includes a power supply having first and second opposing terminals. The power supply is configured to generate a supply voltage. The circuit also includes an electrical load having a first terminal coupled to the first terminal of the power supply and a second opposing terminal coupled to the second terminal of the power supply. The electrical load is configured to receive the supply voltage from the power supply. The circuit also includes a switching circuit having a first terminal coupled to the first terminal of the electrical load, a second terminal, and a third, control terminal. The first and second terminals provide current conducting terminals of the switching circuit.
The switching circuit includes a plurality of metal-oxide-semiconductor field-effect transistors (MOSFETs). Each of the MOSFETs are provided having a first, source terminal, a second, drain terminal, and a third, gate terminal. The source terminals of the MOSFETs are coupled to the first terminal of the switching circuit, the drain terminals of the MOSFETs are coupled to the second terminal of the switching circuit, and the gate terminals of the MOSFETs are coupled to the control terminal of the switching circuit. The switching circuit also includes a corresponding plurality of diodes. Each of the diodes has a positive terminal and a negative terminal. The positive terminals of the diodes are coupled to the source terminals of the MOSFETs and the negative terminals of the diodes are coupled to the drain terminals of the MOSFETs.
The circuit additionally includes a current sensing circuit having a first terminal coupled to the second terminal of the switching circuit, a second terminal coupled to the control terminal of the switching circuit, and a third terminal. The current sensing circuit is configured to receive a current signal from the second terminal of the switching circuit at the first terminal thereof, measure a direction of the current signal, and provide a current sensing signal corresponding to the direction of the current signal in response thereto at the second terminal of the current sensing circuit.
The circuit further includes at least one battery having a first terminal coupled to the third terminal of the current sensing circuit and a second opposing terminal coupled to the second terminal of the electrical load. The circuit also includes a battery measurement circuit having a first terminal coupled to the control terminal of the switching circuit and at least a second terminal coupled to the first and second terminals of the at least one battery. The battery measurement circuit is configured to measure one or more characteristics of the at least one battery and provide a battery measurement signal in response thereto at the first terminal of the battery measurement circuit. A control signal corresponding to the current sensing signal and the battery measurement signal controls current flow through the current conducting terminals of the switching circuit.
The circuit may include one or more of the following features individually or in combination with other features. In response to measuring the direction of the current signal, the current sensing circuit may further provide a corresponding current sense control signal to a third terminal of the battery measurement circuit to control measurement of the one or more characteristics of the at least one battery. The current sense control signal may also control measurement of current flow rate, and charge into and out of the at least one battery by the battery measurement circuit. The plurality of MOSFETs in the switching circuit may be five MOSFETs.
The circuit may further include a logic gate having a first input coupled to the second terminal of the current sensing circuit, a second input coupled to the first terminal of the battery measurement circuit, and an output coupled to the control terminal of the switching circuit. The logic gate may be configured to receive the current sensing signal from the second terminal of the current sensing circuit and the battery measurement signal from the battery measurement circuit at the first and second terminals thereof. In response thereto, the logic gate may provide a logic gate output signal at the output thereof. The circuit may further include an opto-isolator circuit having an input coupled to the logic gate output and an output coupled to the control terminal of the switching circuit. The opto-isolator circuit may be configured to receive the logic gate output signal at the input thereof and in response thereto provide an opto-isolator circuit output signal at an output thereof. The opto-isolator circuit output signal may control current flow through the current conducting terminals of the switching circuit.
The battery measurement circuit may further include a current source, a ballast resistor. The current source and the ballast resistor may be used by the battery measurement circuit to measure an internal (or characteristic) resistance of the at least one battery. The current sensing circuit may be further configured to measure magnitude and polarity of the current signal received from the switching circuit. The current sensing signal provided by the current sensing circuit may be further indicative of the magnitude and the plurality of the current signal. The switching circuit, the current sensing circuit, and the battery measurement circuit may be provided as part of a battery management circuit for managing the at least one battery. Each of the MOSFETs in the switching circuit may be provided as enhancement mode MOSFETs.
With the above arrangements, circuits and techniques suitable for battery management (e.g., charge control and measurement) are provided.



BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features and advantages of the concepts, systems and techniques described herein will be apparent from the following description of particular embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same elements throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the concepts, systems, circuits and techniques for which protection is sought.
FIG. 1 is block diagram of an example circuit including a battery management circuit;
FIG. 1A is block diagram of an example circuit including a plurality of battery management circuits;
FIG. 2 is a block diagram of an example configuration of a switching circuit suitable for use with the circuits of FIGS. 1 and 1A, for example;
FIG. 2A is a block diagram of another example configuration of a switching circuit suitable for use with the circuit of FIGS. 1 and 1A, for example;
FIG. 3 is a schematic diagram illustrating a circuit topology for an example circuit including a battery management circuit;
FIG. 4 is a schematic diagram illustrating a circuit topology for another example circuit including a battery management circuit; and
FIG. 5 is a flowchart illustrating an example method for measuring a characteristic resistance of a battery that may be implemented in the circuits of FIGS. 1, 1A, 3 and 4, for example.



DETAILED DESCRIPTION
It will be understood that any specific embodiments described herein are shown by way of illustration and not as limitations of the disclosure and the concepts described herein. Features of the subject matter described herein can be employed in various embodiments without departing from the scope of the concepts sought to be protected.
Definitions
For convenience, certain introductory concepts and terms used in the specification are collected here.
As used herein, the term “processor” is used to describe an electronic circuit that performs a function, an operation, or a sequence of operations. The function, operation, or sequence of operations can be hard coded into the electronic circuit or soft coded by way of instructions held in a memory device. A “processor” can perform the function, operation, or sequence of operations using digital values or using analog signals.
In some embodiments, the “processor” can be embodied, for example, in a specially programmed microprocessor, a digital signal processor (DSP), or an application specific integrated circuit (ASIC), which can be an analog ASIC or a digital ASIC. Additionally, in some embodiments the “processor” can be embodied in configurable hardware such as field programmable gate arrays (FPGAs), programmable logic arrays (PLAs) or programmable logic controllers (PLCs). In some embodiments, the “processor” can also be embodied in a microprocessor with associated program memory. Furthermore, in some embodiments the “processor” can be embodied in a discrete electronic circuit, which can be an analog circuit or digital circuit.
While battery packs and battery strings including a select number of batteries are described in several examples below, the select number of batteries are discussed to promote simplicity, clarity and understanding in the drawings as well as in the written description of the broad concepts, systems, circuits and techniques sought to be protected herein and is not intended to be, and should not be construed, as limiting. The concepts, systems, circuits and techniques disclosed herein may, of course, be implemented using more than or less than the select number of batteries. Further, it should be appreciated that the battery packs, battery strings and batteries (e.g., single or multi-cell batteries) described in the examples below may be provided as part of a “larger” system (e.g., a battery bank including a plurality of battery strings, or a monoblock battery including a plurality of battery cells) in some embodiments.
Referring now to FIG. 1, an example circuit in accordance with the concepts, systems, circuits and techniques sought to be protected herein is shown. The circuit includes a battery management circuit 110 coupled between a first portion of the circuit including a power supply 150 and an electrical load 160, and second portion of the circuit including a battery pack 170. The power supply 150 (e.g., a direct-current (DC) power supply) generates a supply voltage for use by the electrical load 160. In the event the power supply 150 fails to provide the necessary supply voltage to the electrical load 160 at power bus 152 (e.g., during a power failure), the battery pack 170, which includes at least one battery (e.g., a single or multi-cell battery), supplies some or all of the necessary supply voltage to the electrical load 160.
The battery management circuit 110 includes a switching circuit 120 serially coupled between a terminal (e.g., a first terminal) of the power supply 150 and a terminal (e.g., a first terminal) of the battery pack 170. A first terminal 120a of switching circuit 120 is coupled to a first terminal 110a of the battery management circuit 110 in the illustrated embodiment. Additionally, a second terminal 120b of switching circuit 120 is coupled to a third terminal 110c of battery management circuit 110 through a current sensing circuit 130 in the illustrated embodiment. In particular, a first terminal 130a of current sensing circuit 130 is coupled to the second terminal 120b of the switching circuit 120 and a third terminal 130c of current sensing circuit 130 is coupled to the third terminal 110c of the battery management circuit 110. Thus, the switching circuit 120 and the current sensing circuit 130 are serially coupled in a circuit path between the first and third terminals 110a, 110c of the battery management circuit 110.
It should be appreciated that current sensing in the circuit is performed in series with the circuit path between the first and third terminals 110a, 110c of the battery management circuit 110. A desirable technique to measure full current through switching circuit 120 is to place current sensing circuit 130 in series with that current. It should, of course, be appreciated that although current sensing circuit 130 is shown as disposed proximate to second terminal 120b of switching circuit 120 (i.e., on the right side of switching circuit 130) in the illustrated embodiment, current sensing circuit 130 can also be disposed proximate to first terminal 120a of switching circuit 130 (i.e., on the left side of switching circuit 120). Current sensing circuit 130 may comprise one or more of several different types of measuring circuits, which will all need to measure total current (i.e., total current of a current signal) passing through switching circuit 120. It should also be appreciated that current sensing circuit 130 may be used to measure magnitude and polarity of the current signal, as well as measure a direction of the current signal.
A second terminal 130b of current sensing circuit 130 is coupled to a third (or control) terminal 120c of the switching circuit 120 through a logic circuit 132. A first terminal 140a of a battery measurement circuit 140 is also coupled to the switching circuit 120 through logic circuit 132. As will become apparent from the description herein below, the logic circuit 132 may receive signals from the current sensing circuit 130 and the battery measurement circuit 140. In response to such signals, logic circuit 132 may provide a control signal (e.g., a logic gate output signal) to control terminal 120c of the switching circuit 120. It should be appreciated that logic circuit 132 (or the function performed by logic circuit 132) may be implemented as part of any or all of the current sensing circuit 130, the switching circuit 120 and/or the battery measurement circuit 140. Alternatively, portions of logic circuit 132 (or the function performed by logic circuit 132) may be distributed among any or all of the current sensing circuit 130, the switching circuit 120 and/or the battery measurement circuit 140. The battery measurement circuit 140 is, in turn, coupled across the battery pack 170 (e.g., through at least a second terminal 140a).
First and second terminals of the switching circuit 120 correspond to current conducting terminals of the switching circuit 120 in the illustrated embodiment (i.e., in a first state, the switching circuit 120 provides a low impedance signal path between the two current conducting terminals of the switching circuit 120 and in a second state, the switching circuit 120 provides a high impedance signal path between the two current conducting terminals of the switching circuit 120). The switching circuit 120 may, for example, be provided from one or more switching elements such as electro-mechanical relays and/or transistors. Additionally, the transistors may be provided as metal oxide semiconductor field effect transistors (MOSFET). Example switching circuits, including those comprising transistors, are described in conjunction with the figures below.
The current sensing circuit 130 receives a current signal from switching circuit 120 that may, for example, be generated during charging or discharging of the battery pack 170. In response thereto, current sensing circuit 130 measures a direction (e.g., charging or discharging direction) of the current signal and produces a current sensing signal corresponding to the direction of the current signal at second terminal 130b of current sensing circuit 130. Current sensing circuit 130 may also provide a corresponding current sense control signal to battery measurement circuit 140, as indicated by the signal path designated by reference numeral 134 in FIG. 1. The current sense control signal may, for example, control measurement of one or more characteristics of the at least one battery, and/or control measurement of current flow rate, and/or charge into and out of the at least one battery in battery pack 170, as will be discussed.
In response to receiving the current sensing signal from the current sensing circuit 130 (or a corresponding signal from either the logic circuit 132, or the battery measurement circuit 140), the switching circuit 120 is placed in either one of two switch states. In a first one of the switch states (i.e., a first switch state), the switching circuit 120 provides a low impedance signal path between the battery pack 170 and the load 160. In a second one of the switch states (i.e., a second switch state), the switching circuit 120 provides a high impedance signal path between the battery pack 170 and the load 160, and the power supply 150. Thus, in the second switch state, the battery pack 170 is electrically de-coupled from the power supply 150.
As noted above, battery pack 170 includes at least one battery. In the illustrated embodiment, battery pack 170 is not properly a part of the battery management circuit 110 and is thus shown separate from the battery management circuit 110 in the example embodiment shown. Battery pack 170 may, for example, include one or more lead acid (LA) or valve regulated lead acid (VRLA) rechargeable batteries or cells, arranged in series or in parallel. Additionally, in one embodiment, battery pack 170 may be provided as a battery bank which includes a plurality of strings with each of the battery strings including a plurality of batteries. Further arrangements and configurations of the battery pack 170 are of course possible.
The battery measurement circuit 140 is configured to measure one or more characteristics of battery pack 170 (e.g., state of charge (SOC) and/or state of health (SOH) characteristics of battery pack 170, or of individual batteries in the battery pack 170). In response thereto, the battery measurement circuit 140 produces a battery measurement signal at the first terminal 140a of the battery measurement circuit 140. The battery measurement signal is coupled to the logic circuit 132. In response to receiving the current sensing signal from the current sensing circuit 130 and/or the battery measurement signal from the battery measurement circuit 140, logic circuit 132 provides a control signal (e.g., a logic gate output signal) to control terminal 120c of switching circuit 120. The control signal places the switching circuit 120 into one of two states (i.e., one of two switch states, as discussed above) and thus controls current flow through the current conducting terminals 120a, 120b of the switching circuit 120. It should be appreciated that both analog and digital control signals are possible.
A digital control signal (or a digital signal approach) would present two possible switch states, ON or OFF. A rapid on/off function (i.e., pulsing), as may be provided by the digital control signal, may, for example, be used by the switching circuit 120 to perform certain functions (e.g., such as battery balancing and sulfation removal). Additionally, in some embodiments, both pulse frequency and duty cycle of the digital control signal may be controlled for controlling the switch state of the switching circuit 120.
An analog control signal (or an analog signal approach) would be utilized, for example, if one wanted to turn the switching circuit 120, or switching functionality of the switching circuit 120, partially on (e.g. to limit current). Additionally, an analog control signal would be utilized, for example, if one wanted to provide a control signal which has a signal shape other than a full amplitude, on/off type of pulse.
In one embodiment, current sensing circuit 130 includes at least one current-carrying conductor (e.g., a wire, a coil, or any other conductor that can produce a magnetic field when a current runs through the conductor) (not shown) and at least one transducer (e.g., a fluxgate transducer or a Hall effect transducer) (not shown) for measuring current flowing through the current-carrying conductor (and the switching circuit 120). The at least one current-carrying conductor can have a first terminal coupled to second terminal 120b of switching circuit 120, and a second opposing terminal coupled to third terminal 110c of battery management circuit 110. Current flowing through the at least one current-carrying conductor will produce a magnetic field which, in turn, can be detected by the at least one transducer and used to determine the current (e.g., magnitude, direction, polarity, and/or changes in the current). The at least one transducer may be positioned adjacent to the at least one current-carrying conductor, on top of the at least one current-carrying conductor, or beneath the at least one current-carrying conductor as a few examples.
The current sensing circuit 130 can additionally include a resistor (not shown) which is placed in series with the at least one current-carrying conductor. A voltage drop across the resistor can be measured (e.g., using a digital volt meter (DVM) or an equivalent thereof) to determine the current flowing through the current-carrying conductor (and the switching circuit 120). Other systems and methods of determining the current are also possible.
Further aspects of the concepts, systems, circuits and techniques sought to be protected herein, with particular emphasis on operation of circuitry of battery management circuits (e.g., 110, shown in FIG. 1), are described in conjunction with the figures below.
Referring now to FIG. 1A, another example circuit is shown. The circuit includes power supply 150 and electrical load 160. The circuit also includes N number of battery packs (here, battery packs 170, 1170) and N corresponding battery management circuits (here, battery management circuits 110, 1110) in the illustrated embodiment. In some embodiments, however, a greater number of battery management circuits may exist than battery packs, and vice versa (e.g., a circuit including five battery packs may have four battery management circuits).
Battery management circuit 1110, which may be the same as or similar to battery management circuit 110, has a first terminal 1110a configured to be coupled to the first terminal of power supply 150 and to the first terminal of electrical load 160. Battery management circuit 1110 also has a second terminal 1110b configured to be coupled to the second terminal of power supply 150 and to the second terminal of electrical load 160. Battery management circuit 1110 additionally has third and fourth terminals 1110c, 1110d configured to be coupled to first and second opposing terminals of battery pack 1170, which may be the same as or similar to battery pack 170.
Similar to the circuit shown in FIG. 1, the power supply 150 generates a supply voltage for use by the electrical load 160. Here, however, in the event the power supply 150 fails to provide the necessary supply voltage to the electrical load 160 (e.g., during a power failure), battery pack 170, battery pack 1170 and/or one or more other battery packs in the circuit (not shown) may collectively or selectively supply some or all of the necessary supply voltage to the electrical load 160. In one embodiment, for example, during a power failure select ones of the battery packs (e.g., 170, 1170) in the circuit (e.g., as may be determined by the battery management circuits) supply the supply voltage to the electrical load 160.
As noted above in conjunction with FIG. 1, current sensing circuit 130 of battery management circuit 110 may be used to measure direction, magnitude and polarity of the current signal passing through switching circuit 120 of battery management circuit 110. In one embodiment, similar techniques apply to the other battery management circuits (e.g., 1110) in the circuit of FIG. 1A.
In particular, the direction of the current signals measured by each of the battery management circuits (e.g., 110, 1110) may indicate if the battery packs (e.g., 170, 1170) coupled to the battery management circuits are being charged or discharged. When the polarity of the current signals are in a battery charge direction (i.e., of a positive polarity), the battery measurement circuit (e.g., 140) of a corresponding battery management circuit has control of the switching circuit (e.g., 120) of the battery management circuit. In contrast, when the polarity of the current signals are in a battery discharge direction (i.e., of a negative polarity), hardware circuits (e.g., current sensing circuit 130) of a corresponding battery management circuit overrides battery measurement circuit operation of the switching circuit and turns it on, to provide efficient power delivery from the battery packs to the power bus 152 (e.g., a DC power bus) of the circuit.
The magnitude of the discharge of the battery packs (as determined by measuring the current signals) may be used to determine how much remaining run-time the electrical load 360 has through use of the battery packs in the circuit. Additionally, the magnitude of the charge of the battery packs (as determined by measuring the current signal) may be used to determine how much the battery packs need to be charged and how much time it will take to charge the battery packs, as a few examples. Measuring the current and voltage of the battery packs (or select ones of the battery packs) over time (e.g., during charging or discharging) will allow for calculation of charge of the battery packs and power removed from the battery packs.
In a circuit or system including a plurality of battery management circuits, as shown in FIG. 1A, for example, the battery management circuits (e.g., 110, 1110) are provided capable of communicating with each other (e.g., through use of one or more processors in the battery management circuits, as will be discussed). The battery management circuits may, for example, communicate with each other to coordinate charging of the battery packs (or individual batteries in the battery packs) to limit excessive battery charge current, which may prevent power supplies (e.g., 150) of the circuit or system from powering electrical loads (e.g., 160) of the circuit or system.
For instance, in a cell site where power (e.g., alternating current (AC) power) has been down for days and then returns, the battery packs (e.g., 170, 1170) of the circuit or system may be severely discharged and may draw very large charging currents during a charging operation when the power returns. If all the battery packs were placed on a power bus (e.g., 152) of the circuit or system during the charging operation, for example, they could place the power supply (or power supplies) of the cell site into a current limit mode. This may, for example, prevent the cell site from becoming operational until the battery packs acquire enough charge to allow the power bus to increase to a point where electrical equipment (e.g., 160) of the cell site will operate. In one aspect of the concepts, systems, circuits and techniques sought to be protected herein, through use of a plurality of battery management circuits described herein in the cell site, the battery management circuits are able to coordinate to allow the cell site to operate substantially immediately after power has returned to the power supply (or power supplies) and then charge the battery packs as quickly as possible, without disrupting operation of the electrical equipment.
Referring now to FIG. 2, an example switching circuit 220, which may be the same as or similar to the switching circuit 120 of FIG. 1 and suitable for use in the circuit of FIG. 1, is provided having a first terminal 220a, a second terminal 220b, and a third terminal 220c. First and second terminals 220a, 220b correspond to current conducting terminals of the switching circuit 220, and third terminal 220c corresponds to a control terminal of the switching circuit 220. The switching circuit 220 includes at least one diode and at least one FET, as represented by diode 222 and FET 224, respectively, in the example embodiment shown. Although the switching circuit 220 may be implemented using a plurality of diodes and/or a plurality of FETs, a single diode 222 and a single FET 224 are shown to promote simplicity, clarity and understanding in the description of the concepts, systems, circuits and techniques sought to be protected herein and is not intended to be, and should not be construed, as limiting. The switching circuit 220 may, of course, comprise more than a single diode 222 and a single FET 224 arranged in series or in parallel depending upon the needs of a particular application.
The diode 222, which may be a parasitic diode of the FET 224, a discrete diode (e.g., a discrete p-n junction diode), or a combination thereof, for example, has a positive terminal (+) and a negative terminal (−). As is known, some FETs (e.g., silicon MOSFETs, silicon carbide MOSFETs) typically contain a parasitic (or “body”) diode that may, for example, be integrated into a substrate of the FET. Such FETs may be found suitable in the example embodiment shown. The positive terminal of the diode 222 is adapted to be coupled to first terminal 220a of switching circuit 220. Additionally, the negative terminal of the diode 222 is adapted to be coupled to second terminal 220b of switching circuit 220. In one embodiment, when conducting current, the diode 222 provides a low impedance signal path between first and second terminals 220a, 220b (i.e., the current conducting terminals) of switching circuit 220. These terminals may, for example, be coupled between a load (e.g., electrical load 160 of FIG. 1) and a battery pack (e.g., battery pack 170 of FIG. 1).
The FET 224, which is provided as an enhancement mode MOSFET in the example embodiment shown, has a source terminal (s), a drain terminal (d), and a gate terminal (g). The source terminal is adapted to couple to first terminal 220a of switching circuit 220, the drain terminal is adapted to couple to second terminal 220b of switching circuit 220 and the gate terminal is adapted to couple to third 220c terminal of switching circuit 220. In some embodiments, the source, drain and gate terminals of the FET 224 correspond to the first, second, and third terminals 220a, 220b, 220c of the switching circuit 220, respectively.
The FET 224 is coupled to receive a control signal (e.g., a control signal from a logic circuit) at the gate terminal, with current flow through the source terminal and drain terminal of the FET 224 (i.e., current conducting terminals of the FET 224) being controlled by the control signal. As one example, current flows through the source terminal and gate terminal of the FET 224 when the control signal has a potential that is substantially greater than a threshold voltage of the gate terminal, and does not flow when the control signal has a potential that is substantially less than the threshold voltage. Operation and switching characteristics of FETs (e.g., MOSFETs) is conventional in the art and, therefore, is not described in detail herein.
Referring now to FIG. 2A, another example switching circuit 1220, which may be the same as or similar to the switching circuit 120 of FIG. 1 and suitable for use in the circuit of FIG. 1, is provided having a first terminal 1220a, a second terminal 1220b, and a third (or control) terminal 1220c. Similar to the switching circuit 220 of FIG. 2, first and second terminals 1220a, 1220b of switching circuit 1220 correspond to current conducting terminals of the switching circuit 1220.
The switching circuit 1220 includes an electro-mechanical relay 1222 and an “RC snubber” circuit comprising a resistor 1226 and a capacitor 1228 in the illustrated embodiment. The electro-mechanical relay 1222 is driven by a coil 1224 (e.g., a solenoid coil). The coil 1224 has a first terminal adapted to couple to first terminal 1220a of switching circuit 1220, and a second, control terminal adapted to couple to third terminal 1220c of switching circuit 1220. The control terminal may, for example, be coupled to receive a control signal from third terminal 1220c of switching circuit 1220, with the control signal capable of controlling current flow through the coil 1224. Operation of electro-mechanical relays, coils and “RC snubber” circuits is conventional in the art and, therefore, is not described in detail herein. In one embodiment, transient-voltage-suppression (TVS) devices (not shown) and “RC snubber” circuits (e.g., the RC snubber circuit shown in FIG. 2A, for example) may be used to protect the FET 224 of FIG. 2, for example, from damage by external arcing and cable inductance.
Referring now to FIG. 3, a battery management circuit 310, which may be the same as or similar to the battery management circuit 110 described above in conjunction with FIG. 1 and in which like elements of FIG. 2 are shown having like reference designations, is coupled between a power supply 350 and an electrical load 360, and a battery string or battery pack 370. The battery pack 370 includes a plurality of batteries. It should be noted that power supply 350, load 360 and battery pack 370 are not properly a part of battery management circuit 310 in the illustrated embodiment. However, in other embodiments, one or more of the power supply 350, load 360, and battery pack 370 may be provided as part of the battery management circuit 310.
The electrical load 360, which can be the same as or similar to the electrical load 160 of FIG. 1, has a first connecting lead (i.e., a first terminal) coupled to a first terminal (e.g., a negative terminal) of the power supply 350 (e.g., a direct-current (DC) power supply). The load 360 also has a second opposing connecting lead (i.e., a second terminal) coupled to the second terminal (e.g., a positive terminal) of the power supply 350. Thus, load 360 is coupled to receive a supply voltage generated by the power supply 350, which can be the same as or similar to the power supply 150 of FIG. 1.
The battery management system 310 includes a switching circuit 220, a switch control circuit 322, a logic gate 324 (e.g., an “OR” logic gate), a current sensing circuit 330, a circuit breaker 332 (e.g., a 90 amp circuit breaker) and a battery measurement circuit 340 in the example embodiment shown. The switching circuit may be the same as or similar to switching circuit 220 described in conjunction with FIG. 2. Additionally, the circuit breaker 332 is optional in some embodiments and is, thus, shown in phantom. The switching circuit 220 has a first terminal coupled to the first connecting lead of the electrical load 360, a second terminal coupled to a first terminal of the current sensing circuit 330 and a third (or control) terminal coupled to an output of the logic gate 324.
The current sensing circuit 330, which can be the same as or similar to the current sensing circuit 130 of FIG. 1, and switching circuit 220, are serially coupled in a signal path between the power supply 350 and the battery pack 370. In this arrangement, the current sensing circuit 330 and the switching circuit 220 each receive current signals flowing in the signal path. The current sensing circuit 330 measures a direction of the current signals flowing in the signal path (e.g., a first current direction or a second current direction). Additionally, in response to measuring the direction of the current signals, the current sensing circuit 330 produces a current sensing signal representative of the direction of the current signals at a second terminal 330b of the current sensing circuit 330. A first current direction, as illustrated, corresponds to current direction during a battery backup operation (i.e., a discharging direction) while a second current direction corresponds to current direction during a battery charging operation (i.e., a charging direction). In one embodiment, the current sensing signal is provided an analog voltage output (i.e., an analog signal) which represents an amount of current flowing through the signal path. A level (i.e., a voltage level) of the analog signal may indicate direction of the current flowing.
Additionally, in one embodiment, a battery backup operation occurs in one or more stages. A first one of the stages (i.e., stage 1) may be when bus voltage of a power bus (e.g., DC power bus 352) powering the load 360 drops below a voltage of the battery pack 370 and a series diode voltage of diode 222 in switching circuit 220. In response thereto, diode 222 seamlessly conducts current from the battery pack 370 onto the power bus. The action of stage 1 produces a reversal of current, as can be measured by current sensing circuit 330, for example. In a second one of the stages (i.e., stage 2), the reversal of current triggers hardware circuitry (e.g., current sensing circuit 330, switch control circuit 322, and/or logic gate 324) to turn on FET 224 in switching circuit 220. In one embodiment, no software is involved in turning on FET 224 during a battery backup operation.
When the bus voltage of the power bus is within a so-called “normal range,” which may correspond to a programmable range threshold in some embodiments, software (e.g., software in controller core 342, as will be discussed) may have control of switch functionality of switching circuit 220 (and FET 224). In one example telecom DC bus with four “healthy” 12V valve regulated lead acid (VRLA) batteries (i.e., four 12V VRLA batteries capable of maintaining a substantially full charge), for example, the programmable threshold may have a minimum value of about 52.5V. The software may also determine when, how and how much to charge battery pack 370 (or individual batteries in the battery pack 370) during a battery charging operation.
In one embodiment in which processor hardware (e.g., controller core 342) in battery management circuit 310 fails or Safety Extra Low Voltage (SELV) power is lost in a system or circuit including the battery management circuit 310, switching circuit 220 may turn on, placing one or more of the batteries in the battery pack 370 in a conventional “float charge” mode, until the system or circuit is otherwise serviced.
The circuit breaker 332 (or electrical switch), which according to some embodiments has an input adapted to couple to second terminal 220b of switching circuit 220, and in the example embodiment shown has an input adapted to couple to a third terminal 330c of the current sensing circuit 330, is coupled to receive a current signal at the input thereof. The current signal may either pass through the circuit breaker 332 to an output thereof or, in response to an overload or short circuit condition, for example, the circuit breaker 332 may prevent current flow to the output thereof. Operation of circuit breakers is conventional in the art and, therefore, is not described in detail herein.
The battery measurement circuit 340, which may be the same as or similar to the battery measurement circuit 140 of FIG. 1, includes a controller core 342, switched current circuitry 344 and voltage measurement circuitry 346 as may be found, for example, in a processor, in the illustrated embodiment. The battery measurement circuit 340 also includes a resistor R which may be provided as a ballast resistor in some embodiments (e.g., to limit amount of current flowing in the battery measurement circuit 340). The switch current circuitry 344, which may include a current source and current measurement circuitry (e.g., an ammeter), is controlled by the controller core 342 (e.g., a current level of current provided by the current source may be controlled by the controller core 342). In one embodiment, the current source (e.g., an internal or built-in current source) is provided as high precision current source (e.g., having an accuracy which is within about one percent or less at about twenty five degrees Celsius (C)). The battery measurement circuit 340 has a first terminal coupled to second terminal 330b of the current sensing circuit 330, at least a second terminal coupled to the battery pack 370 and a third terminal coupled to the second connecting lead of the electrical load 360.
The battery measurement circuit 340 is capable of measuring one or more characteristics of the battery pack 370 (or of each battery in the battery pack 370) through at least the second terminal. In response thereto, the battery measurement circuit 340 provides a battery measurement signal to a first input of the logic circuit 324 (here illustrated as a logic gate 324). The battery measurement signal can, for example, be a two-state signal (i.e., a transistor-transistor logic (TTL) signal having either a logic low value or a logic high value). Application of the battery measurement signal to switching circuit 220 controls current flow through the current conducting terminals (i.e., the first and second terminals) of the switching circuit 220.
The one or more characteristics measured by the battery measurement circuit 310 can include open circuit (OC) voltage and/or OC voltage behavior of the battery pack 370. As one example, the battery measurement circuit 340 can determine state of charge (SOC) and/or state of health (SOH) characteristics of the battery pack 370 (or of individual batteries in the battery pack 370) in response to a measured OC voltage and/or OC voltage behavior of the battery pack 370 (or of individual batteries in the battery pack 370). The battery measurement circuit 340 can also measure a characteristic resistance of the battery pack 370 (or of individual batteries in the battery pack 370). The characteristic resistance of the battery pack 370 may, for example, be used to determine a SOH of the battery pack 370, as will be discussed in conjunction with FIG. 5.
In one embodiment, the switching circuit 220, through the use of device characteristics of FET 224 (e.g., metal oxide semiconductor field effect transistor (MOSFET) device characteristics of FET 224), isolates the battery pack 370 such that the OC behavior of the battery pack 370 can be evaluated by the battery measurement circuit 340, while at a same time maintaining a substantially uninterrupted current flow from the battery pack 370 to the electrical load 360 in the event of a power outage, for example. During a power outage, the power supply 350 may fail to provide power to the electrical load 360.
The switch control circuit 322 (or hardware over-ride circuit), which may perform a toggle switch function or the like, has an input adapted to couple to a second terminal 330b (e.g., an output terminal) of the current sensing circuit 330. The switch control circuit 322 is coupled to receive the current sensing signal from the current sensing circuit 330 at the input thereof. In response to receiving the current sensing signal, switch control circuit 332 generates a switch control signal at an output thereof.
In one embodiment, switch control circuit 322 is provided as a comparator circuit having a programmable threshold which can be set in hardware, software, or both hardware and software, for example. As one example, if a value (e.g., an analog or digital value) of the current sensing signal exceeds a programmed threshold of the switch control circuit 322, then the FET 224 in switching circuit 220 may be turned on (i.e., enabled) through the switch control signal.
The output of switch control circuit 322 is coupled to a second input of logic gate 324. Thus, switch control circuit 322 provides the switch control signal to the second input of the logic gate 324. In one embodiment, a battery measurement signal received from the controller core 342 at the first input of logic gate 324 is to control the charging function (i.e., the charging function when the DC bus voltage is in the normal range). Additionally, in one embodiment, the switch control signal provided from switch control circuit 322 to the second input of logic circuit 324 is a hardware signal to enable the switching circuit 220 for backup operation (hardware override) (e.g., similar to the battery measurement signal produced by the battery measurement circuit 340 in some embodiments). The hardware signal may, for example, correspond to a change in logic state or a change in an analog voltage level.
The logic gate 324 is coupled to receive the battery measurement signal from the battery measurement circuit 340 and the switch control signal from the switch control circuit 322 at first and second inputs, respectively, and produce a logic gate output signal in response thereto at an output thereof. As such, the logic gate output signal can be representative of the battery measurement signal, the switch control signal or a combination thereof. In the example embodiment shown, the logic gate output signal provides the control signal to the control terminal of the switching circuit 220 for controlling current flow through the current conducting terminals (i.e., terminals 220a, 220b) of the switching circuit 220.
In accordance with the concepts, systems, circuits and techniques sought to be protected herein, in the event of a failed battery measurement circuit 340 (e.g., a failure resulting from a failed controller core 342 or a failed internal power supply (not shown) in battery measurement circuit 340), the current sensing circuit 330 will still enable FET 224 of switching circuit 220 (i.e., through the current sensing signal provided to the switch control circuit 322), to maintain efficient back-up power delivery to the electrical load 360 and prevent the diode(s) 222 in the switching circuit 220 from overheating. Such may place the battery pack 370 in a “float condition.”
During one example mode of operation (e.g., a so-called “normal” mode of operation), the power supply 350 supplies power to the electrical load 360 and the battery measurement circuit 340 controls current flow through the current conducting terminals (i.e., terminals 220a, 220b) of switching circuit 220. The battery measurement circuit 340 also performs evaluations such as state of charge (SOC) and state of health (SOH) on the battery pack 370 (or on individual batteries in the battery pack 370). If the battery pack 370 needs charging, the battery measurement circuit 340 takes “control” of the switching circuit 220 functions to charge the battery pack 370 (or individual batteries in the battery pack 370).
For example, the battery measurement circuit 340, through evaluation algorithms and various measurements made on the battery pack 370, may determine that the battery pack 370 shows a need for charging. In response thereto, the battery measurement circuit 340 may manipulate the battery charge process of the battery pack 370 by turning the switching circuit 220 on (i.e., providing for current flow through the current conducting terminals of the switching circuit 220) and bringing the battery pack 370 up to charge and into balance.
When the switch circuit 220 is “on,” the battery pack 370 receives current from the power supply 350 in a manner that follows the “duty-cycle” of the switching circuit 220, which is defined as the ratio of “on time” to “off time.” The duty-cycle can be fixed or varied by software (e.g., software in controller core 342 of battery measurement circuit 340) to influence charge of the battery pack 370.
During a power failure, the power supply 350 output voltage drops until the diode(s) 222 of the switching circuit 220 start to conduct. Diode connection between battery pack 370 and DC power bus 352 engages the battery pack 370 seamlessly until the battery pack 370 is powering the electrical load 360 through the diode(s) 222. When the switch control circuit 322 senses that the current direction of the current signal received from second terminal 220b of switching circuit 220 has shifted to the first direction (i.e. in a battery discharging direction), FET 224 of switching circuit 220 is biased into its conducting (or “ON”) state by switch control circuit 322, reducing the voltage drop across the diode(s) 222 to reduce power loss in the circuit.
Under a “normal” operating condition, where the power supply 350 is supplying power for the electrical load 360, the potential of the DC power bus 352 is greater than the potential across resistor R of the battery measurement circuit 340. This condition keeps diode 222 in switching circuit 220 reverse-biased (i.e. biased into their non-conducting or “off” states). With the diode 222 reverse-biased and FET 224 turned off, substantially no current flows into or out of the battery pack 370. This is a so-called “resting” state (i.e. the batteries are in a neutral state, not being charged or discharged), for the battery pack 370. In the resting state, the battery measurement circuit 340 can measure the open-circuit voltage behavior of the battery pack 370 to determine (SOC and SOH) characteristics of the battery pack 370.
Additionally, in accordance with the concepts, systems, circuits and techniques sought to be protected herein, if the power supply 350 was to drop out or fail, there would be substantially no loss of power to the electrical load 360 because diode 222 in switching circuit 220 insures contiguous power transfer. This contiguous power availability is traditionally not possible with fully isolated switches using dual, series MOSFET or other semiconductor switches of electro-mechanical contractors or relays, for example. As discussed above, the diode 222 can be a parasitic diode(s) which is integrated into FET 224, a discrete diode(s), or a combination thereof.
Next described are battery charging methods enabled by the above-described use of the switching circuit 220.
As is known, an industry standard for charging valve regulated lead acid (VRLA), flooded or lead acid (LA) batteries is to place them on a float charge, which means that they are constantly charged. This charging method accelerates the deterioration of the batteries through dry-out, which is the loss of water in the electrolyte through a process called gassing, and through grid corrosion, which is caused by constantly passing a large float current through the battery.
The battery management circuit 310 described herein above, however, using the switching circuit 220, for example, substantially eliminates gassing and significantly reduces grid corrosion by removing the battery pack 370 from float and placing them in a resting state.
Furthermore, in some embodiments algorithms in the battery measurement circuit 340 (e.g., algorithms in controller core 342) can evaluate the battery pack 370 and determine when to charge the battery pack 370 or cells (i.e., batteries) in the battery pack 370 to keep them optimally charged. The algorithms can also determine when to perform a re-polarization, to further reduce corrosion. The algorithms can additionally adapt and make corresponding adjustments for temperature changes and other parameters (e.g., changes in how well the battery pack 370, or individual batteries in the battery pack 370, hold a charge) to minimize corrosion.
Referring now to FIG. 4, in which like elements of FIG. 3 are shown having like reference designations, a circuit similar to the circuit of FIG. 3 is shown. Here, however, the circuit has a switching circuit 420 that comprises a plurality of FETs (e.g., MOSFETs) and associated diodes (whereas the switching circuit 220 of FIG. 3 is illustrated having only a single FET and an associated diode). Moreover, the circuit has additional circuitry (e.g., complementary driver circuit 480 and opto-isolator circuit 490) coupled to the output of the logic gate 324.
In the illustrated embodiment, the switching circuit 420 comprises a plurality of MOSFETs (424, 424′, 424′′, 424′′′, 424′′′′) with each MOSFET provided having a corresponding diode (422, 422′, 422′′, 422′′′, 422′′′′) and a corresponding pull-down resistor (Rn, Rn′, Rn′′, Rn′′′, Rn′′′′) coupled as shown. The pull-down resistors (Rn, Rn′, Rn′′, Rn′′′, Rn′′′′), which are the same in some embodiments and substantially different in other embodiments, are each provided having a first terminal adapted to couple to a corresponding gate terminal of the MOSFETs and a second terminal adapted to couple to an output of the complementary driver circuit 480 (and a corresponding terminal of the electrical load 360). In some applications it may be desirable to have at least some or even all of the resistors be provided having different characteristics (e.g. different resistance values, for example, so as to make the MOSFET turn-on and turn-off times different).
Although the switching circuit 420 is shown comprising five MOSFETs arranged in parallel in the illustrated embodiment, the switching circuit 420 can, for example, comprise two MOSFETs, three MOSFETs or more than three MOSFETs arranged in series or in parallel. Number and arrangement of the MOSFETs can be selected based at least in part upon a current carrying requirement of the switching circuit 420 and ability of the MOSFETs to reduce heat that may be generated by the switching circuit 420. In at least some embodiments, heat is primarily generated by the on-resistance characteristic of the MOSFET device.
Power is dissipated in the switching circuit 420 as a function of I2R, where I is the current passing through the MOSFET source-drain path and R is the on-resistance characteristic, specific to that MOSFET type. In one aspect, the MOSFETs of the switching circuit 420 are arranged in parallel to reduce power losses resulting from the switching circuit 420. Paralleling the MOSFETs may, for example, reduce the on-resistance of the MOSFETs similar to paralleling resistors reducing the effective resistance of the resistors. Additionally, internal substrate diodes which may be contained within the MOSFET can have inferior switching and/or voltage characteristics in some embodiments. These conditions can be improved by adding external diodes (e.g., 422) in parallel with the MOSFET internal diode to improve performance.
The complementary driver circuit 480, which is adapted to couple to a corresponding terminal of the electrical load 360, includes an inverted MOSFET p-channel MOSFET 482 and complementary n-channel and p-channel MOSFETs 484 and 486, respectively. It should be appreciated that in some applications, it may be desirable to utilize lower cost/performance driver circuits, comprised of a single driver transistor, either pull-up or down. However, this would compromise the robust turn-on/off drive of the MOSFET switches and in cases where MOSFET gate capacitance is very high, could cause the MOSFETs to over-stress and fail.
On example low cost driver circuit can be achieved by driving the MOSFETs directly from the single photo-transistor inside the opto-isolator. While this would not be robust it is still an operable driver configuration. The complementary driver circuit 480 is designed to be powered by a DC power bus (e.g., DC power bus 352, FIG. 3), which during a “normal” mode of operation (i.e., a non-battery backup mode of operation) is substantially generated by the power supply 350. In one aspect, operating the switching circuit 420 and the complementary driver circuit 480 from the DC power bus increases the reliability of the circuit of FIG. 4 since the DC power bus by design generally cannot fail from power loss unless the power supply 350 and the batteries 370 have both failed.
The opto-isolator (or optocoupler) circuit 490, which is a galvanically isolated device, has an input adapted to couple to an output of the logic gate 324 and an output adapted to couple to an input of the complementary driver circuit 480. First and second inputs of the logic gate 324 are coupled to circuitry 500 that may include a current sensing circuit (e.g., 330, shown in FIG. 3), a battery measurement circuit (e.g., 340, shown in FIG. 3), a switch control circuit (e.g., 322, shown in FIG. 3), as described above in conjunction with FIG. 3. The opto-isolator circuit 490 is optional in some embodiments and is thus shown in phantom. The opto-isolator circuit 490 is configured to receive the logic gate output signal at the input thereof and in response thereto provide an opto-isolator circuit output signal at an output thereof. The opto-isolator circuit output signal may, for example, control current flow through the current conducting terminals of the switching circuit 420 (here, first terminals 420a, 420a′, 420a′′, 420a′′′, 420a′′′′, and second terminals 420b, 420b′, 420b′′, 420b′′′, 420b′′′′).
When the opto-isolator circuit 490 is active (i.e., LED in the opto-isolator circuit 490 is on), the inverter MOSFET 482 of the complementary driver circuit 480 is off (or not conducting current). In contrast, when the opto-isolator circuit 490 is inactive (i.e., LED in the opto-isolator circuit 490 is off), the opto-isolator circuit 490 stops conducting current, allowing the gate voltage of the inverter MOSFET 482 to rise and turn on the inverter MOSFET 482. Operation of opto-isolator circuit circuits is conventional in the art and, therefore, is not described in further detail herein.
When the inverter MOSFET 482 turns on, the gate terminals of both complementary MOSFETs 484, 486 of the complementary driver circuit 480 are pulled to the DC Power Bus (−V) potential, but voltage-limited by Zener diodes. In the example embodiment shown, the gate-to-source voltage of the MOSFET 486 is limited to a safe operating voltage by a Zener diode placed between the gate and source terminals of the MOSFET 486. This action allows the MOSFET 486 to turn on, and the complementary, MOSFET 484 to turn off. A result is that current flows through the MOSFET 486 into the gate terminals of the MOSFETs (424, 424′, 424′′, 424′′′, 424′′′′) of the switching circuit 420. Such may, for example, turn the MOSFETs (424, 424′, 424′′, 424′′′, 424′′′′) on, allowing current to flow into the battery string 370 when the DC power bus is supplied power by the power supply 350. In a battery back-up mode, the MOSFETs (424, 424′, 424′′, 424′′′, 424′′′′) are enabled by a current-sense function of a current sensing circuit (e.g., 330, shown in FIG. 3), which detects the direction of current flow in the direction of the DC power Bus.
In the switching circuit 420, each MOSFET (424, 424′, 424′′, 424′′′, 424′′′′) may have a slightly different threshold voltage, particular where the MOSFET (424, 424′, 424′′, 424′′′, 424′′′′) will start to turn on. Such will cause the MOSFET (424, 424′, 424′′, 424′′′, 424′′′′) with the lowest threshold voltage to conduct current before any other parallel MOSFETs. If the MOSFETs (424, 424′, 424′′, 424′′′, 424′′′′) are not properly rated or otherwise externally current-limited, the MOSFETs (424, 424′, 424′′, 424′′′, 424′′′′) can be damaged. To eliminate this potential failure mode, each MOSFET (424, 424′, 424′′, 424′′′, 424′′′′) may, for example, specified to individually handle the maximum design current for the power switch function (e.g., of the switching circuit 420). Such eliminates the efficiency losses associated with utilizing relatively high-speed current-balancing techniques, with source resistors or any type of high-bandwidth, isolated current sense devices.
Fail Safe Conditions:
The following example conditions are enabled by the switching circuit 420 being substantially (or entirely) powered by the DC power bus and by utilizing the opto-isolator circuit 490 to maintain the switching circuit 420 in an “active-off” state (i.e. when the opto-isolator's internal LED is “on or active” the MOSFET switch is held in the off state) and provide the required galvanic isolation. For safety requirements, a safety-qualified isolation device may be employed to isolate hazardous voltages produced by the circuit from SELV circuits (not shown) that people may touch.
Fail-Safe Case 1:
The battery measurement circuit (e.g., 340, shown in FIG. 3) controls measurement taking and controls the switching circuit 420 for charging, but only when the power supply 350 is operating. In the event of a power failure by the power supply 370 or a power failure within the battery measurement circuit (i.e., in a backup mode), the battery measurement circuit is over-ridden by the sensing of current reversal (e.g., by the current sensing circuit 330, shown in FIG. 3), and hardware only activation of the switching circuit. Thus, in backup mode, the current sensing circuit will still enable the switching circuit 420 to maintain efficient back-up power delivery and prevent the diodes (422, 422′, 422′′, 422′′′, 422′′′′) in the switching circuit 420 from overheating.
Fail-Safe Case 2:
In the event of a power failure within the battery management circuit (e.g., 310, shown in FIG. 3), the opto-isolator circuit 490 will turn-off (e.g., since the LED emitter power of the opto-isolator circuit 490 is supplied by SELV circuits). When the opto-isolator circuit 490 turns off, the switching circuit 420 turns on, placing the battery pack 370 (or individual batteries in the battery pack 370) in a float-charging condition where one or more of the batteries in the battery pack 370 are being float-charged by the DC power bus and are also available for backup service to the load 360.
Referring also to FIG. 5, a flowchart illustrates an example method 500 for measuring a characteristic resistance (i.e., an internal resistance) of a battery (e.g., 370, shown in FIG. 1) that can be implemented in a battery measurement circuit (e.g., 340, shown in FIG. 3) of a battery management circuit (e.g., 310, shown in FIG. 3). The result of the characteristic resistance measurement (sometimes referred to as “battery resistance”) may be an indication of a state of health (SOH) of the battery.
Rectangular elements (typified by element 505 in FIG. 3), as may be referred to herein as “processing blocks,” may represent computer software instructions or groups of instructions. The processing blocks can represent steps performed by functionally equivalent circuits such as a digital signal processor circuit or an application specific integrated circuit (ASIC). The flow diagram does not depict the syntax of any particular programming language. Rather, the flow diagram illustrates the functional information one of ordinary skill in the art requires to fabricate circuits or to generate computer software to perform the processing required of the particular apparatus. It should be noted that many routine program elements, such as initialization of loops and variables and the use of temporary variables are not shown. It will be appreciated by those of ordinary skill in the art that unless otherwise indicated herein, the particular sequence of blocks described is illustrative only and can be varied. Thus, unless otherwise stated, the blocks described below are unordered; meaning that, when possible, the blocks can be performed in any convenient or desirable order including that sequential blocks can be performed simultaneously and vice versa.
As illustrated in FIG. 5, a method 500 for measuring an characteristic resistance of a battery begins at block 505 where voltage measurement circuitry, which can be the same as or similar to voltage measurement circuitry 346 of FIG. 3, measures a first voltage of a battery (e.g., 370). In one embodiment, the first voltage of the battery is measured directly across the terminals (i.e., first and second terminals) of the battery to minimize voltage losses (i.e., voltage drops) which may occur between the battery and the voltage measurement circuitry (e.g., as may occur through wire resistance). In another embodiment, the first voltage of the battery is not measured directly across the terminals and any voltage losses which may occur between the battery and the voltage measurement circuitry is accounted for through use of a voltage drop constant. The voltage drop constant may, for example, be computed through knowledge of a voltage drop occurring between the battery and the voltage measurement circuitry.
At block 510, a current source, which can be the same as or similar to the current source which may be provided in switched current circuitry 344 of FIG. 3, provides current (i.e., test current) to the battery for a predetermined (i.e., fixed) time period (e.g., ten seconds). In one embodiment, the current is provided to the battery substantially immediately after the voltage measurement circuitry measures the first voltage of a battery. Additionally, in one embodiment, the current is a substantially constant current (e.g., a precise, fixed constant current) having a predetermined current value (e.g., one ampere (1 A). The predetermined current value may, for example, be selected to provide a meaningful drop in voltage across the battery over the predetermined time period. The predetermined current value and/or the predetermined time period may also be empirically selected in some embodiments. A 1 A constant current was, for example, empirically determined to be suitable for a wide range of batteries (e.g., 20 A to 200 A batteries).
At block 515, current measurement circuitry, which can be the same as or similar to the current measurement circuitry which may be provided in switched current circuitry 344 of FIG. 3, measures current I flowing through a circuit formed between a battery measurement circuit (e.g., 340) and the battery. In one embodiment, the circuit includes a precision resistor (e.g., a ballast resistor) which may be the same as or similar to resistor R of FIG. 3, and the current I is measured between the precision resistor and the battery (or between any other two points in the circuit).
At block 520, after the predetermined time period, the current source discontinues providing current to the battery and, at block 525 the voltage measurement circuitry measures a second voltage of the battery. In one embodiment, the second voltage of the battery is measured substantially immediately after the current source discontinues providing current to the battery. Additionally, the second voltage of the battery may be measured in a similar manner as the first voltage of the battery (e.g., directly across the terminals of the battery).
At block 530, the battery measurement circuit determines a voltage difference (ΔV) between the first voltage and the second voltage of the battery. At block 535, in response knowing ΔV and the current I measured by the current measurement circuitry at block 515, the battery measurement circuit computes a characteristic resistance of the battery (i.e., characteristic resistance=|ΔV/I|). In one embodiment, in computing the characteristic resistance of the battery, the battery measurement circuit is able to determine a SOH of the battery (or use the characteristic resistance as one SOH characteristic in determining the SOH of the battery).
Subsequent to computing the characteristic resistance of the battery, the method 500 may end. The method ending may, for example, be indicative of the characteristic resistance of the battery (e.g., a resistance of a chemical reaction occurring in the battery) having been measured. In one embodiment, the method 500 may be repeated continuously, periodically, or in response to a control signal (e.g., a control signal as may be provided by controller core 342 of battery measurement circuit 340 of FIG. 3) depending on system and application requirements. The method 500 may be repeated, for example, to compute the characteristic resistance of the battery again, or to compute the characteristic resistance of other batteries in a circuit including the battery.
In one embodiment, the method 500 is repeated a predetermined number of times per day (e.g., about six times per day, or about every four hours of the day) for a predetermined number of days (e.g., about seven days) to provide sufficient data for analysis of a trend (i.e., a trend line) of the battery's resistance (and SOH) over a time period. The predetermined number of times may be selected to minimize discharge of the battery (e.g., to improve life of the battery, and such that it is easy to replace the charge removed from the battery as a result of method 500). Additionally, the charge removed from the battery as a result of method 500 may be replaced substantially immediately after (or a predetermined time after) the method 500 is complete.
Precision of the method 500 (e.g., when repeated the predetermined number of times per day) may be based upon repeatability of: (1) the current provided by the current source to the battery (or batteries) at the block 510, (2) the predetermined time period for which the current is provided at the block 510, and (3) the time between when the current source discontinues providing the current to the battery at block 525, and when the voltage measurement circuitry measures a second voltage of the battery at block 530. In one embodiment, for optimal precision the current provided by the current source at the block 510 should be substantially the same from measurement to measurement. Additionally, the predetermined time period for which the current is provided should be substantially the same from measurement to measurement. Further, the time between when the current source discontinues providing current to the battery at block 525, and when the voltage measurement circuitry measures a second voltage of the battery at block 530, should be substantially the same from measurement to measurement.
In one aspect of the concepts, systems, circuits and techniques sought to be protected herein, the above-described method 500 provides for a more consistent and accurate measurement of characteristic resistance of a battery in comparison to conventional characteristic resistance measurement techniques (e.g., by providing a stable, consistent test current, to characterize the characteristic resistance of the battery). While the characteristic resistance of the battery is described as being computed in a sequence of processes, the example method 500 is not limited to performing the processes in the sequence described.
As described above and will be appreciated by one of skill in the art, embodiments of the disclosure herein may be configured as a system, method, or combination thereof. Accordingly, embodiments of the present disclosure may be comprised of various means including hardware, software, firmware or any combination thereof. Furthermore, embodiments of the present disclosure may take the form of a computer program product on a computer-readable storage medium having computer readable program instructions (e.g., computer software) embodied in the storage medium. Any suitable non-transitory computer-readable storage medium may be utilized.
Having described preferred embodiments, which serve to illustrate various concepts, structures and techniques, which are the subject of this patent, it will now become apparent to those of ordinary skill in the art that other embodiments incorporating these concepts, structures and techniques may be used. Additionally, elements of different embodiments described herein may be combined to form other embodiments not specifically set forth above.
Accordingly, it is submitted that that scope of the patent should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the following claims.

## Claims

1. In a system including a power supply configured to generate a supply voltage, an electrical load configured to receive the supply voltage, a battery pack comprising at least one battery and a battery management circuit for managing the battery pack, the battery management circuit having a first terminal and a second terminal configured to be coupled to two opposing terminals of the power supply and two opposing terminals of the electrical load, and having a third terminal and a fourth terminal configured to be coupled to two opposing terminals of the at least one battery, the battery management circuit comprising:
a switching circuit having a first terminal coupled to the first terminal of the battery management circuit, a second terminal, and a control terminal;
a current sensing circuit having a first terminal coupled to the second terminal of said switching circuit, a second terminal coupled to the control terminal of said switching circuit, and a third terminal coupled to the third terminal of the battery management circuit, said current sensing circuit configured to receive a current signal from said switching circuit, measure a direction of the current signal, and provide a current sensing signal indicative of the direction of the current signal at the second terminal of said current sensing circuit; and
a battery measurement circuit having a first terminal coupled to the control terminal of said switching circuit and at least a second terminal coupled to the first and second terminals of the at least one battery, said battery measurement circuit configured to measure one or more characteristics of the at least one battery and provide a battery measurement signal in response thereto at the first terminal of the battery measurement circuit, wherein a control signal corresponding to the current sensing signal and the battery measurement signal controls current flow through the first terminal and the second terminal, that provide current conducting terminals, of said switching circuit.

2. The battery management circuit of claim 1 wherein the one or more characteristics include open circuit voltage and/or open circuit voltage behavior of the at least one battery.

3. The battery management circuit of claim 2 wherein said battery measurement circuit determines state of charge (SOC) and/or state of health (SOH) characteristics of the at least one battery in response the measured open circuit voltage and/or open circuit voltage behavior of the at least one battery.

4. The battery management circuit of claim 1 further comprising:
a logic gate having a first input coupled to the second terminal of said current sensing circuit, a second input coupled to the first terminal of the battery measurement circuit, and an output coupled to the control terminal of said switching circuit; said logic gate configured to receive the current sensing signal from said current sensing circuit and the battery measurement signal from said battery measurement circuit at the first input and the second input thereof and in response thereto provides a logic gate output signal at the output thereof, wherein the logic gate output signal controls current flow through the current conducting terminals of said switching circuit.

5. The battery management circuit of claim 1 further comprising:
a switch control circuit having an input coupled to the second terminal of said current sensing circuit and an output, said switch control circuit configured to receive the current sensing signal at the input thereof and in response thereto produce a switched output signal at the output thereof; and
a logic gate having a first input coupled to the output of said switch control circuit, a second input coupled to the first terminal of said battery measurement circuit, and an output coupled to the control terminal of said switching circuit; said logic gate configured to receive the switched output signal and the battery measurement signal at the first input and the second input thereof and in response thereto provide a logic gate output signal at the output thereof, wherein the logic gate output signal controls the current flow through the current conducting terminals of said switching circuit.

6. The battery management circuit of claim 1 wherein said switching circuit comprises a field-effect transistor (FET) having a source terminal, a drain terminal and a gate terminal, wherein the source terminal corresponds to the first terminal of said switching circuit, the drain terminal corresponds to the second terminal of said switching circuit, and the gate terminal corresponds to the control terminal of said switching circuit.

7. The battery management circuit of claim 6 wherein the field-effect transistor is provided as a metal-oxide-semiconductor field-effect transistor (MOSFET).

8. The battery management circuit of claim 7 wherein the MOSFET is provided as an enhancement mode MOSFET.

9. The battery management circuit of claim 7 further comprising:
at least one diode having a positive terminal and a negative terminal, wherein the positive terminal is coupled to the first terminal of said switching circuit and the negative terminal is coupled to the second terminal of said switching circuit.

10. The battery management circuit of claim 9 wherein said at least one diode is provided as a p-n junction diode.

11. The battery management circuit of claim 9 wherein said at least one diode is provided as a parasitic diode integrated into the MOSFET, a discrete diode or a combination thereof.

12. The battery management circuit of claim 1 wherein said battery measurement circuit is provided as part of a controller, wherein said controller is configured to provide the battery measurement signal.

13. A circuit comprising:
a power supply having a first terminal and a second terminal, which are two opposing terminals, said power supply configured to generate a supply voltage;
a electric load having a first terminal coupled to the first terminal of said power supply and a second terminal, which is opposing the first terminal and coupled to the second terminal of said power supply, said electrical load configured to receive the supply voltage from said power supply;
a switching circuit having a first terminal coupled to the first terminal of said electrical load, a second terminal, and a control terminal, wherein the first terminal and the second terminal provide current conducting terminals of said switching circuit, said switching circuit including:
a plurality of metal-oxide-semiconductor field-effect transistors (MOSFETs), each MOSFET of said plurality of MOSFETs having a source terminal, a drain terminal and a gate terminal, wherein the source terminals of said plurality of MOSFETs are coupled to the first terminal of said switching circuit, the drain terminals of said plurality of MOSFETs are coupled to the second terminal of said switching circuit, and the gate terminals of said plurality of MOSFETs are coupled to the control terminal of said switching circuit; and
a plurality of diodes, each diode of the said plurality of diodes having a positive terminal and a negative terminal, wherein the positive terminals of said plurality of diodes are respectively coupled to corresponding ones of the source terminals of said MOSFETs and the negative terminals of said plurality of diodes are respectively coupled to corresponding ones of the drain terminals of said MOSFETs;

a current sensing circuit having a first terminal coupled to the second terminal of said switching circuit, a second terminal coupled to the control terminal of said switching circuit, and a third terminal, said current sensing circuit configured to receive a current signal from the second terminal of said switching circuit at the first terminal thereof, measure a direction of the current signal, and provide a current sensing signal corresponding to the direction of the current signal in response thereto at the second terminal of said current sensing circuit;
at least one battery having a first terminal coupled to the third terminal of said current sensing circuit and a second opposing terminal coupled to the second terminal of said electrical load; and
a battery measurement circuit having a first terminal coupled to the control terminal of said switching circuit and at least a second terminal coupled to the first terminal and the second terminal of said at least one battery, said battery measurement circuit configured to measure one or more characteristics of said at least one battery and provide a battery measurement signal in response thereto at the first terminal of said battery measurement circuit, wherein a control signal corresponding to the current sensing signal and the battery measurement signal controls current flow through the current conducting terminals of said switching circuit.

14. The circuit of claim 13 wherein in response to measuring the direction of the current signal, said current sensing circuit further provides a corresponding current sense control signal to a third terminal of said battery measurement circuit to control measurement of the one or more characteristics of said at least one battery, and measurement of current flow rate, and charge into and out of the at least one battery by said battery measurement circuit.

15. The circuit of claim 13 wherein the plurality of MOSFETs is five MOSFETs.

16. The circuit of claim 13 further comprising:
a logic gate having a first input coupled to the second terminal of said current sensing circuit, a second input coupled to the first terminal of said battery measurement circuit, and an output coupled to the control terminal of said switching circuit; said logic gate configured to receive the current sensing signal from the second terminal of said current sensing circuit and the battery measurement signal from said battery measurement circuit at the first terminal and the second terminal thereof and in response thereto provide a logic gate output signal at the output thereof; and
an opto-isolator circuit having an input coupled to the logic gate output and an output coupled to the control terminal of said switching circuit, said opto-isolator circuit configured to receive the logic gate output signal at the input thereof and in response thereto provide an opto-isolator circuit output signal at an output thereof, wherein the opto-isolator circuit output signal controls current flow through the current conducting terminals of said switching circuit.

17. The circuit of claim 13 wherein said battery measurement circuit includes a current source and a ballast resistor, and the current source and the ballast resistor are used by said battery measurement circuit to measure an internal resistance of said at least one battery.

18. The circuit of claim 13 wherein said current sensing circuit is further configured to measure magnitude and polarity of the current signal, and the current sensing signal is further indicative of the magnitude and the polarity of the current signal.

19. The circuit of claim 13 wherein said switching circuit, said current sensing circuit, and said battery measurement circuit are provided as part of a battery management circuit for managing the at least one battery.

20. The circuit of claim 13 wherein each MOSFET of said plurality of MOSFETs is provided as an enhancement mode MOSFET.