U.S. patent application number 09/838753 was filed with the patent office on 2002-10-24 for uninterruptible power supply system having an nimh or li-ion battery.
Invention is credited to Hoff, C. Michael, Nelson, James E..
Application Number | 20020153865 09/838753 |
Document ID | / |
Family ID | 25277962 |
Filed Date | 2002-10-24 |
United States Patent
Application |
20020153865 |
Kind Code |
A1 |
Nelson, James E. ; et
al. |
October 24, 2002 |
Uninterruptible power supply system having an NiMH or Li-ion
battery
Abstract
An uniterruptible power supply (UPS) system that includes one or
more NiMH or Li-ion batteries is provided. In one general aspect,
the invention features a power supply system including a power
input to receive input power from a power source, a power output to
provide output power to a load, at least one NiMH or Li-ion battery
having a battery output that provides battery power, at least one
power module coupled to the power input to receive the input power,
coupled to the battery output to receive the battery power and
coupled to the power output to provide the output power, a
controller, coupled to the at least one power module, constructed
and arranged to monitor and control the output power from the at
least one power module. A UPS system using a NiMH or Li-ion battery
typically uses less space and weigh less than a UPS having a lead
acid battery. Additionally, NiMH and Li-ion batteries perform
better at temperature extremes than do comparable lead acid
batteries.
Inventors: |
Nelson, James E.; (Salem,
NH) ; Hoff, C. Michael; (Boxborough, MA) |
Correspondence
Address: |
A. Jason Mirabito, Esq.
Mintz, Levin, Cohn, Ferris
Glovsky and Popeo, P.C.
One Financial Center
Boston
MA
02111
US
|
Family ID: |
25277962 |
Appl. No.: |
09/838753 |
Filed: |
April 19, 2001 |
Current U.S.
Class: |
320/152 ;
320/139 |
Current CPC
Class: |
H02J 9/062 20130101 |
Class at
Publication: |
320/152 ;
320/139 |
International
Class: |
H02J 007/00; H02J
007/04; H02J 007/16 |
Claims
What is claimed is:
1. A power supply system comprising: a power input to receive input
power from a power source; a power output to provide output power
to a load; at least one battery having a battery output that
provides battery power, the at least one battery being selected
from the group consisting of: nickel metal hydride and lithium ion
polymer; at least one power module coupled to the power input to
receive the input power, coupled to each battery output to receive
a power of each battery and coupled to the power output to provide
the output power; and a controller, coupled to the at least one
power module, constructed and arranged to monitor and control the
output power from the at least one power module.
2. The power supply system according to claim 1, wherein the at
least one battery is a nickel metal hydride battery.
3. The power supply system according to claim 1, wherein the at
least one battery is a lithium ion battery.
4. The power supply system according to claim 2, further comprising
means for measuring a current of the battery, wherein the
controller has program code means embodied therein for determining
a state of charge of at least one battery by monitoring the current
of at least one battery.
5. The power supply system according to claim 3, further comprising
means for measuring a current of the battery, wherein the
controller has program code means embodied therein for determining
a state of charge of the battery by monitoring the current of the
battery.
6. The power supply system according to claim 2, further comprising
means for measuring a current, a voltage and a temperature of at
least one of the nickel metal hydride batteries, wherein the
controller has program code means embodied therein for completing
the method of charging the at least one nickel metal hydride
battery, the method comprising: determining a state of charge of
the battery by monitoring the current of the battery; for between
about 0% to about 99% of a charging capacity each battery, charging
each battery at a constant current rate of between about 0.3C to
about 1C; stopping the charge of each battery if the temperature of
each battery starts to rise substantially; stopping the charge if a
temperature of each battery rises above about 40.degree. C. or
about 20.degree. C. above an ambient temperature; and applying a
trickle current to each battery such that a slight temperature
differential is achieved between each battery case and the ambient
temperature.
7. A power supply system comprising: a filter to receive and filter
input power from a power source; a rectifier coupled to the filter
at least one battery having a battery output that provides battery
power, the at least one battery being selected from the group
consisting of: nickel metal hydride and lithium ion polymer; at
least one control switch coupled to the rectifier to receive the
input power, coupled to each battery output to receive a power of
each battery and coupled to an input to provide the output power;
and a controller, coupled to the at least one control switch,
constructed and arranged to monitor and control the output power
from the at least one control switch.
8. The power supply system according to claim 7, further comprising
an inverter coupled between the at least one control switch and the
transformer, wherein the inverter is coupled to the controller.
9. The power supply system according to claim 7, wherein the at
least one battery is a nickel metal hydride battery.
10. The power supply system according to claim 7, wherein the at
least one battery is a lithium ion battery.
11. The power supply system according to claim 9, further
comprising means for measuring a current of the battery, wherein
the controller has program code means embodied therein for
determining a state of charge of the battery by monitoring the
current of the battery.
12. The power supply according to claim 11, wherein the means for
measuring a current of the battery comprises a current shunt.
13. The power supply system according to claim 10, further
comprising means for measuring a current of the battery, wherein
the controller has program code means embodied therein for
determining a remaining run time of the battery by monitoring the
current of the battery.
14. The power supply according to claim 13, wherein the means for
measuring a current of the battery comprises a current shunt.
15. The power supply system according to claim 7, wherein the
rectifier is coupled to the controller.
16. The power supply system according to claim 7, further
comprising a transformer coupled between the battery and the
output.
17. A power supply system comprising: a power input to receive
input power from a power source; a power output to provide output
power to a load; at least one battery having a battery output that
provides battery power, the at least one battery being selected
from the group consisting of: nickel metal hydride and lithium ion
polymer; at least one power module coupled to the power input to
receive the input power, coupled to each battery output to receive
a power of each battery and coupled to the power output to provide
the output power; means for measuring a current of at least one the
batteries; and a controller, coupled to the at least one power
module, constructed and arranged to monitor and control the output
power from the at least one power module, the controller having
program code means embodied therein for completing a method of
charging the at least one Nickel Metal Hydride battery, the method
comprising: for between about 0% to about 99% of a charging
capacity each battery, charging each battery at a constant current
rate of between about 0.5C to about 1C; stopping the charge of each
battery if the temperature of each battery starts to rise
substantially; stopping the charge if a temperature of each battery
rises above about 40.degree. C. or about 20.degree. C. over an
ambient temperature; and applying a trickle current to each battery
such that a slight temperature differential is achieved between
each battery case and the ambient temperature.
18. A method of charging at least one Nickel Metal Hydride battery
in an uninterruptible power supply system having at least one power
module coupled to a power input to receive input power, coupled to
each battery output to receive power from each battery and coupled
to a power output to provide output power to a load, and a
controller, coupled to the at least one power module, constructed
and arranged to monitor and control the output power from the at
least one power module, the method comprising: measuring a current
of each battery; for between about 0% to about 99% of a charging
capacity each battery, applying a current to each battery to charge
each battery at a constant current rate of between about 0.5C to
about 1C; stopping the applied current of each battery if the
temperature of each battery starts to rise substantially; stopping
the applied current if a temperature of each battery rises above
about 40.degree. C. or above 20.degree. C. over an ambient
temperature; and applying a trickle current to each battery such
that a slight temperature differential is achieved between each
battery case and the ambient temperature.
Description
FIELD OF THE INVENTION
[0001] The present application relates generally to an apparatus
for providing uninterruptible, regulated power to critical and/or
sensitive loads. More specifically, the present application relates
to providing battery power for an uninterruptible power supply
(UPS) to ensure power system availability for critical and/or
sensitive loads.
BACKGROUND OF THE INVENTION
[0002] The use of uninterruptible power supplies having battery
back-up systems to provide regulated, uninterrupted power for
critical and/or sensitive loads, such as computer systems, and
other data processing systems is well known. Typically, most UPS
systems use some type of lead acid battery to provide back-up
power. Lead acid batteries, however, have performance limitations
especially when they are discharged well above their rated rates or
when they are operated at temperature extremes.
SUMMARY OF THE INVENTION
[0003] The uninterruptible power supply (UPS) system of the present
application includes one or more NiMH or Li-ion batteries. NiMH and
Li-ion battery chemistries are desirable because they are
respectively about 2 and 5 times volumetrically and gravimetrically
more energy dense than an equivalent lead-acid battery that is
typically used in a UPS. Thus, the size of an NiMH or a Li-ion
battery is much smaller and lighter than a similarly performing
lead acid battery and makes the product into which it is installed
more attractive, versatile and useful to customers. The extra
volume required by similarly performing lead acid batteries
typically requires extra floor space and costly hardware to install
the batteries.
[0004] Another advantage of both NiMH and Li-ion batteries is that
they are relatively temperature immune. Their performance suffers
little at the extremes of the lead acid limits, and their lifetime
is not affected as dramatically by temperature as are lead acid
batteries. It has been estimated that NiMH battery life times are
around 10-15 years. Lead acid batteries can be designed to last
similarly long, but compromise their energy density doing so.
[0005] In one general aspect, the invention features a power supply
system including a power input to receive input power from a power
source, a power output to provide output power to a load, at least
one NiMH or Li-ion battery having a battery output that provides
battery power, at least one power module coupled to the power input
to receive the input power, coupled to the battery output to
receive the battery power and coupled to the power output to
provide the output power, a controller, coupled to the at least one
power module, constructed and arranged to monitor and control the
output power from the at least one power module.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a block diagram of a UPS system having a NiMH or a
Li-ion battery in accordance with the invention.
[0007] FIG. 2 is a block diagram of another embodiment of a UPS
system having a NiMH or a Li-ion battery in accordance with the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0008] One embodiment of the present invention is directed to an
uninterruptible power supply (UPS) system that includes one or more
NiMH or Li-ion batteries. Both NiMH and Li-ion battery chemistries
are more energy dense than an equivalency rated lead acid battery
chemistry. Thus, an NiMH or Li-ion battery typically uses less
space than a comparable lead acid battery. Additionally, NiMH and
Li-ion batteries perform better at temperature extremes than do
comparable lead acid batteries.
[0009] The NiMH battery chemistry is about 2 times more
volumetrically and gravimetrically dense than the equivalent
lead-acid battery as typically used in a UPS. For example, a 7AH
NiMH battery can deliver 6 ampere-hours of current-time when
discharged at 10 times its rated rate (C) or when it is discharged
in 6 minutes. A high rate 18 ampere-hour lead acid battery can
deliver the same energy as the example above, but the comparable
battery can take up more than twice the volume.
[0010] In an embodiment of the present invention, prior art UPS
systems have been modified to include an NiMH battery rather than a
lead acid battery. The power processing and control electronics of
the UPS have been modified to accept a wider battery voltage range
and have been selected to withstand higher charging voltages. The
voltage gain components have been selected to deal with the lower
discharge voltages.
[0011] Additionally, a controller's algorithm to detect the state
of charge of the battery may be different for the NiMH battery than
that used for a lead-acid battery. Because NiMH batteries have very
flat voltage discharge curves, an NiMH battery's output voltage is
an inaccurate gauge to determinate the remaining charge in the
battery. Therefore, a current measuring device is preferably used
such that the UPS microprocessor controller can calculate the state
of charge of the batteries during charge, discharge and standby
modes.
[0012] As an example, a NiMH battery has been retrofitted in a
Legacy UPS system manufactured by the American Power Conversion,
Corp. by making the following changes. The SLA batteries in the
Legacy model have been retrofitted with one or more NiMH batteries
that collectively have a 25% higher nominal voltage. For example, a
24V SLA system was replaced by 25 1.2V cells coupled together in
series to create a 30V NiMH system. If a plurality of NiMH
batteries are used in parallel, it is necessary that the batteries
have equivalent voltage ratings.
[0013] The voltage rating on all the Legacy UPS electrical
components connected to the DC bus are increased to accommodate the
higher charging voltages of the NiMH batteries. It is sufficient to
increase the voltage rating of the DC connected components in the
Legacy UPS by at least 25% (corresponding to the higher charging
voltages).
[0014] In an embodiment of the invention, the one or more NiMH
batteries retrofitted in the Legacy system have been charged
according to a method different than that typically used for lead
acid batteries. For example, for about 0-99% of the charging
capacity of the batteries, the batteries are charged at a constant
current rate of between about 0.3C to about 1C*. The fast charge of
one or more batteries is stopped when the temperature of the
batteries starts to rise substantially, exceeds 40.degree. C. or
exceeds 20.degree. C. above the ambient temperature. After the fast
charge of the batteries is stopped, one or more batteries are
"float" charged by applying a trickle current to achieve a slight
positive temperature differential between the battery cases to the
ambient temperature. This procedure keeps overcharging of the
batteries to a minimum, yet adequately compensates for the loss of
charge due to internal self-discharge. *NOTE C is a constant equal
to the AH rating of the battery in Amps. e g C for a 7AH battery is
7 Amps.
[0015] In another embodiment of the present invention, prior art
UPS systems have been modified to include a battery from the Li-ion
family rather than a lead acid battery. The Li-ion battery
chemistry is desirable because the battery is about five times more
volumetrically and gravimetrically energy dense than an
equivalently rated lead-acid battery types. For example, a 10
ampere-hour Li-ion battery can deliver 9 ampere-hours of
current-time when discharged at 2 times its rated rate (C) or when
it is discharged in 30 minutes. A high rate 18 ampere-hour lead
acid battery can deliver the same energy as example above but takes
up more than 5 times the volume as the Li-ion battery in the above
example.
[0016] The algorithm used for charging the Li-ion battery may be
different and the discharge rate of the batteries should be lower
than that used for a lead acid battery. Typically, a Li-ion based
UPS will be used for long discharges, for example more than one
hour, rather than shorter discharges.
[0017] As an example, a Li-ion battery has been used in a Legacy
UPS system with SLA batteries by making the following changes.
Similar to a NiMH battery, a Li-ion battery has a very flat voltage
discharge curve, so it is not desirable to use a Li-ion battery's
output voltage for determining the remaining charge in the battery.
Therefore, a means for measuring the battery current was used such
that the UPS microprocessor monitored the battery current,
determined the state of charge of the battery and calculated the
remaining run time in the batteries during discharge, charge and
standby modes. The determination of the remaining run time from the
state of charge is known to those of ordinary skill in the art. The
current measuring means can be an ammeter connected in series with
the battery, a volt meter for measuring the voltage across a
resistor in series with a battery such that the current can be
determined, or any other means for detecting or measuring current
to and from the battery.
[0018] It is preferable to replace the Legacy SLA lead acid
batteries with one or more Liion batteries having a nominal voltage
equivalent or somewhat more than that of the lead acid battery
voltage. For example the Legacy's 24 volt SLA system was replaced
by seven 3.7 volt cells coupled in series to create a 26 volt
Li-ion battery system. To charge the Li-ion batteries, the float
voltage setting point and temperature compensation slope was
modified in the UPS microprocessor. As noted above, it is
preferable to monitor current going into the battery for an
indication of state of charge.
[0019] FIG. 1 shows a exemplary UPS 10 system used to provide
regulated uninterrupted power in which a NiMH or Li-ion battery can
be used. The UPS 10 includes a power input 14, a power module 15, a
controller 16, an NiMH or Li-ion battery 18, and a power output 20.
The UPS also includes an input 24 for coupling to an AC power
source and an outlet 26 for coupling to a load. The power input 14
can include, for example, a circuit breaker or filter 112 and/or a
rectifier. The power output 20 can include, for example, an
inverter 120 and optionally an isolation transformer 122. The
controller 16 can be, for example, a microprocessor with code
embedded therein for controlling the functions of the UPS. The
power module 15 can include, for example, a control switch which is
controlled by the controller 16.
[0020] FIG. 2 shows another exemplary UPS 110 used to provide
regulated uninterrupted power in which a NiMH or Li-ion battery can
be used. The UPS 110 includes an input circuit breaker/filter 112,
a rectifier 114, a control switch 115, a controller 116, an NiMH or
Li-ion battery 118, an inverter 120 and optionally an isolation
transformer 122. The UPS also includes an input 124 for coupling to
an AC power source and an outlet 126 for coupling to a load. The
UPS can also include a current meter or other current measuring
means to measure a current of the battery, such as, for example, an
ammeter, a Hall sensor device or a voltmeter that measures the
voltage across a current shunt 117.
[0021] The exemplary UPS 110 can 8 operate as follows. The circuit
breaker/filter 112 receives input AC power from the AC power source
through the input 124, filters the input AC power and provides
filtered AC power to the rectifier 114. The rectifier converts the
filtered AC power to DC power having a predefined voltage value.
The control switch 115 receives the DC power from the rectifier and
also receives DC power from the NiMH or Li-ion battery 118. The
controller 116 determines whether the AC power available from the
power input is within predetermined tolerances, and if so, controls
the control switch to provide the DC power from the rectifier to
the inverter 120. If the AC power from the power input is not
within the predetermined tolerances, which may occur because of
"brown out" or "black out" conditions, or due to power surges, then
the controller controls the control switch to provide the DC power
from the NiMH or Li-ion battery 118 to the inverter 120.
[0022] The inverter 120 of the exemplary UPS 110 receives DC power
from the controller 116, converts the DC power to AC power, and
regulates the AC power to predetermined specifications. The
inverter 120 provides the regulated AC power to the optional
isolation transformer 122. The isolation transformer may be used to
increase or decrease the voltage of the AC power from the inverter
and/or to provide electrical isolation between a load and the UPS.
Depending on the capacity of the battery and the power requirements
of the load, the UPS 110 can provide power to the load during brief
power source "dropouts" or for extended power outages.
[0023] In the UPS system 110. the controller, the control switch
and/or the battery may also contain circuitry to charge the battery
using the DC power supplied by the rectifier. The NiMH or Li-ion
battery can be charged using one of the stated methods above. In
addition, in some UPS systems, the controller provides operating
status information to a user, either locally using, for example,
indicating lights or a display system, or remotely by communicating
with an external monitoring device.
[0024] It should be understood that the foregoing is illustrative
and not limiting and that obvious modifications may be made by
those skilled in the art without departing from the spirit of the
invention. Accordingly, reference should be made primarily to the
accompanying claims, rather than the foregoing specification, to
determine the scope of the invention.
* * * * *