U.S. patent application number 11/318166 was filed with the patent office on 2006-05-11 for direct current/direct current converter for a fuel cell system.
Invention is credited to John T. Bates, Christos A. Kambouris.
Application Number | 20060099463 11/318166 |
Document ID | / |
Family ID | 27737277 |
Filed Date | 2006-05-11 |
United States Patent
Application |
20060099463 |
Kind Code |
A1 |
Kambouris; Christos A. ; et
al. |
May 11, 2006 |
Direct current/direct current converter for a fuel cell system
Abstract
Fuel cell systems and control methods including a fuel cell and
a second energy source, such as a battery that is adapted to
supplement the fuel cell. In addition, the fuel cell system
utilizes a single bipolar switching module, such as an IGBT six
pack module that is configured to implement a DC/DC converter, such
as a DC/DC boost converter, for both the fuel cell and the battery.
The fuel cell system also makes use of a controller that is
configured to control either or both of input current and output
voltage of the DC/DC converter.
Inventors: |
Kambouris; Christos A.;
(Commerce, MI) ; Bates; John T.; (Belleville,
MI) |
Correspondence
Address: |
SEED INTELLECTUAL PROPERTY LAW GROUP PLLC
701 FIFTH AVE
SUITE 6300
SEATTLE
WA
98104-7092
US
|
Family ID: |
27737277 |
Appl. No.: |
11/318166 |
Filed: |
December 23, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10346561 |
Jan 16, 2003 |
7014928 |
|
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11318166 |
Dec 23, 2005 |
|
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60319071 |
Jan 16, 2002 |
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Current U.S.
Class: |
429/7 ; 320/101;
429/431; 429/432; 429/900 |
Current CPC
Class: |
H01M 8/0488 20130101;
H01M 8/0491 20130101; Y02E 60/10 20130101; H01M 8/04947 20130101;
H01M 16/006 20130101; H01M 8/04888 20130101; Y02E 60/50 20130101;
H01M 8/04917 20130101 |
Class at
Publication: |
429/007 ;
320/101; 429/022 |
International
Class: |
H01M 16/00 20060101
H01M016/00; H01M 8/04 20060101 H01M008/04 |
Claims
1. A fuel cell system, comprising: a fuel cell; a second energy
source configured to supplement the fuel cell; a single bipolar
switching module configured to implement a direct current to direct
current (DC/DC) converter for both the fuel cell and the second
energy source; and a controller configured to control at least one
of an input current and an output voltage of the DC/DC
converter.
2. The system of claim 1 wherein the second energy source comprises
a battery.
3. The system of claim 2 wherein the battery is adapted to deliver
power to a load when an amount of power available from the fuel
cell is less than a power demand of the load.
4. The system of claim 2 wherein the battery is adapted to supply a
power demand of a load when the fuel cell is not operating.
5. The system of claim 2 wherein the battery is adapted to absorb
power from the fuel cell when an amount of power available from the
fuel cell is greater than a power demand of the load.
6. The system of claim 2 wherein the single bipolar switching
module comprises an IGBT six pack module.
7. The system of claim 6 wherein the IGBT six pack module is
further configured to be used as a component of a back end
inverter.
8. The system of claim 2 wherein the controller is configured to
control at least one of the input current and the output voltage of
the DC/DC converter by controlling a flow of power to and from the
battery to maintain an average state of charge of the battery
whereby the battery can deliver a predetermined level of power in a
first mode and absorb a predetermined level of power in a second
mode.
9. The system of claim 1 wherein the single bipolar switching
module is configured to implement a DC/DC boost converter.
10. The system of claim 9 wherein the DC/DC boost converter is
adapted to boost a DC voltage from both the fuel cell and the
second energy source to a DC bus capacitor bank and a load.
11. A method of controlling a fuel cell system comprising a fuel
cell, a second energy source, a bipolar switching module and a
controller, the method comprising: operating the bipolar switching
module as a direct current to direct current (DC/DC) converter for
both the fuel cell and the second energy source; and, using the
controller to control at least one of an input current and an
output voltage of the DC/DC converter.
12. The method of claim 11 wherein the second energy source
comprises a battery.
13. The method of claim 12 wherein the method further comprises
delivering power from both the battery and the fuel cell to a load
when an amount of power available from the fuel cell is less than a
power demand of the load.
14. The method of claim 12 wherein the method further comprises
delivering power from the battery to a load when the fuel cell is
not operating.
15. The method of claim 12 wherein the method further comprises
absorbing an excess amount of power from the fuel cell with the
battery when an amount of power available from the fuel cell is
greater than a power demand of the load.
16. The method of claim 12 wherein the single bipolar switching
module comprises an IGBT six pack module.
17. The method of claim 16 wherein the method further comprises
operating the IGBT six pack module as a component of a back end
inverter.
18. The method of claim 16 wherein method further comprises
operating the IGBT six pack module to boost a DC voltage from the
fuel cell and the battery to a DC bus capacitor bank and a
load.
19. The method of claim 19 wherein the method further comprises
operating the controller to control the input current and the
output voltage of the DC/DC converter.
20. The method of claim 19 wherein operating the controller to
control the input current and the output voltage of the DC/DC
converter comprises controlling a flow of power to and from the
battery so as to maintain an average state of charge of the battery
whereby the battery can deliver a predetermined level of power in a
first mode and absorb a predetermined level of power in a second
mode.
21. The method of claim 11 wherein the single bipolar switching
module is configured to implement a DC/DC boost converter.
22. The method of claim 21 wherein the DC/DC boost converter is
adapted to boost a DC voltage from both the fuel cell and the
second energy source to a DC bus capacitor bank and a load.
23. A controller programmed to control a fuel cell system
comprising a fuel cell, a battery, and an IGBT six pack module
comprising three IGBT legs and configured to implement a DC/DC
converter for both the fuel cell and the battery, by: in a first
mode, providing DC/DC conversion for the fuel cell via two of the
three IGBT legs and bi-directional DC/DC conversion for the battery
via the third IGBT leg; in a second mode, providing DC/DC
conversion for the battery via two of the three IGBT legs and DC/DC
conversion for the fuel cell via the third IGBT leg; in a third
mode, providing DC/DC conversion for the fuel cell via all three
IGBT legs; and, in a fourth mode, providing DC/DC conversion for
the battery via all three IGBT legs.
24. A fuel cell system, comprising: a fuel cell; a battery; a
direct current to direct current (DC/DC) converter module coupled
to the battery and the fuel cell, that converts a first DC voltage
from the fuel cell to a DC output voltage and that converts a
second DC voltage from the battery to the DC output voltage; and a
controller configured to control at least one of an input current
and an output voltage of the DC/DC converter.
25. The system of claim 25 wherein the DC/DC converter module is a
single bipolar switching module.
26. The system of claim 25, further comprising: a switch,
comprising: a first position that couples the fuel cell and the
DC/DC converter module; and a second position that couples the
battery and the DC/DC converter module.
27. The system of claim 26 wherein the switch in the first position
couples the fuel cell and the DC/DC converter module so that power
from the fuel cell is converted by the DC/DC converter module.
28. The system of claim 26 wherein the switch in the second
position decouples the fuel cell from the DC/DC converter module
and further couples the battery and the DC/DC converter module so
that only power from the battery is converted by the DC/DC
converter module.
29. The system of claim 28 wherein the switch in the second
position couples the battery to a first leg and to a second leg of
the DC/DC converter module.
30. The system of claim 29 wherein the battery is coupled to a
third leg of the DC/DC converter module.
31. The system of claim 25 wherein the controller controls
operation of the DC/DC converter module so that a first input
current from the fuel cell is controlled to correspond to a first
portion of a total power delivered from the DC/DC converter module,
and wherein the controller controls operation of the DC/DC
converter module so that a second input current from the battery is
controlled to correspond to a second portion of the total power
delivered from the DC/DC converter module.
32. The system of claim 31 wherein the controller controls
operation of the DC/DC converter module so that the second input
current from the battery is controlled, and so that the first input
current from the fuel cell is maintained when the total power
delivered from the DC/DC converter module varies.
33. The system of claim 32 wherein the maintained first input
current from the fuel cell further maintains the first DC voltage
from the fuel cell.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S.
utility application entitled, "DIRECT CURRENT/DIRECT CURRENT
CONVERTER FOR A FUEL CELL SYSTEM," having Ser. No. 10/346,561,
filed Jan. 16, 2003, which is entirely incorporated herein by
reference, which claims the benefit of provisional application
having Ser. No. 60/319,701, filed Jan. 16, 2002.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present fuel cell systems and control methods relate
generally to direct current-to-direct current (DC/DC) converters,
and more particularly to using a DC/DC converter with both a fuel
cell and a second energy source.
[0004] 2. Description of the Related Art
[0005] In an application utilizing an energy source, such as a fuel
cell, the quality of power or the regulation of the direct current
(DC) bus is an issue. For example, a fuel cell is typically not
able to respond immediately to peaks in demand. A further issue in
such an application is that the fuel cell may be subject to power
outages which are unacceptable in an uninterruptible power supply
(UPS) application. There is a present need to address those issues,
utilizing as many of the components of an existing power converter
to implement a DC/DC converter with existing hardware and with as
few alterations and additions to the existing hardware as
possible.
BRIEF SUMMARY OF THE INVENTION
[0006] In one aspect, fuel cell systems and control methods
utilizing a fuel cell with a second energy source, such as a
battery, to supply load leveling capability and back up power
capability are provided. In another aspect, a single bipolar
switching device, such as a single IGBT module, is used in the
DC/DC conversion for both the fuel cell and the second energy
source.
[0007] In a further aspect of the present fuel cell systems and
control methods, a DC/DC converter with independent control of
DC/DC converter input current and output voltage is used, which
increases system efficiency.
[0008] In an additional aspect of the present fuel cell systems and
control methods, a fuel cell system with a second energy source and
utilizing a DC/DC converter with improved output voltage regulation
is utilized.
[0009] An embodiment of the present fuel cell systems and control
methods provides a DC/DC converter that utilizes one leg of an
insulated gate bipolar transistor (IGBT) six pack module to provide
bi-directional DC/DC conversion between a battery pack and an
inverter DC bus. The other two legs of the IGBT six pack module
provide DC/DC conversion between a fuel cell and the inverter DC
bus. This achieves optimization of best use of the power stage to
provide lower system cost topologies by utilizing the IGBT six pack
module configuration. The battery pack can also supply power during
fuel cell outages. One or two legs of the IGBT six pack module can
be added in parallel to the battery leg by using a contactor or
switch to increase power conversion capability.
[0010] Another embodiment of the present fuel cell systems and
control methods includes, for example, a fuel cell and a second
energy source, such as a battery or battery pack, that is adapted
to supplement the fuel cell. The battery can supplement the fuel
cell, for example, by delivering battery power for a load when fuel
cell power available from the fuel cell energy source is
insufficient for a load power demand, and/or by serving as a
primary back-up energy source when the fuel cell is down, and/or by
absorbing power when the power generated by the fuel cell exceeds a
load power demand. In addition, an embodiment of the present fuel
cell systems and control methods utilizes a single bipolar
switching module, such as an IGBT six pack module, that is
configured to implement a DC/DC converter, such as a DC/DC boost
converter, for both the fuel cell and the battery. The DC/DC boost
converter is adapted to boost DC voltage from both the fuel cell
and the second energy source to a DC bus capacitor bank and load.
In one aspect of the present fuel cell systems and control methods,
another IGBT six pack module is also used as a component of a back
end inverter coupled to the DC/DC converter.
[0011] The IGBT six pack module has, for example, three IGBT legs
that are configured to boost the DC voltage from the fuel cell and
the battery to the DC bus capacitor bank and load. In addition, one
of the three IGBT legs of the module is configured to provide for
bi-directional DC/DC conversion for the battery. A first switch
(alternatively referred to herein as a contactor) is adapted to
connect the other two of the three IGBT legs to the battery to
provide two additional DC/DC converter legs to the battery for a
high power load. The first switch is also adapted for switching to
a fuel cell position to provide two legs of the IGBT six pack
module to boost the fuel cell voltage when the fuel cell is the
primary energy source. A second switch (alternatively referred to
herein as a contactor) is adapted to disconnect the battery from
the DC/DC converter.
[0012] The present fuel cell systems and control methods also make
use of a controller that is configured to control either or both of
input current and output voltage of the DC/DC converter. The
controller is configured to control the input current of the DC/DC
converter by controlling a duty cycle of two fuel cell legs of the
IGBT six pack module. The controller is configured to control the
output voltage of the DC/DC converter by controlling a battery pack
leg of the IGBT module and employing a bi-directional capability of
the IGBT module. In addition, the controller is configured to
simultaneously control either or both of the input current and
output voltage of the DC/DC converter by controlling a flow of
power to and from the battery to maintain an average state of
charge of the battery, whereby the battery can deliver or absorb a
required level of power.
[0013] Additional objects, advantages and novel features of the
present fuel cell systems and control methods will be set forth in
part in the description which follows, and in part will become more
apparent to those skilled in the art upon examination of the
following, or may be learned by practice of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] In the drawings, identical reference numbers identify
similar elements or acts. The sizes and relative positions of
elements in the drawings are not necessarily drawn to scale. For
example, the shapes of various elements and angles are not drawn to
scale, and some of these elements are arbitrarily enlarged and
positioned to improve drawing legibility. Further, the particular
shapes of the elements as drawn, are not intended to convey any
information regarding the actual shape of the particular elements,
and have been solely selected for ease of recognition in the
drawings.
[0015] FIGS. 1A and 1B are a schematic diagram that illustrates an
example of a circuit and a control scheme for an embodiment of the
present fuel cell systems and control methods.
DETAILED DESCRIPTION OF THE INVENTION
[0016] In the following description, certain specific details are
set forth in order to provide a through understanding of various
embodiments of the invention. However, one skilled in the art will
understand that the invention may be practiced without these
details. In other instances, well-known structures associated with
electrical circuits and circuit elements have not been shown or
described in detail to avoid unnecessarily obscuring descriptions
of the embodiments of the invention.
[0017] Unless the context requires otherwise, throughout the
specification and claims which follow, the word "comprise" and
variations thereof, such as, "comprises" and "comprising" are to be
construed in an open, inclusive sense, that is as "including, but
not limited to."
[0018] Referring now in detail to an embodiment of the fuel cell
systems and control methods, an example of which is illustrated in
the accompanying drawings, FIGS. 1A and 1B illustrate a circuit and
control scheme for a fuel cell system 10 utilizing a DC/DC
converter 12. System 10 includes, for example, a fuel cell 14, a
battery pack 16, an IGBT six pack module 18, a capacitor bank (or
DC bus) 20, and a load 22. A DC/DC converter controller 24 of the
system includes, for example, a power controller 26, a battery
state of charge (SOC) estimator 28, fault protection 30 including
battery overcharge, overvoltage and overcurrent protection,
contactor controls 32, a fuel cell DC/DC input current controller
34, DC bus voltage controllers 36, 38 (for normal operating mode
and battery backup operating mode, respectively), and IGBT gate
controls 40, 42.
[0019] An embodiment of the present fuel cell systems and control
methods involves a unique way of using a single IGBT module 18 in
the DC/DC conversion for both battery 16 and fuel cell 14, and
using battery 16 to supply a load leveling capability and back up
power capability. DC/DC converter 12 makes use, for example, of
three IGBT legs 44, 46, 48 to boost the DC voltage from fuel cell
14 and battery 16 to DC bus 20 and load 22.
[0020] It is to be noted that without battery 16, it is not
possible to simultaneously control both DC/DC converter input
current I.sub.dcdcin and output voltage, and that control of DC/DC
converter input current I.sub.dcdcin is important to maximize the
fuel cell efficiency. Fuel cell 14 tells DC/DC converter 12 how
much current it can source based on the amount of fuel that fuel
cell 14 is delivering to its stack. If DC/DC converter 12 pulls
more than this amount of current then the fuel cells (referred to
collectively herein as fuel cell 14) may "starve" and damage may
occur. On the other hand, if DC/DC converter 12 pulls less than the
available current, the excess fuel delivered to the cells of fuel
cell 14 will be wasted. Hence, control of DC/DC converter input
current I.sub.dcdcin is important for several reasons.
[0021] Aspects of the present fuel cell systems and control methods
include, for example, supplementing or introducing a second source
of energy and having two sources of energy and also implementing
DC/DC converter 12 with existing hardware. One of the two energy
sources is fuel cell 14, and the other is battery 16, and the fuel
cell is supplemented with the battery pack energy source. The
quality of power or the regulation of DC bus 20 is addressed by
using battery 16. Fuel cell 14 is not as fast as battery 16 in its
ability to deliver energy to load 22. Battery 16 is faster, so
battery 16 is used as a way to deliver small amounts of power in
fast response to a spike in demand. In this way, the quality of the
power is improved.
[0022] An embodiment of the present fuel cell systems and control
methods enables utilizing existing hardware to implement both the
DC/DC conversion for fuel cell 14 and the DC/DC conversion for
battery 16. That aspect involves using IGBT module 18. Currently,
different modules may be used, such as one module for a fuel cell
DC/DC converter and a separate module for a battery DC/DC
converter. In one embodiment, IGBT module 18 used as a component of
a back end inverter to be connected to the fuel cell DC/DC
converter is used to build a battery pack DC/DC converter. Thus,
this aspect of the present fuel cell systems and control methods
uses one IGBT module 18 in DC/DC converter 12 for both battery 16
and fuel cell 14, as opposed to having separate modules.
[0023] IGBT module 18 is used to implement both the fuel cell DC/DC
conversion and the battery DC/DC conversion, and in a further
aspect of the present fuel cell systems and control methods,
battery 16 is used as a supplement to fuel cell 14 to improve the
voltage regulation on DC bus 20. Battery 16 also can be used, for
example, for power outages on fuel cell 14. Battery 16 can deliver
back-up power by itself. For example, battery 16 can be used in an
uninterruptible power supply (UPS) application. Battery 16 can
deliver full power for a brief period of time in situations where
fuel cell 14 may be down.
[0024] Regulation of DC/DC converter output voltage may be required
if load 22 requires a regulated voltage. If load 22 is an inverter,
for example, then voltage regulation is advantageous in that it can
reduce inverter output harmonics, and system performance can be
optimized with respect to the voltage of DC bus 20.
[0025] When fuel cell 14 is the primary energy source, a first
switch or contactor 52 is switched to the fuel cell position, as
shown in FIGS. 1A and 1B, providing two IGBT legs 44, 46 to boost
the voltage of fuel cell 14. The duty cycle of the IGBT legs 44, 46
being used for the fuel cell 14 can be controlled to regulate DC/DC
converter input current I.sub.dcdcin. The remaining IGBT leg 48 is
given to battery 16 for bi-directional DC/DC conversion. With
bi-directional capability, battery 16 can supply energy (battery
discharge) and take away energy (battery charging) from DC bus 20
and/or load 22. The process of supplying energy tends to increase
the converter output voltage, whereas the process of taking away
energy tends to decrease the converter output voltage. Hence the
IGBT leg 48 being used for the battery 16 can be controlled to
regulate the converter output voltage.
[0026] Typically, a battery has a higher power bandwidth than a
fuel cell. In other words, battery 16 can respond faster to
changing power requirements than fuel cell 14. Fuel cell 14 is
slower to respond due to the limited bandwidth of its fuel delivery
system, such as compressor, valves, and the like. In addition,
battery 16 is capable of both sourcing and sinking energy, whereas
fuel cell 14 is only capable of sourcing energy. Given these facts,
an embodiment of the present fuel cell systems and control methods
supplements fuel cell 14 with the sourcing and sinking capabilities
of battery 16 to achieve a better overall energy source than fuel
cell 14 by itself.
[0027] Given the limited power bandwidth of a fuel cell, fuel cell
14 may not be able to react fast enough to a heavy load 22 at
startup. In this case, the power from capacitor bank 20 to load 22
exceeds the power from fuel cell 14 to capacitor bank 20. As a
result, the voltage of capacitor bank 20 drops until the power of
fuel cell 14 can catch up to load 22 power demand. By adding
battery 16 with sufficient capacity, the difference between load 22
power and the power of fuel cell 14 can be supplied by battery 16,
and as a result the voltage of capacitor bank 20 will not drop. On
the other hand, consider a case in which load 22 power demand
suddenly drops, as in a load 22 dump. Without battery 16, the power
from load 22 has no place to go except to capacitor bank 20, since
fuel cell 14 cannot sink power. When capacitor bank 20 absorbs
power, its voltage increases. Battery 16 can absorb the power at
load 22 dump and, hence, maintain the voltage of capacitor bank
20.
[0028] In addition to DC bus voltage regulation, battery 16 can
also serve as the primary energy source when fuel cell 14 is down.
This is useful in UPS applications where uninterruptible power must
be delivered to load 22. The amount of time that battery 16 can
supply power to load 22 depends on such factors as load 22 power
demand and the amp-hour capacity of battery 16. For a high power
load 22, first switch 52 can be switched to battery 16 to provide
additional IGBT legs 44, 46 to battery 16. A second switch or
contactor 54 is provided in order to disconnect battery 16 in case
of servicing or under certain fault conditions.
[0029] Another aspect of the present fuel cell systems and control
methods involves the control scheme, given the complexity of
systems that utilize two sources of energy. Various feedback
signals are provided for the control scheme. Referring again to
FIGS. 1A and 1B, the inputs and outputs for DC/DC converter
controller 24 include a number of feedback signals, such as the DC
bus voltage V.sub.bus, the battery output voltage V.sub.bat, the
fuel cell output voltage V.sub.fc, the converter leg currents
I.sub.L1, I.sub.L2, I.sub.L3, the load power P.sub.L, the battery
temperature T.sub.bat, and the IGBT temperature T.sub.IGBT. Other
inputs and outputs for DC/DC converter controller 24 include
command/setpoint signals, such as the DC bus setpoint voltage
V.sub.bus*, the battery state of charge setpoint SOC*, the fuel
cell output power setpoint P.sub.fc*, the fuel cell output current
setpoint I.sub.fc*, and the DC/DC converter input current setpoint
I*.sub.dcdcin. An additional DC/DC converter controller signal is
the battery mode enable signal BME. (After fault protection 30, the
set points are represented in FIGS. 1A and 1B as V.sub.bus1*,
P.sub.fc1*, etc.)
[0030] The input inductor current feedback--converter leg currents
I.sub.L1, I.sub.L2, I.sub.L3--is required for input current
controller 34 and overcurrent fault protection 30. The converter
output voltage feedback--DC bus voltage V.sub.bus--is required for
DC bus voltage controllers 36, 38 and overvoltage fault protection
30. The fuel cell output voltage V.sub.fc and battery voltage
feedback--battery output voltage V.sub.bat--are required for
overvoltage fault protection 30 and input inductance estimation for
control purposes. IGBT temperature T.sub.IGBT and battery
temperature T.sub.bat feedback are required for overtemperature
fault protection 30. Battery state of charge feedback SOC* is
required for controlling the proper amount of power flow from
battery 16 in conjunction with the power flow from fuel cell
14.
[0031] If, on the one hand, battery 16 is fully charged, battery 16
will have very limited capability to absorb power and, hence,
output voltage regulation may degrade. On the other hand, if
battery 16 is nearly completely discharged, battery 16 will have
very limited capability to supply power to load 22 and, again,
output voltage regulation may suffer. The flow of power to and from
battery 16 is controlled, so that the average state of charge is
such that under most conditions battery 16 can source or sink the
required power. As shown in FIGS. 1A and 1B, the control setpoints
are converter input current setpoint I*.sub.dcdcin and output
voltage DC bus setpoint voltage V.sub.bus*. The controller outputs
are the gating signals 86 to turn the IGBTs on and off. The other
outputs are the contactor controls 88 for backup operation, fault
operation, and general disconnect for power down.
[0032] All of the above U.S. patents, U.S. patent application
publications, U.S. patent applications, foreign patents, foreign
patent applications and non-patent publications referred to in this
specification and/or listed in the Application Data Sheet,
including, but not limited to U.S. Ser. No. 60/319,071, filed Jan.
16, 2002, are incorporated herein by reference, in their
entirety.
[0033] From the foregoing it will be appreciated that, although
specific embodiments of the invention have been described herein
for purposes of illustration, various modifications may be made
without deviating from the spirit and scope of the invention.
Accordingly, the invention is not limited except as by the appended
claims.
* * * * *