U.S. patent application number 11/490348 was filed with the patent office on 2006-11-16 for method and apparatus for the continuous performance monitoring of a lead acid battery system.
Invention is credited to Robert Zaccaria.
Application Number | 20060259280 11/490348 |
Document ID | / |
Family ID | 27739990 |
Filed Date | 2006-11-16 |
United States Patent
Application |
20060259280 |
Kind Code |
A1 |
Zaccaria; Robert |
November 16, 2006 |
Method and apparatus for the continuous performance monitoring of a
lead acid battery system
Abstract
The present invention concerns a battery monitoring system for
monitoring a plurality of batteries serially connected to form a
string. The battery monitoring system includes a number of probes
connected to at least a portion of the string, a daisy chain bus
having a select channel for serially interconnecting the probes,
the bus having other, parallel channels for data communication and
power, and a system server. The probes each have a sensing module
and a communication module. The sensing module senses
characteristics of at least a portion of the string, such as
voltage or current. The communication module receives the sensed
characteristics and converts them into digital form for broadcast
to the system server over the bus. The communication module of the
probes have a memory for storing an address assigned to the
corresponding probe upon reception of an initialization signal sent
by the system server via the bus. In order to readdress all of the
probes, a reset signal is transmitted to all of the probes. The
probes clear the present address, and wait until they are selected
through the select channel. Once the probe has been selected, it
receives an address from the system server, stores the address in
its memory, acknowledges this to the system controller, and sends a
signal on the select channel to the next probe. Accordingly,
initialization of a battery monitoring system is easily performed.
The invention also lies in an interface device for use with a
battery monitoring system.
Inventors: |
Zaccaria; Robert; (St-Lin,
CA) |
Correspondence
Address: |
KENYON & KENYON LLP
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
27739990 |
Appl. No.: |
11/490348 |
Filed: |
July 19, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10626019 |
Jul 24, 2003 |
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11490348 |
Jul 19, 2006 |
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09159497 |
Sep 23, 1998 |
6611774 |
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10626019 |
Jul 24, 2003 |
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Current U.S.
Class: |
702/188 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 10/4285 20130101; H01M 10/425 20130101; H01M 10/46 20130101;
G01R 31/379 20190101; G01R 31/3648 20130101; G01R 31/396
20190101 |
Class at
Publication: |
702/188 |
International
Class: |
G06F 11/00 20060101
G06F011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 19, 1998 |
CA |
2,242,497 |
Claims
1. An interface device for interfacing at least a portion of at
least one string of batteries with a battery monitoring system,
comprising: a) at least one probe means for respectively probing
said portion of said at least one string, each of said at least one
probe means including: i) a controllable sensing means for sensing
a plurality of parameters of the corresponding portion; ii) a
communication means for communicating data to and from the
controllable sensing means, the data including control signals sent
from the battery monitoring system to the controllable sensing
means, and information signals relating to the parameters of the
corresponding portion that are selected by the control signals; and
iii) a memory for memorizing an address assigned to the
corresponding probe means upon reception of an initialization
signal sent by the battery monitoring system via the communication
means; and b) a bus for serially interconnecting the communication
means of each of said at least one probe means to the battery
monitoring system in a daisy chain manner.
2. An interface device according to claim 1, wherein: a) said
communication means includes a multiplexer, an analog to digital
converter, controller means for controlling the operation of said
probe means and optical insulation means for insulating said
communication means from said bus means; and b) said bus is a five
wire bus, where a first wire is used exclusively for addressing
purposes, a second wire is used as a broadcast in channel, a third
wire is used as a broadcast out channel, and a fourth and fifth
wires are used for supplying voltage.
3. An interface device according to claim 2, wherein: a) said
sensing means of said probe includes an AC conditioning section and
an analog front end, said analog front end being connected to said
battery terminals and to said multiplexer of said communication
means.
4. An interface device according to claim 1, wherein said probe
means are a battery performance probe, and said portion of said
string include a positive and negative terminal of a battery, and
said probe means are connected to said positive and negative
terminals of said battery.
5. An interface device according to claim 1, wherein said probe
means are a current probe, and said portion of said string include
a shunt resistor, and said probe means are connected to said shunt
resistor.
6. An interface device according to claim 1, wherein said probe
means are a rectifier voltage probe, and said portion of said
string is said string as a whole having a positive and negative
terminal, and said probe means are connected to said positive and
negative terminals of said string.
7. A battery monitoring system comprising: a) a plurality of
batteries connected in series to form at least one string of
batteries; b) a plurality of probe means for respectively probing a
portion of said at least one string, each of said probe means
including: i) a controllable sensing means for sensing a plurality
of parameters of the corresponding portion of said at least one
string; ii) a communication means for communicating data to and
from the controllable sensing means, the data including control
signals and information signals relating to the parameters of the
corresponding portion of said at least one string that are selected
by the control signal; iii) a memory for memorizing an address
assigned to the corresponding probe means upon reception of an
initialization signal; iv) a bus for serially interconnecting the
communication means of each of said at least one probe means in a
daisy chain manner; and c) a system server connected to said bus
and configured to transmit an initialization signal, to receive
respective addresses from each of said at least one probe means, to
select one of said at least one probe, to transmit control signals
to a selected one of said at least one probe and to receive
information signals relating to the characteristics of the
corresponding portion of said at least one string, memory means for
storing said information signals, calculating means for calculating
a plurality of values relating to said characteristics and alarm
means for raising an alarm when one or more of said values is
outside a predetermined range.
8. A battery monitoring system according to claim 7, wherein: a)
said communication means includes a multiplexer, an analog to
digital converter, microprocessor means for controlling the
operation of said probe means and optical insulation means for
insulating said communication means from said bus means; and b)
said bus is a five wire bus, where a first wire is used exclusively
for addressing purposes, a second wire is used as a broadcast in
channel, a third wire is used as a broadcast out channel, and a
fourth and fifth wires are used for supplying voltage.
9. A battery monitoring system according to claim 8, wherein: a)
said sensing means of said probe includes an AC conditioning
section and an analog front end, said analog front end being
connected to said portion of said string and to said multiplexer of
said communication means.
10. A battery monitoring system according to claim 7, wherein said
probe means includes at least one battery performance probe.
11. A battery monitoring system according to claim 10, wherein said
probe means further includes at least one current probe.
12. A battery monitoring system according to claim 10, wherein said
probe means further includes at least one rectifier voltage
probe.
13. A battery monitoring system comprising: a) a plurality of
batteries connected in series to form at least one string of
batteries; b) a plurality of probe means for respectively probing
one at least a portion of said at least one string, each of said
probe means including: i) a controllable sensing means for sensing
a plurality of parameters of the corresponding portion; ii) a
communication means for communicating data to and from the
controllable sensing means, the data including control signals and
information signals relating to the parameters of the corresponding
portion that are selected by the control signal; iii) a bus for
serially interconnecting the communication means of each of said at
least one probe means in a daisy chain manner; c) at least one
current injection means connected to said at least one string for
injecting a current in said at least one string upon receipt of a
control signal; and d) a system server connected to said bus and
configured to select one of said at least one probe means, to
transmit control signals to a selected one of said at least one
probe means and to receive information signals relating to the
characteristics of the corresponding portion, memory means for
storing said information signals, calculating means for calculating
a plurality of values relating to said characteristics and alarm
means for raising an alarm when one or more of said values is
outside a predetermined range, said system server being operatively
connected to said at least one current injection means for sending
a control signal to said current injection means to inject a
current in said at least one string.
14. A battery monitoring system according to claim 13, wherein said
current that is injected by said current injection means is an AC
current.
15. A battery monitoring system according to claim 13, wherein said
at least one probe means includes at least one battery performance
probe.
16. A battery monitoring system according to claim 15, wherein said
at least one probe means further includes a current probe for each
of said at least one string.
17. A battery monitoring system according to claim 16, wherein said
at least one probe means further includes a rectifier voltage probe
for each of said at least one string.
18. A method of initializing a plurality of probes in a battery
monitoring system, the battery monitoring system including: a) a
plurality of batteries connected in series to form at least one
string of batteries; b) a plurality of probe means for respectively
probing one of said plurality of batteries, each of said probe
means including: i) a controllable sensing means for sensing a
plurality of parameters of the corresponding battery; ii) a
communication means for communicating data to and from the
controllable sensing means, the data including control signals and
information signals relating to the parameters of the corresponding
battery that are selected by the control signal; iii) a memory for
memorizing an address assigned to the corresponding battery upon
reception of an initialization signal; iv) a bus for serially
interconnecting the communication means of each of said at least
one probe means in a daisy chain manner; and c) a system server
connected to said bus and configured to transmit an initialization
signal, to receive respective addresses from each of said at least
one probe means, to select one of said at least one probe, to
transmit control signals to a selected one of said at least one
probe and to receive information signals relating to the
characteristics of the corresponding battery, memory means for
storing said information signals, calculating means for calculating
a plurality of values relating to said characteristics and alarm
means for raising an alarm when one or more of said values is
outside a predetermined range; the method comprising the steps of:
a) sending an initialize request on the bus means to all probes so
that all probes erases their present address and set themselves in
listen mode; b) for each probe in each string: i) selecting a probe
by setting a low voltage on a probe select line; ii) sending from
said probe to the server an active state confirmation; iii) sending
an address to the said probe; iv) registering said address in said
probe and acknowledging said registration; v) upon receipt of said
acknowledgement, sending a signal to said probe to deselect itself
and select the next probe in the chain; and c) performing each of
said steps i) to v) for each of said probes in each of said
strings.
19. A method for measuring the impedance of a plurality of
batteries connected in series to form at least one string of
batteries, each of said batteries being provided with probe means
for measuring the voltage across each of said batteries
respectively, the method comprising the steps of: a) providing a
current injection means for each of said at least one string of
batteries; b) injecting a current in each of said strings; c)
measuring the voltage across each of said batteries; d) calculating
the impedance of each of said batteries by dividing said voltage by
said current for each of said batteries.
20. A method according to claim 19 wherein said step of injecting a
current in each of said strings includes the step of injecting an
AC current.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method and apparatus for
the continuous performance monitoring of a lead acid battery
system, and more particularly to such a method and apparatus which
is easier to install and implement and provides added
flexibility.
DESCRIPTION OF THE PRIOR ART
[0002] Lead acid batteries are a commonly used source of electrical
energy in the case when a main source, typically an AC supply line,
fails. Typically, a bank of batteries will be interconnected in a
system configuration to provide the desired voltage and power for
short term emergency situations, until the AC supply line is
re-established or until a generator can provide the necessary power
requirements. Such systems are often used as back-ups for hospital
equipment, telecommunications equipment, computer equipment,
etc.
[0003] However, battery systems represent what has been termed a
bullet approach, i.e. their performance is only truly evaluated
when they are in use. This is a considerable inconvenience, since
the reliability of the entire system is dependent on each of the
batteries. Should the battery system fail, this can lead to
considerable monetary loss, and considerable loss of service with
critical consequences, particularly in the case of hospital
equipment and telecommunications systems.
[0004] There are a number of symptoms which can be indicative of a
failed battery. Some of these symptoms can lead to entire system
failure and the requirement for premature (and costly) replacement.
One condition in particular can create a dangerous situation for
persons servicing the system or bystanders: thermal runaway.
Thermal runaway is a critical condition arising during constant
voltage charging in which the current and the internal temperature
of a battery produce a cumulative mutually reinforcing effect which
further increases them and can lead to the destruction of the
battery.
[0005] There are a number of systems and devices on the market
which provide either off-line monitoring or in service test.
Depending on the price and complexity level, each of these systems
provide a more or less comprehensive evaluation of system
performance. However, the present systems represent a relatively
complex installation process and do not, according to the
Applicant, provide continuous performance monitoring.
[0006] As an example of the present systems and the parameters
which are monitored, reference may be made to the following U.S.
patents: U.S. Pat. Nos. 4,707,795; 5,546,003; 4,916,438; 4,217,645;
5,206,578.
[0007] These systems generally provide sensing means at each
battery, connecting each sensing means to a remote monitor through
analog communication means such as a pair of copper wires and
sensing a variety of parameters for each battery. The remote
monitor or the sensing means directly perform calculations to
extract from the sensed parameters values for indicia such as
battery voltage, battery temperature, system voltage, ambient
temperature, float current, AC component of the battery voltage, AC
current component, etc. However, each of these systems describes a
complex installation process, and the installation of some of these
systems may require taking the battery system off-line during
set-up which users do not appreciate.
[0008] It is also known in the art to measure a variety of
parameters while charging, discharging, loading or using the
battery system.
[0009] One of the parameters which can be useful to measure is the
battery impedance to provide an indication of the condition of the
battery. Typically, in order to measure the impedance, a current is
imposed on the battery and the resulting voltage measured in order
to calculate the impedance since both voltage and current are
known. One such system for measuring the impedance of a plurality
of batteries (not each individual battery) is described in U.S.
Pat. No. 5,281,920. The system of this patent divides each string
of batteries into two and applies the current only to one half of
the string. The disadvantage with this system is that it is
cumbersome to install, and the voltage that is measured is done so
for the totality of the half-string, not for each individual
battery and so is the resulting value for the impedance.
[0010] Accordingly, it is desirable to continuously monitor a
battery system to provide adequate information in order to evaluate
the performance of the system and to perform preventive maintenance
on the system.
SUMMARY OF THE INVENTION
[0011] It is an object of the invention to provide an interface
device which provides adequate information between at least a
portion of a string of batteries serially connected and which can
be easily installed with a minimum of manipulation.
[0012] In accordance with the invention, this object is achieved
with an interface device for interfacing at least a portion of at
least one string of batteries with a battery monitoring system. The
interface device includes at least one probe means for respectively
probing the portion of the at least one string, each of probe means
including a controllable sensing means for sensing a plurality of
parameters of the corresponding portion, a communication means for
communicating data to and from the controllable sensing means, the
data including control signals sent from the battery monitoring
system to the controllable sensing means, and information signals
relating to the parameters of the corresponding portion that are
selected by the control signals; and a memory for memorizing an
address assigned to the corresponding probe means upon reception of
an initialization signal sent by the battery monitoring system via
the communication means. The interface device further includes a
bus for serially interconnecting the communication means of each of
the at least one probe means to the battery monitoring system in a
daisy chain manner.
[0013] The invention is also concerned with a battery monitoring
system comprising a plurality of interface devices and a system
server.
[0014] It is another object of the invention to provide a battery
monitoring system which accurately and easily measures the battery
impedance for each battery in a string of batteries. A corollary
object of the invention is to provide a method for measuring the
battery impedance of a plurality of batteries serially connected to
form at least one string of batteries.
[0015] In accordance with the invention, this other object is
achieved with a plurality of batteries connected in series to form
at least one string of batteries; a plurality of probe means for
respectively probing at least a portion of the at least one string,
each of the probe means including: a controllable sensing means for
sensing a plurality of parameters of the corresponding portion; a
communication means for communicating data to and from the
controllable sensing means, the data including control signals and
information signals relating to the parameters of the corresponding
portion that are selected by the control signal; a bus for serially
interconnecting the communication means of each of said at least
one probe means in a daisy chain manner.
[0016] The battery monitoring system also includes a current
injection means connected to the at least one string for injecting
a current in the at least one string upon receipt of a control
signal. The system is further provided with a system server
connected to the bus and configured to select one of the probe
means, to transmit control signals to a selected one of the probe
means and to receive information signals relating to the
characteristics of the corresponding portion, memory means for
storing the information signals, calculating means for calculating
a plurality of values relating to the characteristics and alarm
means for raising an alarm when one or more of the values is
outside a predetermined range. The system server is operatively
connected to the current injection means for sending a control
signal to the current injection means to inject a current in said
at least one string.
[0017] The invention further provides for a method for initializing
each probe in a battery monitoring system, and a method for
measuring the internal impedance of a battery within a string of
batteries.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] These and other objects of the present invention and its
advantages will be more easily understood after reading the
following non-restrictive description of preferred embodiments
thereof, made with reference to the following drawings in
which:
[0019] FIG. 1 is a schematic representation of a battery
performance probe according to a preferred embodiment of the
invention;
[0020] FIG. 2 is a schematic representation of a portion of a
current probe according to a preferred embodiment of the
invention;
[0021] FIG. 3 is a schematic representation of a portion of a
rectifier voltage probe according to a preferred embodiment of the
invention;
[0022] FIG. 4 is a block diagram representation of a system server
according to a preferred embodiment of the invention;
[0023] FIG. 5 is a flow chart of the method for initializing a
probe according to a preferred embodiment of the invention;
[0024] FIG. 6 is a flow chart of the method for scanning according
to a preferred embodiment of the invention;
[0025] FIG. 7 is a representation of a digital word for use in
communicating sensed information in a probe to the system
server;
[0026] FIG. 8 is a schematic representation of a discharge event
definition;
[0027] FIG. 9 is a schematic representation of a discharge event
and energy count; and
[0028] FIG. 10 is a schematic representation of a battery
monitoring system according to one configuration of the invention,
where only the serial interconnection of the select wire is
shown.
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
[0029] Traditional back-up battery systems comprise a plurality of
batteries 3 connected in series to form a string 1. A back-up
system can include more than one string 1 (although only one is
shown in FIG. 1), depending on the power requirements of the user.
Such an arrangement is well known in the prior art.
[0030] A battery monitoring system according to the present
invention basically comprises a number of interface devices
including probe means 10 and bus means 50 (shown in FIG. 1) and a
system server 100. The probe means 10 are individually connected to
a corresponding portion of a string 1 of batteries 3, and are
serially interconnected to the bus means 50, which in the preferred
embodiment of the invention is a daisy chain bus having five wires,
two of which are used for power 51, 52, one is a broadcast out 53,
one is a broadcast in 54 and one is a select 55. It should be noted
that only the select 55 wire performs the serial interconnection
(as shown in FIG. 1), and the other four wires 51-54 are a parallel
connection.
[0031] The daisy chain 50 is connected to the system server 100,
which analyses the information assembled by the probe means 10 and
is programmed to trigger alarms and log historical data, among
other functionalities.
[0032] The system according to the invention provides for
modularity, in that any number of batteries 3 in any number of
strings 1 may be monitored. Furthermore, the final configuration of
the batteries 3 to be monitored does not need to be known prior to
installation, and the system allows for additional (or less)
batteries 3 than the original configuration to be present in the
strings 1, without having to spend time and money reconfiguring the
system i.e. manually and physically addressing each of the probe
means, as will be hereinafter explained. Furthermore, the system
should not be interpreted as being limited to the parameters
hereinafter detailed, since the system is fully modular and
reconfigurable, within the end user's specifications, so that one
or a combination of parameters can be monitored.
[0033] To that effect, one of the main objects of the invention is
to provide for an interface device for interfacing at least one
battery 3 with a battery monitoring system, where each of the
interface devices is connected to a system server through a daisy
chain bus, so that upon reception of an initialize signal, each
interface device clears an address present in its memory. The
system server then sends a signal to the first interface device to
set an address and transmit the address to the system server. Once
the address is received, the system server sends a signal to the
interface to deactivate or deselect itself and send a signal to the
next interface device to be selected, and repeat the addressing
process until all interface devices have stored an address.
[0034] It should be noted that the select wire 55 is used
exclusively during the initalization phase. In broad terms, the
battery monitoring system according to the invention operates in
two modes: initialization and regular scanning. During the
initalization phase, the system server sends out a reset signal via
the broadcast out wire. This signal deselects and resets all probe
means connected to the daisy chain. Following the reset signal, the
first probe means in the chain is selected by the system server
through the select channel. The probe (already in the reset stage),
receives an address signal from the broadcast out bus and stores it
in its memory. Once the address is stored, an acknowledge message
is sent to the system server on the broadcast in channel. The probe
then de-selects itself and sends a signal of the select channel to
activate the next probe in the daisy chain. It should be noted that
the next probe is selected by the previous probe, and not by the
system server. Using this sequence, the next probe's address will
be assigned in numerical order. The system server, in this case,
controls only the probe acknowledgement coming via the broadcast in
channel. Once the last address in the chain is received, the system
server selects the first probe in the next daisy chain, if there is
one, and performs the identical steps as above.
[0035] Accordingly, the system initialization is easily performed
once all of the interface devices have been connected to a
respective portion of a string, and interconnected to a bus in a
daisy chain manner.
[0036] Following the initialization phase, the system server
switches to the regular scanning mode. The difference between the
initialization mode or phase and the regular scanning mode or phase
lies in the fact that while all the probe means are de-selected and
in listen mode, the probe means that is being selected by the
system server monitors the broadcast in channel to see if it is
being addressed. If the probe means recognizes its address, it
sends an acknowledgement signal to the system server by repeating
its address on the broadcast out channel. Following the address
acknowledgement, the probe means then transmits to the system
server the data monitored, as will be hereinafter detailed.
[0037] The invention also provides for a battery monitoring system
so interconnected.
[0038] The invention is also concerned with a battery monitoring
system for measuring the impedance of a battery, where the system
server is operatively connected to current injection means. Each
string in the battery system is provided with a corresponding
current injection means. Preferably, however, only one current
injection means are used for all of the strings present in a
battery system. When the system server sends a signal to the
current injection means, a current is fed to all of the batteries
in the string or strings simultaneously. The resulting voltage
appearing at the terminals of each of the batteries is monitored by
each interface device, and transmitted to the system server for
calculation. The system server can then calculate the impedance of
each of the batteries in each of the strings. In a preferred
embodiment, the current that is injected in each of the strings is
an AC current, and more preferably, an AC current having the shape
of a sine wave.
[0039] Each of the components of the battery system will be
hereinafter detailed separately.
Interface Devices
[0040] Referring now to FIGS. 1-3, there is shown a schematic
representation of an interface device. The interface device
basically comprises probe means and a bus. It should be noted that
each portion of a string of batteries is provided with its own
probe. Each probe has a communication module, a sensing module and
an AC module.
[0041] As contemplated by the invention, three different types of
probe means can be used with a battery system: a battery
performance probe, a current probe and a rectifier voltage probe.
It should be noted that the communication module is identical for
each of the three types of probes. It should be further noted that
the battery performance probe and the current probe are further
provided with and have identical AC modules. In fact, the
difference between the three types of probes lies only in the
portion of the sensing module that senses the various
characteristics of the portion of the string.
[0042] The communications module includes controller means, an
analog to digital converter (ADC) and multiplexer (MUX) means.
Preferably, the ADC and the MUX are integrated. The MUX has four
analog inputs, hereinafter referred to as channels 1, 2, 3 and 4,
for receiving information from the sensing module.
[0043] The controller means are connected to the daisy chain
through optical insulation means.
[0044] The sensing module has an analog front end, the analog front
end being connected to the corresponding portion of the string and
to the multiplexer of the communication means.
[0045] Each of the three types of probe means, and more
specifically, each of the sensing modules will be detailed
hereinafter.
Battery Performance Probe
[0046] The battery performance probe measures the performance of
each individual battery in the battery system, and measures the
following parameters: battery DC voltage, temperature of the
negative terminal of the battery and AC voltage drop during
impedance measurements. Accordingly, the respective portion of the
string to which the battery performance probe is connected is the
positive (PT) and negative (NT) terminals of the battery to be
monitored.
[0047] Analog Front End (or Sensing Module)
[0048] The analog front end or sensing module of the battery
performance probe includes a protection circuit consisting of a
fuse F1 and a Zener diode D1. The fuse is connected to the PT of
the battery and is preferably a Polly switch with 90 mA-hold
current. The fuse will be activated in the following cases: when a
short circuit increases the probe's input current; when the battery
voltage exceeds the Zener voltage of diode D1 (i.e. 16V); or when
the PT and NT terminals are reversed.
[0049] Such an arrangement exhausts all possible scenarios of probe
failure. In all cases, when the F1 current increases above the trip
level (200 mA), the Polly switch will heat up thereby causing the
fuse resistance to increase approximately 5 times its magnitude.
Once the failure current returns to normal operating values, the
fuse cools down and its resistance is reduced to a very small
value. Consequently, any voltage exceeding 16V is clamped to the
value of the Zener diode voltage. This is also true for a reversed
voltage, but the input voltage is now clamped to the forward
voltage value of the Zener diode.
[0050] The positive terminal of the battery is further connected to
a voltage divider network R1 and R2, which preferably divides the
input voltage by 3 in order to adjust the ADC input voltage to
match that of the battery. The division by a factor of 3 has been
chosen to fit a maximum range of battery voltages (up to 15 V DC)
to the maximum input voltage for the MUX/ADC, i.e. 5 V DC.
Preferably, since resistors R1 and R2 create an input path between
the negative and positive terminals of the battery, an additional
protection is provided by using R1 as a two-part resistance, one
created by an overrated (0.5W) power, flame-proof resistor and the
other one by a regular SMT resistor.
[0051] The voltage divider circuit is followed by a low pass filter
to eliminate high frequency components. The cut-off frequency of
this filter preferably approximately 5 Hz, which is sufficient for
most applications since the 60 Hz component (typical for industrial
applications) does not exceed 10% of its original value. The output
of the low pass filter is connected to channel 2 of the multiplexer
so that this channel monitors the DC voltage of the battery under
test.
[0052] The negative terminal of the battery is connected to a
thermal probe, the circuit of which is illustrated on FIG. 3 (the
thermal probe circuit is identical for the rectifier voltage probe
and the battery performance probe). The thermal probe includes a
thermistor R.sub.T with a 5K resistance at 25.degree. C. is used as
a thermal sensor. The resistance value of the sensor drops with
increased temperature causing voltage across the positive and
negative terminals of the battery to drop accordingly. The
combination of the resistor RP, the capacitor C4 and the resistance
R.sub.T creates a filter with cut-off frequency at approximately 33
Hz. This threshold eliminates the noise caused by the digital
signal processing switching as well as generated to the battery
during impedance measurements. The output of the thermal probe is
connected to channel 3 of the MUX so that this channel monitors the
battery's internal temperature. Since the thermistor is a
non-linear device, a lookup table is used to calculate the real
temperature. It should be noted that the repeatability of the
thermistor characteristic is better than 0.2.degree. C. for the
entire range between -10.degree. C. and 75.degree. C.
[0053] AC Conditioning Section
[0054] In order to provide accurate measurements relating to AC
components, the probe means further includes an AC conditioning
section (or AC module), to condition the peak voltage used for
calculating the internal impedance of the battery. This section
consists of an input band-pass filter, followed by a peak detector
and a low-pass filter.
[0055] The AC input to the filter section is connected via resistor
RAC, in order to protect the filter input circuitry in the case of
an internal short in the AC section. The resistor preferably has a
value of 33.2K and is preferably rated as a flame retardant 300V DC
resistor with 500 mW power dissipation. This arrangement provides
an additional protection for the input of the AC section which is
normally not protected by the fuse F1.
[0056] The input band-pass filter consisting of a resistor and
capacitor network has a center frequency set at preferably 60 Hz
with a resolution of .+-.0.1 Hz. Preferably, the 5% bandwidth is
0.3 Hz thus providing excellent attenuation of 2.sup.nd and higher
harmonics. The filter's frequency stability is achieved by
preferably using ultra stable COG-type capacitors. The DC reference
for the filter is set by the resistors at approximately 3V. Since
the amplifier is powered by the battery voltage of 12V, the filters
uses the full swing of ADC input (approximately 2V above reference
voltage). At a band-pass filter gain preferably set at 65.65, the
input AC voltage is approximately 14 mV peak to peak of RMS value
of input AC voltage. The DC reference voltage is connected to
channel 4 of the MUX via the low-pass filter with a cut-off
frequency of preferably 1.7 Hz. This voltage is used as the DC
reference, subtracted from the peak voltage.
[0057] The output of the band-pass filter is connected to a peak
detector. The diode Dp charges capacitor Cp up to peak value during
a positive peak (which is the actual value above DC reference).
During a negative peak, the capacitor is discharged via a resistor.
Since the product of the resistor and the capacitor is much larger
than 17 ms ( 1/60 Hz), the voltage drop on the capacitor is very
small during the time between two subsequent peaks. This voltage is
connected to channel 1 of the MUX via a low-pass filter with a
cut-off frequency of preferably 1.7 Hz. This low-pass filter
eliminates the ripples in the voltage caused by the discharge of
the capacitor.
[0058] It should be noted that the AC channel accuracy depends on
the sensitivity threshold of the entire AC section. Assuming a
required accuracy of 1%, at least 100 bits of the channel 1 of the
MUX must be generated. At 1.220703 resolution of the ADC converter,
the minimum input voltage has to be at least 1.3 mV of RMS value.
Practically, due to additional errors of the ADC conversion (due to
linearity, thermal drift, etc.) the minimum required input voltage
is approximately 3 mV. This number has to be used when calculating
the minimum required AC current for selection of the current
transmitter.
[0059] It is important to note that the analog section of the probe
means is powered by the tested battery voltage for 6-cell
batteries. A DC/DC up-converter must be used in the case of 1 to 3
cell batteries.
Rectifier Voltage Probe
[0060] In order to evaluate total system performance, the battery
monitoring system according to the invention can further include a
rectifier voltage probe, which is used to monitor the voltage and
performance of a single string. Accordingly, the voltage input is
considerable (can be up to 600V), and the sensing module thus is
different from the sensing module of the battery performance probe,
although the function is the same. It should however be noted that
the rectifier voltage probe does not monitor the AC components, so
that even though the circuitry may be present, it is
deactivated.
[0061] A system voltage probe, designated as RVP features single
channel input with two ranges: 600 V and 150 V. The analog front
end of the probe operates identically as with the battery
performance probe, but with a slightly different signal
conditioning circuitry (shown on FIG. 3). The R1' and R2' resistors
divide the input voltage to a level suitable for ADC conversion
(max. 5V). The input of the probe is protected by two series, high
voltage flame proof resistors (total of approximately 2 Mohms for
600V probe and 1 Mohm for 150 V). The low pass filter has a cut-off
frequency of 10 Hz to filter out any AC components in the rectifier
voltage output, and the resulting voltage is applied to channel 2
of the MUX.
[0062] The resistor R1' provides protection against eventual short
circuits inside the probe. The value of this resistor will be
dependent on the probe's range. The reliability of the protection
of the circuit is ensured by the use of two 0.5W, flame proof
resistors which make up resistor R1'. Preferably, the analog
circuitry of the probe is powered by the DC/DC converter from the
system server (as shown in FIG. 1).
[0063] As above, channel 3 of the MUX is used to perform ambient
temperature measurements. It should be noted that the thermal probe
circuit is identical for that of the battery performance probe, but
that the thermal probe is not connected to a negative terminal of a
battery, but is located outside, in order to monitor ambient
temperature.
Current Probe
[0064] The current probe is connected in series with any one string
and is used to measure the charge/discharge current, float current
and the AC component of the string current during impedance
measurements.
[0065] The current is measured through a voltage drop across a
shunt resistor. Since a standard 100 mV shunt resistor is used, the
range of the current node depends on the shunt nominal current.
Once the range of the current node is selected, the shunt voltage
conversion factor for different shunts is programmed in the
server's memory.
[0066] The same shunt resistor is used to measure charge/discharge,
float and AC current measurements. The circuitry is shown in FIG.
2.
[0067] The shunt resistor is placed in series anywhere in the
string to be monitored, and the input terminals of the current
probe are connected on either side of the shunt resistor (see FIG.
2).
[0068] The current analog front end, or sensing module, consists of
an instrumentation amplifier for a first stage of the signal
conditioning. Resistor Rg sets the amplifier gain at 12.207. Since
the ADC resolution is 1.2207 mV per bit and the shunt voltage is
100 mV, the amplifier resolution is thus 0.1 A/bit. The middle
point between charge and discharge (zero level) is set by a
reference voltage equal to 2.5000V. A charge current will increase
this value, while a discharge current will decrease this value, by
an amount proportional to the measured current.
[0069] The output signal is filtered by a low-pass filter
consisting of Rf and Cf components, and having a cut-off frequency
of 5 Hz.
[0070] The various ranges for the current node have been obtained
by calculating in the server the various conversion factors. This
type of node is used for currents up to 1500A which is the maximum
range for charge/discharge current. An additional stage of shunt
voltage is used for the float current measurements, as illustrated
in FIG. 2.
[0071] The difference lies essentially in instrumentation amplifier
gain, voltage reference and additional amplifying stage. Since the
float current has only a positive polarity, the reference voltage
is set at a lower value in order to compensate for offset voltage,
as well as to increase the range available for the relatively small
float current. The gain for the float current channel is
approximately 1000. Thus, the above mentioned principle is used for
a shunt current of up to 500 A, thereby providing a maximum
resolution of 2.3 mA/bit. As before, the last stage of the float
current channel is a low-pass filter with a cut-off frequency of 5
Hz.
[0072] The third channel of the current node measures the AC
component of the shunt current, and is used for eventual internal
impedance measurements. This channel is illustrated in FIG. 1,
since it is equivalent to the AC conditioning section of the
battery performance probe. However, since the input signal is taken
from the first stage of the instrumentation amplifier, the total
gain of the channel is 12.20703 times larger than that of the
Battery Performance node. This feature allows for the measurement
of relatively small AC components during the impedance measurement
routine.
Supply and Reference Section
[0073] The supply and reference section, although illustrated only
for the battery performance probe, is identical to each of the
three types of probes.
[0074] In order for the digital components (as well as the analog
components) to be properly powered and the reference voltages
normalized, the interface device includes a supply and reference
section. This section consists of a linear voltage regulator and a
shunt diode type reference. The linear voltage regulator uses a
standard fix 5V regulator to power the microcontroller and
optocouplers. The total output power capability is preferably in
the range of 100 mW.
[0075] The reference section uses a shunt diode voltage reference.
The precise output reference is set by a voltage divider. The +5V
reference is set with a resolution of .+-.1 mV, and is used as the
reference and for VCC for the ADC conversion.
[0076] Both supply and reference voltages use the battery's output
voltage. The minimum voltage required to supply the probe means is
7.5V, but a typical value is 13.5VDC for a fully charged battery in
float mode.
ADC Conversion Section
[0077] The ADC section for each of the three types of probes are
identical.
[0078] Since the various parameters that are measured by each of
the three types of probes produce analog values, and in order to
permit accurate calculations, the parameters must be converted into
digital values. To that effect, the probe means, as mentioned
above, include an analog-to-digital converter. The ADC is
preferably an LT1594 ADC converter, which is a four channel, 5V
micropower, 12 bits sampling converter. However, it should be
readily apparent that any other analog-to-digital converter can be
used. Since the reference voltage used is 5V, the resolution of the
converter is 1.220703 mV at the inpur of the ADC's multiplexer. The
effective resolution of the DC input (channel 2) is 3 times this
value, or 3.67 mV. For a typical value of 13.5Vdc battery voltage
in float mode, the error is approximately 0.03%. However, due to
other factors, such as temperature drift of the voltage divider,
inaccuracy of adjustments, etc., the effective error claimed for
this measurement is 0.2% for the entire range of battery voltages
(from 7.5Vdc to 15Vdc), and 0.15% for the typical range of 12 to 15
Vdc.
[0079] It should also be noted that the operation of the ADC is
controlled by the microcontroller.
Controller Means
[0080] The controller means handle the digital data processing in
the communication means, and essentially provides for communication
with the system server via the broadcast in and broadcast out
channels, controls the MUX and ADC, following the various
measurements compiles the digital word to be sent to the system
server and performs general housekeeping functions such as checksum
generation, LED control, etc.
[0081] An important feature of the controller means is that they
can listen to the broadcast in bus, and include memory means for
storing an address. At all times the controller means listen to the
broadcast in bus in order to recognize at least one of two signals:
a reset and an address. Following the reset signal, the controller
means clears the address within its memory and waits to be selected
by the select channel before responding.
[0082] Once the system is initialized and in monitoring mode, the
controller means listen to the broadcast in channel to see if its
address is on the bus.
[0083] Thus, when the controller means receive a selection signal
from the system server in the form of its address on the broadcast
in channel, the controller means generate an acknowledgement signal
and generate a MUX address to select an analog signal connected to
the input of the multiplexer. The analog signal is converted into
digital form by the ADC. The same process can be repeated for each
of the MUX channels. Alternatively, the selection signal can
include a sub-signal identifying only one channel for which a reply
is required by the system server.
[0084] The digital signal is then packaged by the controller means
into a digital word which consists of 19 hexadecimal characters as
illustrated in FIG. 7. The first two digits are the probe address,
the next three are the digital data from channel 1 of the MUX, the
next three are the digital data from channel 2 of the MUX, the next
three are the digital data from channel 3 of the MUX, the next
three are the digital data from channel 4 of the MUX, the next two
are a checksum generated by the controller means to ensure data
integrity and the last digit is representative of the probe status.
It should be noted that other formats for the digital word can be
used, and are all within the skill of a person expert in this
field.
[0085] The controller means also include a clock which is generated
by an external crystal oscillator with a resonant frequency of
preferably 4 MHz. A resistor network provides for pull-up for
incoming signals. Additional resistors can be used to provide for
current limiting features when the controller means control the
optocouplers. Another resistor is used, and its value is dependent
on the application of the probe means.
[0086] Since the probe means can be connected to different levels
of system voltage, there must be insulation means between the
processor means and the bus, preferably in the form of dual
optocouplers. Preferably, each section of the optocouplers
insulates one channel of the bus. The preferred optocouplers have
breakdown voltages of 2500V DC applied during a one second
period.
[0087] Each probe means is also preferably provided with LEDs to
inform a user on the actual status of the processor. The
configuration that has been chosen is the following: if the LED is
off, the probe is not powered or not selected and is in waiting
mode. If the LED is flashing at a frequency of approximately 2 HZ,
the probe has been resetted and is waiting to be addressed. If the
LED is off, the probe has been selected, but a response has not
been sent due to faulty conditions. Finally, if the LED is flashing
with a periodic on time of 0.5 sec, the probe is selected and
operates properly. It should also be recognized that other
configurations for visual indication of probe status can be
used.
System Server
[0088] As mentioned above, the system server provides the interface
between the probe means, system peripherals and the customer
interface. The system server collects the data monitored by the
probe means, performs digital data processing, including the
required calculations, and provides information to a user via
communications interfaces.
[0089] A block diagram of the system server is shown in FIG. 4. As
can be seen, the system server includes a central processing unit
(including memory means), communications modules for connecting
system connectors such as a local rectifier voltage probe, a local
modem or a TCM module, for connecting a bi-directional
communication port such as an RS232 port, a modem circuit for
connecting an external modem, an equipment watchdog circuit (for
indicating equipment failures). The CPU is also provided with an
auxiliary input-output driver which drives alarm relays and visual
indicators. The bus is directly connected to the CPU. The CPU
allows for customer alarm inputs, which are fully configurable.
Evidently, the system server also includes power up means and reset
means.
[0090] The system server can thus communicate with the outside
world via the RS232 port. Alternatively, the system server can be
accessed via a local computer, such as a laptop, a hand-held PC
unit including a keyboard, or a modem.
[0091] In a preferred embodiment of the system server, the CPU can
be one of two microcontrollers manufactured by Dallas
Semiconductor. The DS2252(T) model can be used for the regular
version of the system server, consisting of all of the above
functions of the system. This microcontroller is an 8051 compatible
microcontroller based on non-volatile RAM technology. This chip has
been designed for systems that need to protect memory contents from
the disclosure, so that any person attempting to tamper with its
contents will trigger the microcontroller to erase the memory
contents, or otherwise deny access thereto. Alternatively, the
DS5000(T) model can be used in reduced cost versions of the battery
monitoring system. This model however does not provide access with
a hand-held unit, nor does it support impedance measurement of each
batteries in the system. This chip is a 8051 fully compatible 8-bit
CMOS microcontroller that offers softness in all aspects of its
application. This is accomplished through the comprehensive use of
non-volatile technology to preserve its content in the absence of
Vcc.
[0092] The processor means preferably operate with a 11.0592 MHz
clock.
[0093] The system server features a standard (or monitoring) mode
of operation, and an active mode of operation. In the standard
mode, the system server performs only passive monitoring of the
system's performance. In the active mode, the server performs
monitoring as well as provides feedback to the system rectifier if
either different thermal ambient conditions are monitored, or
thermal runaway is detected.
[0094] The system server's standard mode of operation includes
system housekeeping and monitored data processing, such as
measurements, calculations, alarms and data storage. Both of these
operate simultaneously during the interrupt routine, however each
mode will be described separately.
System Housekeeping
[0095] The system housekeeping operation includes system
configuration, reset function, system initialization, equipment
failure detection, auto-call management, time keeping and database
management.
[0096] The fact that the system according to the invention is
modular requires that configuration information be provided in the
`system server`s internal memory. The configuration data includes
site identification, number of probes (up to a maximum of 255),
number of cells per battery (1 to 6), number of strings (1 to 5),
number of current probes (1 to 5--same as the number of strings),
number of battery probe means (up to 255), rectifier voltage probe
presence, ambient temperature probe presence (YES/NO), customer
alarm input activation (ON/OFF for each customer alarm input) and
buzzer status (ON/OFF). It should be noted that the above numbers
for the various types of probe means are for the preferred
embodiment of the invention, but that increased numbers, and thus
increased modularity, can easily be integrated by adding memory and
software for controlling the various additional components.
[0097] The battery monitoring system according to a preferred
embodiment of the invention can have a plurality of configurations.
In a simple configuration, as that shown in FIG. 10, the back-up
battery system comprises only one string of ten batteries. Each of
the batteries is provided with a battery performance probe. The
string is provided with a shunt resistor in series with the string,
to which is connected a current probe. The total string is also
provided with a rectifier voltage probe, in order to measure
ambient temperature and total string performance. This setup would
then have 12 probe means, all serially connected to three daisy
chains: battery daisy chain (here 10 probe means); current daisy
chain (here 1 probe means, but can be up to 5); and auxiliary daisy
chain (here RVP). The split into three daisy chains is preferable
in order to reduce the high power requirements to the output
driver. For ease of clarity, only the serial interconnection of the
select channel have been shown on FIG. 10. It should further be
readily apparent that a battery monitoring system according to the
present invention could be limited only to battery performance
probes (in order to monitor only the DC performance of each of the
batteries), or could be further provided with a current probe for
each of the strings (thereby permitting the monitoring of the
internal impedance of each of the batteries), or could be further
or alternatively provided with a rectifier voltage probe for each
of the strings, in order to monitor ambient temperature and
therefore thermal runaway.
[0098] The configuration information can be uploaded to the system
server's memory locally via a portable terminal or remotely via a
modem and a remote PC.
[0099] The reset function, which effectively clears the
configuration of the system server's memory, is performed in the
following cases: during "Power On" routine, so that each powering
up of the system first resets all probes, then re-addresses them
and verifies what equipment, if any, is connected to the RS232
port; on request by pressing the RST button provided on the system
server; and remotely via a command sent through the RS232
port--this type of reset, usually referred to as a soft reset,
resets all probes, but does not verify which equipment is connected
to the RS232 port.
[0100] Following each reset, the addresses of all of the probes are
erased and the system initialization process is performed (see FIG.
5).
[0101] The initialization process includes the following steps:
[0102] review the actual system configuration stored in the system
server's memory;
[0103] send a reset request to all probes, after which each probe
erases its address and sets itself to listen mode;
[0104] verify the number of probes connected to each input of the
server, if the verified configuration agrees with the stored
configuration, continue with initialization process;
[0105] select the first probe by setting a low voltage on the first
probe select channel;
[0106] by the probe, sending an active state confirmation to the
system server via the broadcast in channels;
[0107] if the active state confirmation is not received within a
specified time frame, of the received data is corrupted, the system
server stops the initialization process and sends a "Probe #
error--initialization fail";
[0108] if the active state confirmation is correct, the system
server sends the first address to the first probe;
[0109] the probe registers this address in its own memory and sends
an acknowledgement to the system server via the broadcast in
channels;
[0110] if the response is not received within a specified time of
the received data is corrupted, the system server stops the
initialization process and sends a "Probe # error--initialization
fail";
[0111] if the response is correct, the system server sends a
message to the probe to de-select itself and select the next probe
in the daisy chain;
[0112] the first probe de-selects itself and selects the next one
in the chain by setting a low voltage on the select channel;
[0113] repeat the steps for addressing for each subsequent probe in
each string;
[0114] after the last probe has been addressed, the system server
sends a message to the computer "server initialized successfully",
and the system server switches to regular scanning mode.
[0115] Using the above process ensures that a failed or absent
probe will be quickly identified in the chain when the response
signal is not received by the system server. In such a case, the
system server stops the initialization process and raises an alarm.
The initialization process will be halted until the problem is
fixed or a new configuration is programmed by the user.
[0116] It should be noted that the above process identifies only
nodes which communicate with the system server using the
controller's protocol. Hardware, which does not perform digital
communication, will not be identified during the initialization
process. This might result in an erroneous reading, for example a
reading of 0.degree. C. if the temperature sensor is not
present.
[0117] The regular scanning mode is performed during normal
monitoring process (if no special routine request is received), and
includes the following steps (see FIG. 6):
[0118] when the initialization has been successful, all of the
probes are de-selected and are in listen mode;
[0119] the system server sends an address of a probe to be selected
on the broadcast out channels;
[0120] the probe that recognizes its own address changes its status
to active mode;
[0121] the probe sends an acknowledgement signal via the
broadcast-in channels to the system server; the confirmation
consists of the probe's address;
[0122] if a response from the probe is not received within a
specified time frame, or the data is corrupted, the system server
stops the process and initializes the probe verification
subroutine;
[0123] once the probe is active, the local parameters are
monitored, the information is packaged into a digital word, and the
digital word is sent to the system server via the broadcast-in
channels;
[0124] if the data is not received within a specified time frame,
the system server stops the process and initializes the probe
verification subroutine;
[0125] if the received data is corrupted, the system server ignores
the digital word and continues its regular operation; however, the
information about the corrupt data is stored in the system server's
memory; if the data is corrupt three times in a row, the message
"Probe # fail" is recorded and an equipment alarm message is logged
into the alarm log;
[0126] if the received data is correct, the system server sends a
message to the probe to de-select itself and go off-line; at this
point, the digital word is processed within the system server's
processor;
[0127] the next probe's address is selected, and the process
repeats itself;
[0128] following successful data processing from all of the probes
in all of the strings, the cycle is repeated again starting with
the first probe, at whatever frequency is specified by the
user.
[0129] Equipment failure detection permits the system server to
detect hardware malfunction and report it to the user via the
Equipment Failure Alarm (EFA). Since this type of failure
practically eliminates the system from operation, the EFA alarm is
classified as Major. The EFA section of the software programmed
into the system server performs the following operations:
[0130] the system server monitors probe performance via the probe's
response on the broadcast in channels; if a response is not
received, the software stops addressing the following probes and
repeat the request for data three times approximately 1 second
apart; lack of a response during subsequent calls generates an
error message providing the address of the probe which did not
respond;
[0131] following verification of a not responding probe, the system
server selects the next address in the chain; if the failure of the
probe is due to a break in the chain, each subsequent probe will be
declared as failed; following verification of the last probe in the
chain, the system starts this operation all over again;
[0132] if the failure of a probe is due to a probe malfunction
causing it to broadcast corrupted data, the following probes will
perform correctly; the system server will scan all remaining probes
as during normal operation until it reaches a faulty probe
again;
[0133] during operation when there is a modem connected to the
system server, the controller monitors the presence of the modem on
the RS232 port; if the modem signal is lost, the system server
continues monitoring until the signal is detected again; following
signal detection, the system server sends an initialization string
to the modem in order to establish proper communication via a
telephone line, a wireless link or an optical link.
[0134] The system server also includes an auto-call function. It
can store up to three different telephone numbers each of up to 10
digits. The auto-call function is initiated by a Major Alarm. Once
this priority of the alarm is detected, the system server will
initiate the auto-call function by dialing the first telephone
number in the hierarchy. If this first number does not respond, the
second and then the third number are dialed. The system server will
retry each of the telephone numbers in order until successful
communication is established and the proper information is sent to
the remote monitoring station.
[0135] In order to properly organize the data within the database,
the system server also includes a time-keeping function, in a
proper format.
[0136] As mentioned previously, the system server stores various
events, parameters, calculations, alarms, etc. in a database. The
database record consists of the name of the event, for example
system overcharge, the actual value of the parameter over the set
point, the time of the event, the alarm priority and the alarm
status. In the preferred embodiment of the invention, the system
server's database can store up to 1500 events. Once the events are
reviewed or rewritten to a central, user database, the database can
be cleared.
[0137] After having received the digital word from a given probe,
the system server performs data processing on the information
received in order to perform a number of measurements and calculate
a plurality of values.
[0138] In broad terms, the system server will measure battery
voltage, battery temperature, system voltage, ambient temperature,
discharge numbers, float current, AC voltage of the battery and AC
current component. It should be understood that not all of these
measurements need to be performed, and that additional measurements
can be performed if so required, depending of the user's needs, and
as long as the proper combination of probe means are present in the
final configuration for the battery monitoring system. Each of
these measurements will be described separately.
[0139] Battery voltage is measured by the Battery Performance
Probe. The resolution of the measured voltage is approximately 3.6
mV. However, due to other factors such as temperature drift,
component tolerance, etc., the combined error is .+-.10 mV. Once
the battery voltage reading is sent to the system server, the
controller compares the value with a pre-set value to determine
whether an alarm should be raised if the measured value exceeds a
predetermined range. For example, the system will raise an alarm is
the battery is overcharged, undercharged or discharged. If an alarm
condition is detected, the system sets an alarm priority and the
alarm is logged into the system server's database.
[0140] Battery temperature is measured by the thermal sensor
encapsulated in the negative terminal of the Battery Performance
Probe, as mentioned above. The thermal sensor is connected to the
negative terminal of the associated battery, so that the
temperature inside the battery is transferred to the thermal
sensor. The time constant of the sensor is approximately 5 minutes,
so 1% is achieved after approximately 25 minutes in transient
conditions.
[0141] The thermal sensor, as explained previously, uses an NTC
thermistor with screened characteristics to achieve the 0.2.degree.
C. repeatability over the entire range of -10.degree. C. to
+75.degree. C. Since the thermistor has a non-linear thermal curve,
the output voltage is compared with a look-up table stored in the
system server's database (in the standard system server case), or
is calculated from an equation in the PC software case. It should
be noted that the combined error of the thermal channel is
.+-.0.5.degree. C.
[0142] The internal temperature of the battery can be displayed on
a PC screen in the direct mode of operation. Otherwise, in a data
processing mode of operation, the internal temperature is compared
with the ambient temperature. If the internal temperature exceeds
the ambient temperature by a predetermined amount, a thermal
runaway is declared, the alarm message is logged into the database
and a LED on the front of the faceplate is activated. Since a
thermal runaway will usually have assigned a Major alarm, the
system server also initiates the auto-call function.
[0143] The total system voltage is measured by the Rectifier
Voltage Probe. As explained above, there are, for the system of the
invention, two types: one to measure system voltages in the range
of 20 to 150 Vdc, and another to measure system voltages in the
range of 100 to 600 Vdc. As also mentioned above, the input of the
Rectifier Voltage Probe is protected by overrated, flame proof,
high voltage, 2 Mohm serial resistors. It should be noted that the
signal processing of the Rectifier Voltage Probe is identical to
that of the Battery Performance Probe, and that the combined error
in both cases is better than 0.1% across the entire range of the
Probe.
[0144] The voltage read by the RVP is compared with a set of
pre-programmed set points, such as system overcharge, system
undercharge, system discharge. If alarm conditions are detected, an
alarm message, along with the associated data, is logged into the
system server's database, and a LED corresponding to a pre-set
priority is activated.
[0145] In order to compare the internal battery temperature with
the ambient temperature, two different types of sensors can be
used. The first, and most simple, is the thermal sensor connected
to the RVP. This sensor will be used when all of the batteries
being monitored are located in only one area, such as when all of
the batteries are located in a single cabinet, or when an RVP
function is installed in the system server's hardware. The second,
and more complicated, can measure temperatures in up to four
different areas (convenient for submarines or other installations
where the batteries are scattered). The second alternative requires
that each thermal sensor have batteries associated therewith, so
that the proper comparisons can be made.
[0146] Since the thermal sensor is identical to that of the Battery
Performance Probe, the same signal processing is performed. In
addition to thermal runaway detection, ambient temperature is also
used to detect abnormal temperatures in the area where the
batteries are located, and this can generate an ambient temperature
alarm (for example, if the cooling system fails, since battery
reliability decreases with increased temperature--in this case,
batteries are more susceptible to thermal runaway).
[0147] Another parameter which is useful for evaluating a battery
is the discharge number count. This function measures the number of
discharges which have occurred since the initialization of the
system, or since the system has been monitored. A discharge event
is measured on the basis of the definition presented on FIG. 8.
Accordingly, a discharge event is declared when the current value
exceeds a pre-set discharge current level (event #1). As long as
the current level remains in the discharge area, no new discharges
can be declared. However, once the current crosses the zero level,
identified as the discharge cancellation point, and move into the
charging zone, the discharge number count is ready to declare the
next discharge event which will occur when the current again
crosses the discharge current level (event #2).
[0148] Preferably, the discharge events are classified into two
categories, i.e. short and long duration. The user has of course
the option of setting the period of time for the "short discharge
duration". If the duration of the discharge is less than a pre-set
value, the discharge event is accordingly logged into this category
and can be displayed on a screen accordingly. Discharges which are
longer than this pre-set value are combined with the short
discharge events in order to evaluate overall system discharge. In
a preferred embodiment of the invention, the data that is displayed
is the total number of discharges and the number of short duration
discharges.
[0149] The battery monitoring system can also include a current
probe. Another parameter that is measured is the float current.
Since the float current is measured using the same shunt resistor
as that for the charge/discharge current, the resolution is
considerably affected by the shunt. In a basic configuration (100 A
shunt), the resolution is approximately 2.7 mA/bit. If the shunt
range increases, the shunt's resistance decreases and the
resolution decreases by a proportional amount. Thus, for a 500A
shunt, the resolution is 5.5 mA/bit, whereas for a 1000A shunt, the
resolution is 10.8 mA/bit. The total range of the float current
channel is 2.5A, so that if the float current exceeds this value,
the system server's mode of operation automatically switches into
charge mode.
[0150] As also mentioned previously, each battery probe means has
associated therewith one channel to measure the AC voltage drop
across the battery. This channel is used to measure the AC voltage
following an AC current injection into the battery system. The
range of this channel is 0 to 20 mVpp, and although the
measurements of this channel are performed during every cycle of
the probe's scan, the system server will use this data only
following an impedance measurement request, triggered automatically
or manually. Otherwise, this data is ignored.
[0151] The AC current is also measured by the current probe. The AC
current signal is extracted following the first stage of current
amplification and then applied to the AC channel identical to that
of the battery probe. Further processing of the AC signal in the
current probe is done in the same manner as for the battery
performance node. The range of AC current measurements is from
0.4App to 3.5App. Although, as above, the measurement is performed
during every cycle of the probe's scan, the AC current component is
used by the system server only following an impedance measurement
request. Otherwise, this data is ignored.
[0152] The above parameters are measured by a respective probe
associated with a respective portion of a string of batteries and
then used to perform various calculations in order to evaluate
system performance, such as battery differential temperature (used
to trigger a thermal runaway alarm), battery impedance and total
energy discharged.
[0153] The battery differential temperature is calculated to
trigger a thermal runaway condition. The battery temperature,
measured by the Battery Performance Probe, is subtracted from the
battery ambient temperature. If the difference exceeds a pre-set
value, a thermal runaway condition is declared and the appropriate
alarm is raised. If the monitoring system monitors more than one
ambient temperature, in the case where the batteries are located in
more than one area, the battery differential temperature is of
course measured with respect to the associated ambient temperature,
i.e. the internal temperatures of the batteries located in cabinet
1 are compared against the ambient temperature of cabinet 1
only.
[0154] In order to perform battery impedance calculations, the
system must be equipped with current injection means, and the
system server configured accordingly. The impedance calculations
are performed periodically, such as once every 24 hours, or can be
calculated on demand following a manual request. Following an
impedance request, manual or automatic, the system stops monitoring
each probe. The current injection means inject a current,
preferably an AC current, simultaneously into each string. After
approximately 20 seconds, three subsequent samples of each of the
AC components (voltage and current) are taken and the average value
is calculated. The average components are then used to calculate
the battery impedance following Ohm's law, i.e.
Z.sub.b=V.sub.bac/I.sub.sac, where Z.sub.b is the battery
impedance, V.sub.bac is the battery voltage AC component and
I.sub.sac is the corresponding string current AC component. Since
both AC components are average peak values, the impedance is
calculated in Ohms. Each battery impedance can be displayed on a
computer screen (in the case of a manual request for measurement)
but only the values calculated automatically during regular
scanning are stored in the system server's database.
[0155] It is important to note that the impedance measurements of
each of the batteries is performed only in float conditions, so
that this section of the software is disabled when the lost current
is outside the zone defined by the discharge level and the pre-set
float current level. It should also be recognized that the
impedance values can be manipulated for graphical representation of
the battery impedance trend.
[0156] The total energy discharged is calculated when the discharge
current exceeds a pre-set discharge level, as shown in FIG. 10.
Following detection of a discharge, the energy is calculated using
the following formula:
P(kWh)=(V.sub.s.times.I.sub.s.times.T)/3600
[0157] where: P is the discharged energy in kWh with 0.1 kWh
resolution; [0158] V.sub.s is the system voltage in Volts; [0159]
I.sub.s is the system current in Amps; and [0160] T is the time
interval between subsequent samples, in seconds.
[0161] The discharge condition is detected by the polarity and
level of current. Once a discharge condition is detected, the
system server performs the following steps. A discharge condition
is declared following the last probe reading. At this time, the
system server terminates all other routines expect those required
to perform energy calculations. The serial port is cut off and
therefore no communication can be established. The system server
terminates the present cycle as soon as the data from the last
probe is read. During the customer programmable Short Discharge
Duration interval, the system server will scan only the system
voltage and current probes. Once the samples are taken, the energy
discharge is calculated with a sample rate approximately equal to
1/(t.times.(1+string number))/per second
[0162] where t is approximately 0.2 s.
[0163] In each subsequent category, the sampling interval will
equal the time of a single scan of the entire system (which is
approximately the total number of probes multiplied by 0.2 s).
[0164] Following the termination of discharge status, the
calculated discharge energy is added to the record of the
corresponding discharge category (short or long) and the discharge
count is increased by one. The number of discharges with a duration
shorter than the pre-set time interval are kept in a separate
log.
[0165] The discharge energy is calculated until the discharge
current crosses the zero level and move into the charging zone. The
energy discharged during each discharge event is added to the
previous one to create a cumulative energy discharge value for the
life of the system being monitored.
[0166] Once the measurements and calculations are performed, the
system server manages the alarms associated therewith and manages
the data so accumulated.
[0167] The following alarms will be triggered when the appropriate
conditions are met.
[0168] Cell overcharge alarm will be generated when the battery
voltage exceeds a pre-set overcharge limit multiplied by the number
of cells per battery;
[0169] Cell undercharge alarm will be triggered when the battery
voltage drops below a pre-set cell undercharge limit multiplied by
the number of cells per battery;
[0170] Cell discharge alarm will be triggered when the battery
voltage drops below a pre-set cell discharge limit multiplied by
the number of cells per battery;
[0171] System overcharge alarm will be triggered when the system
voltage exceeds a pre-set value of the system overcharge limit;
[0172] System undercharge alarm will be triggered when the system
voltage exceeds a pre-set value of the system undercharge
limit;
[0173] Ambient temperature alarm will be triggered when the
measured ambient temperature exceeds a pre-set limit;
[0174] Thermal runaway alarm will be triggered when the difference
between the internal temperature of the battery and the
corresponding ambient temperature exceeds a pre-determined
limit;
[0175] Float current alarm will be triggered when a long term
increased float current exceeds a pre-set limit;
[0176] Impedance alarm will be triggered when the impedance of a
battery increases above a pre-set threshold value;
[0177] Configurable customer alarms will be triggered when selected
values other than those previously mentioned exceed pre-determined
values;
[0178] Equipment failure alarm will be triggered when the system
server's processor fails, or any of the probes fail.
[0179] These alarms are used to inform a user about the actual
status of the battery system. In order to simplify the information
provided to the user, the preferred embodiment of the invention
classifies alarms into two categories: major and minor. The alarms
can be assigned a category by the user depending on the user's
needs.
[0180] All alarms are logged into a history log in the system
server. When the history log has been reviewed or downloaded to a
remote location, the log can be cleared.
[0181] Major and Minor alarms activate respective LEDs, or other
visual or audible signals, on the face of the system server.
Alternatively, Major alarms only can activate a visual and an
audible indicator. It is also preferable if the system server is
equipped with a modem that a Major alarm initiates the auto-call
function to report the alarm.
[0182] It should be noted that the thermal runaway alarm can be
classified as a major or a minor alarm. However, in any event, the
thermal runaway will activate a LED on the system server.
[0183] The equipment alarm is preferably assigned a major alarm
priority, since equipment failure practically eliminates any
monitoring by the system server. Again, if the system is provided
with a modem, the equipment alarm will initiate the auto-call
function.
[0184] Preferably, all the events which are defined as system
alarms are recorded in the history log using the following format:
alarm name, status (ON/OFF), location (i.e. probe number), time of
alarm and date. Preferably, the history log is organized in a
first-in first-out configuration, so that if the history log
overflows, the first alarm is removed once the new message causing
the overflow is recorded.
[0185] Thus, it can be seen that the invention lies in an interface
device for interfacing at least one battery with a battery system
monitor and to a battery system monitor incorporating the same. One
of the aspects of the invention lies in the fact that the probes
are "self-addressable", so that each time a reset of the system
occurs, the probes can be automatically re-addressed. Furthermore,
another aspect of the invention lies in the possibility to
calculate the impedance of each battery by injecting an AC current
into a whole string, and measuring the corresponding AC voltage and
current components at each battery terminals. Furthermore, the
invention also provides for methods for initializing a plurality of
probes, and for monitoring a plurality of probes in a battery
monitoring system.
[0186] It should be equally clear from the above description that
not all of the above-mentioned parameters, calculations and various
other features need to be present in each battery monitoring
system, or in each interface device. Furthermore, persons skilled
in this field will readily recognize that a number of peripherals
may be connected to the battery monitoring system, such as a
portable access/display unit, a local LED display, a personal
computer, a laptop computer or any kind of modem, or other
communications, means.
[0187] Although the present invention has been explained
hereinabove by way of a preferred embodiment thereof, it should be
pointed out that any modifications to this preferred embodiment
within the scope of the appended claims is not deemed to alter or
change the nature and scope of the present invention.
* * * * *