Battery management system and related techniques for adaptive, dynamic control of battery charging

A battery management circuit and method for managing a power supply and one or more battery strings includes a current sensing circuit and a battery measurement circuit. The current sensing circuit is configured to: receive a current signal from at least one of the battery strings at a first terminal of the current sensing circuit; measure a magnitude of the current signal; and provide a current sensing signal indicative of the magnitude of the current signal at a third terminal of the current sensing circuit. The battery measurement circuit is configured to: receive a current sensing signal at a third terminal of the battery management circuit; measure one or more characteristics of the at least one of the battery strings; and provide a power supply control signal at a first terminal of the battery measurement circuit.

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.

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 toFIG. 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 circuit110coupled between a first portion of the circuit including a power supply150and an electrical load160, and second portion of the circuit including a battery pack170. The power supply150(e.g., a direct-current (DC) power supply) generates a supply voltage for use by the electrical load160. In the event the power supply150fails to provide the necessary supply voltage to the electrical load160at power bus152(e.g., during a power failure), the battery pack170, 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 load160.

The battery management circuit110includes a switching circuit120serially coupled between a terminal (e.g., a first terminal) of the power supply150and a terminal (e.g., a first terminal) of the battery pack170. A first terminal120aof switching circuit120is coupled to a first terminal110aof the battery management circuit110in the illustrated embodiment. Additionally, a second terminal120bof switching circuit120is coupled to a third terminal110cof battery management circuit110through a current sensing circuit130in the illustrated embodiment. In particular, a first terminal130aof current sensing circuit130is coupled to the second terminal120bof the switching circuit120and a third terminal130cof current sensing circuit130is coupled to the third terminal110cof the battery management circuit110. Thus, the switching circuit120and the current sensing circuit130are serially coupled in a circuit path between the first and third terminals110a,110cof the battery management circuit110.

It should be appreciated that current sensing in the circuit is performed in series with the circuit path between the first and third terminals110a,110cof the battery management circuit110. A desirable technique to measure full current through switching circuit120is to place current sensing circuit130in series with that current. It should, of course, be appreciated that although current sensing circuit130is shown as disposed proximate to second terminal120bof switching circuit120(i.e., on the right side of switching circuit130) in the illustrated embodiment, current sensing circuit130can also be disposed proximate to first terminal120aof switching circuit130(i.e., on the left side of switching circuit120). Current sensing circuit130may 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 circuit120. It should also be appreciated that current sensing circuit130may be used to measure magnitude and polarity of the current signal, as well as measure a direction of the current signal.

A second terminal130bof current sensing circuit130is coupled to a third (or control) terminal120cof the switching circuit120through a logic circuit132. A first terminal140aof a battery measurement circuit140is also coupled to the switching circuit120through logic circuit132. As will become apparent from the description herein below, the logic circuit132may receive signals from the current sensing circuit130and the battery measurement circuit140. In response to such signals, logic circuit132may provide a control signal (e.g., a logic gate output signal) to control terminal120cof the switching circuit120. It should be appreciated that logic circuit132(or the function performed by logic circuit132) may be implemented as part of any or all of the current sensing circuit130, the switching circuit120and/or the battery measurement circuit140. Alternatively, portions of logic circuit132(or the function performed by logic circuit132) may be distributed among any or all of the current sensing circuit130, the switching circuit120and/or the battery measurement circuit140. The battery measurement circuit140is, in turn, coupled across the battery pack170(e.g., through at least a second terminal140b).

First and second terminals of the switching circuit120correspond to current conducting terminals of the switching circuit120in the illustrated embodiment (i.e., in a first state, the switching circuit120provides a low impedance signal path between the two current conducting terminals of the switching circuit120and in a second state, the switching circuit120provides a high impedance signal path between the two current conducting terminals of the switching circuit120). The switching circuit120may, 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 circuit130receives a current signal from switching circuit120that may, for example, be generated during charging or discharging of the battery pack170. In response thereto, current sensing circuit130measures 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 terminal130bof current sensing circuit130. Current sensing circuit130may also provide a corresponding current sense control signal to battery measurement circuit140, as indicated by the signal path designated by reference numeral134inFIG. 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 pack170, as will be discussed.

In response to receiving the current sensing signal from the current sensing circuit130(or a corresponding signal from either the logic circuit132, or the battery measurement circuit140), the switching circuit120is placed in either one of two switch states. In a first one of the switch states (i.e., a first switch state), the switching circuit120provides a low impedance signal path between the battery pack170and the load160. In a second one of the switch states (i.e., a second switch state), the switching circuit120provides a high impedance signal path between the battery pack170and the load160, and the power supply150. Thus, in the second switch state, the battery pack170is electrically de-coupled from the power supply150.

As noted above, battery pack170includes at least one battery. In the illustrated embodiment, battery pack170is not properly a part of the battery management circuit110and is thus shown separate from the battery management circuit110in the example embodiment shown. Battery pack170may, 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 pack170may 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 pack170are of course possible.

The battery measurement circuit140is configured to measure one or more characteristics of battery pack170(e.g., state of charge (SOC) and/or state of health (SOH) characteristics of battery pack170, or of individual batteries in the battery pack170). In response thereto, the battery measurement circuit140produces a battery measurement signal at the first terminal140aof the battery measurement circuit140. The battery measurement signal is coupled to the logic circuit132. In response to receiving the current sensing signal from the current sensing circuit130and/or the battery measurement signal from the battery measurement circuit140, logic circuit132provides a control signal (e.g., a logic gate output signal) to control terminal120cof switching circuit120. The control signal places the switching circuit120into one of two states (i.e., one of two switch states, as discussed above) and thus controls current flow through the current conducting terminals120a,120bof the switching circuit120. 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 circuit120to 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 circuit120.

An analog control signal (or an analog signal approach) would be utilized, for example, if one wanted to turn the switching circuit120, or switching functionality of the switching circuit120, 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 circuit130includes 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 circuit120). The at least one current-carrying conductor can have a first terminal coupled to second terminal120bof switching circuit120, and a second opposing terminal coupled to third terminal110cof battery management circuit110. 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 circuit130can 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 circuit120). 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 inFIG. 1), are described in conjunction with the figures below.

Referring now toFIG. 1A, another example circuit is shown. The circuit includes power supply150and electrical load160. The circuit also includes N number of battery packs (here, battery packs170,1170) and N corresponding battery management circuits (here, battery management circuits110,1110) 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 circuit1110, which may be the same as or similar to battery management circuit110, has a first terminal1110aconfigured to be coupled to the first terminal of power supply150and to the first terminal of electrical load160. Battery management circuit1110also has a second terminal1110bconfigured to be coupled to the second terminal of power supply150and to the second terminal of electrical load160. Battery management circuit1110additionally has third and fourth terminals1110c,1110dconfigured to be coupled to first and second opposing terminals of battery pack1170, which may be the same as or similar to battery pack170.

Similar to the circuit shown inFIG. 1, the power supply150generates a supply voltage for use by the electrical load160. Here, however, in the event the power supply150fails to provide the necessary supply voltage to the electrical load160(e.g., during a power failure), battery pack170, battery pack1170and/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 load160. 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 load160.

As noted above in conjunction withFIG. 1, current sensing circuit130of battery management circuit110may be used to measure direction, magnitude and polarity of the current signal passing through switching circuit120of battery management circuit110. In one embodiment, similar techniques apply to the other battery management circuits (e.g.,1110) in the circuit ofFIG. 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 circuit130) 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 bus152(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 load360has 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 inFIG. 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 toFIG. 2, an example switching circuit220, which may be the same as or similar to the switching circuit120ofFIG. 1and suitable for use in the circuit ofFIG. 1, is provided having a first terminal220a, a second terminal220b, and a third terminal220c. First and second terminals220a,220bcorrespond to current conducting terminals of the switching circuit220, and third terminal220ccorresponds to a control terminal of the switching circuit220. The switching circuit220includes at least one diode and at least one FET, as represented by diode222and FET224, respectively, in the example embodiment shown. Although the switching circuit220may be implemented using a plurality of diodes and/or a plurality of FETs, a single diode222and a single FET224are 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 circuit220may, of course, comprise more than a single diode222and a single FET224arranged in series or in parallel depending upon the needs of a particular application.

The diode222, which may be a parasitic diode of the FET224, 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 diode222is adapted to be coupled to first terminal220aof switching circuit220. Additionally, the negative terminal of the diode222is adapted to be coupled to second terminal220bof switching circuit220. In one embodiment, when conducting current, the diode222provides a low impedance signal path between first and second terminals220a,220b(i.e., the current conducting terminals) of switching circuit220. These terminals may, for example, be coupled between a load (e.g., electrical load160ofFIG. 1) and a battery pack (e.g., battery pack170ofFIG. 1).

The FET224, 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 terminal220aof switching circuit220, the drain terminal is adapted to couple to second terminal220bof switching circuit220and the gate terminal is adapted to couple to third220cterminal of switching circuit220. In some embodiments, the source, drain and gate terminals of the FET224correspond to the first, second, and third terminals220a,220b,220cof the switching circuit220, respectively.

The FET224is 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 FET224(i.e., current conducting terminals of the FET224) being controlled by the control signal. As one example, current flows through the source terminal and gate terminal of the FET224when 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 toFIG. 2A, another example switching circuit1220, which may be the same as or similar to the switching circuit120ofFIG. 1and suitable for use in the circuit ofFIG. 1, is provided having a first terminal1220a, a second terminal1220b, and a third (or control) terminal1220c. Similar to the switching circuit220ofFIG. 2, first and second terminals1220a,1220bof switching circuit1220correspond to current conducting terminals of the switching circuit1220.

The switching circuit1220includes an electro-mechanical relay1222and an “RC snubber” circuit comprising a resistor1226and a capacitor1228in the illustrated embodiment. The electro-mechanical relay1222is driven by a coil1224(e.g., a solenoid coil). The coil1224has a first terminal adapted to couple to first terminal1220aof switching circuit1220, and a second, control terminal adapted to couple to third terminal1220cof switching circuit1220. The control terminal may, for example, be coupled to receive a control signal from third terminal1220cof switching circuit1220, with the control signal capable of controlling current flow through the coil1224. 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 inFIG. 2A, for example) may be used to protect the FET224ofFIG. 2, for example, from damage by external arcing and cable inductance.

Referring now toFIG. 3, a battery management circuit310, which may be the same as or similar to the battery management circuit110described above in conjunction withFIG. 1and in which like elements ofFIG. 2are shown having like reference designations, is coupled between a power supply350and an electrical load360, and a battery string or battery pack370. The battery pack370includes a plurality of batteries. It should be noted that power supply350, load360and battery pack370are not properly a part of battery management circuit310in the illustrated embodiment. However, in other embodiments, one or more of the power supply350, load360, and battery pack370may be provided as part of the battery management circuit310.

The electrical load360, which can be the same as or similar to the electrical load160ofFIG. 1, has a first connecting lead (i.e., a first terminal) coupled to a first terminal (e.g., a negative terminal) of the power supply350(e.g., a direct-current (DC) power supply). The load360also has a second opposing connecting lead (i.e., a second terminal) coupled to the second terminal (e.g., a positive terminal) of the power supply350. Thus, load360is coupled to receive a supply voltage generated by the power supply350, which can be the same as or similar to the power supply150ofFIG. 1.

The battery management system310includes a switching circuit220, a switch control circuit322, a logic gate324(e.g., an “OR” logic gate), a current sensing circuit330, a circuit breaker332(e.g., a 90 amp circuit breaker) and a battery measurement circuit340in the example embodiment shown. The switching circuit may be the same as or similar to switching circuit220described in conjunction withFIG. 2. Additionally, the circuit breaker332is optional in some embodiments and is, thus, shown in phantom. The switching circuit220has a first terminal coupled to the first connecting lead of the electrical load360, a second terminal coupled to a first terminal of the current sensing circuit330and a third (or control) terminal coupled to an output of the logic gate324.

The current sensing circuit330, which can be the same as or similar to the current sensing circuit130ofFIG. 1, and switching circuit220, are serially coupled in a signal path between the power supply350and the battery pack370. In this arrangement, the current sensing circuit330and the switching circuit220each receive current signals flowing in the signal path. The current sensing circuit330measures 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 circuit330produces a current sensing signal representative of the direction of the current signals at a second terminal330bof the current sensing circuit330. 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., stage1) may be when bus voltage of a power bus (e.g., DC power bus352) powering the load360drops below a voltage of the battery pack370and a series diode voltage of diode222in switching circuit220. In response thereto, diode222seamlessly conducts current from the battery pack370onto the power bus. The action of stage1produces a reversal of current, as can be measured by current sensing circuit330, for example. In a second one of the stages (i.e., stage2), the reversal of current triggers hardware circuitry (e.g., current sensing circuit330, switch control circuit322, and/or logic gate324) to turn on FET224in switching circuit220. In one embodiment, no software is involved in turning on FET224during 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 core342, as will be discussed) may have control of switch functionality of switching circuit220(and FET224). 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 pack370(or individual batteries in the battery pack370) during a battery charging operation.

In one embodiment in which processor hardware (e.g., controller core342) in battery management circuit310fails or Safety Extra Low Voltage (SELV) power is lost in a system or circuit including the battery management circuit310, switching circuit220may turn on, placing one or more of the batteries in the battery pack370in a conventional “float charge” mode, until the system or circuit is otherwise serviced.

The circuit breaker332(or electrical switch), which according to some embodiments has an input adapted to couple to second terminal220bof switching circuit220, and in the example embodiment shown has an input adapted to couple to a third terminal330cof the current sensing circuit330, is coupled to receive a current signal at the input thereof. The current signal may either pass through the circuit breaker332to an output thereof or, in response to an overload or short circuit condition, for example, the circuit breaker332may 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 circuit340, which may be the same as or similar to the battery measurement circuit140ofFIG. 1, includes a controller core342, switched current circuitry344and voltage measurement circuitry346as may be found, for example, in a processor, in the illustrated embodiment. The battery measurement circuit340also 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 circuit340). The switch current circuitry344, which may include a current source and current measurement circuitry (e.g., an ammeter), is controlled by the controller core342(e.g., a current level of current provided by the current source may be controlled by the controller core342). 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 circuit340has a first terminal coupled to second terminal330bof the current sensing circuit330, at least a second terminal coupled to the battery pack370and a third terminal coupled to the second connecting lead of the electrical load360.

The battery measurement circuit340is capable of measuring one or more characteristics of the battery pack370(or of each battery in the battery pack370) through at least the second terminal. In response thereto, the battery measurement circuit340provides a battery measurement signal to a first input of the logic circuit324(here illustrated as a logic gate324). 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 circuit220controls current flow through the current conducting terminals (i.e., the first and second terminals) of the switching circuit220.

The one or more characteristics measured by the battery measurement circuit310can include open circuit (OC) voltage and/or OC voltage behavior of the battery pack370. As one example, the battery measurement circuit340can determine state of charge (SOC) and/or state of health (SOH) characteristics of the battery pack370(or of individual batteries in the battery pack370) in response to a measured OC voltage and/or OC voltage behavior of the battery pack370(or of individual batteries in the battery pack370). The battery measurement circuit340can also measure a characteristic resistance of the battery pack370(or of individual batteries in the battery pack370). The characteristic resistance of the battery pack370may, for example, be used to determine a SOH of the battery pack370, as will be discussed in conjunction withFIG. 5.

In one embodiment, the switching circuit220, through the use of device characteristics of FET224(e.g., metal oxide semiconductor field effect transistor (MOSFET) device characteristics of FET224), isolates the battery pack370such that the OC behavior of the battery pack370can be evaluated by the battery measurement circuit340, while at a same time maintaining a substantially uninterrupted current flow from the battery pack370to the electrical load360in the event of a power outage, for example. During a power outage, the power supply350may fail to provide power to the electrical load360.

The switch control circuit322(or hardware over-ride circuit), which may perform a toggle switch function or the like, has an input adapted to couple to a second terminal330b(e.g., an output terminal) of the current sensing circuit330. The switch control circuit322is coupled to receive the current sensing signal from the current sensing circuit330at the input thereof. In response to receiving the current sensing signal, switch control circuit332generates a switch control signal at an output thereof.

In one embodiment, switch control circuit322is 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 circuit322, then the FET224in switching circuit220may be turned on (i.e., enabled) through the switch control signal.

The output of switch control circuit322is coupled to a second input of logic gate324. Thus, switch control circuit322provides the switch control signal to the second input of the logic gate324. In one embodiment, a battery measurement signal received from the controller core342at the first input of logic gate324is 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 circuit322to the second input of logic circuit324is a hardware signal to enable the switching circuit220for backup operation (hardware override) (e.g., similar to the battery measurement signal produced by the battery measurement circuit340in 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 gate324is coupled to receive the battery measurement signal from the battery measurement circuit340and the switch control signal from the switch control circuit322at 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 circuit220for controlling current flow through the current conducting terminals (i.e., terminals220a,220b) of the switching circuit220.

In accordance with the concepts, systems, circuits and techniques sought to be protected herein, in the event of a failed battery measurement circuit340(e.g., a failure resulting from a failed controller core342or a failed internal power supply (not shown) in battery measurement circuit340), the current sensing circuit330will still enable FET224of switching circuit220(i.e., through the current sensing signal provided to the switch control circuit322), to maintain efficient back-up power delivery to the electrical load360and prevent the diode(s)222in the switching circuit220from overheating. Such may place the battery pack370in a “float condition.”

During one example mode of operation (e.g., a so-called “normal” mode of operation), the power supply350supplies power to the electrical load360and the battery measurement circuit340controls current flow through the current conducting terminals (i.e., terminals220a,220b) of switching circuit220. The battery measurement circuit340also performs evaluations such as state of charge (SOC) and state of health (SOH) on the battery pack370(or on individual batteries in the battery pack370). If the battery pack370needs charging, the battery measurement circuit340takes “control” of the switching circuit220functions to charge the battery pack370(or individual batteries in the battery pack370).

For example, the battery measurement circuit340, through evaluation algorithms and various measurements made on the battery pack370, may determine that the battery pack370shows a need for charging. In response thereto, the battery measurement circuit340may manipulate the battery charge process of the battery pack370by turning the switching circuit220on (i.e., providing for current flow through the current conducting terminals of the switching circuit220) and bringing the battery pack370up to charge and into balance.

When the switch circuit220is “on,” the battery pack370receives current from the power supply350in a manner that follows the “duty-cycle” of the switching circuit220, 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 core342of battery measurement circuit340) to influence charge of the battery pack370.

During a power failure, the power supply350output voltage drops until the diode(s)222of the switching circuit220start to conduct. Diode connection between battery pack370and DC power bus352engages the battery pack370seamlessly until the battery pack370is powering the electrical load360through the diode(s)222. When the switch control circuit322senses that the current direction of the current signal received from second terminal220bof switching circuit220has shifted to the first direction (i.e. in a battery discharging direction), FET224of switching circuit220is biased into its conducting (or “ON”) state by switch control circuit322, reducing the voltage drop across the diode(s)222to reduce power loss in the circuit.

Under a “normal” operating condition, where the power supply350is supplying power for the electrical load360, the potential of the DC power bus352is greater than the potential across resistor R of the battery measurement circuit340. This condition keeps diode222in switching circuit220reverse-biased (i.e. biased into their non-conducting or “off” states). With the diode222reverse-biased and FET224turned off, substantially no current flows into or out of the battery pack370. This is a so-called “resting” state (i.e. the batteries are in a neutral state, not being charged or discharged), for the battery pack370. In the resting state, the battery measurement circuit340can measure the open-circuit voltage behavior of the battery pack370to determine (SOC and SOH) characteristics of the battery pack370.

Additionally, in accordance with the concepts, systems, circuits and techniques sought to be protected herein, if the power supply350was to drop out or fail, there would be substantially no loss of power to the electrical load360because diode222in switching circuit220insures 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 diode222can be a parasitic diode(s) which is integrated into FET224, a discrete diode(s), or a combination thereof.

Next described are battery charging methods enabled by the above-described use of the switching circuit220.

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 circuit310described herein above, however, using the switching circuit220, for example, substantially eliminates gassing and significantly reduces grid corrosion by removing the battery pack370from float and placing them in a resting state.

Furthermore, in some embodiments algorithms in the battery measurement circuit340(e.g., algorithms in controller core342) can evaluate the battery pack370and determine when to charge the battery pack370or cells (i.e., batteries) in the battery pack370to 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 pack370, or individual batteries in the battery pack370, hold a charge) to minimize corrosion.

Referring now toFIG. 4, in which like elements ofFIG. 3are shown having like reference designations, a circuit similar to the circuit ofFIG. 3is shown. Here, however, the circuit has a switching circuit420that comprises a plurality of FETs (e.g., MOSFETs) and associated diodes (whereas the switching circuit220ofFIG. 3is illustrated having only a single FET and an associated diode). Moreover, the circuit has additional circuitry (e.g., complementary driver circuit480and opto-isolator circuit490) coupled to the output of the logic gate324.

In the illustrated embodiment, the switching circuit420comprises 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 circuit480(and a corresponding terminal of the electrical load360). 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 circuit420is shown comprising five MOSFETs arranged in parallel in the illustrated embodiment, the switching circuit420can, 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 circuit420and ability of the MOSFETs to reduce heat that may be generated by the switching circuit420. In at least some embodiments, heat is primarily generated by the on-resistance characteristic of the MOSFET device.

Power is dissipated in the switching circuit420as 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 circuit420are arranged in parallel to reduce power losses resulting from the switching circuit420. 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 circuit480, which is adapted to couple to a corresponding terminal of the electrical load360, includes an inverted MOSFET p-channel MOSFET482and complementary n-channel and p-channel MOSFETs484and486, 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 circuit480is designed to be powered by a DC power bus (e.g., DC power bus352,FIG. 3), which during a “normal” mode of operation (i.e., a non-battery backup mode of operation) is substantially generated by the power supply350. In one aspect, operating the switching circuit420and the complementary driver circuit480from the DC power bus increases the reliability of the circuit ofFIG. 4since the DC power bus by design generally cannot fail from power loss unless the power supply350and the batteries370have both failed.

The opto-isolator (or optocoupler) circuit490, which is a galvanically isolated device, has an input adapted to couple to an output of the logic gate324and an output adapted to couple to an input of the complementary driver circuit480. First and second inputs of the logic gate324are coupled to circuitry500that may include a current sensing circuit (e.g.,330, shown inFIG. 3), a battery measurement circuit (e.g.,340, shown inFIG. 3), a switch control circuit (e.g.,322, shown inFIG. 3), as described above in conjunction withFIG. 3. The opto-isolator circuit490is optional in some embodiments and is thus shown in phantom. The opto-isolator circuit490is 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 circuit420(here, first terminals420a,420a′,420a″,420a′″,420a″″, and second terminals420b,420b′,420b″,420b′″,420b″″).

When the opto-isolator circuit490is active (i.e., LED in the opto-isolator circuit490is on), the inverter MOSFET482of the complementary driver circuit480is off (or not conducting current). In contrast, when the opto-isolator circuit490is inactive (i.e., LED in the opto-isolator circuit490is off), the opto-isolator circuit490stops conducting current, allowing the gate voltage of the inverter MOSFET482to rise and turn on the inverter MOSFET482. Operation of opto-isolator circuit circuits is conventional in the art and, therefore, is not described in further detail herein.

When the inverter MOSFET482turns on, the gate terminals of both complementary MOSFETs484,486of the complementary driver circuit480are 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 MOSFET486is limited to a safe operating voltage by a Zener diode placed between the gate and source terminals of the MOSFET486. This action allows the MOSFET486to turn on, and the complementary, MOSFET484to turn off. A result is that current flows through the MOSFET486into the gate terminals of the MOSFETs (424,424′,424″,424′″,424″″) of the switching circuit420. Such may, for example, turn the MOSFETs (424,424′,424″,424′″,424″″) on, allowing current to flow into the battery string370when the DC power bus is supplied power by the power supply350. 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 inFIG. 3), which detects the direction of current flow in the direction of the DC power Bus.

In the switching circuit420, 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 circuit420). 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 circuit420being substantially (or entirely) powered by the DC power bus and by utilizing the opto-isolator circuit490to maintain the switching circuit420in 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.

The battery measurement circuit (e.g.,340, shown inFIG. 3) controls measurement taking and controls the switching circuit420for charging, but only when the power supply350is operating. In the event of a power failure by the power supply370or 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 circuit330, shown inFIG. 3), and hardware only activation of the switching circuit. Thus, in backup mode, the current sensing circuit will still enable the switching circuit420to maintain efficient back-up power delivery and prevent the diodes (422,422′,422″,422′″,422″″) in the switching circuit420from overheating.

In the event of a power failure within the battery management circuit (e.g.,310, shown inFIG. 3), the opto-isolator circuit490will turn-off (e.g., since the LED emitter power of the opto-isolator circuit490is supplied by SELV circuits). When the opto-isolator circuit490turns off, the switching circuit420turns on, placing the battery pack370(or individual batteries in the battery pack370) in a float-charging condition where one or more of the batteries in the battery pack370are being float-charged by the DC power bus and are also available for backup service to the load360.

Referring also toFIG. 5, a flowchart illustrates an example method500for measuring a characteristic resistance (i.e., an internal resistance) of a battery (e.g.,370, shown inFIG. 1) that can be implemented in a battery measurement circuit (e.g.,340, shown inFIG. 3) of a battery management circuit (e.g.,310, shown inFIG. 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 element505inFIG. 5), 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 inFIG. 5, a method500for measuring an characteristic resistance of a battery begins at block505where voltage measurement circuitry, which can be the same as or similar to voltage measurement circuitry346ofFIG. 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 block510, a current source, which can be the same as or similar to the current source which may be provided in switched current circuitry344ofFIG. 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 block515, current measurement circuitry, which can be the same as or similar to the current measurement circuitry which may be provided in switched current circuitry344ofFIG. 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 ofFIG. 3, and the current I is measured between the precision resistor and the battery (or between any other two points in the circuit). It should, of course, also be appreciated that current sensing can be accomplished by other means, including Hall Effect sensors and Inductive sensors High accuracy current measurements can be achieved using a closed-loop type of current sensor called a Flux Gate sensor. In one illustrative embodiment, FG technology may be used. In some embodiments, both of these latter techniques, may be used because they both provide galvanic isolation from the hazardous voltages present with long series battery strings.

At block520, after the predetermined time period, the current source discontinues providing current to the battery and, at block525the 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 block530, the battery measurement circuit determines a voltage difference (ΔV) between the first voltage and the second voltage of the battery. At block535, in response knowing ΔV and the current I measured by the current measurement circuitry at block515, 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 method500may 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 method500may be repeated continuously, periodically, or in response to a control signal (e.g., a control signal as may be provided by controller core342of battery measurement circuit340ofFIG. 3) depending on system and application requirements. The method500may 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 method500is 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 method500). Additionally, the charge removed from the battery as a result of method500may be replaced substantially immediately after (or a predetermined time after) the method500is complete. It should be appreciated that in some embodiments this is a continuous process and in some cases provides a starting point for charging of the battery (or batteries).

Precision of the method500(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 block510, (2) the predetermined time period for which the current is provided at the block510, and (3) the time between when the current source discontinues providing the current to the battery at block525, and when the voltage measurement circuitry measures a second voltage of the battery at block530. In one embodiment, for optimal precision the current provided by the current source at the block510should 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 block525, and when the voltage measurement circuitry measures a second voltage of the battery at block530, 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 method500provides 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 method500is not limited to performing the processes in the sequence described.

Referring now toFIG. 6, in which like elements ofFIG. 1are provided having like reference designations, another example circuit includes a controllable power supply650, an electrical load160and a battery pack (or battery string)170. The circuit also includes a battery management circuit610for managing the power supply650and the battery pack170and a battery balancer circuit680for balancing charges between one or more batteries of the battery pack170. Battery balancer circuit680is optional in some embodiments and, thus, is shown in phantom.

Controllable power supply650(e.g., a direct-current (DC) power supply), similar to power supply150ofFIG. 1, has a first terminal coupled to a first terminal of the electrical load160and a second opposing terminal coupled to a second opposing terminal of the electrical load160. In the illustrated embodiment, the power supply650also includes a power supply controller652which may be separate from or integrated with power supply650. A control terminal653is coupled to an input of the power supply controller652and a corresponding terminal of the battery management circuit610, as will be discussed.

Battery management circuit610, similar to battery management circuit110ofFIG. 1, includes a switching circuit120, a current sensing circuit130and a logic circuit132. In the illustrated embodiment, battery management circuit610also includes a battery measurement circuit640and a temperature sensing circuit690. The switching circuit120, logic circuit132and temperature sensing circuit690are optional in some embodiments and may be provided separate from battery management circuit610in some embodiments and are, thus, shown in phantom. In one embodiment, battery management circuit610includes switching circuit210when the battery management circuit610is coupled to two or more battery packs or strings (e.g.,170). Switching circuit210may, for example, isolate each battery string of the two or more battery strings from the power supply650.

Battery management circuit610has a first terminal610acoupled to a first terminal of power supply650and to a first terminal of electrical load160. Battery management circuit610also has a second terminal610bcoupled to a second terminal of power supply650and to a second terminal of electrical load160. Battery management circuit610additionally has third and fourth terminals610c,610dcoupled to first and second opposing terminals of battery pack170. In the illustrated embodiment, battery management circuit610also has a fifth terminal610ecoupled to the control terminal of the power supply650in a so-called “closed loop” arrangement.

Power supply650generates a supply voltage for use by the electrical load160and for charging the battery pack170, if necessary. In the event the power supply650fails to provide a necessary supply voltage to the electrical load160(e.g., during a power failure), battery pack170supplies some or all of the necessary supply voltage to the electrical load160. Here, however, under a “normal” operating condition, where the power supply650is able to provide a necessary supply voltage to the electrical load160, the battery management circuit610controls a voltage level of the supply voltage (e.g., for charging, resting, evaluating, and/or reducing dry-out or corrosion of batteries in the battery pack170).

Specifically, battery measurement circuit140of battery management circuit610controls (i.e., adjusts) the voltage level of the power supply voltage based upon one or more measurements made by the battery measurement circuit140and/or one or more signals received by the battery measurement circuit140.

As noted above in conjunction withFIG. 1, the battery measurement circuit140is configured to measure one or more characteristics of battery pack170(e.g., voltage measurements of battery pack170, state of charge (SOC) and/or state of health (SOH) characteristics of battery pack170, or of individual batteries in the battery pack170). Additionally, the battery measurement circuit140is coupled to receive a current sense control signal from the current sensing circuit130. The battery measurement circuit140is also coupled to receive a temperature sense control signal from temperature sensing circuit690in the illustrative embodiment ofFIG. 6.

Current sensing circuit130, which has a first terminal130acoupled to a second terminal120bof switching circuit120of the battery management circuit610, is configured to measure a direction, a magnitude and/or a polarity of current signals passing through switching circuit120(which may be the same as or similar to any of the switching circuits described in the figures above). In some embodiments, the switching circuit120is provided as at least one of a power switch, a switching semiconductor (e.g., a MOSFET), an electromechanical relay and an electromechanical contactor (e.g., an LVBD contactor). In embodiments in which an LVBD contactor is used, the contactor would be paralleled with a diode or a group of diodes (e.g., a diode array). The diode function is a function that is generally inherent in MOSFET devices.

In particular, if a contactor were used, a diode or group of parallel diodes would be placed across the contactor such that batteries would supply power in a contiguous manner if the power supply650dropped out. In a minimal scenario, a switch function is not needed due to the battery measurement circuit140being coupled to the power supply650in a closed loop arrangement (e.g., the switch function may be reduced or ideally eliminated by using the closed loop voltage control to essentially provide the same functionality that “switched” products possess). In some embodiments, switching circuit120may be eliminated by operation of the power supply control functionality provided by the battery measurement circuit140, where the battery management circuit610and battery measurement circuit140essentially perform the functions of the switching circuit120. In response to measuring the current signals, the current sensing circuit130may generate and provide a current sense control signal indicative of the measured current signals to a corresponding input of battery measurement circuit140of the battery management circuit. As noted above in conjunction withFIG. 1, the current sense control signal may control measurement of one or more characteristics of the battery pack170, measurement of current flow rate, and/or charge into and out of the battery pack170.

Temperature sensing circuit690, which has a terminal coupled to a corresponding terminal of the battery measurement circuit640, is configured to measure ambient temperature proximate to the battery pack170. Temperature sensing circuit690is also configured to provide a corresponding temperature signal indicative of the measured temperature to the battery measurement circuit640. The battery measurement circuit640may, in turn, use one or more of the measurements (e.g., voltage measurements) made by the battery measurement circuit640, the current sense control signal received from current sensing circuit130, and the temperature signal from the temperature sensing circuit690to determine a voltage level (or amount) by which the voltage level of the supply voltage should be adjusted. In particular, the voltage level may be adjusted by providing a power supply control signal to the control terminal of the power supply650.

Additionally, the voltage level may, for example, be adjusted (e.g., increased) to charge one or more of the batteries in battery pack170during a battery charge operation and to substantially reduce (or ideally minimize) corrosion of the battery pack170(e.g., during a “normal” operating condition), as will be described further in conjunction with figures below. Further, the voltage level may be adjusted (e.g., decreased) during a battery discharge operation (e.g., to test battery capacities and/or state of health (SOH) of one or more of the batteries in the battery pack170). Control of the power supply voltage allows systems operating in accordance with the concepts described herein for the controlling of charging rates of the batteries, maximizing battery life, by managing the charging current level(s). This may reduce internal heating and gassing during charging. In other words, the voltage level may be adjusted in a closed loop manner such that particular battery management functions are achieved (e.g., such that the battery management circuit draws small and short duration current from at least one of the one or more battery strings during a battery discharge operation).

In one embodiment, the battery pack170is a single battery pack (or string) and the voltage level of the supply voltage is controlled such that the battery management circuit610is capable of substantially eliminating current flow through the single battery string170without the switching circuit120. The foregoing is one example result of the coupling of the battery management circuit610and the power supply650in the closed loop arrangement.

Battery balancer circuit680, which is shown as having a first terminal coupled to the first terminal of battery pack170and a second terminal coupled to the second terminal of the battery pack170in the illustrated embodiment, is, in actuality, coupled to each battery (or cell) of the battery pack170. Battery balancer circuit680may, for example, balances charges of the batteries in the battery pack170by performing charge transfers between the batteries. This may, for example, extend battery run time of the battery pack170as well as battery life of the battery pack170. Operation of battery balancing circuits is conventional in the art and, therefore, is not described in detail herein.

Additional aspects of the circuit ofFIG. 6, particularly operation thereof, will described further in conjunction with figures below. It should be appreciated that there is substantially no restriction to the number of batteries (e.g. series batteries) that can be managed in a single battery bank or string (e.g.170, shown inFIG. 6). Substantially any number of batteries may be provided.

Referring now toFIG. 6A, another example circuit is shown. The circuit includes power supply650and electrical load160. The circuit also includes N number of battery packs (here, battery packs170,1170) and N corresponding battery management circuits (here, battery management circuits610,1610) 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 circuit1610, which may be the same as or similar to battery management circuit160, has a first terminal1610acoupled to the first terminal of power supply650and to the first terminal of electrical load160. Battery management circuit1610also has a second terminal1610bcoupled to the second terminal of power supply650and to the second terminal of electrical load160. Battery management circuit1610additionally has third and fourth terminals1610c,1610dcoupled to first and second opposing terminals of battery pack1170, which may be the same as or similar to battery pack170. In the illustrated embodiment, battery management circuit1610further has a fifth terminal1610ecoupled to the control terminal of power supply650.

Similar to the circuit shown inFIG. 6, the power supply650generates a supply voltage for use by the electrical load160and the battery management circuit610controls a voltage level of the supply voltage (e.g., for charging the battery pack170). Here, however, battery management circuits610,1610both control the voltage level of the supply voltage (e.g., for charging battery packs170,1170). Additionally, in the event the power supply650fails to provide the necessary supply voltage to the electrical load160(e.g., during a power failure), battery pack170, battery pack1170and/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 load160. 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 load160. In one embodiment, when a switch function is used, the system can selectively charge individual batteries of strings of batteries, to get each one (ideally) charged, without over-charging those already fully charged. Without switches or switching functions provided by the battery management circuit610or battery measurement circuit140, parallel strings or batteries may endure a same charge energy, possibly overcharging some batteries, defeating one purpose of the battery management circuit610.

Referring now toFIG. 7, another example circuit includes a power supply750, an electrical load760and a battery string (or battery pack)770including a plurality of batteries (e.g., series and/or parallel coupled). The circuit also includes a controller710, an analog-to-digital converter (ADC)720, a switching circuit730and a current sensing circuit740, one or more of which may be provided as part of a battery management circuit in accordance with the concepts, systems, circuits and techniques sought to be protected herein. The ADC720and the switching circuit730are optional in some embodiments.

Power supply750, which may be the same as or similar to power supply650ofFIG. 6, includes a power supply controller752and has a first terminal coupled to a first terminal of ADC720, a first terminal of battery string770, a first terminal of battery balancer circuit780, and a first terminal of electrical load760. Power supply750also has a second terminal coupled to a second terminal of ADC720, a second terminal of current sensing circuit740, a second terminal of battery balancer circuit780, and a second terminal of electrical load760. Power supply750additionally has a third, control terminal coupled to a corresponding terminal of controller710.

Controller710, similar to battery measurement circuit610ofFIG. 6, is coupled to the power supply750in a closed loop arrangement and configured to control a voltage level of a supply voltage generated by the power supply750based upon one or more measurements made by the controller710and/or signals received by the controller710. In the illustrated embodiment, the controller710is coupled to ADC720which monitors a voltage of the battery string770and voltages of the batteries in the battery string770. The ADC720is coupled to receive a voltage signal from each of the batteries and is configured to provide a corresponding converted digital signal to the controller710. The converted digital signal may, for example, be used to determine a voltage (e.g., a measured voltage) of each of the batteries in the battery string770.

In the illustrated embodiment, the controller710is also coupled to current sensing circuit740, which may be the same as or similar to current sensing circuit130ofFIG. 6. The current sensing circuit740is coupled to receive current signals from battery string770at a first input and is configured to measure a magnitude and a direction of current flowing through the battery string770as represented by the current signals. The current sensing circuit740also provides a corresponding current sense signal indicative of the measured current flow to ADC720. The ADC720, in turn, provides a corresponding converted digital signal to the controller710for processing.

In response to receiving the converted voltage signal and the converted current sense signal from the ADC720, controller710may generate and provide a power supply control signal to power supply controller750to adjust (e.g., increase or decrease) a voltage level of the supply voltage generated by power supply750. In one embodiment, the voltage level is adjusted in order to charge one or more of the batteries in the battery string770, as described further below in conjunction withFIGS. 8 and 9, for example. Additionally, in one embodiment, the voltage level is adjusted to provide a predetermined amount of current (e.g., maintenance current) to the batteries in the battery string770for substantially reducing (or eliminating) dry-out or corrosion of the batteries, as described further below in conjunction withFIG. 10. The amount of the voltage level adjustment may, for example, be determined using one or more software algorithms in the controller710.

Controller710may, for example, operate to monitor the battery string770(or one or more of the batteries in the battery string770) and, based on the monitoring, may adjust the voltage level to optimize charge level and maximize battery life of the battery string770(e.g., by charging and resting currents). An increase in the supply voltage may, for example, cause a corresponding current increase through the battery string770. Such controller operation may be implemented via software, hardware or through a combination of hardware and software. Additionally, a decrease in the supply voltage may cause a corresponding current decrease through the battery string770. The supply voltage may also provide substantially zero current to the batteries, which can be used to “rest” the batteries and to take voltage measurements (e.g., virtual open circuit voltage (Voc) measurements) using ADC720. It should be appreciated that battery management functions are performed within the normal operating range of the batteries and the load equipment (e.g., the supply voltage is supplying just enough power to the load). In one embodiment, the batteries are rested and decoupled from the supply voltage through use of the switching circuit730, which is may be the same as or similar to switching circuits220and1220ofFIGS. 2 and 2Ain some embodiments. Switching circuit730is coupled to controller710and coupled between battery string770and current sensing circuit740, as shown inFIG. 7.

Once each of the batteries the battery string770is substantially fully charged, the controller710may continue to monitor voltages of the batteries in the battery string770with ADC720and current flow through the battery string770with the current sensing circuit740. In charge recovery mode (e.g., a battery recharge operation subsequent to a power failure), algorithms in the controller710attempt to optimize current supplied to the battery string770while keeping the voltage level of the supply voltage within a so-called “low-stress” operating range for the electrical load760.

The circuit ofFIG. 7also includes an optional cell balancing circuit790, which may be a conventional (i.e., commercial off-the-shelf (COTS)) cell balancing circuit, for example. The cell balancing circuit790is coupled to and controlled by controller710and configured to measure voltages of each of the batteries in the battery string770. The controller710may operate, for example, control the voltage level of the supply voltage and the cell balancing circuits790to ensure that no batteries in the battery string770are undercharged or overcharged (e.g., by removing charge from fully charged batteries and charging undercharged batteries until all batteries are fully charged). Such controller operation may be implemented, for example, via software, hardware or through a combination of hardware and software. In a so-called active mode, for example, charge from overcharged batteries is transferred to undercharged batteries, thereby conserving charge energy needed to charge the batteries.

Similar to battery management circuit610ofFIG. 6, in one embodiment the battery management circuit ofFIG. 7(i.e., one or more of controller710, ADC720, switching circuit730and current sensing circuit740) includes switching circuit730when the battery management circuit is coupled to two or more battery packs or strings (e.g.,770). Switching circuit730may, for example, isolate each battery string of the two or more battery strings from the power supply750.

Additionally, in one embodiment the battery string770is a single battery pack (or string) and the voltage level of the supply voltage is controlled such that the battery management circuit ofFIG. 7is capable of substantially eliminating current flow through the single battery string770without the switching circuit730. The foregoing is one example result of the coupling of the battery management circuit and the power supply750in the closed loop arrangement.

Referring now toFIG. 7A, in which like elements ofFIG. 7are provided having like reference designations, another example circuit includes controller710, power supply750and electrical load760. The circuit also includes N number of battery strings (here, battery string #1 to battery string #N), N corresponding analog-to-digital converters (here, ADC #1 to ADC #N), N corresponding current sensing circuits (here, current sensing circuit #1 to current sensing circuit #2), N corresponding battery balancer circuits (here, battery balancer circuit #1 to battery balancer circuit #N) and N corresponding switching circuits (here, switching circuit #1 to switching circuit #N) in the illustrated embodiment. In some embodiments, however, a greater number of ADCs, current sensing circuits, battery balancer circuits and/or switching circuits may exist than battery strings, and vice versa (e.g., a circuit including five battery strings may have four ADCs, four current sensing circuits, four battery balancer circuits and four switching circuits). When there are less ADCs, current sensing circuits, battery balancer circuits and/or switching circuits than battery strings, the ADCs, current sensing circuits, battery balancer circuits and/or switching circuits may, for example, be selectively multiplexed to the battery strings. Multiplexing is conventional in the art and, thus, is not described in detail herein.

In the illustrated embodiment, each ADC (e.g., ADC #1), current sensing circuit (e.g., current sensing circuit #1), battery balancer circuit (e.g., battery balancer circuit #1) and switching circuit (e.g., switching circuit #1) is coupled to the controller710. Each ADC provides a converted digital signal to a corresponding input of the controller710, each current sensing circuit provides a current sensing signal to a corresponding input of the controller710, each battery balancer circuit provides a battery balancing signal to a corresponding input of the controller710, and each switching circuit receives a switch control signal from a corresponding output of the controller710.

Similar to controller710ofFIG. 7, controller710ofFIG. 7Ais configured to control a voltage level of a supply voltage generated by the power supply750based upon one or more measurements made by the controller710(e.g., voltage measurements through ADC720) and/or signals received by the controller710(e.g., current sense signals received from current sensing circuit740). Here, however, the controller710controls the voltage level of the supply voltage by providing power supply control signals to power supply controller1752, which is coupled to but provided external to the power supply750in the illustrated embodiment. Additionally, here, the controller710controls the voltage level of the supply voltage for each battery string in the circuit. In one embodiment, the voltage level of the supply voltage is controlled for each battery string in the circuit using the above and below described methods (e.g., in conjunction withFIGS. 8-10).

Referring toFIGS. 8-10, several flowcharts (or flow diagrams) are shown. Rectangular elements (typified by element805inFIG. 8), as may be referred to herein as “processing blocks,” may represent computer software instructions or groups of instructions. Diamond shaped elements (typified by element810inFIG. 8), as may be referred to herein as “decision blocks,” represent computer software instructions, or groups of instructions, which affect the execution of the computer software instructions represented by the processing blocks. The processing blocks and decision blocks can represent steps performed by functionally equivalent circuits such as a digital signal processor circuit or an application specific integrated circuit (ASIC).

The flowcharts do not depict the syntax of any particular programming language. Rather, the flowcharts illustrate 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.

Referring toFIG. 8, a flowchart illustrates an example method800for managing (e.g., monitoring, charging and/or discharging) a battery string (e.g.,770, shown inFIG. 7) that can be implemented in a battery management circuit (e.g.,610, shown inFIG. 6). A result of the method may be improved performance and/or battery life of the battery string. The figure is also illustrating two processes. First is the charging process which ends at block820. Second is setting the current, which could be setting to Zero Current, to rest the batteries. Then a waiting period begins for batteries to rest for a substantially long time (e.g. hours). During the wait, the system measures battery voltage behavior and adjusts current to maintain zero if resting.

As illustrated inFIG. 8, a method800for a battery string begins at block805where voltage measurement circuitry, which can be the same as or similar to the voltage measurement circuitry ofFIG. 7(i.e., controller710taken alone or in combination with ADC720), measures a first voltage (e.g., an open-circuit voltage) of one or more batteries in a battery string (e.g.,770). In one embodiment, the first voltage is measured directly across the terminals (i.e., first and second terminals) of each of the batteries in the battery string (or select ones of the batteries in the battery string) to minimize voltage losses (i.e., voltage drops) which may occur between the batteries and the voltage measurement circuitry (e.g., as may occur through wire resistance). In another embodiment, the first voltage is not measured directly across the terminals of the batteries. In such embodiment, any voltage loss which may occur between the batteries 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 batteries and the voltage measurement circuitry.

At block810, a battery measurement circuit, which can be the same as or similar to the battery measurement circuit ofFIG. 7(i.e., controller710taken alone or in combination with ADC720), determines a state of charge (SOC) of the batteries (i.e. if the batteries in the battery string are fully charged (or substantially fully charged)) based upon a comparison of the measured first voltage (e.g. an open circuit with a factor added or subtracted due to battery temperature) with a predetermined voltage value. In one embodiment, the batteries should rest for some period of time such that their voltage settles. Additionally, the predetermined voltage value may, for example, be a substantially fixed voltage value or a voltage value which changes based, at least in part, on the condition and environment of the batteries. If the battery measurement circuit determines that the batteries are fully charged, the method proceeds to a block825. Alternatively, if the battery measurement circuit determines that the batteries are not fully charged (or substantially fully charged), such as may be determined based on a measured DC resistance of a batteries, the method proceeds to a block815.

At block815, a current source, which can be the same as or similar to the power supply current source described in conjunction with figures above, provides current (e.g., a maintenance or charge current) to the batteries for a predetermined (i.e., fixed) time period (e.g., ten seconds). If the first voltage of the batteries is below a fixed threshold, one or more of the batteries may be charged in accordance with a charge routine, for example, which may include:Start charging of the batteries;Charge the batteries for a charge time (e.g., a variable charge time);Subsequent to the charge time, measure voltage(s) of the batteries;Compare the measured voltage(s) to a previously measured voltage(s);If a difference between the voltages (i.e., the measured voltage(s) and the previously measured voltage(s)) is less than a predetermined difference value, then end charge; andIf the difference is greater than the predetermined difference value, then charge one or more of the batteries again for a charge time.

In one embodiment, the current (e.g., charge current based on the charge routine) is provided to the batteries substantially immediately after the voltage measurement circuitry measures the first voltage of the batteries. 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 determined by a value required to yield a “meaningful” voltage drop in the battery, such that the drop can be repeatedly and accurately measured. Larger batteries, for example, may need more current passed through them to yield an accurate measurement. Also, discharge time can be increased to provide additional voltage drop, for a reliable measurement. 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 first range of batteries (e.g., 20 A to 200 A batteries). Additionally, a 10 A constant current was empirically determined to be suitable for a second range of batteries (e.g., batteries greater than 200 A). In some instances, the 10 A current value may be higher, which may necessitate an effort to recycle the energy.

At block820, after the predetermined time period, the current source discontinues providing current to the batteries and, at block805the voltage measurement circuitry measures the first voltage of the batteries again. In one embodiment, the first voltage is measured substantially immediately after the current source discontinues providing current to the batteries where the current source is used for measuring DC resistance. At block810, the battery measurement circuit determines if the batteries are fully charged (or substantially fully charged) based upon a comparison of the measured first voltage with a predetermined voltage value. If the battery measurement circuit determines that the batteries are fully charged, the method proceeds to a block825. Alternatively, if the battery measurement circuit determines that the batteries are still not fully charged (or substantially fully charged), blocks815,820and805are repeated again.

At block825, the battery measurement circuit provides a power supply control signal to a power supply controller, which may be the same as or similar to power supply controller752shown inFIG. 7, to adjust (i.e., control) a voltage level of a supply voltage generated by a power supply (e.g.,750, shown inFIG. 7). In one embodiment, the voltage level is adjusted (e.g., decreased) during a battery discharge operation (e.g., a battery capacity test) to provide a predetermined amount of discharge current through each of the batteries in the battery string. The predetermined amount of discharge current may, for example, be a same value or values determined for the current source previously described. Such closed loop current setting is a functional equivalent of the discrete current source circuits used in conventional battery management circuit and systems.

For example, the voltage level may be adjusted by the power supply control signal such that the battery management circuit draws so-called “small” and “short” duration current from the batteries (or at least one of the battery strings) during the battery discharge operation. As one example, the “small” current draw can be between about zero point five and about one point five amps. Additionally, the “short” duration of the current draw can be for up to tens of seconds (e.g., less than about one second to about 20 seconds) such that the batteries are discharged, but not completely or substantially completely discharged (e.g., to end of discharge voltage). It should be appreciated that the current draw and duration of the current draw can vary, for example, based on battery type.

The discharge is used to produce a voltage drop in the batteries, so that a battery internal resistance can be determined. If the batteries are loaded for a few seconds, the voltage may be measured (loaded voltage), the load (current) removed, the voltage substantially immediately measured again (i.e., with substantially no-load voltage), and a voltage difference may be calculated. This voltage difference, divided by the load current used, gives the battery internal resistance, by Ohm's Law (R=V/I). The power supply voltage adjustment may be used to drop the supply voltage, such that the batteries start to supply the load current. This current may be held substantially constant by the closed-loop nature of the current measurement feeding information back to the controller, and the controller sending voltage adjustment messages via the power supply control signal to the power supply to hold the current constant.

It should be appreciated that the power supply control signal can be an analog, digital, or mixed signal indicative of an amount by which the voltage level needs to be adjusted (i.e., increased or decreased). The type of signal (e.g., analog, digital, or mixed signal) may, for example, be based on acceptable input signal type(s) of the power supply controller752.

At block830, a current sensing circuit, which can be the same as or similar to the current sensing circuit740shown inFIG. 7, measures a magnitude of current flow through the battery string (or of each battery in the battery string) The current sensing circuit may also measure direction of current flow. Additionally, the current sensing circuit provides a current sensing signal corresponding to the magnitude of the current (or simply “current magnitude”) to a corresponding input of the battery measurement circuit. At block835, the battery measurement circuit processes the current sensing signal and determines if the current magnitude is substantially equal to a first current value. Current for DC resistance measurement falls within the small windows described previously. For determining charging currents, many factors are involved, including battery size, temperature, SOC, available power supply current, etc. If the battery measurement circuit determines that the current magnitude is substantially equal to the first current value, the method proceeds to a block840. Alternatively, if the battery measurement circuit determines that the current magnitude is not substantially equal to the first current value, the method returns to block825and blocks825,830and835are repeated.

At block840, the current sensing circuit measures average current flow through each of the batteries in the battery string and, at block845the current source (e.g., a static current source) continues providing current (e.g., a discharge current) to the batteries for a predetermined discharge time period as may be suitable for measuring DC resistance. At block850, after the predetermined discharge time period, the current source discontinues providing current to the batteries and, at block855the voltage measurement circuitry measures a second voltage of the batteries. In one embodiment, the second voltage of the batteries is measured substantially immediately after the current source discontinues providing current to the batteries. Additionally, the second voltage of the batteries may be measured in a similar manner as the first voltage of the batteries (e.g., directly across the terminals of the batteries).

At block860, the battery measurement circuit determines a voltage difference (ΔV) between the first voltage and the second voltage of each of the batteries. At block865, the voltage difference is stored in a memory device (e.g., EEPROM or flash memory) in the battery measurement circuit. At block870, in response to knowing the voltage difference and the average current measured by the current sensing circuitry at block840, the battery measurement circuit determines a state of health (SOH) of the batteries (e.g., through use of one or more software algorithms in the battery measurement circuit). In one embodiment, the battery measurement circuit is able to determine the SOH of the batteries by computing a characteristic resistance of the batteries (i.e., characteristic resistance=|ΔV/I|) and using the characteristic resistance as at least one SOH characteristic in determining the SOH of the batteries.

At block875, in response to determining the SOH of the batteries, the battery measurement circuit may provide an indication of the SOH of the batteries. The indication may be a visual indication, for example, such as may be provided through one or more light emitting diodes (LEDs) or a display (e.g., a monitor). It should be appreciated that the DC resistance measurement is one of several key elements to determination of SOH. If a battery is flagged as bad, the processor may provide a message (e.g., based on program parameters) to a pc or a phone of a maintenance person, manager, etc. that oversees management of the batteries. A bad battery may also be indicated on a software dashboard, in a product web interface and/or in a software interface of associated battery management software of the battery management system (e.g.,610, shown inFIG. 6).

Subsequent to block875, the method800may end. The method ending may, for example, be indicative of the SOH of each battery in the battery string having been determined. In one embodiment, the method800may be repeated continuously, periodically, or in response to a control signal (e.g., a control signal as may be provided to the battery management circuit or battery measurement circuit) depending on system and application requirements. The method800may be repeated, for example, to determine the SOH of the batteries in the battery string again, or to determine the SOH of other batteries (or battery strings) in the circuit including the battery management circuit. As described above, the circuits described herein may include one or more battery strings (or battery banks) with each of the battery strings including one or more batteries.

Referring also toFIG. 9, a flowchart illustrates an example method900for charging a battery string (e.g.,770, shown inFIG. 7) that can be implemented in a battery management circuit (e.g.,610, shown inFIG. 6) and alone or in combination with the method800ofFIG. 8. The method900includes a first sub-method1900for dV/dt charging (i.e., change in voltage over time charging) and a second sub-method2900for dI/dt charging (i.e., change in current over time charging) which may be implemented alone or in combination. A result of method900, similar to method800, may be improved performance and/or battery life of the battery string (e.g., due to reduced temperature dependency during a charge).

As illustrated inFIG. 9, a method900for charging a battery string begins at block905where voltage measurement circuitry (e.g., processor710taken alone or in combination with ADC720) measures a voltage (e.g., an open-circuit voltage) of one or more batteries in a battery string (e.g.,770). Similar to method800, in one embodiment the voltage is measured directly across the terminals (i.e., first and second terminals) of each of the batteries in the battery string (or select ones of the batteries in the battery string) in differential measurement arrangement to reduce and ideally minimize voltage losses (i.e., voltage drops) which may occur between the batteries and the voltage measurement circuitry (e.g., as may occur through drops between inter-battery wiring.

At block910, a battery measurement circuit (e.g., controller710taken alone or in combination with ADC720) determines if the batteries in the battery string are fully charged (or substantially fully charged) based upon a comparison of the measured voltage with a predetermined voltage value. The predetermined voltage value may, for example, be a substantially fixed voltage value or a voltage value which changes based, at least in part, on the battery temperature. If the battery measurement circuit determines that the batteries are fully charged, the method proceeds to a block935where the batteries are placed in a resting state (i.e., an open circuit condition). The batteries may, for example, remain in the resting state (i.e., a zero charge current state) for a predetermined time period or until the batteries are needed (e.g., during a battery discharge operation or a power failure). Alternatively, if the battery measurement circuit determines that the batteries are not fully charged (or substantially fully charged), the method proceeds to either a sub-method1900or a sub-method2900(and either a block1915or a block2915) based on whether dV/dt or dI/dt charging is being used. Sub-method1900includes blocks1915,1920,1925and1930. Additionally, sub-method2900includes blocks2915,2920,2925,2930,2935and2940.

If dV/dt charging is being used, the method proceeds to a sub-method1900and a block1915. At block1915, the battery measurement circuit provides a first control signal (e.g., analog, digital or mixed signal) to a power supply controller (e.g.,752, shown inFIG. 7) to adjust a voltage level of a supply voltage generated by a power supply (e.g.,750, shown inFIG. 7). In one embodiment, the voltage level is adjusted (i.e., increased or decreased) to provide a predetermined amount of charge current to each of the batteries in the battery string. This predetermined amount of charge current is determined based on a battery SOH calculation. At block1920, a timer (e.g., a process timer) in the battery measurement circuit begins to count time, for example, once the voltage level of the supply voltage has been adjusted. The time at which the voltage level of the supply voltage has been adjusted may, for example, correspond to a reference point in time. At block1925, the battery measurement circuit provides a second control signal to the power supply controller to adjust the voltage level of the supply voltage such that substantially no current (i.e., zero battery current) is provided to the batteries as a result of the supply voltage. Zero current allows for the assessing of the electrochemical behavior of the batteries, at rest (no current flow).

At block1930, the voltage measurement circuitry measures a second voltage of the batteries and determines if each of the batteries has experienced a change in voltage over time (dV/dt) which is less than a predetermined (or set) change in voltage over time. Specifically, the battery measurement circuit determines a voltage difference (ΔV) between the first voltage and the second voltage of each of the batteries over a predetermined time period (i.e., dt). The predetermined time period may, for example, correspond to a time period between the reference point in time and when the voltage measurement circuitry measures the second voltage of the batteries at block1930. If the battery measurement circuit determines that the measured change in voltage over time is less than the predetermined change in voltage over time, the method proceeds to block935. Alternatively, if the battery measurement circuit determines that the measured change in voltage over time is not less than the predetermined change in voltage over time, the method returns to block1915and blocks1915,1920,1925and1930may be repeated.

Alternatively, if dI/dt charging is being used, the method proceeds to a sub-method2900and a block2915. At block2915, similar to block1915, the battery measurement circuit provides a first control signal to a power supply controller to adjust a voltage level of a supply voltage generated by a power supply. At block2920, current measurement circuitry, which can be the same as or similar to the current sensing circuit ofFIG. 6, measures a first current flowing through the batteries. At block2925, a timer in the battery measurement circuit begins to count time, for example, once the voltage level of the supply voltage has been adjusted or the current measurement circuitry measures the first current. The time at which the voltage level of the supply voltage has been adjusted or the current measurement circuitry measures the first current may, for example, correspond to a reference point in time. At block2935, after a predetermined time period at a block2930, the battery measurement circuit provides a second control signal to the power supply controller to adjust the voltage level of the supply voltage such that substantially no current (i.e., zero battery current) is provided to the batteries as a result of the supply voltage.

At block2940, the current measurement circuitry measures a second current of the batteries and determines if each of the batteries has experienced a change in current over time (dI/dt) which is less than a predetermined (or set) change in current over time. Specifically, the battery measurement circuit determines a current difference (ΔI) between the first current and the second current of each of the batteries over a predetermined time period (i.e., dt). The predetermined time period may, for example, correspond to a time period between the reference point in time and when the current measurement circuitry measures the second current of the batteries at block2940. If the battery measurement circuit determines that the measured change in current over time is less than the predetermined change in current over time, the method proceeds to block935. Alternatively, if the battery measurement circuit determines that the measured change in current over time is less than the predetermined change in current over time, the method returns to block2915and blocks2915,2920,2925,2930,2935and2940may be repeated.

Subsequent to block935, the method900(e.g., a maintenance charging method) may end. The method ending may be indicative of a maintenance charge having been completed. The method900may be repeated continuously, periodically, or in response to a control signal (e.g., a control signal as may be provided to the battery management circuit or battery measurement circuit) depending on system and application requirements.

Referring also toFIG. 10, a flowchart illustrates an example method1000for substantially reducing (or eliminating) corrosion of a battery string (e.g.,770, shown inFIG. 7) that can be implemented in a battery management circuit (e.g.,610, shown inFIG. 6) alone or in combination with method800ofFIG. 8and/or method900ofFIG. 9, for example. As is known, corrosion may occur in the plates of batteries Due to over-charging A result of method1000, which may, for example, be implemented during a “normal” operating condition (e.g., where power supply is able to provide a necessary supply voltage to the electrical load), may be improved performance and/or battery life of a battery string due to reduced or eliminated corrosion of the battery string. It should be appreciated that this sequence is invoked on fully charged batteries, to keep proper level of plate ionization.

As illustrated inFIG. 10, a method1000for substantially reducing (or eliminating) corrosion of a battery string begins at block1005where a battery measurement circuit (e.g., controller710taken alone or in combination with ADC720) determines a level of current to be provided to batteries in the battery string. The type of charge may include, for example, a float charge or a boost charge, maintenance charge, balance charge. At block1010, voltage and current parameters associated with the type of charge are stored in a memory device (e.g., EEPROM or flash memory) in the battery measurement circuit. These parameters may include minimum voltage and current levels and maximum voltage and current levels as a few examples.

At block1015, the battery measurement circuit provides a power supply control signal (e.g., analog, digital or mixed signal) to a power supply controller (e.g.,725, shown inFIG. 7) to adjust a voltage level of a supply voltage generated by a power supply (e.g.,750, shown inFIG. 7). In one embodiment, the voltage level is adjusted (i.e., increased or decreased) to provide a predetermined amount of current (e.g., maintenance current) to each of the batteries in the battery string to minimize deterioration of the batteries (and to provide a desired anti-corrosion performance). Anti-corrosion currents may be set according to known techniques.

In accordance with one aspect of the concepts described herein, it has been discovered that at elevated temperatures, holding a certain current does not correspond with maintaining proper charge and thus it may be necessary to interrogate the batteries several times per day, to ensure proper charge level. Additionally, in one embodiment, a substantially constant voltage is provided on the electrodes or battery plates of the batteries in the battery string. In embodiments, ranges of the currents are either determined by battery manufacturers for type and size of battery, ambient temperatures also tell how to adjust currents and voltages. A key product quality is that the processes are dynamic and the systems adapt to increase (and ideally optimize) the battery SOH. For instance, if system has a battery the requires more frequent charges than other similar batteries, it attempts to optimize that battery. If the temperature starts to drop, the system will increase battery charge levels to ensure 100% charge is maintained. Charge cycle times and currents are varied by temperature and trended battery discharge rates, etc.

At block1020, a current sensing circuit (e.g.,740, shown inFIG. 7) measures a magnitude of current flow through the battery string (or of each battery in the battery string). The current sensing circuit may also measure direction of current flow. In some embodiments, current direction is always monitored. It tells when the system is nominal or in backup mode. Additionally, the current sensing circuit provides a current sensing signal corresponding to the magnitude of the current to a corresponding input of the battery measurement circuit. At block835, the battery measurement circuit processes the current sensing signal and determines if the current magnitude is substantially equal to a predetermined (or target) current value.

When measuring or maintaining the batteries, the current is held constant, within substantially narrow windows which may be adjusted for temperature. When charging, the system does not exert much current control until batteries are greater than 75% charged. And this is only for the approach where the system is adjusting the supply voltage within a narrow range, of a few volts. Majority of charge control is adaptive on/off, meaning the system adapts to maintain optimal charge levels. The current may be measured to calculate the amount of charge that goes into and out of the batteries. This helps to track charge efficiency, which is an SOH parameter. If the battery measurement circuit determines that the current magnitude is substantially equal to the predetermined current value, the method proceeds to a block1030. Alternatively, if the battery measurement circuit determines that the current magnitude is not substantially equal to the predetermined current value, the method proceeds to a block1040.

At block1040, the battery measurement circuit determines a voltage level to provide the predetermined amount of current to minimize deterioration of the batteries. In one embodiment, the voltage level is based, at least in part, on ambient temperature proximate to the batteries as may be measured by a temperature sensing circuitry (e.g.,690, shown inFIG. 6). Subsequent to block1040, the method returns to block1015and blocks1015,1020,1025and1030are repeated.

At block1035, voltage measurement circuitry (e.g., controller710taken alone or in combination with ADC720) measures a voltage of one or more batteries in a battery string (e.g.,770) and determines if the measured voltage is substantially equal to a predetermined (or target) voltage value. In some embodiments, the target voltage is empirically determined. If the voltage measurement circuitry determines that the measured voltage is substantially equal to the predetermined voltage value, the method proceeds to a block1045. Alternatively, if the voltage measurement circuitry determines that the measured voltage is not substantially equal to the predetermined voltage value, the method proceeds to a block1040.

At block1045, temperature sensing circuitry measures and stores ambient temperature values in a memory device (e.g., EEPROM or flash memory) in the battery management circuit. Subsequent to block1045, the method1000proceeds to block1040where the measured ambient temperature values are provided to the battery measurement circuit for processing. Additionally, subsequent to block1040, method1000may end (not shown) or blocks1015,1020,1025,1030,1035,1040and1045may be repeated a predetermined number of times. The method1000may also be started and stopped for other routine testing and charging regimens on the batteries to take place.

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. As one example, while some of the figures show circuitry (e.g., current sensing circuit740, shown inFIG. 7) coupled to particular terminals (e.g., a negative terminal) of a circuit element (e.g., battery string770, shown inFIG. 7), such is shown 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 are not intended to be, and should not be construed, as limiting. The concepts, systems, circuits and techniques disclosed herein may, of course, be configured and coupled in different manners than that which is shown (e.g., depending on the particular system, such as a positive ground system or a negative ground system) as will be apparent to one of ordinary skill in the art.

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.