# Patent

## Title
Monitoring system and method

## Abstract

A method and system for monitoring a voltage of a battery cell or a battery stack. A first monitoring unit has a first plurality of battery monitoring nodes, first and second data ports, a first supply port switchably coupled to the first plurality of battery monitoring nodes, a second supply port switchably coupled to the first plurality of battery monitoring nodes, and a third supply port. A controller is connected to the first monitoring unit. Alternatively, a reference voltage may be connected to the controller or it may be connected to the first monitoring unit.

## Background
TECHNICAL FIELD
The present invention relates, in general, to batteries and, more particularly, to monitoring a battery stack.
BACKGROUND
Battery stacks are used in many applications including automotive, aerospace, airline, nautical, computer, communications, heavy equipment, remote sensing, etc. The battery stacks are typically arranged in series with one another to provide a power supply of a particular rated voltage to drive an electrical load. Each battery within the battery stack comprises a number of individual battery cells. The lifetime of the battery is strongly dependent on the way in which the battery is charged and discharged and will be reduced by over-charging the cells or over-discharging the cells. In addition, it is desirable to keep all the cells of a battery stack at the same capacity. This corresponds to keeping all the cells at about the same open circuit voltage. Use of the battery and over-discharge of one cell will impact the lifetime of that cell and of the battery. For example, the capacity of a battery cell that is 50 millivolts (mV) different from a battery cell operating at its nominal voltage is 5 percent (%) lower than the capacity of the battery cell operating at its nominal voltage. This difference may be unacceptable in the applications described above. Thus, battery manufacturers are constantly striving to find better and more accurate measurement techniques for measuring the voltage across battery cells. Along with improving measurement techniques, battery manufacturers are searching for ways to balance the cell voltages within a battery stack.
It has been found that one source of error in a battery monitoring and control unit is the voltage reference source of the unit. These units are typically only accurate to +/−1% over the temperature range from −40 degrees Celsius (° C.) to 150° C. For a maximum cell voltage of 4.2V this gives a possible range of error of +/−42 mV, which is typically too high for many battery applications.
Accordingly, it would be advantageous to have a circuit and a method for monitoring and balancing the voltage of a battery stack and the voltages of the cells within a battery stack. It would of further advantage for the circuit and method to be cost efficient.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures, in which like reference characters designate like elements and in which:
FIG. 1 is a schematic diagram of a portion of a battery system in accordance with an embodiment of the present invention;
FIGS. 2A, 2B, and 2C are a schematic diagram of a battery system in accordance with an embodiment of the present invention;
FIG. 3 is a schematic diagram of a portion of the battery system of FIG. 1;
FIG. 4 is a schematic diagram of another portion of the battery system of FIG. 1;
FIGS. 5A, 5B, and 5C are a schematic diagram of a battery system in accordance with another embodiment of the present invention;
FIG. 6 is a schematic diagram of a battery system in accordance with another embodiment of the present invention; and
FIG. 7 is a schematic diagram of a switch suitable for use with battery systems in accordance with the present invention.



DETAILED DESCRIPTION
Generally, the present invention provides a monitoring system and a method for monitoring one or more battery cells or one or more batteries. In accordance with an embodiment of the present invention, a first monitoring unit is used to measure a voltage of a first cell of a first battery and to generate a first measurement result. Measuring the voltage of the first cell of the first battery includes using a first reference voltage. A second monitoring unit is used to measure the first reference voltage and to generate a second measurement result. A first correction factor suitable for use in correcting a set of measurements from at least one of the first and second monitoring units is calculated using the first measurement result and the second measurement result.
In accordance with another embodiment, a first monitoring unit has a first plurality of battery monitoring nodes, first and second data ports, a first supply port switchably coupled to the first plurality of battery monitoring nodes, a second supply port switchably coupled to the first plurality of battery monitoring nodes, and a third supply port. A controller has at least first, second, and third nodes, the first node coupled to the first data port, the second node coupled to the second supply port, and the third node coupled for receiving a reference voltage.
In accordance with yet another embodiment, a monitoring system, comprises a first monitoring unit that has a first plurality of battery monitoring nodes, first and second data ports, a first supply port switchably coupled to the first plurality of battery monitoring nodes, a second supply port switchably coupled to the first plurality of battery monitoring nodes, a third supply port, and a first reference port switchably coupled to the first plurality of battery monitoring nodes and second reference port switchably coupled to the first plurality of battery monitoring nodes. A controller has at least one port coupled to the first data port.
Referring to FIG. 1, a local battery module 22m comprising a battery unit 20m coupled to a battery monitor control unit 16m is illustrated. It should be noted that the subscript “m” represents an integer. Battery monitor control unit 16m is comprised of a high side interface (IFH) circuit 26m and a low side interface (IFL) circuit 28m coupled to a logic circuit 30m. IFH circuit 26m is referred to as a high side interface circuit because it is connected to a higher voltage potential of battery unit 20m than IFL circuit 28m. Similarly, IFL circuit 28m is referred to as a low side interface circuit because it is connected to a lower voltage potential of battery unit 20m than IFH circuit 26m. IFH circuit 26m has a terminal coupled to an input/output node 32m for receiving a source of operating potential VCCEm and a terminal coupled to an input/output node 34m for transmitting and receiving control signals Tx/Rx1m. IFL circuit 28m has a terminal coupled to an input/output node 42m for receiving a source of operating potential VCCm and a terminal coupled to an input/output node 44m for transmitting and receiving control signals Tx1/Rx2m. Input/output nodes 32m and 42m may be referred to as supply nodes and input/output nodes 34m and 44m may be referred to as data nodes. Input/output nodes 32m and 42m and input/output nodes 34m and 44m serve as selectable input ports. Battery monitor control unit 16m further comprises a selection device 54m such as, for example, a multiplexer having inputs 54I0,m, 54I1,m, . . . , 54I(n−1),m, 54In,m, 54I(n+1),m, outputs 54O1,m and 54O2,m, a positive supply input terminal 54Pm, and a negative supply input terminal 54Mm. It should be noted that the subscript “n” represents an integer. Selection device 54m is not limited to being a multiplexer, but may be a switch, a plurality of switches, or the like.
Supply input terminal 54Pm is connected to an input of IFH circuit 26m and to output 54O2,m through a switch 62m. IFH circuit 26m is coupled to supply node 32m for receiving source of operating potential VCCEm, and to supply input terminal 54Pm, which serves as a local ground. Supply input terminal 32m is connected to an input of IFH circuit 26m and to output 54O1,m through a switch 63m. Output 54O2,m is connected to an input of a gain stage 64m through a switch 66m and to a source of operating potential such as, for example, ground through a switch 70m, i.e., output 54O2,m is switchably coupled to the input of gain stage 64m through switch 66m and to the source of operating potential through switch 70m. Output 54O1,m is connected to another input of gain stage 64m through a switch 68m, i.e., output 54O1,m is switchably connected to the other input of gain stage 64m. An output of gain stage 64m is connected to an input of an analog-to-digital converter (ADC)72m. By way of example, gain stage 64m is an operational amplifier having an inverting input, a non-inverting input, and an output. Thus, output 54O2,m is switchably connected to the inverting input of operational amplifier 64m, output 54O1,m is switchably connected to the non-inverting input of operational amplifier 64m, and the output of operational amplifier 64m is connected to an input of an analog-to-digital converter (ADC)72m. One or more outputs 72q of ADC72m is connected to one or more corresponding inputs of logic circuit 30m. By way of example, ADC72m is a 10 bit analog-to-digital converter and therefore has ten outputs 72q coupled to corresponding inputs of logic circuit 30m. ADC72m generates measurement results that appear at outputs 72q. A control input of ADC72m is coupled for receiving a source of operating potential such as, for example VCCm. A voltage regulator 76m has an input coupled for receiving a reference potential or voltage reference VREFm from a reference voltage source 75m, an input coupled to supply input terminal 54Pm for receiving another source of operating potential VPP, and an input coupled for receiving a source of operating potential such as, for example, ground, at input 54Mm. The output of voltage regulator 76m, i.e., supply VCCm, is commonly connected to the reference input of ADC72m and as a supply of IFL circuit 28m. Source of operating potential VCCm, i.e., supply VCCm, is derived from reference voltage VREFm. It should be noted that reference voltage source 75m serves as a voltage reference and the output of voltage regulator 76m serves as supply output VCCm and as a supply and a reference for ADC72m. Supply VCCm also serves as a supply input for battery monitor control unit 16m−1. Preferably, an external capacitor 77m is coupled between supply VCCm and node 54Mm to stabilize supply voltage VCCm. A capacitor 78m has a terminal connected to node 36m and a terminal connected to node 38m. Nodes 36m and 38m are also referred to as stabilization nodes or ports.
In accordance with an embodiment of the present invention, multiplexer 54m comprises a switch 800,m having a terminal that serves as input 54I0,m and a terminal connected to output 54O1,m and a switch 80(n+1),m having a terminal that serves as input 54I(n+1),m and a terminal connected to output 54O2,m. In addition, multiplexer 54m includes a switch 801,m having a terminal that serves as input 54I1,m, a terminal connected to output 54O1,m and a terminal connected to output 54O2,m, a switch 802,m having a terminal that serves as input 54I2,m, a terminal connected to output 54O1,m and a terminal connected to output 54O2,m, a switch 803,m having a terminal that serves as input 54I3,m, a terminal connected to output 54O1,m and a terminal connected to output 54O2,m, . . . , a switch 80(n−1),m having a terminal that serves as input 54I(n−1),m, a terminal connected to output 54O1,m and a terminal connected to output 54O2,m, and a switch 80n,m having a terminal that serves as input 54In,m, a terminal connected to output 54O1,m and a terminal connected to output 54O2,m. By way of example, switches 800,m and 80(n+1),m are single pole single throw switches and switches 801,m, . . . , 80n,m are single pole double throw switches.
Briefly referring to FIG. 7, an alternative switch network 80A suitable for use in multiplexer 54m is illustrated. In accordance with embodiments of the present invention, switches 800,m, 801,m, 802,m, . . . , 80(n−1),m, 80n,m, 80(n−1),m can be replaced with switching network 80A. Switching network 80A comprises switches 226 and 236 where terminals of switches 226 and 236 are connected to inputs 54I0,m, 54I1,m, 54I2,m, . . . , 54I(n−1),m, 54In,m, 54I(n+1),m. The other terminal of switch 226 is connected to terminals of switches 228 and 230. The other terminal of switch 228 is connected to output 54O1,m and the other terminal of switch 230 is connected to terminal 54Mm. The other terminal of switch 236 is connected to terminals of switches 238 and 240. The other terminal of switch 238 is connected to output 54O2,m and the other terminal of switch 240 is connected to terminal 54Mm. Switches 226, 228 and 230 are used to connect the top-side of the cell 20n,m to be measured. The connection for cell 20n,m from 54I(n−1),m to 54O1,m is valid when switches 226 and 228 are closed and switch 230 is open. The connection is broken when switches 226 and 228 are open and the switch 230 is closed to 54Mm. No cross-coupling through the open-switches 226 or 228 will influence input 54I(n−1),m or output 54O1,m because any cross-coupling through the switches 226 or 228 is shorted too 54Mm. Switches 236, 238 and 240 are used to connect the bottom-side of the cell 20n,m to be measured. The connection for cell 20n,m from 54In,m to 54O2,m is valid when switches 236 and 238 are closed and switch 240 is open. The connection is broken when switches 236 and 238 are open and the switch 240 is closed to 54Mm. No cross-coupling through the open-switches 236 or 238 will influence input 54I(n−1),m or output 54O1,m because any cross-coupling through the switches 226 or 228 is shorted too 54Mm.
In addition, FIG. 1 illustrates a battery unit 20m which comprises a series connected plurality of battery cells 201,m, 202,m, 203,m, . . . , 20(n−1),m, 20n,m, 20(n+1),m. More particularly, a positive terminal of battery cell 201,m is coupled to input 54I0,m through a resistor 860,m, a positive terminal of battery cell 202,m and a negative terminal of battery cell 201,m are commonly coupled to input 54I1,m through a resistor 861,m, a positive terminal of battery cell 203,m and a negative terminal of battery cell 202,m are commonly coupled to input 54I2,m through a resistor 862,m, a negative terminal of battery cell 203,m is coupled to input 54I3,m through a resistor 863,m, . . . , a positive terminal of battery cell 20n,m and a negative terminal of battery cell 20(n−1),m are commonly coupled to input 54I(n−1),m through a resistor 86(n−1), a positive terminal of battery cell 20(n+1),m and a negative terminal of battery cell 20n,m are commonly coupled to input 54In,m through a resistor 86n,m, and a negative terminal of battery cell 20(n+1),m is coupled to input 54Im,(n+1) through a resistor 86(n+1),m. A capacitor 881,m has a terminal connected to input 54I0,m and a terminal connected to input 54I1,m, a capacitor 882,m has a terminal connected to input 54I1,m and a terminal connected to input 54I2,m, a capacitor 883,m has a terminal connected to input 54I2,m and a terminal connected to input 54I3,m . . . , a capacitor 88(n−1),m has a terminal connected to input 54I(n−1),m, a capacitor 88n,m has a terminal connected to input 54I(n−1),m and a terminal connected to input 54In,m, and a capacitor 88(n+1),m has a terminal connected to input 54In,m and a terminal connected to input 54I(n+1),m. A capacitor 90m has a positive terminal connected to supply input terminal 54Pm and a negative terminal connected to supply input terminal 54Mm. Resistors 860,m, 861,m, . . . , 86(n−1),m, 86n,m, 86(n+1),m cooperate with corresponding capacitors 881,m, 882,m, . . . , 88(n−1),m, 88n,m, 88(n+1),m to filter any signal noise that may occur at inputs 54I0,m, 54I1,m, . . . , 54I(n−1),m, 54In,m, 54I (n+1),m. It should be noted that resistors 860,m, 861,m, . . . , 86(n−1),m, 86n,m, 86(n+1),m and capacitors 881,m, 882,m, . . . , 88(n−1),m, 88n,m, 88(n+1),m may also be connected in different configurations as long as they filter the signal noise and protect inputs 54I0,m, 54I1,m, . . . , 54I(n−1),m, 54In,m, 54I(n+1),m against voltage transients that could damage input circuitry.
FIGS. 2A, 2B, and 2C are a schematic diagram of a battery system 10 having battery terminals 12 and 14. For the sake of clarity, battery system 10 has been drawn on three separate sheets where reference characters “A,” “B,” and “C” have been appended to reference character “2” to distinguish the sheets. It should be noted that FIGS. 2A, 2B, and 2C are intended to be viewed together. Battery system 10 is comprised of a plurality of local battery modules 22m in which battery monitor control units 16m are coupled in a daisy-chain configuration to a controller 100. It should be noted that the daisy-chain configuration is realized by connecting a data or data input/output node 34m to a succeeding data or data input/output node 44m. The daisy-chain connection will be further described below. What is shown in FIGS. 2A, 2B, and 2C are battery monitor control units 161, 162, . . . , 16m connected to battery units 201, 202, . . . , 20m, respectively. As previously discussed, battery monitor control units 16m are coupled to corresponding battery units 20m to form local battery control modules 22m. Thus, battery monitor control unit 161 is coupled to battery unit 201 to form a local battery module 221, battery monitor control unit 162 is coupled to battery unit 202 to form a local battery module 222, . . . , and battery monitor control unit 16m is coupled to battery unit 20m to form a local battery module 22m. Battery monitor control units 161, 162, . . . , 16m and corresponding battery units 201, 202, . . . , 20m are not limited to being directly adjacent to each other. Accordingly, battery monitor control units 161, 162, . . . , 16m may be on one or more Printed Circuit Boards (PCBs), while battery units 201, 202, . . . , 20m may be close to the PCB containing the corresponding battery monitor control units 161, 162, . . . , 16m. For example, battery monitor control unit 161 may be on one PCB with battery unit 201 near battery monitor unit 161 whereas battery control unit 16m may be on a different PCB with battery unit 20m near battery monitor unit 16m. It should be noted that FIGS. 2A, 2B, and 2C illustrate a plurality of battery monitor control units 16m coupled together and a plurality of battery units 20m coupled to corresponding battery monitor control units 16m in a daisy-chain configuration, whereas FIG. 1 illustrates a single battery monitor control unit 16m to which a single battery unit 20m is connected. It should be noted that subcripts m and n have been included in FIGS. 1 and 2 to distinguish the circuit elements of battery monitor control units 16m from each other and to distinguish the circuit elements of battery units 20m from each other.
Still referring to FIG. 2, a main controller 100 is connected to battery monitor control unit 161. Main controller 100 has an ADC102 coupled to VCC input 421 through a gain stage 103 and a data node 104 connected to data node 441 of battery monitor control unit 161. An input 106 of main controller 100 is connected to battery terminal 14 of battery unit 201. Terminal 14 is coupled for receiving a source of operating potential such as, for example, ground, which serves as a local ground. An external reference voltage 108 for providing a reference voltage VREF is connected to main controller 100.
In operation, battery monitor control unit 161 and controller 100 communicate with each other through data nodes 441 and 104. Because battery monitor control unit 161 and controller 100 are connected in a daisy-chain configuration that is bidirectional, controller 100 can send data to or receive data from battery monitor control units 161, . . . , 16m. Controller 100 is capable of sending data to or receiving data from selected battery monitor control units 161, . . . , 16m. In accordance with an embodiment, controller 100 assigns addresses for the battery monitor control units 161, . . . , 16m at initialization. Accordingly, at start-up, addresses are not assigned to battery monitor control units 161, . . . , 16m. Controller 100 communicates with battery monitor control unit 161, i.e., the battery monitor control unit to which it is directly connected, and assigns it an address. Thus, battery monitor control unit 161 serves as a slave. Once battery monitor control unit 161 has an address, controller 100 allows it to send a command to the next battery monitor control unit and controller 100 assigns an address to this battery monitor control unit. Once this second battery monitor control unit has received an address, the communication to the next battery monitor control unit is enabled. Controller 100 continues this process until all the battery monitor control units are enabled. After controller 100 assigns the addresses, it can communicate with each of battery monitor control units 161, . . . , 16m. The daisy chain connection through data nodes 441 and 104 can be a single connection for single ended communication, two connections for differential communication, or a serial peripheral interface (SPI), or the like. Differential communication permits communication at higher baud rates with a more acceptable electromagnetic emission than can be achieved with single ended communication.
Controller 100 instructs battery monitor control unit 161 to measure the voltages of cells 201,1, . . . , 20(n−1),1, 20n,1, 20(n+1),1. In response to the instructions from controller 100, logic circuit 301 actuates switches 800,1, . . . 80(n−1),1, 80n,1, 20(n+1),1 of multiplexer 541 so that the voltage across the desired cell can be measured, i.e., switches 800,1, . . . , 80(n−1),1, 80n,1, 80(n+1),1 are set to select a pair of input nodes 54I0,1, 54I1,1, . . . , 54I(n−1),1, 54In,1, 54I(n+1),1 which are connected to the desired cell to be measured. For example, to measure cell 202,2 of battery unit 202, ports 54I1,1, and 54I2,1 are selected as inputs. Capacitor 782 charges to the potential of the cell under test. Once capacitor 782 is charged, multiplexer 542 is opened and capacitor 782 floats. Logic circuit 302 closes switches 682, 662, and 702 thereby applying the voltage that is across capacitor 782 as an input to gain stage 642. The output of gain stage 642 is applied to ADC722, which uses voltage VCC2 as a reference voltage. ADC722 generates an output signal that is a digital value of the voltage for cell 202,2 and serves as the measurement data. Typically, battery monitor control units 161, . . . , 16m take measurements in a cyclic fashion and store the data in corresponding storage elements until controller 100 requests the information. The data is stored in storage elements (not shown) that form portions of logic circuits 301, . . . , 30m. Alternatively, the measurement data can be transferred directly to controller 100. In a next cycle, capacitor 782 is charged to the voltage of another cell under test, e.g., one of cells 201,2, 203,2, . . . , 20(n+1),2. It should be noted that the next measurement can be performed without discharging capacitor 782 and that the desirable charging of capacitor 782 can be achieved by adding extra diagnostics to ensure that none of pins 54I2,n are open or floating. Typically, controller 100 causes the cells of a battery unit 20m to be measured in a sequence such that the first cell measured is between pair of nodes 54I0,2 and 54I1,2 and the last cell measured is between nodes 54In,2 and 54I(n+1),2.
Switches 622 and 632 are included to measure voltage VCCE2. More generally, switches 62n and 63n are included to measure corresponding voltages VCCEm.
In accordance with embodiments of the present invention, a calibration or correction factor CORR100 for battery monitor control unit 161 can be determined using the circuit elements shown in FIG. 3. ADC102 is used to measure voltage VCC1 and the resulting correction factor is used to correct the error of battery monitor control unit 161. What is shown in FIG. 3 is ADC102 coupled for receiving an input signal from gain stage 103 and a reference voltage VREF108 from a precision external reference voltage source 108. Gain stage 103 receives a voltage VCC1 from battery monitor control unit 161 and ADC102 outputs digital values ADC102 for main controller 100. Voltage VCC1 output by voltage regulator 76m is given by Equation 1 (EQT. 1) as:

VCC1=K103*(ADC102(VREF108)/FS100)*VREF108   EQT. 1

where:

K103 is a gain factor for gain stage 103 and ADC102;
ADC102(VREF108) is the digital value for the voltage from voltage regulator 761 that is output by ADC102;
FS100 is a full scale factor for ADC102; and
VVREF108 is a reference voltage derived from precision reference voltage source 108.
Setting voltage VCC1 equal to VREF108 in EQT. 1 and solving for gain factor K103 yields EQT. 2, which is used in the calibration for ADC102.

K103=FS100/ADC102(VREF108).   EQT. 2

Substituting gain factor K103 of EQT. 2 into EQT 1 yields EQT. 3:

VCC1=(ADC102(VCC1)/ADC102(VREF108))* V(VREF108).   EQT. 3

The correction factor CORR100 is defined as the ratio of the voltage at the output of voltage regulator 761, i.e., VCC1, to the voltage at the output of reference voltage source 108, i.e., VREF108. Rearranging EQT. 3 yields EQT. 4, i.e., an equation defining correction factor CORR100:

CORR100=VCC1/VREF108=ADC102(VCC1)/ADC102(VREF108).   EQT. 4

Correction factor CORR100 is used to correct the voltages of battery cells 201,1, . . . , 20n,1 of battery monitor control unit 161.
Using the schematic shown in FIG. 4, the cell voltage V20n,1 of battery cell 20n,1 of local battery module 221 is given by EQT. 5 as:

V20n,1=K1*(ADC721(20n,1)/FS1)*VCC1   EQT. 5

where:

K1 is a gain factor for gain stage 641 and ADC721;
ADC721(20n,1) is the digital value for battery cell 20n,1 that is output by ADC721;
FS1 is a full scale factor for ADC721; and
VCC1 is a source of operating potential derived from local reference VREF1.
In the calibration process for ADC721, setting voltage V20n,1 equal to voltage VCC1 in EQT. 5 and solving for gain factor K1 yields EQT. 6:

K1=FS1/ADC721(20n,1)   EQT. 6

Substituting gain factor K1 of EQT. 6 into EQT. 5 yields EQT. 7:

V20n,1=(ADC721(20n,1)/ADC721(VCC1)*VCC1   EQT. 7

Substituting correction factor CORR100 into EQT. 7 yields EQT. 8, which gives the corrected cell voltage VCORR20n,1:

VCORR20n,1=(ADC721(20n,1)/ADC721(VCC1))*CORR100*V(VREF108).   EQT. 8

Correction factors can be determined for each battery monitor control unit 16m using the circuit elements shown in FIG. 4 and equations similar to equations 1-8. For example, a correction factor CORR1 may determined as follows:

VCC2=(ADC721(VCC2)/ADC721(VCC1))*VCC1 

where:

ADC721(VCC1) is the digital value for the voltage from voltage regulator 761 that is output by ADC721;
ADC721(VCC2) is the digital value for the voltage from voltage regulator 762 that is output by ADC721.
The correction factor CORR1 for battery monitor control unit 162 is given by EQT. 9:

CORR1=VCC2/VCC1=(ADC721(VCC2))/ADC721(VCC1)).   EQT. 9

The cell voltage V20n,2 of battery cell 20n,2 of local battery module 222 is given by EQT. 10 as:

V20n,2=(ADC722(20n,2)/ADC722(VCC2))*VCC2   EQT. 10

where:

ADC722(20n,2) is the digital value for battery cell 20n,2 that is output by ADC722; and
VCC2 is a source of operating potential derived from local reference VREF2.
Substituting correction factor CORR1 into EQT. 10 yields EQT. 11, which gives the corrected cell voltage VCORR20n,2:

VCORR20n,2=(ADC722(20n,2)/ADC722(VCC2))*CORR1*CORR100*V(VREF108)   EQT. 11

By combining all the correction factors, the measurements of all the cells are correlated with the same precision reference, i.e., voltage reference 108. Thus, corrected cell voltages VCORR20n,m are given by:

VCORR20n,m=(ADC72m(20n,m)/(ADC72m(VCCm))*CORR(m−1)* . . . *CORR2*CORR1* CORR100* V(VREF108).   EQT 12

Controller 100 applies the corresponding correction factor to the output signals of corresponding analog-to-digital converters ADC721, ADC722, . . . , ADC72m.
In a calibration step, logic circuits 30m generate control logic signals which cause battery monitor control units 16m to perform a series of measurements that include measuring zero voltages across sampling capacitors 78m and measuring local reference voltages VCCm across sampling capacitors 78m. The zero voltages across sampling capacitors 78m are used to correct voltage offset that may appear in battery control units 16m and the local reference voltage measurement, i.e., the measurement of voltages VCCm, is used to calibrate the gain of the measurement channel. The zero voltage across capacitors 78m is measured by setting the voltages at nodes 36m and 38m equal to each other and the voltage at node 38m substantially equal to a ground potential. The local voltage reference measurement is achieved by setting the voltage at node 36m substantially equal to reference voltage VCCm and the voltage at node 38m substantially equal to a ground potential. The voltages between these two points can be corrected using interpolation or through a local correction factor of ADC72m.
FIGS. 5A, 5B, and 5C are a schematic diagram of a battery system 150 in accordance with another embodiment of the present invention. For the sake of clarity, battery system 10 has been drawn on three separate sheets where reference characters “A,” “B, ” and “C” have been appended to reference character “5” to distinguish the sheets. It should be noted that FIGS. 5A, 5B, and 5C are intended to be viewed together. Like battery system 10, battery system 150 is comprised of a plurality of local battery modules in which battery monitor control units 16Am are coupled in a daisy-chain configuration to a controller. Battery monitor control units 16Am are similar to battery monitor control units 16m, except that they have additional switches and input/output nodes. Thus, battery system 150 differs from battery system 10 in that each battery monitor control unit includes a switch 154m having a terminal connected to node 54O2,m and a terminal connected to a node 160m and a switch 156m having a terminal connected to node 54O1,m and a terminal connected to a node 158m. In addition, a precision external reference voltage 164 is connected to at least one set of nodes 158m and 160m rather than to a controller 152. By way of example, precision external reference voltage 164 is connected to nodes 1582 and 1602. The battery monitor control unit 16A2 to which precision external reference voltage 164 is connected is not a limitation of the present invention. The precision external reference voltage can be connected to battery monitor control unit 16A1, 16A2, 16A3, or 16Am. Controller 152 is connected to nodes 441A and 441B through signal couplers 166 and 168, respectively.
Correction factors for battery system 150 can be determined in a fashion similar to that for determining the correction factors for battery system 10. For example, the correction factors when integer “m” is three are given in EQTS. 13-15 as:

CORR1=VCC2/VCC1=(ADC721(VCC2))/ADC721(VCC1));   EQT. 13

CORR2=VCC3/VCC2=(ADC722(VCC3))/ADC722(VCC2));   EQT. 14

CORRVREF=VCC2/VREF=(ADC722(VCC2))/ADC722(VREF)); and   EQT. 15

CORRm−1=VCCm/VCC(m−1)=ADC72m−1(VCCm))/ADC72m−1(VCC(m−1)))   EQT. 16

The corrected ADC voltage for ADC722 can be calculated in the same way as for battery system 10: The uncorrected value is given by EQT. 17 as:

V20n,2=(ADC722(20n,2)/ADC722(VCC2))*VCC2.   EQT. 17

Applying the correction factor gives EQT. 18:

VCORR20n,2=(ADC722(20n,2)/ADC722(VCC2))*CORRVREF*VREF.   EQT. 18

The corrected value for ADC721 can be obtained in the same way and is given by EQT. 19 and EQT. 20 as:

V20n,1=(ADC721(20n,1)/ADC721(VCC1))*VCC1   EQT. 19

VCORR20n,1=(ADC721(20n,1)/ADC721(VCC1))*1/CORR1*CORRVREF*V(VREF)   EQT. 20

For battery monitor control units higher than battery monitor control unit 162, the corrected values are given by EQT. 21 and EQT. 22 as:

V20n,m=(ADC72m(20n,m)/ADC72m(VCCm))*VCCm   EQT. 21

VCORR20n,m=(ADC72m(20n,m)/ADC72m(VCCm))*CORR(m−1)* . . . *CORR2*CORRVREF* V(VREF).   EQT. 22

Thus, using the different correction factors , all the measured cell voltages can be corrected towards the precision of reference voltage 164.
The number of reference voltages associated with battery monitor control units 16A1, . . . , 16Am is not a limitation of the present invention. FIG. 6 illustrates a battery system 200 in accordance with another embodiment of the present invention. What is shown in FIG. 6 is a battery system 200 that is similar to battery system 150 except that battery system 200 includes a precision external reference voltage 1651 connected to nodes 1582 and 1602 and a precision external reference voltage 1652 connected to nodes 158m and 160m. Connecting an extra external reference voltage to more than one battery monitor control unit 16Am, i.e., connecting extra external reference voltage 1651 to battery monitor control unit 16A2 and connecting extra external reference voltage 1652 to battery monitor control unit 16Am, improves the overall accuracy and provides redundancy within the battery system. It should be noted that precision external reference voltages 1651 and 1652 may be at the same voltage level or at different voltage levels.
By now it should be appreciated that a method and structure for monitoring one or more batteries have been provided. In accordance with embodiments of the present invention, an internal reference voltage is input to an internal voltage regulator which generates a low voltage local supply voltage (VCCm) that is stabilized by an external capacitor. The local supply voltage is input to another battery monitor control unit at input 32m as serves as a voltage VCCEm. The measurement of the voltage at input 32m, i.e., voltage VCCEm provides an indication of the voltage of the reference voltage used to generate the local supply voltage VVCCm. which allows for the calculation of a correction factor for each battery monitor control unit. Connecting battery monitor control units 16m in a daisy-chain configuration, i.e., the daisy-chain connection of voltages VCCm and VCCEm enables the calculation of a correction factor for each battery monitor control unit 16m within the daisy-chain. Using a precision voltage reference allows improving the absolute accuracy of the voltages within the daisy-chain. An accuracy of +/−0.2% can be achieved. Because the internal reference voltage is used as the reference for ADC's 72m, the accuracy of all the measurements carried out by ADC's 72m are directly proportional to supply voltage VCC. In addition, ADC's 72m measure voltages VCCEm, which allows for correcting of all the ADC values including that of the controller.
Although specific embodiments have been disclosed herein, it is not intended that the invention be limited to the disclosed embodiments. Those skilled in the art will recognize that modifications and variations can be made without departing from the spirit of the invention. It is intended that the invention encompass all such modifications and variations as fall within the scope of the appended claims.

## Claims

1. A method for monitoring one or more batteries, comprising:
measuring a voltage of a first cell of a first battery using a first monitoring unit to generate a first measurement result, wherein measuring the voltage of the first cell of the first battery includes using a first reference voltage and simultaneously inputting the first reference voltage and a voltage generated in response to the voltage of the first cell into a first analog-to-digital (A/D) converter;
measuring the first reference voltage using a controller to generate a second measurement result, wherein measuring the first reference voltage includes using a precise external reference voltage and simultaneously inputting the external reference voltage and a voltage generated in response to the first reference voltage into a second A/D converter, the second A/D converter in the controller; and
using the first measurement result and the second measurement result to calculate a first correction factor suitable for use in correcting a set of measurements from at least one of the first and second monitoring units.

2. The method of claim 1, further including:
measuring a voltage of a second cell of the first battery using the first monitoring unit, wherein measuring the voltage of the second cell includes using the first reference voltage; and
using the first correction factor to correct the measurement of the voltage of the second cell.

3. The method of claim 1, further including:
measuring voltages of a plurality of additional cells of the first battery using the first monitoring unit, wherein measuring the voltages of the plurality of additional cells includes using the first reference voltage; and
using the first correction factor to correct the measurements of the voltages of the plurality of cells.

4. The method of claim 1, further including:
measuring a voltage of a first cell of a second battery using a second monitoring unit to generate a third measurement result, wherein measuring the voltage of the first cell of the second battery includes using a second reference voltage;
measuring the second reference voltage using the first monitoring unit to generate a fourth measurement result; and
using the third measurement result and the fourth measurement result to calculate a second correction factor suitable for use in correcting a set of measurements from at least one of the first and second monitoring units.

5. The method of claim 4, further including using the first and second correction factors to correct the set of measurements from at least one of the first and second monitoring units.

6. The method of claim 4, further including configuring at least one of the first and second monitoring units to measure a voltage across the first cell or a group of cells.

7. The method of claim 6, further including providing a first selectable input port for coupling to an adjacent monitoring unit and that is capable of measuring a voltage that is a function of the reference voltage of the adjacent monitoring unit and providing a second selectable input port for measuring a voltage of an external reference voltage.

8. The method of claim 4, further including using the controller to calculate the first and second correction factors.

9. The method of claim 4, further including: coupling the controller to at least one of the first and second monitoring units.

10. The method of claim 4, further including:
coupling the controller to at least one of the first and second monitoring units;
coupling the first reference voltage to the first monitoring unit; and
coupling the second reference voltage to the second monitoring unit.

11. The method of claim 1, further including:
measuring a first voltage at a first node in the first monitoring unit;
measuring a second voltage at a second node in a second monitoring unit;
using the first voltage at the first node and the second voltage at the second node to calculate a second correction factor suitable for use in correcting a set of measurements from at least one of the first and second monitoring units.

12. A method for monitoring one or more batteries, comprising:
configuring at least one of a first monitoring unit and a second monitoring unit to measure a voltage across a first cell or a group of cells;
providing a selectable input port to at least one of the first and second monitoring units, the selectable input port for coupling to a controller, the controller adjacent to at least one of the first and second monitoring units;
measuring a voltage of the first cell of a first battery using the first monitoring unit to generate a first measurement result, wherein measuring the voltage of the first cell of the first battery includes using a first reference voltage and simultaneously inputting the first reference voltage and a voltage generated in response to the measured voltage of the first cell into a first analog-to-digital (A/D) converter;
measuring the first reference voltage using the controller to generate a second measurement result, wherein measuring the first reference voltage includes using a precise external reference voltage and simultaneously inputting the external reference voltage and a voltage generated in response to the first reference voltage into a second A/D converter, the second A/D converter in the controller; and
using the first measurement result and the second measurement result to calculate a first correction factor suitable for use in correcting a set of measurements from at least one of the first and second monitoring units.

13. The method of claim 12, further including:
measuring a voltage of a second cell of the first battery using the first monitoring unit, wherein measuring the voltage of the second cell includes using the first reference voltage; and
using the first correction factor to correct the measurement of the voltage of the second cell.

14. The method of claim 12, further including:
measuring voltages of a plurality of additional cells of the first battery using the first monitoring unit, wherein measuring the voltages of the plurality of additional cells includes using the first reference voltage; and
using the first correction factor to correct the measurements of the voltages of the plurality of cells.

15. The method of claim 12, further including:
measuring a voltage of a first cell of a second battery using the second monitoring unit to generate a third measurement result, wherein measuring the voltage of the first cell of the second battery includes using a second reference voltage;
measuring the second reference voltage using the first monitoring unit to generate a fourth measurement result; and
using the third measurement result and the fourth measurement result to calculate a second correction factor suitable for use in correcting a set of measurements from at least one of the first and second monitoring units.

16. A method for monitoring one or more batteries, comprising:
coupling a controller to at least one of a first monitoring unit and a second monitoring unit;
coupling a first reference voltage of the first monitoring unit to a selectable port to measure a voltage of the first reference voltage;
measuring a voltage of a first cell of a first battery using the first monitoring unit to generate a first measurement result, wherein measuring the voltage of the first cell of the first battery includes using the first reference voltage and simultaneously inputting the first reference voltage and a voltage generated in response to the measured voltage of the first cell into a first analog-to-digital (A/D) converter;
measuring the first reference voltage using the second monitoring unit to generate a second measurement result, wherein measuring the first reference voltage includes using a precise external reference voltage, and simultaneously inputting the external reference voltage and a voltage generated in response to the measured first reference voltage into a second A/D converter in the second monitoring unit; and
using the first measurement result and the second measurement result to calculate a first correction factor suitable for use in correcting a set of measurements from at least one of the first and second monitoring units.

17. The method of claim 16, further including using the controller to calculate the first correction factor.

18. The method of claim 16, further including:
measuring a voltage of a second cell of the first battery using the first monitoring unit, wherein measuring the voltage of the second cell includes using the first reference voltage; and
using the first correction factor to correct the measurement of the voltage of the second cell.

19. The method of claim 16, further including:
measuring voltages of a plurality of additional cells of the first battery using the first monitoring unit, wherein measuring the voltages of the plurality of additional cells includes using the first reference voltage; and
using the first correction factor to correct the measurements of the voltages of the plurality of cells.

20. The method of claim 16, further including:
measuring a voltage of a first cell of a second battery using the second monitoring unit to generate a third measurement result, wherein measuring the voltage of the first cell of the second battery includes using a second reference voltage;
measuring the second reference voltage using the first monitoring unit to generate a fourth measurement result; and
using the third measurement result and the fourth measurement result to calculate a second correction factor suitable for use in correcting a set of measurements from at least one of the first and second monitoring units.