U.S. patent application number 12/970406 was filed with the patent office on 2011-11-24 for variable speed machine assembly and method for making the same.
Invention is credited to Jan Hemmelmann, Michal-Wolfgang Waszak.
Application Number | 20110285132 12/970406 |
Document ID | / |
Family ID | 44971887 |
Filed Date | 2011-11-24 |
United States Patent
Application |
20110285132 |
Kind Code |
A1 |
Waszak; Michal-Wolfgang ; et
al. |
November 24, 2011 |
VARIABLE SPEED MACHINE ASSEMBLY AND METHOD FOR MAKING THE SAME
Abstract
A variable speed machine assembly includes an input shaft, a
variable speed magnetically geared generator coupled to the input
shaft, an electrical machine coupled to the input shaft, and a
power converter coupled to the variable speed magnetically geared
generator and the electrical machine. The power converter is
configured to use electrical power output by the electrical machine
to control a frequency of power output by the variable speed
magnetically geared generator.
Inventors: |
Waszak; Michal-Wolfgang;
(Munich, DE) ; Hemmelmann; Jan; (Munich,
DE) |
Family ID: |
44971887 |
Appl. No.: |
12/970406 |
Filed: |
December 16, 2010 |
Current U.S.
Class: |
290/52 ;
29/592.1; 322/61 |
Current CPC
Class: |
F03D 7/028 20130101;
F03D 9/25 20160501; Y02P 70/50 20151101; H02K 7/11 20130101; H02P
9/007 20130101; Y02E 10/725 20130101; Y02E 10/72 20130101; H02K
7/1838 20130101; Y02E 10/723 20130101; H02K 16/04 20130101; Y02P
70/523 20151101; H02K 17/42 20130101; Y10T 29/49002 20150115 |
Class at
Publication: |
290/52 ; 322/61;
29/592.1 |
International
Class: |
H02K 7/18 20060101
H02K007/18; H05K 13/00 20060101 H05K013/00; H02P 9/26 20060101
H02P009/26 |
Claims
1. A variable speed machine assembly comprising: an input shaft; a
variable speed magnetically geared generator coupled to said input
shaft; an electrical machine coupled to said input shaft; and a
power converter coupled to said variable speed magnetically geared
generator and said electrical machine, said power converter
configured to use electrical power output by said electrical
machine to control a frequency of power output by said variable
speed magnetically geared generator.
2. A variable speed machine assembly in accordance with claim 1,
wherein said variable speed magnetically geared generator
comprises: a rotor coupled to said input shaft; a first set of
windings coupled to a grid and configured to output substantially
constant-frequency electrical power to the grid; and a second set
of windings coupled to said power converter and configured to at
least one of transfer electrical power to said power converter and
receive electrical power from said power converter.
3. A variable speed machine assembly in accordance with claim 2,
wherein said power converter is configured to output electrical
power to said second set of windings to control the frequency of
the power output by said first set of windings.
4. A variable speed machine assembly in accordance with claim 1,
wherein said electrical machine comprises: a rotor coupled to said
input shaft; and a set of windings coupled to said power converter
and configured to at least one of transfer electrical power to said
power converter and receive electrical power from said power
converter.
5. A variable speed machine assembly in accordance with claim 4,
wherein said electrical machine further comprises a stator
including a permanent magnet.
6. A variable speed machine assembly in accordance with claim 1,
wherein said power converter is configured to: receive electrical
power from said electrical machine; adjust a frequency of the
received electrical power; and output the adjusted electrical power
to said variable speed magnetically geared generator to control the
frequency of the power output by said variable speed magnetically
geared generator.
7. A variable speed machine assembly in accordance with claim 1,
wherein said power converter is configured to: receive
variable-frequency electrical power from said variable speed
magnetically geared generator; adjust the variable-frequency
electrical power; and output the adjusted electrical power to said
electrical machine to control a rotation of said input shaft at
said electrical machine to control said variable speed magnetically
geared generator.
8. A turbine comprising: a main shaft assembly including an input
shaft; at least one blade coupled to said main shaft assembly and
configured to rotate said main shaft assembly; and a variable speed
machine assembly coupled to said main shaft assembly, the variable
speed machine assembly comprising: a variable speed magnetically
geared generator coupled to said input shaft; an electrical machine
coupled to said input shaft; and a power converter coupled to said
variable speed magnetically geared generator and said electrical
machine, said power converter configured to use electrical power
output by said electrical machine to control a frequency of power
output by said variable speed magnetically geared generator.
9. A turbine in accordance with claim 8, wherein said variable
speed magnetically geared generator comprises: a rotor coupled to
said input shaft; a first set of windings coupled to a grid and
configured to output substantially constant-frequency electrical
power to the grid based on a mechanical rotation of said main shaft
assembly; and a second set of windings coupled to said power
converter and configured to at least one of transfer electrical
power to said power converter and receive electrical power from
said power converter.
10. A turbine in accordance with claim 9, wherein said power
converter is configured to output electrical power to said second
set of windings to control the frequency of the power output by
said first set of windings.
11. A turbine in accordance with claim 9, wherein said power
converter is configured to adjust at least one of a speed and a
direction of rotation of a magnetic field within said variable
speed magnetically geared generator with respect to a mechanical
rotation of said input shaft within said variable speed
magnetically geared generator.
12. A turbine in accordance with claim 8, wherein said electrical
machine comprises: a rotor coupled to said input shaft; and a set
of windings coupled to said power converter and configured to at
least one of transfer electrical power to said power converter and
receive electrical power from said power converter.
13. A turbine in accordance with claim 12, wherein said electrical
machine further comprises a stator, one of said rotor and said
stator comprising a permanent magnet.
14. A turbine in accordance with claim 8, wherein said power
converter is configured to: receive electrical power from said
electrical machine; adjust a frequency of the received electrical
power; and output the adjusted electrical power to said variable
speed magnetically geared generator to control the frequency of the
power output by said variable speed magnetically geared
generator.
15. A turbine in accordance with claim 8, wherein said power
converter is configured to: receive variable-frequency electrical
power from said variable speed magnetically geared generator;
adjust the variable-frequency electrical power; and output the
adjusted electrical power to said electrical machine to control a
rotation of said input shaft at said electrical machine to control
said variable speed magnetically geared generator.
16. A method for making a variable speed machine assembly, said
method comprising: coupling a variable speed magnetically geared
generator to an input shaft and a power grid; coupling an
electrical machine to the input shaft; and coupling a power
converter to the variable speed magnetically geared generator and
the electrical machine, the power converter configured to use
electrical power output by the electrical machine to control a
frequency of power output to the grid by the variable speed
magnetically geared generator.
17. A method in accordance with claim 16, wherein the variable
speed magnetically geared generator includes a first set of
windings and a second set of windings, said method further
comprising: coupling the first set of windings to the grid, the
first set of windings configured to output the power to the grid;
and coupling the second set of windings to the power converter, the
second set of windings configured to at least one of transfer
electrical power to the power converter and receive electrical
power from the power converter.
18. A method in accordance with claim 16, wherein the electrical
machine includes a rotor and a set of windings, said method further
comprising: coupling the rotor to the input shaft; and coupling the
set of windings to the power converter, the set of windings
configured to at least one of transfer electrical power to the
power converter and receive electrical power from the power
converter.
19. A method in accordance with claim 16, wherein coupling a power
converter to the variable speed magnetically geared generator and
the electrical machine further comprises coupling the power
converter to the variable speed magnetically geared generator and
the electrical machine, wherein the power converter is configured
to receive electrical power from the electrical machine, adjust a
frequency of the received electrical power, and output the adjusted
electrical power to the variable speed magnetically geared
generator to control the frequency of the power output by the
variable speed magnetically geared generator.
20. A method in accordance with claim 16, wherein coupling a power
converter to the variable speed magnetically geared generator and
the electrical machine further comprises coupling the power
converter to the variable speed magnetically geared generator and
the electrical machine, wherein the power converter is configured
to receive variable-frequency electrical power from the variable
speed magnetically geared generator, adjust the variable-frequency
electrical power, and output the adjusted electrical power to the
electrical machine to control a rotation of the input shaft at the
electrical machine to control the variable speed magnetically
geared generator.
Description
BACKGROUND OF THE INVENTION
[0001] The embodiments described herein relate generally to a
variable speed machine and, more particularly, to a variable speed
machine assembly for use with a fluid turbine, such as a wind
turbine.
[0002] At least some known wind turbines include machines for
converting variable speed mechanical input from blades of the wind
turbine into electric power that is compliant with an electrical
grid. For example, some known wind turbines include a doubly fed
induction generator (DFIG) for converting the variable speed
mechanical input. The DFIG includes a converter that has a rating
that is a percentage of a rated capacity of the wind turbine, such
as about 35% of rated capacity. Such a converter is also referred
to as a partial-rated converter. Further, the DFIG includes slip
rings and may have less reactive power control and/or lower
efficiency, as compared to other variable speed machines.
[0003] At least some other known wind turbines include permanent
magnet generators (PMG) that have a higher efficiency than at least
some known DFIGs. PMGs include a converter at the rated capacity,
also referred to as a full-rated converter. Typically, full-rated
converters include complex power electronics, which have
disadvantages, such as large size, high maintenance requirements,
and/or high cost, as compared to partial-rated converters.
BRIEF DESCRIPTION OF THE INVENTION
[0004] In one aspect, a variable speed machine assembly is
provided. The variable speed machine assembly includes an input
shaft, a variable speed magnetically geared generator coupled to
the input shaft, an electrical machine coupled to the input shaft,
and a power converter coupled to the variable speed magnetically
geared generator and the electrical machine. The power converter is
configured to use electrical power output by the electrical machine
to control a frequency of power output by the variable speed
magnetically geared generator.
[0005] In another aspect, a turbine is provided. The turbine
includes a main shaft assembly including an input shaft, at least
one blade coupled to the main rotor shaft and configured to rotate
the main rotor shaft, and a variable speed machine assembly coupled
to the main rotor shaft. The variable speed machine assembly
includes a variable speed magnetically geared generator coupled to
the input shaft, an electrical machine coupled to the input shaft,
and a power converter coupled to the variable speed magnetically
geared generator and the electrical machine. The power converter is
configured to use electrical power output by the electrical machine
to control a frequency of power output by the variable speed
magnetically geared generator.
[0006] In yet another aspect, a method for making a variable speed
machine assembly is provided. The method includes coupling a
variable speed magnetically geared generator to an input shaft and
a power grid, coupling an electrical machine to the input shaft,
and coupling a power converter to the variable speed magnetically
geared generator and the electrical machine. The power converter is
configured to use electrical power output by the electrical machine
to control a frequency of power output to the grid by the variable
speed magnetically geared generator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIGS. 1-3 show exemplary embodiments of the system and
method described herein.
[0008] FIG. 1 is a perspective view of an exemplary wind
turbine.
[0009] FIG. 2 is a schematic view of an exemplary variable speed
machine assembly that may be used with the wind turbine shown in
FIG. 1.
[0010] FIG. 3 is a cross-sectional view of an exemplary first
machine that may be used with the variable speed machine assembly
shown in FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The variable speed machine assembly described herein
converts variable speed mechanical power into constant frequency
electric power. The machine assembly includes a power converter and
two machines operating on a single shaft. The first machine is
based on a planetary magnetic gearbox and includes two sets of
windings and one rotor. The second machine includes a rotor, a
stator, and one set of windings. The second machine can be referred
to herein as an "exciter" and includes a permanent magnet rotor or
a permanent magnet stator. The power converter is configured to
transfer electrical power between one of the winding sets of the
first machine and the winding set of the second machine. Notably, a
rating of the power converter is a fraction of a rating capacity of
a turbine with which the variable speed machine assembly is used.
As such, the power converter is a partial-rated converter. In one
embodiment, the power converter has a capacity of between about 4%
and about 15% of the rated capacity.
[0012] The first machine described herein is configured to split
mechanical input power between the two sets of windings therein. A
first portion of the power is directly fed to a grid at constant
frequency by a first set of the two sets of windings. A second
winding of the two sets of windings is connected to the power
converter. The power converter is also connected to terminals of
the second machine. The power converter is configured to adjust a
frequency of the second machine to a frequency that maintains a
grid terminal frequency at a substantially constant value at the
first machine. As such, the herein-described embodiments eliminate
the slip rings used in DFIGs, while including a partial-rated power
converter.
[0013] Although a wind turbine embodiment is illustrated herein for
purposes of example, the variable speed machine assembly disclosed
herein is useful with other types of variable speed mechanical
inputs, such as, for example, a marine hydrokinetic energy
device.
[0014] FIG. 1 is a schematic view of an exemplary wind turbine 100.
In the exemplary embodiment, wind turbine 100 is a horizontal-axis
wind turbine. Alternatively, wind turbine 100 may be a
vertical-axis wind turbine. In the exemplary embodiment, wind
turbine 100 includes a tower 102 extending from and coupled to a
supporting surface 104. Tower 102 may be coupled to surface 104
with anchor bolts or via a foundation mounting piece (neither
shown), for example. A nacelle 106 is coupled to tower 102, and a
main shaft assembly 108 is coupled to nacelle 106. Main shaft
assembly 108 includes a rotatable hub 110 and a plurality of rotor
blades 112 coupled to hub 110. In the exemplary embodiment, main
shaft assembly 108 includes three rotor blades 112. Alternatively,
main shaft assembly 108 may have any suitable number of rotor
blades 112 that enables wind turbine 100 to function as described
herein. Tower 102 may have any suitable height and/or construction
that enables wind turbine 100 to function as described herein.
[0015] Rotor blades 112 are spaced about hub 110 to facilitate
rotating main shaft assembly 108, thereby transferring kinetic
energy from wind 114 into usable mechanical energy, and
subsequently, electrical energy. Main shaft assembly 108 and
nacelle 106 are rotated about tower 102 on a yaw axis 116 to
control a perspective of rotor blades 112 with respect to a
direction of wind 114. Rotor blades 112 are mated to hub 110 by
coupling a rotor blade root portion 118 to hub 110 at a plurality
of load transfer regions 120. Load transfer regions 120 each have a
hub load transfer region and a rotor blade load transfer region
(both not shown in FIG. 1). Loads induced to rotor blades 112 are
transferred to hub 110 via load transfer regions 120. Each rotor
blade 112 also includes a rotor blade tip portion 122.
[0016] In the exemplary embodiment, rotor blades 112 have a length
of between approximately 30 meters (m) (99 feet (ft)) and
approximately 120 m (394 ft). Alternatively, rotor blades 112 may
have any suitable length that enables wind turbine 100 to function
as described herein. For example, rotor blades 112 may have a
suitable length less than 30 m or greater than 120 m. As wind 114
contacts rotor blade 112, lift forces are induced to rotor blade
112 and rotation of main shaft assembly 108 about an axis of
rotation 124 is induced as rotor blade tip portion 122 is
accelerated.
[0017] A pitch angle (not shown) of rotor blades 112, i.e., an
angle that determines the perspective of rotor blade 112 with
respect to the direction of wind 114, may be changed by a pitch
assembly (not shown in FIG. 1). More specifically, increasing a
pitch angle of rotor blade 112 decreases an amount of rotor blade
surface area 126 exposed to wind 114 and, conversely, decreasing a
pitch angle of rotor blade 112 increases an amount of rotor blade
surface area 126 exposed to wind 114. The pitch angles of rotor
blades 112 are adjusted about a pitch axis 128 at each rotor blade
112. In the exemplary embodiment, the pitch angles of rotor blades
112 are controlled individually. Further, wind turbine 100 includes
a main gearbox 130 and a variable speed machine assembly 200 within
nacelle 106. In the exemplary embodiment, main shaft assembly 108
includes a first shaft 132 (shown in FIG. 2) that extends into main
gearbox 130 and a second shaft 134 (shown in FIG. 2) extends
through variable speed machine assembly 200. As such, second shaft
134 is also referred to herein as input shaft 134.
[0018] FIG. 2 is a schematic view of an exemplary variable speed
machine assembly 200 that may be used with wind turbine 100 (shown
in FIG. 1). FIG. 3 is a cross-sectional view of an exemplary first
machine 202 that may be used with variable speed machine assembly
200. Variable speed machine assembly 200 includes a first machine
202, a second machine 204, and a power converter 208. In the
exemplary embodiment, input shaft 134 extends through second
machine 204 to first machine 202. Alternatively, second machine 204
is included within first machine 202 and input shaft 134 extends to
the combined machine. Physically there is no difference between
separate machines 202 and 204 and the combined machine because all
components rotate with the same speed. In the exemplary embodiment,
power converter 208 is coupled to first machine 202 using
multi-phase leads 210 and to second machine 204 using multi-phase
leads 212. Multi-phase leads 212 extend between power converter 208
and second machine 204 and include circuit breakers 214.
[0019] First machine 202 is also referred to herein as a
variable-speed magnetically geared generator (MGG). In the
exemplary embodiment, MGG 202 includes a first set of windings 216,
a rotor 217, a second set of windings 218, a first stator 222, and
a second stator 220. Rotor 217 includes a plurality of soft
magnetic pole pieces 223. In the exemplary embodiment, a number of
pole pairs of rotor 217 and stators 220 and 222 are design
variables of variable speed machine assembly 200 and/or wind
turbine 100. A selected nominal input speed is also a design
variable of variable speed machine assembly 200 and/or wind turbine
100. More specifically, according to the selected number of pole
pairs and the input speed, in one embodiment, converter 208 only
feeds power to first machine 202, and thus second machine 204 acts
as a generator only. In an alternate embodiment, second machine 204
only acts as a motor and converter 208 only feeds power to second
machine 204. In the exemplary embodiment, second machine 204 acts
as a motor and a generator.
[0020] Further, a selection of the input speed and pole pair
numbers for stators 220 and 222 enables adjustment of a speed where
a lowest power is transferred through converter 208, which is the
point of highest system efficiency. Because wind turbine 100
usually operates at a certain wind speed, which can be described
with the statistical Weibull wind speed distribution, it is
possible to adjust first machine 202 to operate most efficiently at
the certain wind speed, and increasing the overall produced energy.
Moreover, for a given power rating of machine assembly 200 and a
given number of pole pairs of first set of windings 216 and second
set of windings 218, a higher nominal machine input speed decreases
an amount of required converter power rating, but increases a
torque and, thus, a size of the electromagnetic design.
[0021] Main shaft assembly 108 extends to rotor 217. First set of
windings 216 are coupled to first stator 222 and coupled to a power
grid 224 via circuit breakers 226. Second set of windings 218 is
coupled to second stator 220 and to power converter 208. As used
herein with reference to rotors and stators, the term "coupled to"
or variations thereof include attaching, directly or indirectly, at
least two separate parts together and/or integrally-forming at
least two parts with each other. In the exemplary embodiment, MGG
202 is configured to divide mechanical power input into two
portions of power. More specifically, first set of windings 216 is
configured to feed a first portion of power to grid 224 at a
constant frequency, and second set of windings 218 is configured to
feed a second portion of power to power converter 208 at a variable
frequency. Second set of windings 218 is also configured to receive
electrical power from power converter 208. In one embodiment, the
second portion of power is fed intermittently to power converter
208 when main shaft assembly 108 experiences a mechanical
rotational speed transient, for example, during a gust of wind.
[0022] In the exemplary embodiment, variable-speed mechanical power
input to MGG 202 is transformed into constant-frequency electric
power at first set of windings 216, and is transformed into
variable-frequency electric power at second set of windings 218.
The frequency and power variability at second set of windings 218
accounts for the speed variability of input shaft 134. More
specifically, the amount of power transferred from second set of
windings 218 to second machine 204 accounts for the speed
variability of input shaft 134 and/or main shaft assembly 108
because a relationship between the frequency of sets of windings
216 and 218 and speed of input shaft 134 is linear and follows the
rules of an electromagnetic planetary gear.
[0023] More specifically, first set of windings 216 has P.sub.S
pole-pairs, and a winding electrical frequency is .omega..sub.S.
Second set of windings 218 has P.sub.R pole-pairs, and a winding
electrical frequency is .omega..sub.R. A rotating set of soft
magnetic pole pieces 223 includes N.sub.M modulator pole pieces,
and a rotation speed is defined as .OMEGA..sub.M In the exemplary
embodiment, N.sub.M=P.sub.S.+-.P.sub.R. An equivalent rotational
speed of first set of windings 216 is defined
.OMEGA..sub.S=.omega..sub.S/P.sub.S, and an equivalent rotational
speed of second set of windings 218 is defined as
.OMEGA..sub.R=.omega..sub.R/P.sub.R. A gearing ratio i is defined
as i=P.sub.S/P.sub.R.
[0024] From the speed equations for a mechanical planetary gear
set, the gearing ratio can be defined as
i = .OMEGA. R - .OMEGA. M .OMEGA. S - .OMEGA. M , ##EQU00001##
where for mechanical planetary gears, R is a sun gear, M is a
planet carrier, and S is a ring gear. Reformulated, this becomes
.OMEGA..sub.R-.OMEGA..sub.M=i.OMEGA..sub.S-i.OMEGA..sub.M, and
substituting variables gives
.omega. R P R - i .omega. S P S = ( 1 - i ) .OMEGA. M .
##EQU00002##
For a grid connected machine where first set of windings 216 has a
frequency fixed at .omega..sub.S=.omega..sub.grid, then a resulting
electrical frequency .omega..sub.R of second set of windings 218 is
calculated as
.omega. R = [ ( 1 - i ) .OMEGA. M + i .omega. grid P S ] P R .
##EQU00003##
[0025] The power balances of power W.sub.E of second machine 204
and power W.sub.R of second set of windings 218 can be defined as
W.sub.E+W.sub.R=0,
T E .OMEGA. M + T R .omega. R P R = 0 , and T E .OMEGA. M + T R ( (
1 - i ) .OMEGA. M + .omega. S P R ) = 0. ##EQU00004##
The power balance of mechanical input power W.sub.M and electrical
power W.sub.S fed into grid 224 by first set of windings 216 can be
defined as W.sub.M+W.sub.S=0 and
T M .OMEGA. M + T S .omega. S P S = 0. ##EQU00005##
The torque balance is defined as T.sub.M+T.sub.S+T.sub.E T.sub.R=0.
Inserting the power balances into the torque balance solves the
equations for the various torque components based on the rules of
an electromagnetic planetary gear as follows:
T R = T M .OMEGA. M P S .omega. R - 1 i + .omega. S P R .OMEGA. M
##EQU00006## T E = - T R .omega. R P R .OMEGA. M ##EQU00006.2## T S
= - T M .OMEGA. M P S .omega. S ##EQU00006.3##
[0026] In the exemplary embodiment, the second portion of electric
power associated with second set of windings 218 is converted by
power converter 208 and fed into second machine 204, as described
in more detail below. The power transfer between second set of
windings 218 and second machine 204 is bidirectional and, as such,
second machine 204 also transfers power to second set of windings
218 of MGG 202 via power converter 208.
[0027] Second machine 204 includes a permanent magnet excited
machine, also referred to herein as an "exciter" and/or an
"electrical machine". Electrical machine 204 is operable as a motor
and/or a generator, as described in more detail herein. In the
exemplary embodiment, electrical machine 204 includes a rotor 228,
a stator 230 including a permanent magnet, and a set of windings
232. Alternatively, rotor 228 includes a permanent magnet, rather
than stator 230 including a permanent magnet. However, in such an
embodiment, slip rings may be used. In the exemplary embodiment,
rotor 228 is coupled to input shaft 134 for rotation of rotor 228.
Alternatively, second machine 204 is combined with first machine
202. In the exemplary embodiment, electrical machine 204 is
configured to produce electric energy to control an output
frequency of MGG 202. More specifically, electrical machine 204 is
configured to control a frequency of the power output by first set
of windings 216 to be substantially at a grid terminal frequency,
such as 50 Hertz (Hz) or 60 Hz.
[0028] Power converter 208 is a partial-rated converter. For
example, power converter is rated between about 4% of rated
capacity and about 15% of the rated capacity of wind turbine 100
(shown in FIG. 1). In the exemplary embodiment, power converter 208
is coupled to second set of windings 218 of MGG 202 and set of
windings 232 of electrical machine 204 and is configured to
bidirectionally transfer electrical power between second set of
windings 218 of MGG 202 and set of windings 232 of electrical
machine 204. When stator 230 of electrical machine 204 includes a
permanent magnet, power converter 208 rotates with input shaft 134
and/or rotor 228 of electrical machine 204. In an alternative
embodiment, electrical machine 204 can include a slip ring and/or
any other suitable device for transferring signals and/or power
between a stationary component and a rotating component.
Alternatively, when rotor 228 includes a permanent magnet, power
converter 208 is stationary, and no slip rings are required.
[0029] In the exemplary embodiment, power converter 208 is
configured to adjust a frequency of electrical machine 204 to
maintain a frequency of power output from first set of windings 216
of MGG 202 at a substantially constant value, such as a value
substantially equal to the grid terminal frequency. For example,
power converter 208 supplies electrical power from electrical
machine 204 to MGG 202 at a frequency that maintains the output
power frequency at substantially the grid terminal frequency.
During certain operational conditions, power converter 208 controls
a frequency of second set of windings 218 of stator 220 of MGG 202
such that a substantially constant angular velocity of input shaft
134 can be maintained. More specifically, machine assembly 200 can
be operated to rotate main shaft assembly 108 as a predetermined
speed depending on produced electrical power.
[0030] During normal operating conditions, MGG 202 and electrical
machine 204 act as generators--MGG 202 generates power to be fed to
grid 224, and electrical machine 204 generates power to be fed to
MGG 202 via power converter 208. In the exemplary embodiment, power
converter 208 is configured to receive electrical power from
electrical machine 204, adjust a frequency of the received
electrical power, and output the adjusted electrical power to MGG
202 to control the frequency of the power output by MGG 202. More
specifically, power converter 208 uses electrical power from
electrical machine 204 to adjust a rotation of a magnetic field
within MGG 202. By adjusting a speed and/or a direction of magnetic
field rotation with respect to mechanical rotation of input shaft
134 in MGG 202, power converter 208 adjusts the frequency of power
output to grid 224 to substantially the grid terminal frequency. In
the exemplary embodiment, a frequency of electrical power output
from electrical machine 204 is adjusted by power converter 208
based on a differential rotational speed within MGG 202, a gear
ratio, a slip, and/or any other suitable parameter before being fed
to MGG 202.
[0031] During mechanical power input transients, variable frequency
electrical power is transferred from MGG 202 to electrical machine
204 via power converter 208, and electrical machine 204 acts as a
motor to drive MGG 202 for maintaining power output at the grid
terminal frequency. More specifically, in the exemplary embodiment,
power converter 208 is configured to receive variable-frequency
electrical power from MGG 202, adjust the variable-frequency
electrical power, and output the adjusted electrical power to
electrical machine 204 to control a rotation of input shaft 134 at
electrical machine 204 to control MGG 202.
[0032] To make, assemble, and/or otherwise manufacture variable
speed machine assembly 200, MGG 202 is coupled to main shaft
assembly 108 and power grid 224. More specifically, first set of
windings 216 is coupled to grid 224. Electrical machine 204 is
coupled to input shaft 134. More specifically, rotor 228 is coupled
to input shaft 134. Further, power converter 208 is coupled to MGG
202 and electrical machine 204. More specifically, second set of
windings 218 and set of windings 232 are coupled to power converter
208. Second set of windings 218 and set of windings 232 are
configured to transmit power to, and receive power from, power
converter 208.
[0033] The embodiments described herein provide variable speed
operation with power electronics limited to a fraction of a rating
capacity. More specifically, the variable speed machine assembly
described herein includes a partial-rated power converter coupled
to a variable-speed magnetically geared generator and an exciter.
As such, the variable speed machine assembly has less power
electronics and increased reliability, as compared to variable
speed machines having a full-rated power converter. Further, it may
be possible to eliminate a transformer since the herein-described
machine assembly can be at grid voltage. Moreover, the variable
speed machine assembly described herein eliminates the use of a
slip ring, as is used in a DFIG. Additionally, the embodiments
described herein have superior efficiency and better reactive power
control, as compared to DFIGs.
[0034] Exemplary embodiments of a variable speed machine assembly
and method for making the same are described above in detail. The
methods and apparatus are not limited to the specific embodiments
described herein, but rather, components of systems and/or steps of
the methods may be utilized independently and separately from other
components and/or steps described herein.
[0035] Although specific features of various embodiments of the
invention may be shown in some drawings and not in others, this is
for convenience only. In accordance with the principles of the
invention, any feature of a drawing may be referenced and/or
claimed in combination with any feature of any other drawing.
[0036] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal language of the claims.
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