U.S. patent application number 12/012990 was filed with the patent office on 2009-08-13 for reconfigurable power system using multiple phase-set electric machines.
This patent application is currently assigned to Direct Drive Systems, Inc.. Invention is credited to Raed Ahmad, Zhiguo Pan, Daniel M. Saban.
Application Number | 20090200809 12/012990 |
Document ID | / |
Family ID | 40934295 |
Filed Date | 2009-08-13 |
United States Patent
Application |
20090200809 |
Kind Code |
A1 |
Saban; Daniel M. ; et
al. |
August 13, 2009 |
RECONFIGURABLE POWER SYSTEM USING MULTIPLE PHASE-SET ELECTRIC
MACHINES
Abstract
A reconfigurable power system that includes a gas turbine,
flywheel, a first electric machine coupled to the gas turbine, a
second electric machine coupled to the flywheel, the first and
second electric machines being substantially similar in
configuration, a first power device for coupling power from the
first electric machine to a power grid, a second power device
coupled to the second electric machine for driving the flywheel and
coupling power from the second electric machine to the power grid,
and a switch for coupling either the power generated by the first
electric machine or the second electric machine to the grid.
Inventors: |
Saban; Daniel M.; (Corona,
CA) ; Ahmad; Raed; (Placentia, CA) ; Pan;
Zhiguo; (Rowland Heights, CA) |
Correspondence
Address: |
IRVING KESCHNER
21535 HAWTHORNE BOULEVARD, SUITE 385
TORRANCE
CA
90503
US
|
Assignee: |
Direct Drive Systems, Inc.
|
Family ID: |
40934295 |
Appl. No.: |
12/012990 |
Filed: |
February 7, 2008 |
Current U.S.
Class: |
290/4R ; 307/67;
322/4 |
Current CPC
Class: |
H02J 3/30 20130101; Y02E
60/16 20130101 |
Class at
Publication: |
290/4.R ; 322/4;
307/67 |
International
Class: |
H02J 9/00 20060101
H02J009/00; F02C 6/14 20060101 F02C006/14; H02K 7/02 20060101
H02K007/02 |
Claims
1. A power system for supporting an AC network comprising: a gas
turbine; a flywheel for providing power when the peak loads exceed
a predetermined level; a first electric machine having a first AC
interface coupled to said gas turbine; a second electric machine
having a second AC interface coupled to said flywheel, said first
and second electric machines being substantially identical; a first
power device for coupling power from said first electric machine to
an AC power grid; a second power device coupled to said second
electric machine for driving said flywheel and coupling power from
said second electric machine to said AC power grid, said first
power device and said second power device being substantially
identical; and means for interconnecting first and second switch
means at said first and second AC interfaces or through said AC
power grid.
2. The system as defined in claim 1 wherein in a first mode of
operation said first electric machine delivers power to said grid
and wherein said second electric machine drives said flywheel.
3. The system of claim 2 wherein in a second mode of operation said
first electric machine is inhibited from generating power and
wherein said flywheel causes said second electric machine to
deliver power to said grid.
4. The system of claim 3 wherein in said second mode of operation
said second electric machine delivers power to said grid through
said first power device.
5. The system of claim 4 wherein in a third mode of operation said
first and second electric machines deliver power to said grid
simultaneously.
6. A method for supporting an AC network utilizing a power system
comprising the steps of: providing a gas turbine; providing a
flywheel to provide power when the peak loads exceed a
predetermined level; coupling a first electric machine having a
first AC interface to said gas turbine; coupling a second electric
machine having a second AC interface to said flywheel, said first
and second electric machines being substantially identical;
providing a first power device for coupling power from said first
electric machine to an AC power grid; providing a second power
device coupled to said second electric machine for driving said
flywheel and coupling power from said second electric machine to
said AC power grid, said first power device and said second power
device being substantially identical; and providing means for
interconnecting first and second switch means at said first and
second AC interfaces or through said AC power grid.
7. The method as defined in claim 6 wherein in a first mode of
operation said first electric machine delivers power to said grid
and wherein said second electric machine drives said flywheel.
8. The method of claim 7 wherein in a second mode of operation said
first electric machine is inhibited from generating power and
wherein said flywheel causes said second electric machine to
deliver power to said grid.
9. The method of claim 8 wherein in said second mode of operation
said second electric machine delivers power to said grid through
said first power device.
10. The method of claim 9 wherein in a third mode of operation said
first and second electric machines deliver power to said grid
simultaneously.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] A reconfigurable power system that comprises multiple loads
and prime movers and electric machines connected to an AC bus via
power electronic devices.
[0003] 2. Description of the Prior Art
[0004] Efforts have been underway to develop high-speed generators
and power converters used to transfer power between a high speed
turbine, a high speed energy storage flywheel and a 450 Vrms,
3-phase, 60 Hz distribution system. The system would incorporate
high speed generators which convert rotational energy to electrical
energy, rectifiers that convert high frequency AC power to DC power
and inverters which convert DC power to AC power. The system also
includes a high frequency drive motor to allow charging of the
flywheel energy store directly from the 450 Vrms 3-phase Hz
distribution grid. During discharge of the flywheel energy store,
the power flow can be directed to the 450 Vrms distribution grid or
be rectified and routed through the inverters.
[0005] Although the system noted hereinabove when implemented, will
meet the system requirements, it would be desireable if the system
had the capability of being reconfigured such that the flywheel
portion is essentially capable of operating as a full back-up to
the turbine portion of the system. In addition, it would be
desireable if the high speed generators were multiple phase-set
electric machines.
SUMMARY OF THE INVENTION
[0006] The present invention provides a reconfigurable power system
that comprises multiple loads and prime movers and electric
machines connected to an AC bus utilizing multiple phase-set
electrical machines in conjunction with suitable power electronic
devices.
[0007] The advantages of this system is that common power
electronic devices can be used for both the flywheel and turbine
(both potential loads and prime movers), and common electric
machines can be used for coupling with both flywheel and turbine.
The nature of the power requirements of a flywheel are well suited
for a multiple phase set electric machine. In particular, when
providing power to the flywheel, the power demand is low and when
power is extracted from the flywheel a much higher power capacity
electric machine is needed. A multiple phase set electric machine
can be configured to run on one phase set (or any number of phase
sets corresponding to the number of power electronic devices
dedicated for a variable frequency drive), when motoring the
flywheel and all of the phase sets when providing power to the grid
through the same power electronic devices normally used to provide
power to the grid from the multiple phase set electric machine
coupled to the turbine. Some built-in system redundancy can be
provided, but if common electric machines are used and common
electric power electronic devices are used, then what would
otherwise be a special purpose variable frequency drive for
motoring the flywheel can be eliminated in favor of one of the
common power electronic devices. If a common power electronic
device normally feeding generating power to the grid fails, then
the system user has the option of re-configuring the system using
the common power electronic device normally serving as a variable
frequency device and vice versa. This system re-configuration could
be performed on a real-time as needed basis; for example the
flywheel could be powered periodically rather than continuously as
the needs and priority of the system change.
[0008] The present invention thus provides an efficient power
system comprising a number of electric machines with multiple phase
set stators and power electronic devices (which may or may not
include switch gear and filters) configured to provide
bi-directional power flow through at least one of the electric
machines. In particular, a first electric machine is coupled to a
turbine engine and a second electric machine is coupled to a
flywheel. The first electric machine is used as a motor to start
the turbine and as a generator when the turbine is producing power.
The second machine is used as a motor to "spin up" the flywheel and
as a generator when the flywheel is providing power.
DESCRIPTION OF THE DRAWINGS
[0009] For a better understanding of the present invention as well
as other objects and further features thereof, reference is made to
the following description which is to be read in conjunction with
the accompanying drawing wherein:
[0010] FIG. 1 illustrates a preferred embodiment of the system of
the present invention;
[0011] FIG. 2 illustrates an operating mode of the preferred
embodiment shown in FIG. 1 wherein the electric machine acts as a
motor to start the turbine and the flywheel portion of the system
is charging, both sub-systems being independent;
[0012] FIG. 3 illustrates an operating mode of the preferred
embodiment shown in FIG. 1 wherein the turbine operates to run the
elective machine as a generator and the flywheel is charging, each
sub-system acting independently;
[0013] FIG. 4 illustrates an operating mode of the preferred
embodiment shown in FIG. 1 wherein the gas turbine is off-line and
the flywheel is discharging, both sub-systems acting
cooperatively;
[0014] FIG. 5 illustrates an alterative embodiment wherein a DC
connection is provided; and
[0015] FIG. 6 illustrates an operating mode of system shown in FIG.
5 wherein the gas turbine is on-line and the flywheel is
discharging, both sub-system acting cooperatively.
DESCRIPTION OF THE INVENTION
[0016] Referring to FIG. 1, the reconfigurable power system 10
using multiple phase-set electric machines in accordance with the
teachings of the present invention is illustrated. Electric
machines 12 and 14 (although only two machines are illustrated,
more than that number can be utilized) are illustrated as being
coupled to turbine 16 and flywheel 18, respectively (although other
prime movers can be utilized). System 10 is configured to provide
bi-directional power flow in at least one of the electric machines
12 and 14. Electric machine 12, coupled via shaft 20 to turbine 16,
can be used as a motor to start turbine 16 and, alternately, as a
generator when turbine 16 is producing electric power. Electric
machine 14, coupled to flywheel 18 via shaft 22, is used as a motor
to "spin up" flywheel 18 and as a generator when the flywheel is
generating electric power. As is well known, flywheels store
kinetic energy to be used in driving a machine for a short time
period and functions essentially as a back-up in case of a system
power failure.
[0017] The preferred electric machine for use in system 10 is
disclosed in copending application Ser. No. 11/751,450, filed May
21, 2007 and assigned to the assignee of the present invention. The
advantages of using such a machine is described in that application
and the teachings thereof necessary for an understanding of the
present invention is incorporated herein by reference. The
multi-phase winding sets used in the machine can be independent,
space shifted, three phase winding sets. Each set is supplied by a
dc-ac power electronics building block ("PEBB"), such as block 156
discussed hereinafter. Permanent-magnet machines are the preferred
machine topology.
[0018] Referring to that portion of system 10 involving turbine 16,
the output from four sets of three phase windings 30, 32, 34 and 36
from machine 12 is coupled to switches 40, 42, 44 and 46
respectively. The output from switches 40, 42, 44 and 46 are
coupled to input/output filters 50, 52, 54 and 56, respectively
(the system can operate without the filters if necessary). The
output from the filters are coupled to block 70 comprising a series
of AC/DC and DC/AC converters, the output therefrom being coupled
to input/output filters 80, 82, 84 and 86, the outputs of which are
coupled to three-phase AC bus 100, bus 100 operating at a frequency
range between 50 and 60 hz and at a voltage range between 450V and
1000 VAC. The AC/DC converters comprise blocks 71, 72, 73 and 74
and the DC/AC converters comprise blocks 75, 76, 77 and 78. It
should be noted that the converter blocks are bi-directional i.e.
they can be used as either AC/DC or DC/AC converters.
[0019] Referring to that portion of system 10 involving flywheel
18, the output from four sets of three phase winding 110, 112, 114
and 116 are, in one version, coupled to switches 40, 42, 44 and 46,
the system then operating in the manner described hereinabove with
reference to machine 12. In some modes of operation, three phase
winding 116 is connected to VFD (variable frequency drive) 150
comprising switch 152, input/output filter 154, AC/DC converter 156
DC/AC converter 158 and input/output filter 160. The output of VFD
150 is connected to three phase AC bus 101. Blocks 41, 43 and 45
are part of the dual-pole double system throw switches that either
connect the high speed turbine 16 and motor/generator 12 to grid
100 or motor/generator 14 and flywheel 18 to grid 101.
[0020] The flywheel generates power while the gas turbine 16 is
generating power through the high speed generator 12 or when gas
turbine 16 is disconnected from the system 10.
[0021] The system 10 described hereinabove has three modes of
operation. In the first mode, blocks 150, powered by bus 101,
causes machine 14 to operate as a motor to spin-up flywheel 18
(switch 152 closes the connection between machine 14 and PEBB 150)
and switches 40, 42, 44 and 46 connect machine 12, operating as a
generator, to grid 100 through the filters and block 70. In the
second mode (FIG. 3), blocks 150, powered by bus 101, causes
machine 14 to operate as a motor to maintain power on the flywheel
18 (switch 152 is open) and switches 40, 42, 44 and 46 connect
machine 12, operating as a generator, to grid 100 through the
filters and block 70. When there is a failure (FIG. 4) in gas
turbine 16 or generator 12 (or if there is a requirement for power
from the flywheel), switches 40, 42, 44 and 46 disconnect generator
12 and turbine 16 and instead connect to machine 14 which is
running as a generator as flywheel 18 feeds power back to grid 100
through the filters 50, 52, 54 and 56 and block 70.
[0022] In an alternate mode of operation, when the system requests
power simultaneously from gas turbine 16 and flywheel 18, flywheel
18 is sized to handle the peak load (turbine power, base load and
any pulsed load or overload) so when flywheel 18 is on line it
provides sufficient power for the total peak load. This eliminates
the need for gas turbine 16 to supply power to the load thereby
providing a system with improved efficiency over the prior art
since gas turbine 16 is optimized for the base load only and would
be unloaded when the load increases beyond the base load.
[0023] Under normal operation, the switch blocks are connecting the
gas turbine 16 to PEBB block, or converter, 70 and then to AC grid
100; at this time, switch 152 is connecting the motor 14 to
flywheel 18 to keep the flywheel spinning, i.e. storing energy and
ready for use. When the generator 12 and turbine 16 is disconnected
from the system by switches 40, 42 . . . 46 the flywheel generator
14 is connected to feed the base load and the additional pulsed or
peaking load. When a pulsed or peaking load is completed, switches
40, 42 . . . 46 reconnect gas turbine 16 which is still operational
even through having been disconnected from the system. The switch
152 connecting flywheel 18 is the same as switches 40, 42 . . . 46
and comprise dual pole transfer switches, either for connecting the
generator turbine/generator to the AC grid 100 or for connecting
the flywheel/generator 14, 18 to the grid 100.
[0024] The PEBB is used to control the electric machine coupled to
the turbine such that it switches between functioning as a motor or
a generator "on the fly" i.e. the direction of power flow
determines if the electric machine is a motor or generator (the
PEBB corresponds to the AC/DC blocks forming converter 70).
Alternatively, a separate active module could be used for motoring
and a separate possible module used for generating. In this case, a
contactor can be used to toggle which PEBB is active. In the case
of starting the turbine 16 and then using the turbine as a prime
mover, the contactor would only be switched after the rotation of
the turbine is self-sustained. Otherwise, any active PEBB would be
used without a contactor.
[0025] Each PEBB preferably comprises a three-phase diode bridge or
active rectifiers (diode blocks are not used as dc-ac blocks; if a
2-level insulated-gate bipolar transistor three phase bridge is
used as a AC/DC converter then the same bridges can be used as
DC/AC converter).
[0026] The time-dominant mode of operation for the electric machine
coupled to the flywheel is low power motoring (only providing
make-up and initial spin-up power).
[0027] The key differences between both power paths are the time
involved and the disparate power levels for motoring and generating
for the turbine and flywheel.
[0028] Since the charge/discharge (motoring/generating) cycles of
the flywheel are significantly disproportionate in power
requirements, the ability to have a variable frequency device 150
essentially .chi./N (wherein .chi. is preferably 1 and N the number
of phase sets) allows the system to use the same PEBB's for both
turbine generating and flywheel generating.
[0029] In summary, system 10 provides a power generation system
that consists of a gas turbine/generator (or multiples thereof) and
a motor/generator that is spinning a flywheel. System 10 can be a
stand alone network or can be used to support an existing AC
network handling peak loads. For example, the AC network might be
able to handle 5 MW continuously, but there can be loads that can
come in and out intermittently that are approximately 10 MW. In
that case, system 10 can be used to support the extra load. A
unique feature of the system 10 is that the same machine,
configured as a space shifted split stator as disclosed in the
copending '450 application can be used to be the generator rotated
by gas turbine 16 and also the motor/generator 14 spinning flywheel
18 (as a motor) and rotated by the flywheel acting as a generator.
The PEBB's used in the system can also be identical on the AC/DC
side and DC/AC side. One block that is AC/DC can be used to spin,
or rotate, the motor that spins up flywheel 18. Multiples (N) of
the same blocks can be utilized to convert the energy from the
flywheel/generator 18 to feed back to the bus, or grid, 100. The
same blocks are used to convert the energy from the gas turbine
generator 16 to the common AC bus, or grid 100. The reconfiguration
enables switching between the flywheel/generator 14, 18 and gas
turbine/generator 12, 16 without having to bring in new PEBB's
assuming that the gas turbine generator and flywheel do not have to
be on at the same time.
[0030] System 10 can be adapted to the following configurations:
(1) using multiple PEBB's that are switched from the flywheel
subsystem to the gas turbine subsystem; (2) the flywheel subsystem
contains at least one conventionally wound three-phase machine; (3)
the flywheel sub-system contains multiple flywheels,
motor/generators, PEBB modules, not necessarily in a 1:1:1
relationship.
[0031] FIG. 2 illustrates a variation of the system shown in FIG.
1. In particular, system 100' comprises subsystems 102 and 104,
sub-system 102 functioning to start gas turbine (generator) 106 via
motor 108. Sub-system 104 functions to charge (rotate) flywheel 110
utilizing motor 112. The power flow of sub-systems 102 and 104 is
in the direction illustrated by arrow 114. Subsystems 102 and 104
function independently of each other.
[0032] FIG. 3 illustrates the system of FIG. 1 wherein (system 200
comprising sub-systems 202 and 204) gas turbine 206 in sub-system
202 operates in a manner such that generator 208 generates AC power
in the direction of arrows 210. Sub-system 204 utilizes motor 212
to charge (rotate) flywheel 214. Power flows in the direction of
arrow 216. Sub-system 202 and 204 act independently of each other.
In this mode of operation, motor 212 is used to provide make-up and
initial spin-up power for flywheel 214.
[0033] FIG. 4 illustrates the system of FIG. 1 wherein the gas
turbine 16 is off-line and flywheel 18 is discharging (rotating)
and causing generator 12 to generate power. Since sub-systems 300
and 302 act cooperatively, the power from generator 14 flows to the
switches in sub-system 302 and then to the grid 100 as illustrated
by arrows 306.
[0034] FIG. 5 illustrates system 400 comprising sub-systems 402 and
404. The system provides a DC connection wherein prime movers 406
and 408 operate simultaneously. In particular, sub-systems 402 and
404 share a DC connection whereas in FIG. 4 an AC connection is
shared.
[0035] FIG. 6 illustrates system 500 comprising sub-systems 502 and
504, an operating mode of system 400. System 500 is used to meet
temporary peak power demand. In particular, flywheel 504 has the
capacity to work simultaneously with gas turbine 508 to meet peak
power demand. In this system the gas turbine DC/AC modules are
rated for peak power and can use passive rectification and flywheel
AC/DC modules are selected for active rectification and are rated
for flywheel charging. The negative DC connection can be always
active; the positive DC connection requires a contactor for safety
and/or margin reasons.
[0036] While the invention has been described with reference to its
preferred embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the true
spirit and scope of the invention. In addition, many modifications
may be made to adapt a particular situation or material to the
teachings of the invention without departing from its essential
teachings.
* * * * *