Note: Descriptions are shown in the official language in which they were submitted.
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HYBRID BATTERY CONFIGURATION
FIELD OF THE INVENTION:
[0001 ] This invention relates to hybrid battery configurations, and
particularly to
configurations of hybrid batteries where the hybrid battery comprises a first,
high rate, high power
device - a capacitor or a supercapacitor, or a high power battery - and a
second, high energy battery.
Configurations in keeping with the present invention may employ a variety of
batteries and energy
storage devices having the same, similar, or disparate chemistries.
BACKGROUND OF THE INVENTION:
[0002] There is a long standing need to maximize battery performance for
applications which
require both high discharge rates and long run times. Invariably, attempts to
maximize the
configuration and characteristics of a single battery to satisfy all
requirements, results in
compromise. Neither the requirement for high discharge rate, particularly over
a significant interval,
nor long run times at low discharge rate, over a long interval in time, will
be fully satisfied.
[0003] The high surface area interface which is required for low impedance,
high rate
systems is achieved in battery designs by a net reduction in the amount of
active material. For
example, recently developed organic electrolyte lithium ion and lithium
polymer battery systems are
designed with thin components that have exceptionally high surface area. This
allows efficient
discharge at higher rates.
~=0004] However, notwithstanding that the energy content of the active
materials is reasonably
high, it still requires that the ampere hour capacity of such batteries be de-
rated. On the other hand,
the implementation of high surface area designs using low rate chemistries,
results in thermal
problems when such a battery system is used in high rate applications.
[0005] Moreover, of course, addition of active material to provide higher
capacity will
typically result in a slower acting system, with a relatively low ratio of
surface area to active material
mass, resulting in the inability of such battery systems to react quickly and
to provide high rate
discharge or charge.
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[0006] A particular approach which is now being studied is to improve overall
performance
and to increase the safety of batteries that are used in high discharge rate
applications, and to separate
those functions of high current delivery and energy delivery. Particularly, a
large, low impedance
double layer capacitor, may be configured with a battery system in such a
manner that the double
layer capacitor can potentially supply large current spikes which pose
problems to low discharge rate,
high energy batteries.
[0007] A battery component of such a hybrid battery configuration, on the
other hand,
provides the energy for an extended operating range, particularly a long
period of time at low
discharge conditions. As well, as will be noted hereafter, the battery
component of such a hybrid
battery configuration provides the energy required to recharge the high rate
capacitor, in some
circumstances.
[0008] However, problems will arise when the total time of high current drain
exceeds the
capability of even the largest of capacitors. Thus, the solution of providing
a hybrid battery system
resolves that problem, by combining a high rate, high power device - typically
a high rate battery,
but possibly a capacitor or supercapacitor - together with a lower rate, high
energy density design
of battery.
[0009] The problem then becomes the management of the hybrid battery
configuration so
as to supply a load which has varying current requirements that range from
short periods of high
current to extended periods of low to medium current. As noted, that solution
lies in the parallel
provision, within a hybrid battery configuration, of a high rate, high power
device - typically a high
power battery, but possibly a high power supercapacitor-together with a high
energy battery, where
l:he devices are connected in parallel.
[0010] Such a combination can provide enhanced performance in situations which
require
both high energy density and high power density. The parallel configuration
enables the high power
device to deliver high current on demand. This high rate, high power device
must have low
impedance, and it must always be available for discharge.
[0011] As will be noted hereafter, there is no requirement for the use of
identical battery
chemistries; however the high energy battery should be capable of rechwging
the high power device
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during "off' periods, or during periods of lower power delivery. Various
configurations are
contemplated, some using a DC to DC converter, others without such an element.
[0012] An optimal configuration is highly dependent on the application to
which the hybrid
battery is to be put. Some possibilities exist, such as:
A) The combination of a high energy density primary battery, with a secondary
battery
which is capable of higher rates of discharge.
B) The combination of a fuel cell together with a secondary battery which is
capable
of higher rates of discharge.
C) The combination of a high energy density secondary battery, together with a
high
power secondary battery of identical chemistry.
D) The combination of a high energy density secondary battery, together with a
high
power secondary battery of different chemistry.
[0013] In each instance, of course, the two batteries, or high power device
and battery, or fuel
cell and battery, are configured in parallel one to the other as a hybrid
battery, which in turn is in
series with its load. Quite often, the high rate battery is designed with a
low active material loading,
so that it must be periodically recharged by the high energy battery.
[0014] Indeed, all of the types of possible configurations which ~~re noted
above may operate
solely with the high power battery in the circuit, if the ampere hour capacity
of the high power
battery is sufficient to sustain the load over an operating cycle such that
the battery may be recharged
during the "off' period of the operating cycle. In such situation, then, the
high power battery
provides the power for the load, over the complete duty cycle, without load
sharing between the two
power sources.
[0015] More likely is the situation where the duty cycle is comprised of
extended periods of
low to medium rate discharges, interspersed with shorter periods of high rate
discharges. In those
situations, where the periods of high rate discharge are longer than would
normally be supported
even by a supercapacitor, such high rate discharges may be supported by a high
power battery, and
the low rate discharges may be supported by the high energy battery.
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[0016] In such circumstance, the high power battery is recharged by the high
energy battery
during periods of low current drain. Moreover, during discharge, the high
power battery and the high
energy battery can be switched into and out of the circuit.
[0017] For example, the high energy battery can be switched out during high
current pulses,
and the high power device can be switched out during extended periods of low
current drain so as
to provide a time dependant load sharing. Of course, such a scheme requires
current motoring and
microprocessor control.
[0018] Alternatively, both batteries may operate in a parallel configuration.
In that case,
during periods of high current delivery the voltage of the parallel
combination of the high power
battery and the high energy battery, will become depressed. The proportion of
current drawn from
each battery will then be dependant on the relative state of charge of the
batteries, and the impedance
difference between the batteries, as well as the duration and magnitude of the
current pulse.
[0019] Medium rate, short duration pulses may be supported by the discharge of
the double
layer capacity of a high power battery. Higher current pulses would depress
the voltage levels into
the Faradaic operational region of the high power unit, so that long term high
current pulses can be
;sustained. It follows that removal of a low impedance load will allow charge
to be predominately
transferred from the high energy battery.
[0020] The load current level above which the current is predominately
supported by the high
powered battery is a design parameter which is dictated by the application,
and determined by the
discharge characteristics of the two batteries in the system. The transition
can be modified by
adjustment of the number of unit cells in each battery, by variation of
battery chemistries, and by the
individual mechanical and chemical design of the respective batteries.
[0021 ] Of course, it is also possible to actively control the proportion of
current being
delivered by each battery in a parallel hybrid battery configuration, by the
use of FETs in one or more
legs of the parallel string.
DESCRIPTION OF THE PRIOR ART:
[0022] United States patent 6049141, issued April 1 l, 2000 to Sieminski at et
al, teaches a
device and a method for allowing multiple batteries to share a common load. In
this case, however,
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the discussion of load sharing is directed to the control of two parallel
batteries without any recharge
process which would be necessary for extremely high rate units that are
designed with low active
material loading. In other words, there is no recharge capability within the
parallel battery system
contemplated in this patent; and the only charge capability is by the use of
an external charger in
respect of any battery in the battery system.
[0023] In contradistinction, the present invention provides for recharging of
a high power
device - typically, a high power battery but possibly a high rate, high power
capacitor - by delivering
energy to it from the high energy battery with which it is in parallel.
SUMMARY OF THE INVENTION:
[0024] In accordance with one aspect of the present invention, there is
provided a hybrid
battery configuration for supplying a load having varying current requirements
which range from
short periods of high current to extended periods of low to medium current.
The hybrid battery
configuration comprises a first, high rate, high power, energy storage device;
a high energy battery;
a current monitoring device; a microprocessor controller; and at least one
switch device.
[0025] The high rate, high power energy storage device and the high energy
battery are
connected in parallel with each other, and in series with a load.
X0026] The current monitoring device is connected in series with the parallel
connected high
rate, high power device and high energy battery, and in series with the load.
[0027] The switch means is controlled by the microprocessor so as to switch at
least one of
the high power device and the high energy battery into and out of a series
connection with the load.
[0028] One prevision of the present invention is that the high rate, high
power energy storage
device is a high rate, high power capacitor. If so, the at least one switch
may be connected to the
high rate, high power capacitor, so as to take it into and out of a series
connection with the load.
[0029] Typically, in any configuration of hybrid battery in keeping with the
present
invention, the at least one switch may be a Field Effect Transistor (FE1').
[0030] In most configurations of hybrid battery in keeping with the present
invention, the
high rate, high power energy storage device is a high power battery. If so,
then typically such a
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hybrid battery configuration may also comprise a DC to DC converter in series
connection between
the high power battery and the high energy battery.
[0031] Here, the switch device is arranged so as to connect the high power
battery and the
high energy battery directly to each other when in a first switch position,
and to connect the high
power battery and the high energy battery to each other through the DC to DC
converter when in a
second switch position.
[0032] The present invention contemplates that the microprocessor controller
may be adapted
to control a recharge operation of the high rate, high power energy storage
device from the high
energy battery. If so, this recharge operation will be in keeping with
predetermined criteria for the
state of charge of the high rate, high power energy storage device, and the
level of current being
drawn by the load.
[0033] The present invention contemplates that the high rate, high power
energy storage
device may be chosen from the group which consists of capacitors and
supercapacitors, thin film lead
acid batteries, thin plate lead acid batteries, thin film nickel zinc
batteries, thin film silver zinc
batteries, thin film lithium ion batteries, and high rate nickel oxide
alkaline batteries.
[0034] Likewise, the present invention contemplates that the high energy
battery may be
.chosen from the group which consists of high energy density primary
batteries, fuel cells, and high
energy density secondary batteries.
~[0035] Still further, the high energy density secondary battery may be one
which is chosen
from the group consisting of high energy lithium ion batteries, high energy
lead acid batteries, high
energy lithium polymer batteries, high energy nickel zinc batteries, and high
energy nickel metal
hydroxide batteries.
[0036] If there is a Field Effect Transistor associated with each of the high
rate, high power
energy storage device and the high energy battery, and each of the FETs is
under the control of the
microprocessor, then load sharing delivery of energy to the load is
controlled, in keeping with
predetermined criteria of current flow requirements by the load, and in
keeping with predetermined
criteria concerning state of charge of each of the high rate, high power
energy storage device and the
high energy battery.
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BRIEF DESCRIPTION OF THE DRAWINGS:
[0037] The novel features which are believed to be characteristic of the
present invention,
as to its structure, organization, use and method of operation, together with
further objectives and
advantages thereof, will be better understood from the following drawings in
which a presently
preferred embodiment of the invention will now be illustrated by way of
example. It is expressly
understood, however, that the drawings are for the purpose of illustration and
description only and
are not intended as a definition of the limits of the invention. Embodiments
of this invention will
now be described by way of example in association with the accompanying
drawings in which:
(0038] Figure 1 is a simple schematic of a battery configuration for hybrid
batteries in
keeping with the present invention;
[0039] Figure 2 is similar to Figure 1, showing utilisation of different
switch elements;
[0040] Figure 3 shows a further configuration where a DC to DC converter is
connected
between the batteries of the hybrid battery configuration;
1 S DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0041 ] The novel features which are believed to be characteristic of the
present invention,
.as to its structure, organization, use and method of operation, together with
further objectives and
advantages thereof, will be better understood from the following discussion.
(0042] Referring first to Figures 1 and 2, simplified configurations are
illustrated for a hybrid
battery. In each of those Figures, a high rate, high power device 12 is shown
connected in parallel
to a high energy battery 14. That parallel connection is connected in series
with a load 16, which is
also in series with a current monitoring device - an ammeter - shown at 18.
[0043] A microprocessor controller 20 is shown, and it will typically be
connected to the
devices 12 and 14, and the ammeter 18, in manners well known to persons
skilled in the art.
[0044] Also, the microprocessor controller 20 is connected to switches 22, one
or either of
which will be present in the circuit, if not both, as described hereafter.
[0045] In Figure 2, the switches 22 are replaced by FETs 24.
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[0046] A similar configuration is shown in Figure 3. However, in this case, it
is seen that
a DC to DC converter 26 is provided, and its connection between the high rate,
high powered battery
12 a is dependent on the switch position of switch 28.
[0047] Typically, switch 28 is a solid state switching device, but for
purposes of simplicity
it is shown as being a double throw, single pole - or two-position - switch.
[0048] In a configuration in such as that shown in Figure 1, in some
circumstances ifthe load
16 requires a very high current, the microprocessor controller 20, in
association with the current
monitoring device 18, may open the bottom switch 22b, so that a high current
pulse is provided to
the load from the high rate, high power device 12.
[0049] In other circumstances, if the load is a very low rate load, the switch
22b will be
closed, and switch 22a will be opened.
[0050] Moreover, in some circumstances if the energy storage of the device 12
has been
depleted to some extent, such that its terminal voltage has reduced, then
switch 22a may be closed,
or cycled from an open to a closed position by the microprocessor 20, so as to
recharge the high rate,
high power device - a capacitor or battery - from the high energy battery 14.
[0051 ] In the circuit shown in Figure 2, the same functions may be followed.
[0052] Moreover, because of the presence of the FETs 24a and 24b, it is
evident that load
sharing under the control of microprocessor controller 20 can be effected, in
the manner well known
to those skilled in the art.
j[0053] Similarly, in a circuit such as that shown in Figure 3, a decision may
be made by the
.microprocessor controller to connect the high rate, high power battery 12a in
parallel with the high
energy battery 14 by placing the switch 28 in its first position. Then, a
simple parallel connection
i.s made between the batteries. Of course, FETs may be placed in the parallel
legs, in the same
manner as shown in Figure 2.
[0054] Moreover, in the event that a decision is made for the high rate, high
power battery
12a to be recharged from the high energy battery 14, through the DC to DC
converter 26 - which is
typically a pulse output device adapted for high rate charging of the battery
12a - then the switch 28
is placed into its second position.
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[0055] Indeed, any operation of any of the switches and FETs, as described
above, may be
essentially instantaneous, and for very short periods of time, depending on
the load characteristics
and demands as required by the load 16, and as sensed using the current
monitoring device 18
together with the microprocessor controller 20.
[0056] Thus, as noted, the microprocessor controller 20 may reach a decision
to control the
recharge operation of the high rate, high power energy storage device 12 or
12a from the high energy
battery 14, in keeping with predetermined criteria for this state of charge of
that device 12 or 12a,
and the level of current being drawn by the load 16.
[0057] While the device 12 may be a supercapacitor, it is more likely to be a
thin film lead
acid battery, a thin plate lead acid battery, a thin film nickel zinc battery,
a thin film silver zinc
battery, a thin film lithium ion battery, or a high rate nickel oxide alkaline
battery.
[0058] A high energy battery may be a fuel cell, it may be a high energy
density primary
battery; or more likely, it is a high energy density secondary battery.
[0059] If so, typical high energy density secondary batteries which may be
employed in
keeping with the present invention include high energy lithium ion batteries,
high energy lithium
polymer batteries, high energy nickel zinc batteries, and high energy nickel
metal hydroxide
batteries.
[0060] Finally, it has been noted that load sharing between the devices 12 or
12a, and 14, is
through the FETs 24, under the control of the microprocessor controller 20 in
keeping with
predetermined criteria of current flow requirements by the load 16 and the
state of charge of each
of the high rate, high power energy storage device 12 or 12a and the high
energy battery 14.
[0061 ] There has been described a hybrid battery configuration for supplying
a load, where
typically the load has varying current requirements which may range from short
periods of high
current to extended periods to low to medium current. Alternative
configurations have been
described with respect to the manner in which current and energy flow from the
batteries to the load,
or from the high energy battery to the high power device, may be effected. An
alternative
arrangement providing for specific recharging of a high rate, high power
battery from the high energy
battery, using a DC to DC converter - and thereby independent of any external
battery charger
requirements - has also been described.
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[0062] It is evident to those skilled in the art that hybrid battery
configurations may be
assembled, without departing from the spirit and scope of the appended claims.
[0063] Throughout this specification and the claims which follow, unless the
context requires
otherwise, the word "comprise", and variations such as "comprises" or
"comprising", will be
understood to imply the inclusion of a stated integer or step or group of
integers or steps but not to
the exclusion of any other integer or step or group of integers or steps.
