U.S. patent application number 13/246007 was filed with the patent office on 2012-01-26 for measuring and monitoring a power source.
This patent application is currently assigned to PHOENIX BROADBAND TECHNOLOGIES, LLC. Invention is credited to Michael L. Quelly, Joseph D. Rocci.
Application Number | 20120022817 13/246007 |
Document ID | / |
Family ID | 41201841 |
Filed Date | 2012-01-26 |
United States Patent
Application |
20120022817 |
Kind Code |
A1 |
Rocci; Joseph D. ; et
al. |
January 26, 2012 |
Measuring and Monitoring a Power Source
Abstract
The disclosed battery monitoring systems and methods may
minimize measurement errors due to noise and/or other disruptions.
The sensor may generate a pulse width modulated signal that when
applied to the battery forms an AC test signal having a defined
waveform, frequency, amplitude, and/or duration. The sensor may
measure the battery's response to the test signal. The resultant
response signal may be measured to determine the health of the
battery, including its internal admittance. The sensor may
determine an optimum frequency to test the battery by scanning a
frequency range and measuring the amount of noise present.
Inventors: |
Rocci; Joseph D.; (Lansdale,
PA) ; Quelly; Michael L.; (Quakertown, PA) |
Assignee: |
PHOENIX BROADBAND TECHNOLOGIES,
LLC
Montgomeryville
PA
|
Family ID: |
41201841 |
Appl. No.: |
13/246007 |
Filed: |
September 27, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12104126 |
Apr 16, 2008 |
8032316 |
|
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13246007 |
|
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Current U.S.
Class: |
702/63 |
Current CPC
Class: |
G01R 31/3835 20190101;
G01R 31/382 20190101; G01R 31/396 20190101; G01R 31/389 20190101;
G06F 15/00 20130101 |
Class at
Publication: |
702/63 |
International
Class: |
G01R 31/36 20060101
G01R031/36 |
Claims
1. A sensor for a battery monitoring system comprising wires
connectable to the terminals of battery to be monitored, a
processor programmed to generate a pulse width modulated signal for
application to the battery via the wires and to measure via the
wires a response signal from the battery, a memory in communication
with the processor and having stored therein a plurality of
alternating current signal data values, the pulse width modulated
signal having a duty cycle that varies in accordance with the
values stored in the memory.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No.: 12/104,126, filed Apr. 16, 2008, the
disclosure of which is hereby incorporated by reference as if set
forth in its entirety herein.
BACKGROUND
[0002] Many industries and applications use storage batteries.
Power utilities, transportation companies, alternative energy
companies, data centers, banks, office complexes, etc. use storage
batteries to backup a primary power source. For example,
communications and computing equipment in telecommunication central
offices, datacenters, and wireless network cell sites use a direct
current (DC) power source, typically -48V or -24V. Typically, the
commercial alternating current (AC) power feed that supplies a site
is converted to DC to appropriately match the requirements of the
individual equipment.
[0003] Because commercial AC power is not always reliable enough
for mission critical systems, it is common to provide backup power
in the event of a failure of the commercial feed. The backup power
is typically provided by a collection of power sources or
electrochemical batteries, known as a battery plant. The batteries
may be located within the site and coupled with power distribution
bars, to feed DC equipment, and with inverters, to feed AC
equipment. The batteries may be located within an uninterruptible
power supply (UPS). Regardless of where the batteries are located,
they are often oriented in groups, wired in series up to a required
voltage.
[0004] In order to obtain the maximum battery run-time and life
expectancy, it is necessary to perform periodic maintenance tests.
These tests are commonly performed by maintenance personnel who
travel to the remote site. Using complex and expensive equipment,
the personnel take measurements and readings from the batteries.
This work is made more difficult when the batteries are located in
areas with electromagnetic noise, such as that emitted by the
equipment being powered. In order to increase battery plant
reliability and lower maintenance costs, it is desirable to perform
these tests in a manner that minimizes measurement errors and
perhaps without the need to physically dispatch maintenance
personnel.
SUMMARY
[0005] The disclosed battery monitoring systems and methods may be
used to remotely measure the condition of one or more batteries.
The systems and methods may minimize measurement errors due to
noise and/or other disruptions, such as noise caused by related
equipment.
[0006] One or more battery monitoring sensors may be mechanically
and electrically attached to the terminal posts of the monitored
batteries. Each respective battery sensor may measure attributes of
a respective battery. The attributes may include internal
admittance, voltage, current, temperature, etc. The attributes may
be used to determine internal battery characteristics. The internal
battery characteristics may be correlated with battery performance
and/or overall battery condition.
[0007] The sensors may each generate a pulse width modulated signal
that when applied to the battery from an AC test signal having a
defined waveform, frequency, amplitude, and/or duration. The sensor
may measure the battery's response to the test signal. The
resultant response signal may be measured to determine the health
of the battery, including its internal admittance.
[0008] The sensor may determine an optimum frequency to test the
battery. The sensor may scan a frequency range and measure the
amount of noise present. The sensor may select a frequency with
little noise for testing the battery.
[0009] By testing the battery, it may be determined that the
battery is overcharged. The state of charge of individual batteries
within a string of similar batteries may be equalized by varying
the duration and regularity of the battery test process, drawing
current to effectively protecting the batteries from
overcharging.
[0010] A site control unit may be electrically attached to the
battery sensors by way of interconnection cables. The site
controller may poll one or more of the battery sensors
periodically. The poll may collect measurement data from the
sensors and/or send control commands to the sensors. The site
controller may include an network interface. The network interface
may enable connection to a general purpose data network. The site
controller may interface with software/server systems, via the data
network. The software/server systems may use the sensor information
as part of an overall battery population monitoring and management
program.
[0011] The disclosed measurement systems and methods provide a
range of measurement types, able to adapt the measurement device to
a wide range of battery types. The disclosed system provides
improved accuracy in a simplified and reproducible digital
implementation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 depicts an example battery monitoring system.
[0013] FIG. 2 depicts an example circuit diagram of battery model
test circuit.
[0014] FIG. 3 depicts an example circuit diagram of an example
battery sensor.
[0015] FIGS. 4A & 4B depict an example sinusoidal signal and a
corresponding pulse width modulated signal, respectively.
[0016] FIG. 5 depicts a signal trace of an example pulse width
modulated test signal.
[0017] FIG. 6 depicts an example excitation signal, as measured
from a battery under test.
[0018] FIG. 7 depicts an example filtered excitation signal.
[0019] FIG. 8 depicts an example timing diagram for sampling.
[0020] FIG. 9 depicts an example flow chart for testing an internal
characteristic of a battery.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0021] FIG. 1 depicts a battery monitoring system. One or more
battery monitoring sensors 105A-B may be mechanically and
electrically attached to the terminal posts of the monitored
batteries 107A-B. Each respective battery sensor 105A-B may measure
attributes of a respective battery 107A-B. The attributes may
include the internal admittance (i.e., the inverse of impedance),
the voltage, the current, the temperature, etc.
[0022] A site control unit 102 may be electrically attached to the
battery sensors 105A-B by way of interconnection cables 102A-B. The
site control unit 102 may be connected to the battery sensors
105A-B via a wireless channel including radio frequency (RF),
optical, magnetic field induction, or the like. The site control
unit 102 may poll one or more of the battery sensors 105A-B
periodically. The poll may collect measurement data from the
sensors 105A-B and/or send control commands to the sensors 105A-B.
The site control unit 102 may include a network interface. The
network interface may enable connection to a general purpose data
network 101. The data network 101 may be an Internet Protocol (IP)
network, or it may use another network protocol. The data network
may employ T1, ISDN, DSL, broadband, Ethernet, WiFi, or other
transport suitable for data transfer. The site control unit 102 may
interface with software systems, via the data network 101. The
software systems may use the sensor information as part of an
overall battery population monitoring and management program. With
this system, any number of batteries 107A-B may be monitored.
[0023] As shown, two strings of batteries 107A-B may be monitored
by an exemplary remote battery monitoring system. Batteries 107A
may be connected in series to form a first battery string.
Likewise, batteries 107B may connected in series to form a second
battery string. Each battery 107A-B in each string may be connected
to a sensor unit 105A-B. Each sensor unit within the first string
107A may be interconnected via a communications cable 104A.
Likewise, each sensor unit within the second string 107B may be
interconnected via a communications cable 104B. Communications
cables 104A-B may be four-conductor telephone cables or any other
cable suitable for data transmission. Communication cables 104A-B
enable data communication between the sensor units 105A-B and a
site control unit 102. This communication may be serial and/or
parallel data communication. Strings of sensor units 105A-B may be
connected to the site control unit 102. The site control unit 102
may include a number of interfaces 103 to support many
communication cables 104A-B and, in turn, many batteries 107A-B
under test. The site control unit 102 may be connected to a data
network 101.
[0024] Each sensor unit 105A-B may test its respective battery
107A-B and may communicate data indicative of the battery's
condition (e.g., admittance, temperature, voltage, etc.) to the
site control unit 102. The site control unit 102 subsequently
performs mathematical calculations on the received data to report
metrics indicative of battery condition. The site control unit may
report the battery metrics via the data network 101. It may provide
a regular report via File Transfer Protocol (FTP), Hypertext
Transport Protocol (HTTP), and/or another protocol. It may provide
the metrics as requested or polled by a user or management system
via Simple Network Management Protocol (SNMP) and/or another
protocol. The site control unit 102 may include a web server to
display battery metrics and to receive management controls.
[0025] Each sensor unit 105A-B within a string may determine the
total voltage of the respective string of batteries 107A-B. The
site controller 102 may measure this voltage with respect to the
string of batteries' overall minus voltage. The result is an
overall voltage of the string. The site controller 102 may report
this voltage to all sensors 105A-B within the string via a
broadcast message over the communication cable 104A-B.
[0026] Each sensor 105A-B may determine its relative position
within the respective string of batteries 107A-B. Once each sensor
unit 105A-B determines its relative position within the string, it
may assume a logical address for purposes of communications with
the site controller 102. Thus, the system may identify an
individual battery from the population of batteries under test.
[0027] FIG. 2 depicts a circuit diagram of a battery model test
circuit. A simplified model of an electrochemical battery may
include an ideal voltage source (Vb 202), two significant
resistance elements (Ri 204 and Rm 206), and a capacitive element
(C 208) arranged as shown in FIG. 2. Other arrangements of Ri 204,
Rm 206, and C 208 may be used. The model as shown is commonly
called the "Randles Battery Model."
[0028] In this model, the ideal voltage source may be represented
as "Vb" 202. An equivalent internal resistance attributable to the
Vb source 202 may be represented as "Ri" 204. The resistance due to
metallic connections may be represented as "Rm" 206. The equivalent
internal capacitance may be represented as "C" 208.
[0029] For example, in practical applications of lead-acid
batteries with capacities of 100-200 ampere-hours, Ri 20 and Rm 206
combined may be valued at between about 1.0 milliohm to about 10
milliohm. Rm 206 may be approximately 45% of the total internal
resistance. Ri 204 may be attributed to current generating
limitations of the electrochemical process. Ri 204 may be
approximately 55% of total internal resistance. C 208 may be valued
at about 1.5 Farads per 100 ampere-hours of capacity. Rm 206 may be
attributed to the internal metallic connections.
[0030] Applying an AC current from an AC current source 210 of
known frequency and amplitude and observing the resultant AC
voltage developed at the battery terminals may enable a
determination of values of the parameters of the circuit model. A
sinusoidal AC test current (Itest) of known frequency and amplitude
may be applied to the battery terminals. The AC component of the
voltage developed across the battery terminals (Vt) may be a
frequency dependent function. The AC component of the voltage
developed across the battery terminals (Vt) may relate to the
values of Ri 204, Rm 206, C 208, the amplitude of the AC test
current (Itest), and the frequency of the AC test current
(Itest).
[0031] For example, at low frequencies, approaching DC, the AC
component of Vt may reach a maximum value determined by the
combined resistance of Ri 204 and Rm 206 (Rb=Ri+Rm). At high
frequencies, approaching infinity, the low reactance of capacitor C
208 may form an effective short-circuit such that Vt is primarily
determined by Rm 206. Thus, the values of Ri 204, Rm 206, and C 208
may be characterized by varying the frequency of the test signal
while observing the magnitude of the AC component of Vt.
[0032] To illustrate, in a typical lead-acid battery, this process
may be simplified by use of the following approximations:
[0033] C=1.5 F per 100 amp-hours of battery capacity
[0034] 1/(Rb)=150 mho per 100 amp-hours of battery capacity
[0035] Ri=1.25*Rm
[0036] These approximations generally scale linearly with amp-hour
capacity. These constants may be stored in memory and used to
calculate the internal battery characteristics. This linear scaling
may provide an acceptable first-order approximation of a lead-acid
battery's performance when subjected to the AC test current as
described above. The Randles circuit equivalent, shown in FIG. 2,
may be modeled with a software circuit analysis tool, SPICE for
example. In the modeling, the frequency response of Vt may be shown
to be relatively flat at frequencies below about 25 Hz and to
reduce by about 50% as the test frequency is increased to 60 Hz.
Thus, an example test frequency may include up to the 20 Hz range.
Since Ri 204, Rm 206, and C 208 vary fairly linearly with a
battery's amp-hour capacity, this generalized approach is useful
for a wide range of battery sizes.
[0037] FIG. 3 depicts a circuit diagram of an example battery
sensor 300. The sensor 300 is merely one embodiment; other circuits
that measure similar parameters are contemplated. The sensor 300
may generate a low-frequency sinusoidal test signal by using high
frequency pulse-width modulated rectangular signals to excite the
battery under test. This method may achieve a low frequency
sinusoidal test signal excitation using high-frequency rectangular
signals.
[0038] The sensor 300 may be connected to a battery 301 under test.
The positive terminal 303 of the battery 301 may be connected to a
first node of a resistive load 304 with a resistance value of Rt.
The second node of the resistive load 304 may be connected to one
contact of a switch 314. The second contact of the switch 314 may
be connected to the negative terminal 302 of the battery 301. The
switch 314 may be a single pole single throw switch and may open
and close current flow from the battery 301 across the resistive
load 304. The switch 314 may be controllable, such as a FET switch
implementation, for example.
[0039] One node of a capacitor 313 may be connected to the positive
terminal of the battery 301. The other node of the capacitor 313
may be connected to the input of a voltage amplifier 312. The
voltage amplifier 312, may amplify changes in voltage Vt measured
at the positive terminal 303 of the battery 301 with respect to the
negative terminal 302 of the battery 301.
[0040] The output of the voltage amplifier 312 may be input to a
microcontroller 310. The microcontroller 310 may be a single-chip
microcontroller, for example. The microcontroller 310 may include a
built-in analog-to-digital converter. The microcontroller 310 may
include a dual-port optically isolated serial communications
interface with a first port 308 and a second port 309.
[0041] In an embodiment, the sensor 300 may include a diode 307.
The anode side of diode 307 may be connected both to the
microcontroller 310 and the positive terminal 304 of the battery
301. The cathode side of the diode 307 may be connected both to the
microcontroller 310 and the first 308 and second 309 communications
interface ports. The diode 307 in this arrangement may provide a
summing function, such that when the sensor 400 is placed in a
string with other like sensors, the sensor 300 may determine its
position within the string.
[0042] In an embodiment, the sensor 300 may include a resistor 306
in connection with a diode 311 to measure temperature. A first node
of the resistor 306 may be connected to a voltage regulator 305. A
second node of the resistor 306 may be connected to both the
microcontroller 310 and the anode side of the diode 311. The
cathode side of the diode 311 may be connected to the negative
terminal of battery 301. In this arrangement, the DC voltage across
the diode 311 at the microcontroller may be proportional to the
battery's temperature. Other temperature sensors, such as an
electrical resistance thermometer, an infrared thermometer, a
silicon bandgap temperature sensor, a thermistor, a thermocouple, a
coulomb blockade thermometer, etc. may be used as well.
[0043] The voltage regulator 305 may provide DC power to the remote
measurement sensor 300. One node of the voltage regulator 305 may
be connected to the positive terminal 303 of the battery 301. The
other node of the voltage regulator 305 may be connected to the
temperature sensor 306, the voltage amplifier 312 and the
microcontroller 310. The voltage amplifier 312 and the
microcontroller 310 may also be connected to the negative terminal
302 of the battery 301.
[0044] The output voltage of the amplifier 312, the voltage of the
temperature sensor 306, and the voltages at both sides of the
summing diode 307 may be input to the analog-digital converter in
the microcontroller 310. Each voltage may be measured, quantified,
and used in the mathematical and logical processes of
characterizing the battery 301.
[0045] The microcontroller 310 may be programmed to activate the
switch 314. For example, the microcontroller 310 may cause a
current (Itest) to flow in the battery when the switch FET gate is
driven high. The current Itest may be determined by the battery
voltage (Vb) and the value of Rt according to the formula
Itest=Vb/Rt.
[0046] FIGS. 4A & 4B depict an example sinusoidal signal 402
and a corresponding pulse width modulated signal 404, respectively.
The microcontroller may have a stepwise approximation of a sinusoid
signal 402 stored as a lookup table in its nonvolatile memory. For
example, the stepwise approximation may include 256 points. More or
fewer points in the lookup table can be used with varying
resolution.
[0047] The microcontroller may generate a pulse width modulated
signal 404 that corresponds to the sinusoidal signal. The
microcontroller may include software or hardware to implement a
pulse width modulator (PWM). The PWM may step through the values in
the sinusoid lookup table. The microcontroller may activate the FET
switch for a time proportional to each table value.
[0048] The switch may be activated (or closed) for a time (Ton) and
then deactivated (or opened) for a time (Toff) such that the duty
cycle of the test signal varies in accordance with the stepwise
approximation. The duration of Ton and/or Toff may be determined by
the sinusoid values from the look up table. Each on-off cycle
(i.e., Ton+Toff) may have a constant time period (Tperiod). The
value Tperiod may be determined according to the desired low
frequency test sinusoid frequency (Ft) and the number of points
(Np) in the sinusoid lookup table. For example, Tperiod may be
equal to the result of 1/(Ft*Np).
[0049] FIG. 5 depicts a signal trace of an example pulse width
modulated test signal 502. The microcontroller may generate the
pulse width modulated test signal 502. The pulse width modulated
test signal 502 may have a rectangular "carrier" frequency. The
pulse width modulated test signal 502 may be pulse-width modulated
with a lower frequency sinusoidal signal. This example pulse width
modulated test signal 502 may drive the switching element S1 314,
as shown in the circuit in FIG. 3, thus applying the test signal
502 to the battery under test.
[0050] To illustrate, where Ft=20 Hz and Np=256,
Tperiod=1/(Ft*Np)=195 usec, or 5128 Hz. A 5128 Hz sinusoidally
pulse width modulated rectangular signal, if integrated, may yield
a 20 Hz sinusoid. In this illustration, the battery under test may
be excited by a rectangular signal with a peak value equal to
Itest. Because the instantaneous duty-cycle of this rectangular
pulse-train may be modulated by a 20 Hz sinusoid, the average
current of the test signal, if integrated, may vary at a 20 Hz
rate. The RC time constant of the battery itself may perform the
first part of this signal integration, and the circuitry and
software within the sensor may provide additional integration.
[0051] In an embodiment, the microcontroller can vary the frequency
of the test signal 502 by implementing a phase-increment algorithm.
In this process, a frequency variable is added to the lookup table
location pointer such that every second, third, or nth table
location is accessed. The frequency variable defines the number of
lookup table positions between each sample being output to the PWM.
As the frequency variable is increased, the frequency of the
generated signal 502 may increase.
[0052] In an embodiment, the current of the integrated sinusoidal
frequency test signal may be adjusted by consistently scaling the
values in the lookup table before they are passed to the PWM. For
example, if each table value is halved before being output to the
PWM, then the average current in the integrated sinusoidal
frequency test signal will also be halved, even though the higher
frequency peak rectangular current is fixed. Finally, the values in
the microcontroller's PWM lookup table can be altered, if desired,
in order to generate any desired waveform including sinusoid,
triangle, sawtooth, rectangular, or virtually any other test signal
which may be advantageous.
[0053] FIG. 6 depicts an example excitation signal 602, as measured
from a battery under test. The sensor may measure the excitation
signal 602, which results from the pulse width modulated test
signal having been impressed on the battery. The excitation signal
602 illustrates the AC voltage that develops across the battery
terminals as a result of the pulse-width modulated rectangular
excitation current shown in FIG. 5. At this point, the excitation
signal 602 has been partially filtered due to the RC
characteristics of the battery. The battery, owing to its behavior
as an RC equivalent circuit, provides a preliminary low-pass
filtering function which attenuates some of the high frequency
switching carrier and begins to reveal the desired low frequency
sinusoidal frequency component.
[0054] FIG. 7 depicts an example filtered excitation signal 702.
The filtered excitation signal 702 illustrates the result of fully
filtering the voltage that developed across battery. The filtered
excitation signal 702 may be measured by the microcontroller.
[0055] Further filtering inside the sensor may eliminate or
significantly reduce the residual high frequency switching
component, leaving the low frequency sinusoidal modulation
component as the primary signal to be measured. For example, the
sensor may include a high-gain amplifier that is AC coupled (e.g.,
capacitive coupled) to the battery under test. The output of the
high gain amplifier may be fed into the analog-to-digital converter
in the microcontroller for measurement.
[0056] The gain of the amplifier may be controlled by the
microcontroller so that a wide range of battery types with
differing internal resistances can be measured. For example, the
amplifier gain may be in the range of about 200 to about 1000. Also
for example, the total internal resistance Ri=(Ri+Rm) of the
battery under test may be equal to 0.005 ohm. The integrated
component of the low frequency test signal may be equal to 1 ampere
peak-to-peak. Then, the AC component of Vt may be Vt=Itest*Rb=1.0
A*0.005 ohm=5 mV peak to peak. This signal may be amplified by a
factor of 200, and the result may be a 1.0 volt peak-to-peak signal
that is fed to the analog-to-digital converter in the
microcontroller for measurement.
[0057] FIG. 8 depicts an example timing diagram for sampling.
Because the microcontroller may generate the pulse width modulated
signal point-by-point, the resultant filtered excitation signal
also may be measured point-by-point. The sensor may sample the
waveform 802 at defined sample points 804. The sample points 804
may correspond to the signal peaks and valleys. (i.e., the
alternating maximums and minimums of the filtered response signal
from the battery under test.)
[0058] The microcontroller can determine when to sample the
recovered signal at the signal peaks and valleys. Each signal peak
may be a local maximum. Each signal valley may be a local minimum.
Via a correlating synchronous sampling detection process the
microcontroller can measure the resultant waveform. Such a process
may have a bandpass amplitude response that can discriminate
against unwanted signals at frequencies that differ from the
sampling rate. The bandwidth of this bandpass response decreases as
the number of averaged samples is increased.
[0059] For example, as the microcontroller generates each point in
the digitally synthesized excitation current sinusoid, it measures
at the peaks of the resultant voltage sinusoid. The microcontroller
may make multiple measurements at the sinusoidal signal peaks
repetitively and may perform an arithmetic average of the
measurements.
[0060] Since the microcontroller is generating the pulse width
modulated test signal while simultaneously measuring the batteries
response, the microcontroller may determine when the peaks of the
amplified signal will occur and measure the precise peak-to-peak
value of the amplified Vt signal. The microcontroller may measure
the response signal in accordance with a signal value that produces
a peak. The microcontroller may be programmed to measure a
plurality (e.g., 256) positive and negative signal peaks. The
microcontroller may perform a mathematical average of the measured
values.
[0061] Although FIGS. 4A-8 show waveforms with differing scale
factors, it should be appreciated that scale factors may be set
appropriate for the type of battery being measured. For example,
the rectangular excitation waveform, as shown in FIG. 5, may switch
between zero amps and a peak excitation current appropriate for the
type of battery being measured. In typical applications, this peak
current may range from about 1-2 amps, and the frequency of the
modulating sinusoid may range from 10-30 Hz. The peak-to-peak value
of the unfiltered (e.g., as shown in FIG. 6) and fully filtered
waveform (e.g., as shown in FIG. 7) may be a function of the peak
excitation current and the internal impedance (Z) of the battery.
The value of this voltage will typically follow Ohm's Law:
Vbat=Ipeak.times.Zbat. The admittance of the battery may be
calculated as the inverse of the impedance (i.e., Zbat).
[0062] FIG. 9 depicts an example flow chart for testing an internal
characteristic of a battery. At 902, the sensor may generate a
characterization of a frequency spectrum at the battery. The sensor
may determine a frequency at which to test the battery. Generally,
in battery power-plant systems, the battery charging sub-system,
the load subsystem, and various other influences often produce
noise and other disturbances that generate interference. The sensor
may characterize the signal spectrum around the frequency where a
battery test is proposed to be made in order to determine if
background noise and interference levels are sufficiently low to
make an accurate measurement. The sensor may make frequency agile,
frequency selective measurements of AC signals.
[0063] The disclosed correlating detection process may be used by
the sensor in order to scan a range of frequencies around a
proposed measurement frequency. For example, the sensor may operate
in a receive-only mode, altering the detection sampling frequency
in a stepwise manner, making a signal measurement at each sampling
frequency. If the frequency selective detection process is run
without generating a corresponding test signal, the detection
process may measure the level of signals at the sampling frequency.
If this receive-only measurement process is repeated for multiple
frequencies within some spectral range, then a spectrum-analysis
data set is available. This spectrum analysis data set can be
analyzed to determine a frequency or for measurements that reduces
the effect of interfering signals.
[0064] After a range of frequencies are scanned and characterized
in this manner, the sensor may choose a frequency at which the
measured background noise is at a minimum and/or sufficiently low
to make the measurement. The sensor may then proceed to operate the
FET current switch to generate the test signal and make the battery
test measurements. In an embodiment, the sensor may report the
receive-only frequency point measurements to the control unit so
that the result can be displayed as a spectrum analysis display.
The sensor may report the battery test results and battery test
data to the control unit.
[0065] At 904, sensor may generate a pulse width modulated test
signal. The duty cycle of the pulse width modulated test signal may
vary in accordance with a plurality of alternating current signal
data values. For example, the plurality of alternating current
signal data values may be stored in memory as a stepwise
approximation of a sinusoidal waveform. The frequency of the
sinusoidal waveform may be selected based on the results at
902.
[0066] At 906, the battery may be excited with the pulse width
modulated test signal. For example, the sensor may apply the test
signal to the terminals of a battery under test. The sensor may
apply the signal to the battery under test concurrently with
generating the test signal. For example, the sensors may drive a
controllable switch with the test signal. The switch when closed
may drive a test current across the battery under test.
[0067] The battery may alter the test signal, producing a response
signal. The response signal may be a version of the test signal
altered due to the RC characteristics of the battery. The battery,
owing to its behavior as an RC equivalent circuit, may provide a
preliminary low-pass filtering function that attenuates some of the
high frequencies of the pulse width modulated test signal. The
resultant response signal may reveal a desired low frequency
sinusoidal frequency component. The response signal may be further
filtered by the sensor.
[0068] At 908, the response signal of the battery as excited by the
pulse width modulated test signal may be measured. The response
signal may be sampled in accordance with the generating of the test
signal. For example, the response signal may be sampled via
correlating synchronous sampling detection process. The response
signal may be measured by sampling at each peak and valley of the
response signal by the microcontroller based on the data that the
microcontroller used to generate the test signal.
[0069] Correlated detection measurement may, in effect, produce a
frequency selective, bandpass filtered, detection function on the
amplified signal. This detection function may result in the
detection of the desired signal's amplitude while rejecting the
high-frequencies generated by the sensor's PWM and other noise
sources in the battery plant system. As more measurements are
averaged the detection process may become more selective and the
measurement time may increase.
[0070] From the measurements, the microcontroller may determine the
RC characteristics of the battery. For example, the microcontroller
may determine the admittance of the battery. The microcontroller
may measure the resultant amplitude to determine the RC
characteristics of the battery including the admittance. The
admittance may be used as an indication of the health of the
battery.
[0071] At 910, it may be determined that the battery is
overcharged. If it is determined that the battery is overcharged,
current may be drawn from the battery to correct the overcharged
state. For example, the microcontroller may be used to draw current
from the battery. In an embodiment, current may be drawn from a
battery selected from a string of batteries.
[0072] The sensor may equalize the charge of an individual battery
within a monitored string of batteries. The sensor may measure the
DC terminal voltage of the battery. The sensor and/or sensors may
perform a variable charge equalization of the individual batteries
in the string, by impressing a variable current load on the
battery, which may remove charge from the battery.
[0073] The central site control unit may monitor the terminal
voltages of each battery in each string. The site controller can
determine which batteries might be overcharged and which batteries
might be undercharged. The site controller may send commands to the
sensors on the overcharged batteries instructing them to generate a
continuous programmed test current on the battery until the excess
charge is removed. In this manner, battery life may be extended
because overcharging, a leading cause of battery failure, may be
mitigated.
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