U.S. patent application number 12/644028 was filed with the patent office on 2010-11-11 for broad speed range generator.
Invention is credited to RICHARD B. FRADELLA.
Application Number | 20100283252 12/644028 |
Document ID | / |
Family ID | 41479490 |
Filed Date | 2010-11-11 |
United States Patent
Application |
20100283252 |
Kind Code |
A1 |
FRADELLA; RICHARD B. |
November 11, 2010 |
BROAD SPEED RANGE GENERATOR
Abstract
A brushless generator with permanent-magnet multi-pole rotor
disks and coreless stator winding disks includes integral
electronics to efficiently generate regulated DC current and
voltage from shaft input power over a broad speed range. Its power
rating is scalable, and it incurs no cogging torque, or friction
from gearing. Integral power control electronics includes
high-frequency pulse-width-modulated boost regulation, which
provides regulated current at requisite voltage over its broad
speed range. A main embodiment to produce DC power at widely
variable speeds includes signal processing so output power varies
according to the third power of speed. A version for use with
vertical-axis wind turbines has a relatively large diameter to
facilitate a large number of poles. Combined boost-regulation, zero
cogging torque, and no gearing, enable a wide speed range, for
better power quality and higher wind energy yields. An alternate
embodiment is intended to produce DC power from a variety of shaft
drive sources, with selectable shaft torque.
Inventors: |
FRADELLA; RICHARD B.; (San
Juan Capistrano, CA) |
Correspondence
Address: |
LEIGH HUNT FIRESTONE
7100 NORFOLK ROAD
BERKELEY
CA
94705
US
|
Family ID: |
41479490 |
Appl. No.: |
12/644028 |
Filed: |
December 22, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12463295 |
May 8, 2009 |
7646178 |
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12644028 |
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Current U.S.
Class: |
290/55 ; 290/1R;
290/54; 310/114; 310/52; 310/68D; 310/77; 322/28 |
Current CPC
Class: |
H02K 1/2793 20130101;
H02K 7/1838 20130101; H02P 2101/30 20150115; H02K 11/215 20160101;
H02K 21/24 20130101; H02P 2101/10 20150115; H02K 3/47 20130101;
H02P 2101/15 20150115; H02P 9/48 20130101 |
Class at
Publication: |
290/55 ;
310/68.D; 322/28; 310/52; 310/77; 310/114; 290/54; 290/1.R |
International
Class: |
F03D 3/00 20060101
F03D003/00; H02K 11/04 20060101 H02K011/04; H02P 9/48 20060101
H02P009/48; F03D 1/00 20060101 F03D001/00; H02K 9/22 20060101
H02K009/22; H02K 7/102 20060101 H02K007/102; H02K 16/02 20060101
H02K016/02; F03B 13/00 20060101 F03B013/00; F03G 5/06 20060101
F03G005/06 |
Claims
1. A generator, including a coreless stator and rotor assembly, and
integral power control electronics, for producing regulated DC
current and voltage, from mechanical shaft input power, over a
broad range of shaft speeds, comprising: stator disks holding
2-phase stator windings in a non-conductive non-magnetic matrix,
axially juxtaposed with abutting conductor insulation, said
windings angularly juxtaposed relative to each other 180.degree.
divided by the number of poles, said disks angularly aligned with a
selectable number of like disks, that each produce across their
windings a substantially sinusoidal voltage having amplitude and
frequency proportional to shaft speed; rotor disks holding a
plurality of axially-magnetized alternating pole permanent-magnets,
attached therein in a symmetrical circular array around and
attached to a rotatable center shaft, said rotor disks angularly
aligned with a selectable number of like disks numbering one more
than the number of stator disks, the axial magnetic field from the
rotor disks at the stator varying substantially sinusoidally with
rotor angle; two rotor angle sensors, responsive to the magnetic
field from the rotor disks, the two sensors respectively aligned
with the center of a stator winding radial segment of corresponding
phase, to sense the rotor magnetic field and produce constant peak
amplitude substantially sinusoidal signals varying with rotor
angle; and integral power control electronics, responsive to the
signals from the rotor angle sensors, and to a DC output voltage
feedback signal, and to user settings, and to stator winding
current feedback signals processed by circuits having wide dynamic
range, for controlling current through the stator windings by
high-frequency pulse-width-modulation, to provide DC power by
filtered high-frequency PWM boost-regulation fly-back, having
regulated current and voltage, for a DC load, from shaft power,
over a broad range of shaft speeds.
2. The generator of claim 1, wherein said integral power
electronics in a generator embodiment intended to produce regulated
DC current and voltage from wind turbines, with output power
proportional to the third power of speed, over a broad speed range,
further comprises: means to compare a reference command signal with
DC voltage feedback, and to provide a corrective signal therefrom;
means to provide from sinusoidal and cosinusoidal rotor angle
sensor signals, a signal proportional to rotor speed squared; means
to process the rotor angle sensor signals to provide their absolute
values, and to multiply the respective absolute values by the
speed-squared signal, for providing respective stator current
command signals; means to sense and process over a wide dynamic
range, respective stator winding currents, to obtain respective
stator winding current absolute values; means to compare the
respective stator current command signals, with the stator winding
current signals, to provide respective PWM stator current control;
and over-voltage protection means, to inhibit PWM stator current
output if DC output voltage exceeds a prescribed level.
3. The generator of claim 1, wherein said integral power control
electronics in a generator embodiment intended to generate electric
power from varied mechanical shaft power sources further comprises:
means to compare a reference command signal with DC voltage
feedback, and to provide a corrective signal therefrom; means to
compare said corrective signal with an effort level selection, to
provide an effort level signal that optimizes mechanical shaft
load; means to process the rotor angle sensor signals, to provide
their respective absolute values, and to multiply the respective
absolute values by the effort level signal, for providing
respective stator current command signals; means to sense and
process over a wide dynamic range, respective stator winding
currents, to obtain respective stator winding current absolute
values; means to compare the respective stator current command
signals, with the current absolute values, to provide respective
PWM stator current control; and over-voltage protection means, to
inhibit PWM stator current output if DC output voltage exceeds a
prescribed level.
4. The generator of claim 1, wherein said careless stator and rotor
generator assembly further comprises a vertical rotation axis and
relatively large diameter, containing a plurality of rotor disks
holding a relatively high number of poles intended to obviate
speed-up gearing, to generate regulated DC current and voltage,
over a wide speed range partly enabled by its zero cogging torque
and absence of gear friction, from vertical-axis wind turbine shaft
power.
5. The generator of claim 1, wherein said careless stator and rotor
generator assembly further comprises a horizontal rotation axis, to
generate regulated DC current and voltage over a wide speed range
partly enabled by its zero cogging torque and absence of gear
friction, from horizontal-axis wind turbine shaft power.
6. The generator of claim 1, wherein said rotor disks further
comprise axially magnetized permanent-magnets having contours to
provide nearly sinusoidal flux variation with rotor angle, for the
stator winding radial segments and for the rotor angle sensors.
7. The generator of claim 1, wherein said coreless stator and rotor
generator assembly further comprises stator disks having an
electrically non-conducting matrix that is thermally conductive, to
transfer heat from stator winding copper loss to the generator
assembly outer diameter.
8. The generator of claim 1, including the electronics of claim 2,
further comprising sliding brake surface means to limit shaft speed
when otherwise not limited by a wind turbine coupled to its shaft,
to provide continued regulated output power from the generator,
during high winds that would otherwise result in shaft speeds
beyond the generator regulated voltage range, without series buck
regulators that compromise low speed range efficiency.
9. The generator of claim 1, further comprising at least one buck
regulator in series with its output, to provide various regulated
output voltages.
10. The generator of claim 1, further comprising a 3-phase inverter
in series with its output, to provide regulated 3-phase power with
minimal distortion and selectable phase.
11. The generator of claim 1, further comprising signal processing
circuits to control pulse-width-modulation with high precision over
a very broad dynamic range.
12. The generator of claim 1, in further combination with a wind
turbine having a shaft coupled to drive said generator, wherein a
selectable number of rotor and stator disks is matched with said
wind turbine, to optimize the wind turbine load for producing
maximum generated electric power over a very broad wind speed
range.
13. The generator of claim 1, in further combination with a water
turbine coupled to drive said generator, wherein said selectable
number of rotor and stator disks is matched with said water
turbine, to optimize the water turbine load for maximum generated
power.
14. The generator of claim 1, in further combination with pedals to
drive its shaft, installed in an electric vehicle, to provide a
battery charger and recumbent cycling exercise option in the
vehicle, that also extends the vehicle driving range.
15. The generator of claim 1, further comprising an iron disk at
one end of the rotor disks and another iron disk at the opposite
end, to provide return flux paths for the axial-field rotor magnets
therebetween.
16. The generator of claim 1, further comprising a multi-pole
magnetized disk at one end of the rotor disks and another
multi-pole magnetized disk at the opposite end, to provide
continuous axial and tangential flux path rotor magnets at each
end, for an ironless generator embodiment.
17. The generator of claim 1, further comprising means to prevent
drawing even relatively low quiescent generator power compared to
electric power normally delivered to a load connected thereto, said
quiescent generator power normally needed for signal processing
electronics and status monitoring, by blocking reverse current from
the load with a relay and a diode whenever the generator output
power is less than said quiescent power.
18. The generator of claim 1, further comprising means to prevent
drawing even relatively low quiescent generator power compared to
electric power delivered to a load connected thereto, said
quiescent generator power normally needed for signal processing
electronics and status monitoring, by blocking reverse current from
the load by including a diode in series with the load.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention pertains generally to rotary dynamoelectric
machines, and more particularly to dynamoelectric machines having
novel rotor and stator structures, to generators having
permanent-magnet axial-field rotor and stator disks, and further to
cooperative integrated electronics for wide range power control and
efficient electric power interface with loads.
[0003] Applicant sets forth a brushless self-synchronous generator
with permanent-magnet rotor disks and stator winding disks,
including integral electronics, to efficiently generate DC
(direct-current) electric power, at current and voltage regulated
by the electronics, from broadly variable speed rotary mechanical
drive. Its various embodiments are intended to generate useful
electric power efficiently, especially at low speed and torque,
from a wide variety of variable speed and torque drive sources.
Moreover, it is intended to substantially improve and expand
sustainable environmentally responsible energy options, such as
wind power, hydrodynamic power, and human-power-assisted electric
vehicles. A main embodiment is intended to generate better quality
electric power from wind turbines, and higher energy yields,
compared to prior art electric power output generators powered by
wind turbines.
[0004] 2. Description of the Related Art
[0005] Poly-phase (usually 3-phase) alternating-current (AC)
salient-pole induction machines, having wound stators and rotors,
are presently directly connected to power grids in "wind farms" to
augment grid power from windy locations. They do not incur major
grid synchronization problems, as do directly connected synchronous
generators, which are mostly used in generating plants where their
shaft speed is regulated and output carefully synchronized prior to
parallel connection with on-line generators. However, induction
machines generate power only when shaft speed exceeds that needed
at zero slip speed. They cannot self-start from turbine drive, and
consume grid power (not augment it) whenever their speed falls
below a critical zero slip speed level. Moreover, their power is
unregulated, and they must be disconnected from the grid at very
high wind speeds, because their power fluctuations and internal
generator heating are excessive. For a comprehensive analysis and
Thevenin equivalent circuits of induction machines, see, for
example, the textbook "Electric Machinery" (an integrated treatment
of AC and DC machines) McGraw-Hill Book Co. 1952, by Fitzgerald
& Kingsley, Massachusetts Institute of Technology, Chapter 3
(especially page 131 and Chapter 9). For further analysis and
performance prediction of broader speed range but less efficient
2-phase induction machines, see "Effects of Phase-Shift and
Distortion on Servomotor Performance," 1960, by Richard B.
Fraclella, MSEE research and thesis, California Institute of
Technology.
[0006] Peripheral equipment needed for augmenting grid power from
wind turbines, which drive induction generators, may include gears
to increase generator shaft speed, switchgear to connect and
disconnect said generators from the grid as wind speed varies, gear
lubricant, pumps and heat exchangers to cool the lubricant, a
generator cooling system, and external heat-dumps.
[0007] Over the past two decades, power electronics has been
developed to provide a power control interface between induction
machines and DC voltage supplies such as chemical batteries. This
electronics converts the DC voltage to substantially
variable-frequency poly-phase voltage (albeit with high distortion)
at the induction machine poly-phase terminals, enabling these
machines to perform as bi-directional motors or generators. For
example, an induction machine with applied fundamental frequency
component appropriately higher than its electrical frequency at a
given shaft speed can be driven as a variable-speed induction
motor, from zero to a desired speed. With its shaft driven by
rotary power, the same induction machine with applied poly-phase
voltage having a frequency appropriately lower than its electrical
frequency at a given shaft speed can instead generate power as a
variable-speed induction generator. By reversing the poly-phase
sequence, the induction machine can likewise drive in the opposite
direction, or can generate power from a shaft driven in the
opposite direction. Silicon Controlled Rectifier (SCR) power
switching semiconductors are useful as the DC to poly-phase power
switching interface for induction machines, because they are rugged
and can control considerably higher power than comparable cost
high-frequency switching semiconductors. Moreover, the iron cores
of said induction machines have high inductance, so it is not
feasible to use a series low-loss ferrite core inductor as
described for the present invention. Induction machine core loss
would be very high, with attendant heating problems, if subjected
to high-frequency switching pulse-duration-modulation (PWM) to
provide poly-phase sinusoidal voltages having low harmonic
distortion across the induction machine stator winding
terminals.
[0008] Prior art inventions that provide examples of power
interface electronics for variable-speed induction machines that
are driven by chemical batteries and regenerate power thereto
include: U.S. Pat. No. 5.099,186 by Rippel et al; and U.S. Pat. No.
5,355,070 by Cocconi.
[0009] Synchronous AC generators include salient-pole alternators
having wound stators and permanent-magnet rotors. Their output
voltage and frequency are substantially proportional to their shaft
speed. Brushless salient-pole reluctance machines having wound
stator poles with magnetic bias from permanent magnets, is one
type. Those generators may include field windings, to afford
limited voltage regulation. Homopolar machines are also a
synchronous brushless type, with their power output frequency
proportional to speed; they afford wider range voltage adjustment.
If their field is derived only from a field winding, they will need
electric startup power for that winding. Coning torque (wherein the
rotor angle aligns its iron cores with and holds minimum magnetic
reluctance positions), like stiction and friction in gears, may
cause wind turbines to stall at low wind speeds. These shortcomings
and too low output voltage at low shaft speeds prevent usable power
generation at low wind speeds from this prior art machine. Adding a
boost regulator in series with the rectified and filtered
alternator type generator output can facilitate higher voltages at
low shaft speeds, needed for loads such as chemical batteries, but
the boost regulator incurs tandem losses and machine cogging may
stall the wind turbine driving it so no electric power output is
produced from this prior art machine at low wind speeds.
[0010] By comparison, the present invention is intended to generate
power at requisite voltage over its entire wide speed range, will
not need electric startup power from its load or any other external
source, and will efficiently generate power even from very low
shaft torque rotation from low wind speeds, not stalled by cogging
torque, stiction, or friction.
[0011] Besides their use for AC power generation in power plants,
applications for synchronous generators range widely, usually with
their AC outputs rectified, to charge batteries and the like.
However, their varying voltage and frequency can be a major
drawback. Generated and rectified voltage must be sufficient, and
usually regulated, to meet needs of given applications. Moreover,
very low frequency ripple at low shaft speed requires large filter
capacitors, which cost more and have shorter lifetimes than ceramic
or film capacitors. These properties usually limit synchronous
generator applications to high shaft speeds. Their cogging torque
is another drawback. Peripheral equipment needed for augmenting
grid power, from alternators used as generators driven by wind
turbines, usually include gears to increase generator shaft speed,
rectifiers to convert their AC outputs to DC, and power inverters
to convert the DC to regulated AC, if connected to augment grid
power. Chemical battery charging applications require a DC voltage
equivalent to the battery voltage. Said alternators generally
produce output voltage proportional to their shaft speed.
Therefore, they cannot deliver battery charging current at low
shaft speeds, and a battery charger may be required to control
charging current and voltage.
[0012] Brush-commutated DC generators may have permanent-magnet
field excitation. They may also have field excitation windings, for
limited output voltage adjustment. Besides shorter lifetimes due to
their commutator brush and armature wear, commutator sparking can
be troublesome; and, similar to most prior art generators, their DC
output voltage is proportional to shaft speed. Moreover, their
varying output voltage precludes many low shaft speed applications,
unless their output is connected to loads via boost regulator
circuits. Alternatively, their varying output voltage and current
may require a buck regulator, between the generator output and its
load. Such external and series electronics reduces overall power
efficiency, particularly at low turbine shaft speeds.
[0013] Regardless of said drawbacks, these machines are widely used
as generators for some applications. Peripheral equipment, for use
as generators driven by wind turbines, may include speed-up gearing
and output rectifiers. Said rectifiers may be needed, to prevent
power from a DC power-bus load, which it feeds, such as chemical
batteries it is meant to charge, from driving said DC generator as
a motor, and discharging connected batteries whenever the generator
output voltage is less than the battery voltage. Power regulator
circuits, such as battery chargers, are usually needed. Besides
these limitations, brush-commutated generators also need periodic
commutator maintenance; as their commutators are damaged with use,
by wear and sparking.
[0014] Gearing needed to increase prior art generator shaft speed,
so prevalent in wind power systems, also needs bearings for the
gears, is subject to wear, needs periodic maintenance, and incurs
power losses. The gearing stiction further inhibits and usually
prevents power generation at low wind speeds. Conversely, the
present invention, having no cogeing torque and no speed-up
gearing, is intended to generate power over a very wide speed
range.
[0015] Most electric motors can be used as generators. There is
fundamentally no difference, between most prior art motors and
generators, of a specific type, except for how they are used to
meet needs of specific applications. For example, an induction
machine can serve as an induction motor or as a generator. Motors
used in ubiquitous machinery, tools, and appliances can be
configured mechanically and electrically as generators.
[0016] Insofar as drive speed and torque is regulated at steam
driven and large hydroelectric power plants, the prior art
generators described above have provided acceptable options, to
generate most of the electric power that is distributed by power
grids, for over a century.
[0017] Smaller and portable versions of said generators, driven by
fuel-burning engines, also serve viable small markets. However,
need for wider speed range has been lone recognized.
[0018] Some prior art inventions have intended to accommodate
variable-speed drives, by means substantially different from my
present invention:
[0019] U.S. Pat. No. 4,694,187 "Electromechanical Constant Speed
Drive Generating System" by Baker, includes a mechanical
differential gear, to obtain constant speed drive for a generator.
It is mainly intended to accommodate variable-speed aircraft engine
drive, by including controlled variable compensatory drive. It does
not teach a generator assembly similar to the present invention,
nor does it include electronics similar to the present
invention.
[0020] U.S. Pat. No. 6,969,922 "Transformerless Load Adaptive Speed
Controller" by Welches, includes electromechanical means, to obtain
constant speed generator drive, from a variable-speed drive source.
Its generator assembly is substantially different from the present
invention, and it does not teach electronics similar to the present
invention.
[0021] U.S. Pat. No. 5,982,074 "Axial Field Motor/Generator" by
Smith et al and my U.S. Pat. No. 4,520,300 teach, with some
differences, a motor/generator assembly having multi-pole axial
magnetic field rotor disks and stator disks between them, but they
do not set forth electronics similar to the present invention,
intended to efficiently generate regulated electric power over a
broad speed range.
[0022] U.S. Pat. No. 5,245,238 "Axial Gap Dual Permanent Magnet
Generator" by Lynch et al. describes means for generating constant
output voltage that do not include electronics similar to the
present invention. Its generator assembly and rotor disks are also
distinctly different from those herein described in all embodiments
of the present invention.
[0023] U.S. Pat. No. 7,190,101 "Stator Coil Arrangement for an
Axial Airgap Electric Device Including Low-Loss Materials" by
Hirzel, teaches a substantially different generator assembly and
materials, and does not set forth electronics similar to the
present invention.
[0024] U.S. Pat. No. 5,021,698 "Axial Field Electrical Generator"
by Pullen et al. describes a high-speed generator assembly
substantially different from the present invention, and does not
describe electronics.
[0025] U.S. Pat. No. 6,217,398 "Human-Powered Or Human-Assisted
Energy Generation And Transmission System With Energy Storage Means
And Improved Efficiency" by Davis; and U.S. Pat. No. 7,021,978
"Human-Powered Generator System With Active Inertia And Simulated
Vehicle" by Jansen; describe means to use variable effort pedal
power. They teach using electric generators with operator
adjustable control means, and their advantages over mechanical
drives, for augmenting vehicle power, in applications including
electric vehicles, watercraft, and the like. However, they do not
teach generator assembly configurations nor an electronics power
interface as set forth in the present invention.
[0026] Other exemplary patents for rotary dynamoelectric machines
and for other apparatus which may or may not be related but which
provide illustration from which the teachings are incorporated
herein by reference, include: U.S. Pat. No. 295,534 by Frick; U.S.
Pat. No. 459,610 by Desroziers; U.S. Pat. No. 1,566,693 by
Pletscher; U.S. Pat. No. 2,743,375 by Parker; U.S. Pat. No.
2,864,964 by William Kober; U.S. Pat. No. 3,050,650 by Jacques;
U.S. Pat. No. 3,069,577 by Royal; U.S. Pat. No. 3,090,880 by Henri;
U.S. Pat. No. 3,091,711 by Jacques; U.S. Pat. No. 3,124,396 by
Barager; U.S. Pat. No. 3,219,861 by Burr; U.S. Pat. No. 3,230,406
by Jacques; U.S. Pat. No. 3,231,807 by Willis; U.S. Pat. No.
3,239,702 by Van De Graaff; U.S. Pat. No. 3,304,598 by Jacques;
U.S. Pat. No. 3,337,122 by Johann; U.S. Pat. No. 3,375,336 by
Hayner et al; U.S. Pat. No. 3,401,284 by Park; U.S. Pat. No.
3,407,320 by Mclean; U.S. Pat. No. 3,441,761 by Milton et al; U.S.
Pat. No. 3,569,753 by Babikyan; U.S. Pat. No. 3,584,276 by Ringland
et al; U.S. Pat. No. 3,696,277 by Liska et al; U.S. Pat. No.
3,731,984 by Habermann; U.S. Pat. No. 3,796,039 by Lucien; U.S.
Pat. No. 3,845,339 by Heinzmaim et al; U.S. Pat. No. 3,899,731 by
Smith; U.S. Pat. No. 3,982,170 by Glitter et al; U.S. Pat. No.
4,127,799 by Nakamura et al; U.S. Pat. No. 4,207,510 by Woodbury;
U.S. Pat. No. 4,228,391 by Owen; U.S. Pat. No. 4,264,856 by
Frierdich et al; U.S. Pat. No. 4,295,083 by Leenhouts; U.S. Pat.
No. 4,358,723 by Scholl et al; U.S. Pat. No. 4,371,801 by Richter;
U.S. Pat. No. 4,384,321 by Rippel; U.S. Pat. No. 4,390,865 by
Lauro; U.S. Pat. No. 4,394,597 by Mas; U.S. Pat. No. 4,415,963 by
Rippel et al; U.S. Pat. No. 4,417,194 by Curtiss et al; U.S. Pat.
No. 4,426,613 by Mizuno et al; U.S. Pat. No. 4,483,570 by Inoue;
U.S. Pat. No. 4,513,214 by Dieringer; U.S. Pat. No. 4,618,806 by
Grouse; U.S. Pat. No. 4,645,961 by Malsky; U.S. Pat. No. 4,656,413
by Bourbeau; U.S. Pat. No. 4,694,187 by Baker; U.S. Pat. No.
4,734,339 by Barthold; U.S. Pat. No. 5,021,698 by Pullen et al;
U.S. Pat. No. 5,117,141 by Hawsey et al; U.S. Pat. No. 5,204,569 by
Hino et al; U.S. Pat. No. 5,258,697 by Ford et al; U.S. Pat. No.
5,289,361 by Vinciarelli; U.S. Pat. No. 5,341,075 by Cocconi; U.S.
Pat. No. 5,392,176 by Anderson; U.S. Pat. No. 5,419,212 by Smith;
U.S. Pat. No. 5,441,222 by Rosen; U.S. Pat. No. 5,495,221 by Post;
U.S. Pat. No. 5,514,923 by Gossler et al; U.S. Pat. No. 5,525,894
by Heller; U.S. Pat. No. 5,614,777 by Bitterly et al; U.S. Pat. No.
5,681,012 by Rosmann et al; U.S. Pat. No. 5,705,902 by Merritt et
al; U.S. Pat. No. 5,712,549 by Engel; U.S. Pat. No. 5,717,303 by
Engel; U.S. Pat. No. 5,729,118 by Yanagisawa et al; U.S. Pat. No.
5,754,425 by Murakami; U.S. Pat. No. 5,783,885 by Post; U.S. Pat.
No. 5,798,591 by Lillington et al; U.S. Pat. No. 5,847,480 by Post;
U.S. Pat. No. 5,861,690 by Post; U.S. Pat. No. 5,880,544 by Ikeda
et al; U.S. Pat. No. 5,883,499 by Post; U.S. Pat. No. 5,969,446 by
Eisenhaure et al; U.S. Pat. No. 5,977,677 by Henry et al; U.S. Pat.
No. 5,977,684 by Lin; U.S. Pat. No. 6,011,337 and U.S. Pat. No.
6,049,149 by Lin et al; U.S. Pat. No. 6,121,704 by Fukuyama et al;
U.S. Pat. No. 6,130,831 by Matsunaga; U.S. Pat. No. 6,137,187 by
Mikhail et al; U.S. Pat. No. 6,166,472 by Pinkerton et al; U.S.
Pat. No. 6,246,146 by Schiller; U.S. Pat. No. 6,259,233 by Caamano;
U.S. Pat. No. 6,262,505 by Hockney et al; U.S. Pat. No. 6,288,670
by Villani et al; U.S. Pat. No. 6,388,347 by Blake et al; U.S. Pat.
No. 6,407,466 by Caamano; U.S. Pat. No. 6,750,588 by Gabrys; U.S.
Pat. No. 6,815,934 by Colley; U.S. Pat. No. 6,858,962 by Post; U.S.
published patent application 2006/0208606 by Hirzel.
[0027] Additional patents by the present inventor, the teachings
which, are additionally incorporated herein by reference, include:
U.S. Pat. Nos. 4,085,355 and 4,520,300 by Fradella; U.S. Pat. Nos.
6,566,775 and 6,794,777 by Fradella.
OBJECTS OF THE INVENTION
[0028] There is a great need for generators that are more
compatible with widely variable speed and torque rotary shaft power
from wind turbines. Generators having such useful attributes can
enable vast sustainable power systems, without shortcomings
associated with prior art power generators. A few such examples are
described next.
[0029] Optimally loaded wind turbines can harvest sustainable
mechanical power from highly variable winds. My present invention
generator can convert highly variable shaft power to usable
electric power having regulated current and voltage. An embodiment
for wind power efficiently generates electric power that is
proportional to the third power of speed, over a very broad speed
range. It would greatly enhance power quality and produce
approximately double the prior art generator electric power energy
yields from wind, by harvesting electric power during prevalent low
wind speeds and continue to harvest electric power over the entire
wind speed spectrum.
[0030] Moreover, its scalability facilitates optimal wind turbine
loading, without incurring re-tooling expenses to achieve a broad
power rating range. The importance of optimal loading is best
explained by considering extreme mismatch between a wind turbine
and the generator it drives. Potential wind turbine output power is
not substantially harvested if generator power capacity is so
slight that the wind turbine coupled to it has minuscule torque
load. Conversely, output power is zero when generator loading is so
high that it causes the wind turbine to stall. Those versed in the
art of generating electric power from wind turbines know that
potential wind turbine output power as a function of wind speed is
a continuous function, whose maximum power yield corresponds to
optimal loading, facilitated by matching a generator to the wind
turbine that can best drive it, over a broad wind speed range. Said
speed and load scaling and matching is a primary attribute of the
present invention.
[0031] Considering another alternate embodiment, a generator that
can convert variable-speed pedal power from a recumbent cyclist, in
an electric vehicle, that charges onboard batteries and thereby
extends the practical vehicle range, while affording a healthy
exercise option, is an example of an alternate embodiment of the
present generator invention. Considering yet another alternate
embodiment example, fitness exercise gyms, having exercise
equipment connected to such generators, could meet their onsite
power needs and perhaps even return power to a utility grid.
Considering another application, wave motion and water flow from
rivers and streams is variable. Nevertheless, locations exist where
the present generator invention can afford an opportunity for
environmentally responsible electric power therefrom.
[0032] Accordingly, a general objective of the present invention is
to provide a generator, which does not require speed-up gearing to
increase its shaft speed, and which has zero cogging torque. A main
objective is to provide a generator, which can efficiently generate
better quality electric power, with controlled current and voltage,
especially at very low shaft speeds, over a very broad speed range.
It also should facilitate optimal wind turbine loading. Its shaft
would preferably be powered by wind turbines having means to limit
maximum speed by varying blade pitch or deflecting wind from the
blades when a desired maximum speed is reached. When that is not
feasible, a friction brake may be added to limit turbine shaft
speed.
[0033] Power generation from wind turbines is expected to be a
major application for the present invention. Since turbine shaft
speed usually is substantially proportional to wind speed, and
shaft torque is usually proportional to wind speed squared, loading
the turbine shaft and outputting electric power so it is
proportional to the third power of shaft speed, will extract
maximum power over a very broad wind speed range, from essentially
all types of wind turbines.
[0034] Accordingly, a specific objective for a primary embodiment
of the present invention, especially at relatively low typical wind
speeds, is to regulate output current and voltage, so that useful
regulated electrical output power is proportional to the third
power of shaft speed.
[0035] Another objective is to provide a variable speed generator
responsive to user selected torque settings, which can efficiently
generate electric power at requisite voltage, from human power, to
pedals driven by a driver who would benefit from recumbent cycling
exercise. This would also increase driving distance range and
thereby appreciably enhance ultra-light electric road vehicles
having on-board batteries and a plug-in charger, photovoltaic
exterior top surfaces, and brushless regenerative ultra-efficient
motors in wheels, which include radial-compliant springs to hold
relatively large diameter tire rims. Such an electric road vehicle
is one of many examples of practical, sustainable,
environment-responsible, low-cost transportation means that would
be enhanced by the present invention generator.
[0036] Means to achieve said objectives and attributes of the
present invention are described and illustrated herein, by
explanations that will be clear to multi-disciplinary science
engineers and to those versed in the art of electric power
generators. It will be understood that those versed in the art can
apply various other implementations and parts, to achieve the means
and functions described herein.
BRIEF SUMMARY OF THE INVENTION
[0037] The present generator invention is intended to provide
useful electric power, from rotary mechanical power, over a very
broad speed range, by combining a coreless (i.e., having no salient
high-permeability iron cores) permanent-magnet assembly, with
integral electronics to control its stator winding current. This
coreless assembly is constituted by axial-field rotor magnets,
affixed within rotor disks, forming an alternated pole circular
array. With rotation, the magnets provide a time-varying magnetic
field pattern that interacts with preferably 2-phase stator
windings in the assembly. Said windings are connected to integral
PWM (Pulse-Width-Modulation) high-frequency-switching control
electronics in a boost regulator configuration.
[0038] Substantially sinusoidal voltage generated, across the
stator winding terminals, has amplitude and frequency proportional
to rotor disk rotational speed. Said voltage causes current in the
stator windings and a series inductance, controlled by PWM
power-switching transistors, in series with the windings and the
inductance when ON, that are switched ON/OFF at a very high
frequency. When the transistors are switched ON, the stator voltage
causes current to increase through the series inductance. Then,
each time the transistors are switched to OFF, free-wheeling diodes
provide an alternate path to high-frequency filter capacitors in
parallel with a DC load, for resulting high-frequency current
pulses, sustained by the series inductors. Current through the
stator windings and series inductance is thus controlled by
high-frequency PWM switching, so it is substantially sinusoidal, in
phase with the voltage across the stator windings, and includes an
inherent (preferably very small) triangular-wave component at the
relatively high PWM ON/OFF switching frequency.
[0039] Current pulses through the diodes, from each of the 2
phases, are filtered by the capacitors, and preferably also by a
small series inductor between the capacitors and the DC load. The
filtered current from each phase is substantially a sinusoid,
having a frequency double that of the sinusoidal stator voltage and
current, and a DC average half the rectified sinusoidal current
peak value. Said rectified sinusoidal currents from each phase have
opposite polarities relative to each other. Thus, when the current
from one phase is at its peak, current from the other phase is
zero. Main system elements and combinations, of the present
invention, include: [0040] (1) Rotor magnets to provide a rotating
nearly sinusoidal field pattern to each phase of a coreless stator
winding, with relative motion therebetween, as the rotor spins,
without magnetically cycling iron or magnets in their closed
magnetic flux paths, and thus not incurring magnetic hysteresis
losses and togging torque. [0041] (2) Rotor magnet sensors,
responsive to rotor angle, each aligned with a respective stator
conductor phase, to each provide an alternating nearly sinusoidal
feedback signal responsive to rotor angle, used by integral
electronics to control respective stator winding current. [0042]
(3) Current sensors, to each provide a respective current feedback
signal over a very broad dynamic range, corresponding to respective
stator conductor current. [0043] (4) Signal processing electronics,
normally responsive to the rotor magnet and current sensors, and to
DC voltage feedback, to control stator current by PWM and thereby
efficiently generate regulated DC current and voltage, from wide
speed range rotational power, by boost regulation (fly-back
inductor and free-wheeling diode pulse current generation and
rectification filtered by high-frequency pulse averaging
capacitors). This enables useful DC power generation at requisite
DC voltage over a very broad speed range. [0044] (5) Scalable
combinations of these elements, that facilitate a wide power range,
without need for many different size parts and the tooling required
to manufacture them.
[0045] Improvements to the prior art will be apparent to those
versed in the art and in the various engineering disciplines
encompassed by it, from the following description of the invention,
when considered in conjunction with the accompanying drawings,
wherein:
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0046] FIG. 1 illustrates the main features of my present
invention, by a functional block diagram and schematic, which
concisely conveys its integrated system elements. It will be
clearly understood by electronic engineers and those versed in the
art.
[0047] FIG. 2 illustrates the main features of a present invention
embodiment intended as a generator for use with wind turbines, by a
detailed functional circuit schematic of the Power Control
Electronics shown in FIG. 1. It will be clearly understood by
electronic engineers.
[0048] FIG. 2A illustrates an alternate embodiment for a
self-starting generator system that never draws power from its
load. Other embodiments may draw up to a few watts for signal
processing quiescent power and status display, when wind power is
below this amount.
[0049] FIG. 3 illustrates the main features of an embodiment
intended mainly as a generator for use with human-power-assisted
electric vehicles, by a detailed functional circuit schematic of
the Power Control Electronics shown in FIG. 1.
[0050] FIG. 4 shows a typical location wind speed Rayleigh
statistical distribution, normal wind turbine mechanical power as a
function of wind speed, and resulting predicted available wind
turbine energy yield over the entire wind speed range.
[0051] FIG. 5A illustrates a detailed cross-sectional view of a
vertical spin axis present invention generator assembly, intended
mainly for vertical-axis wind turbines.
[0052] FIG. 5B shows an isometric projection view of the vertical
spin axis generator assembly shown in FIG. 5A.
[0053] FIG. 6A illustrates a detailed cross-sectional view of a
horizontal spin axis generator assembly, intended for
horizontal-axis wind turbines and general applications.
[0054] FIG. 6B shows an isometric projection view of the horizontal
spin axis generator assembly shown in FIG. 6A.
[0055] FIG. 7A-B illustrates two among many options of a rotor disk
in the generator assembly, each having a circular array of
receptacles to hold affixed therein an even number of alternated
pole axial-field magnets.
[0056] FIG. 8A illustrates the electrically non-conductive,
thermally conductive, body of each stator disk, including space
within it for holding and connecting to its two stator
windings.
[0057] FIG. 8B illustrates the two stator windings, each pre-formed
to fit axially abutted to each other, within the stator disk shown
in FIG. SA.
[0058] FIG. 9A-B shows two circuits that respectively provide from
a current sensor having a nominal 2.5 vdc offset at zero current
and 1 v to 4 v maximum range output signal corresponding to
respective peak current at plus and minus polarity, a precise and
very broad range output voltage signal proportional to the absolute
value of said current.
[0059] FIG. 10A-B-C shows nearly sinusoidal 2-phase stator voltages
V.sub.s sin(wt) and V.sub.s cos(wt), with stator currents I.sub.s
sin(wt) and I.sub.s cos(wt), in phase relation to filtered PWM
pulse output currents I.sub.s sin.sup.2(wt) and I.sub.s
cos.sup.2(wt), as functions of time.
[0060] FIG. 11A illustrates a buck regulator in series with the
FIG. 1 generator DC output, to limit load current and voltage, for
use with Wind turbines having substantially no speed limiting
means.
[0061] FIG. 11B illustrates a 3-Phase inverter in series with the
DC Power Bus output of the generator shown in FIG. 1, to provide
high quality, regulated and synchronized current, from
variable-speed wind turbines and various shaft drive sources, for
3-Phase power grids.
[0062] FIG. 12 shows a circuit for providing regulated and closely
tracking +12 vdc, -12 vdc, and +5 vdc supplies, for the generator
rotor angle sensors and the signal processing circuits.
DETAILED DESCRIPTION OF THE INVENTION
[0063] Main elements and combinations of this new generator are set
forth herein and illustrated in FIG. 1. This invention implements a
new cooperative combination of elements based upon several
engineering disciplines. They include electronics, magnetics,
feedback control systems, thermal, magnetic and stress
finite-element-analysis, SPICE dynamic circuit and system
simulation, rotational dynamics, aerodynamics, hydrodynamics, and
materials science, Each discipline has standard terminology and
illustration methods, to convey its structures and system
combinations in the most concise and understandable way to persons
versed in those disciplines. The descriptions and illustrations
herein are intended to convey the most essential features of the
present invention accurately, clearly, and concisely. Features set
forth in prior art, with new improvements facilitated by the
present invention, are herein briefly described, to explain
differences and to provide clear comparisons. While dimensions,
tolerances and the like are presented throughout this document to
facilitate better understanding of the design of the preferred
embodiment, it will be understood that other dimensions, tolerances
and the like are additionally contemplated and will be clearly
apparent to those versed in the appropriate arts and sciences.
[0064] Manifested in this generator assembly and integral power
control electronics, main elements and combinations of the present
invention are set forth herein and illustrated in FIG. 1. This
generator system provides a unique combination of a coreless
axial-field generator and cooperative power control electronics.
The axial-field generator has a closed magnetic field, produced by
a circular array of alternated pole axially magnetized permanent
magnets, affixed within two or more rotor disks. This magnetic
field interacts with pulse-width-modulation (PWM) controlled
preferably 2-phase current through 2-phase radial stator winding
segments, in one or more coreless stator disks juxtaposed between
the rotor disks.
[0065] Since the stator windings are not surrounded by
high-permeability iron cores, forces due to current through their
radial segments, interacting with the magnetic field, act directly
on the stator windings. In contrast, most prior art generators
forces act mainly on iron core poles. Disks holding the stator
windings are non-magnetic and electrically non-conductive.
[0066] The stator disks must have sufficient thermal conductivity
to transfer heat due to stator current copper losses, from the
stator windings to the generator exterior. Additive molding
materials and methods to increase thermal conductivity of
electrically non-conductive materials are broadly available from
many commercial sources. Powdered aluminum is one exemplary and
widely used additive, which is mixed with injection-molded resins.
The small aluminum particles are pre-treated so a thin
non-conductive surface layer covering each particle insulates it
from adjoining particles, resulting in an electrically
non-conductive mix that has relatively high thermal
conductivity.
[0067] The generator assembly design and manufacturing processes of
the present invention enables stator disks having considerably
higher and consistent thermal conductivity, compared to other
electrically non-conductive materials. Moreover, these generator
assemblies are readily scalable, by varying their number of rotor
and stator disks, to optimize load matching with various turbines
while minimizing production and inventory costs.
[0068] Most significantly, this generator system does not have
cogging torque, magnetic hysteresis power loss, and eddy loss that
would otherwise result from iron cores of prior art salient pole
generators. With integral electronics boost regulation, relatively
large diameter rotor and stator disk assemblies, and relatively
large number of poles thereby facilitated, need for speed-up
gearing is also obviated. Prior art generator cogging torque and
gearing stiction prevent shaft rotation at the low torque levels
produced at low wind speeds, so said prior art can generate
electric power only during high wind speeds. Therefore, prior art
generators relinquish power over a prevalent wind speed range.
Conversely, the present invention provides steady power having both
current and voltage control, compared to prior art generators that
too frequently need to be disconnected or generate high power
bursts with no current or voltage control. These power
characteristics are known by electrical engineers and by the
electric power industry as factors that determine merit and a
measure of power quality.
[0069] Stator winding radial segments of the present invention are
in a magnetic field varying with both position and time (whereas,
in most prior art generators, the magnetic field flux is mainly
confined within surrounding iron poles). Therefore, the stator
winding conductor options are a design trade-off, between spiral
Litz wire having many individually insulated strands, so it does
not incur substantial eddy losses as the rotor spins, and
single-strand magnet wire. Besides lower eddy losses, multi-strand
wire is easily formed, without specialized tooling. However, spiral
Litz wire, and a sleeve around it, has a substantially larger
diameter than equivalent wire-gauge single-strand magnet wire, and
is considerably more costly. Moreover, eddy loss in stator
conductors is not a significant problem at low rotor speeds (where
maximum generator efficiency is most important). Therefore,
single-strand magnet wire, formed by new methods enabled by the new
stator disk geometric details of the present invention, provides a
compact lower cost option. The stator windings will preferably be
preformed, and then placed in a mold, to become the functional
electromagnetic element of each injection-molded stator winding
disk. Magnet wire having a square cross-section is preferable over
a round cross-section, mainly because it accommodates about 20%
more copper area in a given space.
[0070] Additionally, the present invention includes integral
electronics, to enable high-efficiency controlled output current
and voltage, over a shaft speed range of at least 10-to-1. For
shaft drives having speed with no limits, whence the generator
stator winding peak voltage (generated by shaft rotation) exceeds
the desired DC output voltage, a commercially available buck
regulator 2 can be added to generator 1, to maintain requisite load
current and voltage, as shown in FIG. 11A. Alternatively, to
provide high quality, current regulated 3-Phase power, synchronized
at a desired phase shift, to a 3-Phase power grid, a commercially
available DC-to-AC 3-Phase power inverter 2 can be added to
generator 1, as illustrated in FIG. 11B.
[0071] With reference to FIG. 11A, the generator of FIG. 1 is
designated block 1. Its output voltage, which increases
proportional to shaft speed when driven beyond its control range,
is applied to the DC Power Bus, with capacitance C1 to power
ground, and input to commercially available Buck Regulator 2. The
Buck Regulator preferably has internal PWM current control and is
also responsive to negative voltage feedback. Its PWM output
applies pulses at voltage peaks essentially equal to the DC Power
Bus voltage level. V.sub.DC. Inductor 3 maintains current, with
minimal high-frequency PWM ripple, to the Regulated Power Load.
Free-wheeling diode D provides a current path from power ground,
when the Buck Regulator output PWM power switch is OFF, such that
Regulated Power Load
Voltage=(V.sub.DCload)(T.sub.on)/(T.sub.on+T.sub.off). Input
capacitor C2 should have low equivalent resistance and inductance,
to filter voltage ripple due to the current pulses drawn by Buck
Regulator 2. Capacitors C1 and C2 facilitate relatively large
distance between generator 1 and buck regulator 2. Possible slip
rings 4 and 5, in series with the two conductors between 1 and 2,
are intended to accommodate unlimited axis direction change of
axial-flow wind turbines, in response to wind direction changes.
The rotational axis of said turbines is substantially maintained
parallel to wind direction. Output capacitor C3 need only filter a
slight ripple current. Inductor 3 preferably includes a ferrite
core having low losses at Buck Regulator 2 relatively
high-frequency PWM switching.
[0072] With reference to FIG. 11B, the generator of FIG. 1 is
designated by block 1. Its output voltage, which increases
proportional to shaft speed if driven beyond its control range, is
applied to the DC Power Bus, with capacitance C1 to power ground,
and preferably fed to a commercially available 3-Phase Power
Inverter 2. For a "Y" connected 3-Phase power grid having 3
balanced lines with their respective sinusoidal peak voltages
V.sub.ac relative to "neutral" (usually "ground"), the inverter,
responsive to the voltages on each of the 3 grid power lines 3a,
3b, and 3c, provides regulated sinusoidal peak currents I.sub.ac
that are synchronized to said respective voltages. Current fed to
the grid can be selectively in-phase with the grid voltage, leading
phase, or lagging phase. It will be understood by those versed in
the art, that respective averaged current I.sub.DC at voltage
V.sub.DC drawn from generator 1, by 3-Phase Inverter 2, feeds power
to Inverter 2 equal to (I.sub.DC)(V.sub.DC). Further, it can be
shown that (I.sub.DC)(V.sub.DC)=(1.5)(I.sub.ac)(V.sub.ac). Yet
further, it can be shown that current drawn by 3-Phase Inverter 2
has essentially no 60-Hz or 120-Hz ripple components. However, said
current will be drawn as high-frequency PWM pulse current,
requiring relatively small filter capacitor C2. Slip rings 4 and 5
may also be included, to facilitate unlimited horizontal-axis wind
turbine yaw angle with wind direction change.
[0073] Conversely, a single-phase 60-Hz power inverter draws
current (I.sub.DC)[1+sin(wt)], where frequency (w) is 120-Hz. This
requires a relatively large capacitance, to filter the sinusoidal
component of current drawn from DC sources that are effectively
current-regulated, such as photovoltaic solar panels, and the
flywheel batteries described in my U.S. Pat. Nos. 6,566,775 and
6,794,777. For sinusoidal 60-Hz peak output voltage V.sub.ac, a
single-phase inverter provides a regulated sinusoidal peak current
I.sub.ac to augment AC line power, which is synchronized to the AC
line voltage. With adequate capacitance to filter the 120-Hz
current component drawn from generator 1, it can be shown that
(I.sub.DC)(V.sub.DC)=(0.5)(I.sub.ac)(V.sub.ac).
[0074] Those versed in the art will understand that the same
generator assembly of my present invention, combined with power
control electronics different from the electronics set forth
herein, can function as a variable-speed reversible brushless
regenerative motor. Detailed descriptions of such motor system
configurations are taught in my U.S. Pat. No. 4,085,355
"Variable-speed Regenerative Brushless Electric Motor and
Controller System", and my U.S. Pat. No. 4,520,300 "Brushless
Ultra-Efficient Regenerative Servomechanism." the contents of each
which are incorporated hereinabove by reference.
[0075] The general embodiment of my present invention is
illustrated by FIG. 1, which shows integration of the generator
assembly, electronics components connected thereto, and power
control electronics. It is applicable to all embodiments of the
invention. Equations shown below are considered in conjunction with
the current and voltage waveforms shown in FIG. 10A-B-C; and the
remaining figures, and will be clearly understood by electronic
engineers and by those reasonably versed in the art.
[0076] With reference to FIG. 1, Phase 1 stator current is
controlled by pulse-width-modulated (PWM) Q1 and Q2 switching;
concurrently with like Phase 2 stator current control by Q3 and Q4.
The 2-phase current control circuits, connected to a DC power bus,
by diodes D1, D2, D3, and D4, results in PWM pulse currents that,
when PWM pulses are filtered, are equal to I.sub.a sin.sup.2(wt)
from Ph.1 stator winding 1 and I.sub.a cos.sup.2(wt) from Ph.2
stator winding 2. Said filtered bus currents combine so generated
currents are I.sub.a=V.sub.sI.sub.s/V.sub.DC, with virtually zero
ripple component. Electrical frequency (w) is proportional to rotor
spin speed, which may vary over a normal 10-to-1 power generating
range. The 2-phase circuits in FIG. 1, including high-frequency
preferably ferrite core inductors L1 and L2, the two current
sensors, along with their power control electronics, are known in
the art as boost regulators. Prior art generators, intended to
supply DC current (and only at relatively high speed over a narrow
speed range), need costly large filter capacitors. The present
invention obviates need for such capacitors, by combining (after
high-frequency Pulse-Width-Modulation filtering) current from the
respective 2 phases, substantially I.sub.a
sin.sup.2(wt)+cos.sup.2(wt)=I.sub.a. It will be noted that the
inverter shown in FIG. 11B is 3-Phase. A single-phase inverter, to
supply 60-Hz AC power, would draw current from the generator in
FIG. 1 (or from any DC source that supplies its power) with
considerable 120-Hz ripple. So, for such a requirement, capacitor
C2 would need to be substantially larger than when the generator is
used to supply DC power for poly-phase inverters.
[0077] Current through stator windings 1 and 2 are essentially in
phase with voltage generated in the respective windings, due to PWM
current control, responsive to two Hall sensors, each aligned with
a respective stator winding and which detect rotor angle, to
provide respective feedback signals sin(A) and cos(A) denoted 3 and
4 in FIG. 1. Signal processing electronics in Power Control
Electronics 5 combine variables 3 and 4 with control variables
specific to the various embodiments of the present invention. The
resulting signals, applied to two respective minor-loop current
feedback circuits, having negative feedback denoted Ph.1 Current FB
and Ph.2 Current FB, produce signals that control respective Ph.1
PWM and Ph.2 PWM outputs. These PWM outputs drive Q1 and Q2 gates,
connected in parallel as shown, at variable PWM duty-cycle
T.sub.on/(T.sub.on+T.sub.off) to attain desired current through Phi
Stator Winding 1. Meanwhile, Q3 and Q4 gates, connected in
parallel, are likewise controlled, to attain desired current
through Ph.2 Stator Winding 2. Said current control can be attained
only when the DC Power Bus voltage exceeds the maximum level of
peak voltage generated across respective stator windings. That
result is illustrated by the nearly sinusoidal current and voltage
waveforms across each respective 2-Phase stator winding terminal
pair, as a function of time, and resulting averaged current (from
capacitor filtered high-frequency PWM current pulses) fed to the DC
power bus, as illustrated in FIG. 10. The combined averaged
currents, fed to the DC power bus, have effectively zero ripple
components when peak stator voltage is less than the DC power bus
voltage. This will be understood by those versed in the all.
[0078] It can be readily shown that the combined PWM current pulses
from each of the two phases, averaged by high-frequency ceramic or
film capacitors, can be reduced somewhat by staggering ON/OFF
timing for one of the PWM drivers relative to the other phase. Said
current pulses would then be staggered (i.e., alternated from each
phase). However, a design compromise between less capacitance
enabled by said staggered pulses and the additional signal
processing needed to achieve that result, tends to favor the
circuits shown and described herein. This preference is partly
because current from one phase is zero when current from the other
phase is maximum and partly because too much added circuitry is
needed to reduce the pulse currents only a small amount that can be
accommodated by only slightly more high-frequency filter
capacitance.
[0079] Whenever the maximum voltage generated across respective
stator windings exceeds the DC Power Bus voltage, the generator
will charge capacitors in parallel with the DC Power Bus, to
substantially the stator winding voltage peaks, by full-wave
rectifier action. Then, if shaft speed exceeds levels where the DC
Voltage Feedback in FIG. 1 can control generator output voltage by
boost-regulation, a buck regulator would preferably be added in
series with the DC Power Bus, as shown in FIG. 11A. Additionally.
Q1-Q4 and D1-D4 and capacitance C voltage ratings must be
accordingly increased. DC-to-DC buck regulators are available
commercially. They achieve regulated DC output voltages at various
power levels, at about 95% efficiency, by straightforward PWM
circuit means, DC-to-AC power inverters can also provide
buck-regulation, at about 95% efficiency. Preferably, said
inverters would be poly-phase, and synchronized to grid power lines
they would feed, as shown in FIG. 11B. Single-phase inverters would
draw current having very high ripple, from the DC Power Bus.
Therefore, they would not be a favorable peripheral for use with
this generator. With buck regulation inverters, the DC Power Bus
voltage, fed to the DC-to-AC inverters, must be greater than the
peak AC voltage on the power grid fed by the generator.
[0080] A preferred embodiment of the Power Control Electronics 5 in
FIG. 1, which does not include a buck regulator in series with its
output, is illustrated by the functional block diagram FIG. 2. It
is configured as a generator for wind turbines preferably having
means to limit rotation speed by varying their blade pitch or
limiting wind-speed channeled to them by exterior means.
[0081] The Compare function block 1 in FIG. 2 may be implemented by
a differential amplifier circuit, including logic that inhibits
negative voltage feedback from the DC power bus, unless the bus
voltage exceeds a prescribed voltage reference (Ref) setting, Ph.1
rotor angle A sensor feedback signal sill (A) is applied to rate
function block 9. (d/dt), which provides its time-derivative
(dA/dt) cos(A), and is applied to AbsVal function block 4, which
provides its absolute value /sin(A)/. The rate signal is applied to
square function block 8, which provides as its output a squared
rate (the second power of rotational speed) signal (dA/dt).sup.2
cos.sup.2 (A).
[0082] Likewise, Ph.2 rotor angle sensor feedback signal cos (A) is
processed by like electronics, to provide signals (dA/dt).sup.2
sin.sup.2 (A) and /cos(A)/. Respective squared rate signals are
then added, with negative DC voltage feedback, by the sum function
block 2. Since sin.sup.2 (A) and cos.sup.2 (A) is equal to 1.
output from function block 2 is the square of speed, with virtually
zero ripple. This (speed).sup.2 signal is applied to multiplier
function blocks 5, along with respective inputs /sin(A)/and
/cos(A)/, to provide respective output signals (speed)" /sin(A)/
and (speed)" /cos(A)/.
[0083] Substantially sinusoidal Ph.1 current feedback signal is
applied to function block 10. (AbsVal), to provide the signal
variable Ph.1 stator current amplitude /sin(A)/. Likewise, the Ph.2
stator current feedback signal is converted to Ph.2 stator current
amplitude /cos(A)/. Each of these absolute value signals is applied
to respective difference amplifiers, shown as sum function blocks
6. This signal processing provides negative current feedback, to
respective minor feedback loops, whose outputs modulate respective
PWM function blocks 7. The PWM circuits provide ON/OFF drive (Ph.1
PWM), to Q1 and Q2 in FIG. 1, for Phase 1 stator current control
proportional to (speed).sup.2 and ON/OFF drive (Ph.2 PWM) to Q3 and
Q4 for Phase 2 stator current control that is likewise proportional
to (speed).sup.2.
[0084] Abs Val function blocks 4 and 10 in FIG. 2 may be
implemented by various circuits, depending upon respective signal
dynamic range accuracy needed. FIG. 9A-B illustrates two circuits
that provide the absolute value, which is precise over a very broad
range, of output signals from stator current sensors in this
generator. Note that the diodes are inside the operational
amplifier feedback loops, which compensates for diode forward
voltage drop. Electronic engineers who design analog circuits are
familiar with such techniques, and with their considerable circuit
enhancements and various limitations.
[0085] FIG. 3 illustrates a functional block diagram for the Power
Control Electronics 5 in FIG. 1, which is intended for general
applications. Like the circuit in FIG. 2, compare block 1 is also
responsive to a reference command (Ref) and to the DC power bus
voltage. However, in FIG. 3, the resulting negative voltage
feedback is then compared by sum circuit 2 (which is preferably
implemented by an operational amplifier circuit) with an Effort
level selection signal. Abs Val 4 likewise provides respective
absolute value /sin(A)/ and /cos(A)/ signals from Ph.1 and Ph.2
preferably Hall-effect sensor output signals. Abs Val 8 circuits
provide the absolute values of respective Phase 1 and Phase 2
current feedback signals, which serve as current feedback to
respective sum 6 circuits, which are responsive to level commands
from respective multiplier blocks 5. Thus, stator current level
control is synchronized with respective stator winding voltage, by
PWM blocks 7, which provide respective Ph.1 PWM and Ph.2 PWM
high-frequency ON/OFF drive to Q1-Q2 and Q3-Q4 shown in FIG. 1.
[0086] Over-Voltage Protection (function blocks 3), shown in both
FIG. 2 and FIG. 3, is a vital and much preferred element of the
integrated electronics, which protects the electronics if the load
connection is suddenly opened. The negative voltage feedback to
block 1 is generally processed by electronics that incur too much
delay to always prevent damage from over-voltage. Therefore, a
Transient Voltage Suppressor (TVS) device that is commercially
available from various suppliers conducts within pico-seconds
whenever its conduction voltage is exceeded. The TVS is basically a
very large junction area zener diode. Its thermal capacity, with
parallel filter capacitors, is sufficient to absorb without damage
all energy stored in inductors L1 and L2 shown in FIG. 1. Whenever
the TVS conducts, current through it is sensed by a circuit that
inhibits PWM 7 from driving Q1, Q2, Q3, and Q4 for an extended
time, thereby stopping the normal boost regulation of the generator
electronics, and allowing sufficient time for TVS heat to
dissipate.
[0087] Power from Ph.1 stator winding is effectively the
root-mean-square (rms) value of its stator current multiplied by
its rms stator voltage=(Ph.1 peak current)(Ph.1 peak voltage)(0.5).
Likewise, Ph.2 power=(Ph.2 peak current)(Ph.2 peak voltage)(0.5).
Since Ph.1 and Ph.2 are essentially equal in magnitude and time
displaced by 90.degree. phase relative to each other, the Ph.1 plus
Ph.2 power sum is (peak current)*(peak voltage) of either Phase 1
or Phase 2.
[0088] Inasmuch as peak current and voltage of Ph.1 and Ph.2 are
equal to each other, and each is sinusoidal with 90.degree.
relative phase, and sin.sup.2(A) cos.sup.2(A)=I, and the stun of
power from Ph.1 and Ph.2 equals power fed to the DC power bus
I.sub.DCV.sub.DC, then, for either phase; (peak stator
current)(peak stator voltage)=(I.sub.DC=V.sub.DC).
[0089] The above equation explains why controlling peak stator
current so it is proportional to speed squared, when multiplied by
peak stator voltage, which is proportional to speed, results in
output power (I.sub.DCV.sub.DC) proportional to the third power of
speed. Coupling this generator to a wind turbine capable of
changing its configuration to limit its speed maximizes energy
yield from the most prevalent winds, when power usually is most
needed. It also protects the turbine from mechanical stress
incurred by turbines that do not have said speed-limiting features,
while still providing controlled electric power at levels the power
loads can accept.
[0090] Generator power and efficiency with wind turbine drive is
computed below, for a representative example of the present
invention, at maximum shaft speed, mid-speed, and minimum usable
speed, using a few simplifying approximations. Shaft speed, power,
and the other variables in the computations herebelow are
exemplary, and not intended as limiting the present invention in
any way. This will help explain FIG. 1 and FIG. 2 configuration
operation, distinctions and improvements over the prior art.
[0091] Let maximum speed equal 1000 revolutions per minute (rpm),
mid-speed equal 500 rpm, and minimum speed equal 100 rpm. Also, let
maximum stator current I.sub.max=10 amperes, and nominal
V.sub.DC=100 volts. Further, let Q1-Q4 power MOSFET ON resistance
R.sub.dson=0.01 ohm, inductor L1-L2 winding resistance R.sub.L=0.1
ohm. Also, stator winding resistance R.sub.5=0.15 ohm, stator
voltage V.sub.max=100 volts at 1000 rpm, and fly-back
(free-wheeling) diode D1-D8 forward drop V.sub.f=1-volt at 10 amp.
These parameters are consistent with a test prototype, according to
the present invention, developed to generate power from wind
turbines.
[0092] At 1000 rpm, V.sub.max=100 volts, so PWM duty-cycle
(T.sub.on)/(T.sub.on+T.sub.off) is essentially zero. Therefore,
losses I.sub.max.sup.2(R.sub.L+R.sub.s)+2 V.sub.fI.sub.max=(10
amp).sup.2(0.25 ohm)+(2 volt)(10 amp), amounting to 45 watts loss.
Output power=(I.sub.max)(V.sub.max)=(I.sub.max)(V.sub.DC)=(10
amp)(100 volts)=1000 watts. Therefore, generator efficiency at
maximum speed and maximum power is about 95% for this example of
generator and integrated electronics parameters.
[0093] At 500 rpm, I.sub.max=(10 amp)/(4)=2.5 amps; and
V.sub.max=(100 volts)*(0.5)=50 volts. So PWM duty-cycle=1/2.
Average pulse power
generated=(I.sub.max)(V.sub.max)=(I.sub.max)(V.sub.DC)/2=(2.5
amp)(50 volt)=125 watts. Losses to maintain inductor
current=I.sub.max.sup.2(R.sub.L+R.sub.s+R.sub.on)=(2.5
amp).sup.2(0.26 ohm)=1.6 watts. Fly-back diode losses=2
V.sub.fI.sub.max/2=(0.6 v)(2.5 amp)=1.5 watts. So total losses=3.1
watts. Therefore, mid-speed generator efficiency is about 97%.
[0094] At 100 rpm. I.sub.max=(10 amp)/(100)=0.1 amp; and
V.sub.max=(100 volts)/(10)=10-volts. So PWM duty-cycle=9/10.
Average pulse power
generated=(I.sub.max)(V.sub.max)=(I.sub.max)(V.sub.DC)/10=(0.1
amp)(10 v)=1 watt. Losses to maintain stator and inductor
current=I.sub.max.sup.2(R.sub.L+R.sub.s+2R.sub.dson)=(0.1
amp).sup.2(0.27 ohm)=0.0027-watt. Fly-back diode
losses=(2V.sub.f)(I.sub.max)/10=(0.6 v)(0.1a)/5=0.012 watts. So
total losses=0.015-watt. Thus, generator efficiency at low speed is
about 98%.
[0095] Note that, although the generator according to the present
invention is self-starting (meaning that it need not be connected
to a power source, to begin power generation), the minimum speed of
the above power and efficiency computation must be reached, before
the signal processing electronics will function as required. Also.
MOSFET gate driver under-voltage lockout may prevent PWM drive to
Q1-Q4 in FIG. 1 until the minimum voltage is reached. Moreover,
almost all the nominal minimum 1-watt generated power will be used
to supply Power Control Electronics 5.
[0096] At the lowest usable shaft speed of 100 rpm in the above
representative example, the 10-volt peak stator voltage generated
would be adequate for all signal processing and PWM drive
electronics, so this generator would be self-starting when turbine
speed reaches 100 rpm. However, with 1-watt quiescent power for the
Power Control Electronics, power supplied to the load at 100 rpm
would be zero until wind speed increases a small amount, which for
example can drive the turbine at approximately 125 rpm, where
output power would be about 2-watts.
[0097] As illustrated in FIG. 4, maximum 1000-watts power from a
wind turbine that is the optimum power range for the generator of
the above example, is normally considerably less frequent than
intermediate power output. In circumstances where wind power is
below this minimum that produces 100-rpm turbine speeds for
extended periods, it may be desirable to prevent the Power Control
Electronics from drawing quiescent power from a load. Circuit means
is shown in FIG. 2A for essentially disconnecting the Power Control
Electronics until it supplies at least a small current to the load.
The power disconnect is by means of relay contact K opening when
the current through relay control winding L is below its toggle
threshold. The inductance of relay winding L is also useful for
filtering PWM pulse currents cooperative with high-frequency
capacitance C and with load capacitance. Relay winding L needs to
have very low resistance, very high sensitivity that will open the
relay contact with only 0.01-amp input and be capable of
accommodating a maximum 10-amp current, or diode D alone may be a
preferable choice to prevent the load from supplying the
electronics quiescent current.
[0098] For the high power (1000 watts generator output) example, if
the relay winding resistance is 0.1-ohm, it would dissipate
10-watts at 10-amps to the 100-vdc load. That would decrease the
generator power efficiency at 1000 watts from about 95% to about
94%. Also for example, if diode D forward drop is 1-volt at
10-amps, including only diode D would likewise dissipate
approximately 10-watts. Although these losses are higher at
1000-watt maximum power, at low power levels the alternate
embodiment that includes the relay would have lower losses than an
embodiment that includes the diode alone.
[0099] For a lower power example, at 100-vdc, 1-amp and 100-watt
output, the relay loss from 0.1-ohm winding resistance and
negligible contact resistance at 1-amp is 0.1-watt; whereas the
diode loss with approximately 0.6-volt forward drop at 1-amp is
0.6-watt. A 0.1-watt loss from 100-watts output would result in
only 0.1% lower efficiency with the relay in series with the
generator load. When PWM current pulse filtering benefits are
considered, an appropriate relay that has lower losses when
generator output power is low and therefore usually most needed,
and can also serve as a filter inductor, is a preferred option.
[0100] When a relay as shown in FIG. 2A is not included with the
generator system, an inductor in series with the load is a
preferred additional component that is not illustrated herein, to
reduce high-frequency current ripple to the load due to
pulse-width-modulation and also to minimize
electro-magnetic-interference (EMI) that could interfere with
international communications standards. Further, a Faraday shield
is preferred for surrounding and inclosing the Power Control
Electronics, constructed from high electrical conductivity material
such as aluminum. And yet further, all conductors that connect
between the Power Control Electronics and external components such
as the generator assembly and the load, will preferably be
connected through EMI suppressors. These devices provide a small
series inductance that is lossy at very high frequencies. They are
familiar to electronic engineers and to those versed in the
art.
[0101] Note that, for uses requiring higher DC Power Bus voltages,
power MOSFET drain-source ON resistance R.sub.dson usually
increases considerably with voltage rating. Moreover, power MOSFET
voltage ratings beyond 500 volts begin to limit available fast
power switching MOSFET options. Also, at DC power voltages higher
than 50 volts, a substitute for the LT1076 regulator IC (Integrated
Circuit) shown in FIG. 12, having a higher input voltage rating,
will be needed. Topswitch PWM buck regulator ICs, by Power
Integrations Inc., are likely options, for both signal processing
electronics and DC power current and voltage control. At DC power
voltages higher than 500 volts. IGBTs (Insulated Gate Bipolar
Transistors) would become a likely option, over MOSFETs (Metal
Oxide Silicon Field Effect Transistors).
[0102] Note also that, when no wind turbine shaft speed limiting is
provided, by means briefly described hereabove, such that DC Power
Bus voltage and current must be controlled by buck regulation,
series (tandem) power losses are incurred in the buck regulators.
With 95% efficiency buck regulation, combined with higher
R.sub.dson power MOSFETs Q1-Q4, overall generator power conversion
efficiency would be reduced to typically 90% at maximum and
mid-speed wind, and typically reduced to about 60% at one-tenth
maximum speed. Although DC-to-AC power inverters are not called
buck regulators by their suppliers, it should be noted that they
control their output current, fed to AC power lines, by buck
regulation.
[0103] The most advantageous applications, for the wind turbine
generator shown in FIG. 1 and FIG. 2, would be as wind turbine DC
generators for distributed on-site power systems, wherein the wind
turbine maximum speed is limited. Said generators are also uniquely
compatible with flywheel batteries described in my U.S. Pat. Nos.
6,566,775 and 6,794,777. Said generator output current is DC and
does not include significant current ripple components. Said
flywheel batteries require DC input current and DC current loads,
with essentially zero ripple components.
[0104] FIG. 4 illustrates available power (KW) from typical wind
turbines, as a function of wind speeds from zero to 50 miles/hour
(mph). Since turbine rotational speed is typically proportional to
wind speed, and turbine torque is typically proportional to wind
speed squared, available power from the turbine is typically
proportional to wind speed cubed. FIG. 4 also shows, for a location
with 10-mph average wind speed, the probable mean hours duration at
each wind speed, known as a Rayleigh Statistical Wind Speed
Distribution.
[0105] From the probable mean hours duration curve illustrated,
note that the most probable wind speed (the prevailing wind speed
present for the longest duration) is about 8-mph for a 10-mph
average wind speed location, as shown. With turbine shaft torque
proportional to the second power of wind speed, torque at 8-mph is
about (8/25).sup.2=10% of available torque at 25-mph. With shaft
power proportional to the third power of wind speed, power
available at 8-mph is (8/25).sup.3=less than 4% of available power
at 25-mph. A shaft torque of only 10% that at 25-mph (and less than
3% that at 50-mph) will usually not be enough to overcome speed-up
gear friction and cogging torque, of prior art wind turbine
generators. Moreover, prior art synchronous generators do not
produce sufficient output voltage to feed typical loads, at wind
speeds below about 1/3 maximum generating speed (over 16 mph for
the example illustrated by FIG. 4).
[0106] Moreover, induction machines would draw power--not supply
power--if connected at low wind speeds, and consequently, low shaft
speeds. Besides that drawback, induction generators do not supply
regulated power. Their power fluctuates with wind speed. Moreover,
heating and need for cooling increases as induction generator
efficiency falls drastically at speeds only several percent above
their maximum power speed. Conversely, the present invention can
efficiently generate high-quality power, at wind speeds here shown
in a 5 to 50 mph range, which can yield very substantial energy,
particularly at low wind speeds, over prior art generators.
[0107] By multiplying KW at MPH by Mean Hours at MPH, we obtain the
statistical distribution Mean KWH at MPH, which is illustrated in
FIG. 4. Note that the Mean KWH at MPH curve is a maximum at about
16-mph. Moreover, note that the area under the curve Mean KWH at
MPH, over the entire speed range (here 0 to 50 mph) is the
statistically probable energy yield potentially available from
typical wind turbines, over a usual 1-year time-period. Considering
that prior art generators, installed in locations like this
example, cannot generate useful power at wind speeds under 16-mph,
the area under the curve and therefore the potential harvested
energy, at all wind speeds below 16-mph, is relinquished by them.
That amounts to about half the total probable yearly energy
potential of wind turbines. Power is also lost in their speed-up
gears and generators at all wind speeds, amounting to over 10% of
the potential turbine power. Moreover, cooling needs of prior art
generators add further power losses and costs.
[0108] Conversely, the present invention is intended to generate
high quality power over the entire 5 to 50 mph wind speed range
illustrated in FIG. 4, with total generator losses under 5% of the
potential turbine power. That wide wind speed range and high
efficiency can produce more than double the energy yield of prior
art generators, from the same wind turbines. Power from the present
generator invention is also higher quality, because it has
ripple-free regulated DC current, has regulated voltage, is
compatible with flywheel batteries that connect to a DC power bus,
compatible with photovoltaic solar panel installations, compatible
with chemical battery charging, and compatible with poly-phase
DC-to-AC inverters to augment utility grid power.
[0109] Most importantly, for applications to augment grid power,
the present invention produces power that need never be
disconnected (unlike the intermittent wind-farm power, turned ON
and OFF as wind speed fluctuates, by the switchgear of prior art
generators). Such unregulated power peaks and disruptions, by prior
art generators, have serious negative consequences; so most
electric power utilities are reluctant to connect their grids to
prior art generators.
[0110] Moreover, the present invention generator produces power at
times when it is most useful, and does not incur nearly as much
transmission line losses, because it can provide steady power at
lower wind speeds, and regulated power at higher wind speeds,
compared to the high and usually unregulated intermittent power of
prior art generators.
[0111] The cross-section view in FIG. 5A shows main elements of a
vertical axis generator, according to the present invention.
Rotational input power is typically supplied to it by a vertical
axis wind turbine, having a power output shaft coupled to the
generator shaft 1, by means of a flexible coupling affixed to the
respective shafts. A plurality of rotor magnet disks 2 closely fit
around shaft 1, aligned therewith preferably by means of a key-way
in shaft 1 and juxtaposed key-way grooves in each disk 2 inner
diameter. Each rotor disk 2 supports a circular array of alternated
pole axial-field magnets 3 attached therein. A return path, for the
magnetic fields of magnets 3, in the disks 2 at each end, is
preferably provided by high magnetic permeability iron disks 4a and
4b attached at each end of rotor disks 2. Rotor disks 2 are
non-magnetic and have low magnetic permeability, to maximize flux
density between the disks 2, which interacts with stator winding
radial segments within stator disks 5. The stator disks 5 are
preferably injection molded with the 2 stator windings they hold,
and composed of a material that is electrically non-conductive,
which has high thermal conductivity so that heat generated by
current in the stator windings is conducted to the disk and
generator outer surfaces.
[0112] Preferably, 2 phases are included in the present invention,
because more phases would require more stator windings and more
winding connections. One stator winding 6, of the two, is shown in
cross-section FIG. 5A. The second stator winding axially abuts
winding 6, and is disposed relative to winding 6 an angle [180
degrees divided by the number of poles].
[0113] Note that all rotor magnet disks 2 are identical parts. Note
also that all stator disks 5 are identical parts, including axial
channel 5a for connecting their respective stator windings. Stator
ring 7 holds magnetic field sensors, shown by detail 7a. which
provide substantially sinusoidal rotor angle signals from the
revolving rotor magnets 3. Each sensor is aligned with a radial
segment of a corresponding stator winding 6. Stator rings 7 and 8
facilitate accurate alignment of radially interlocking stator disks
5 and accurate axial clearances with rotor magnet disks 2.
[0114] Top enclosure disk 9 and bottom disk 10 are preferably a
metal such as aluminum. Disk 10 supports preferably axial thrust
ball bearing 11, which supports center shaft 1 axially and
radially, at its lower end, while facilitating rotation about its
center with minimal friction and drag torque. Top disk 9 supports
preferably deep groove radial ball bearing 12, and facilitates a
precise axial preload by accurate axial hold of its outer race,
cooperative with a wave spring that exerts a prescribed upward
thrust on its inner race.
[0115] FIG. 5B illustrates an orthographic projection view of the
vertical axis generator. It shows exterior views of shaft 1; stator
disk 5 with winding connection channel 5a; stator ring 7 with
sensor hold detail 7a; and stator ring 8. It also shows enclosure
top disk 9; bottom support and enclosure disk 10; and four drilled,
tapped, counter-sunk holes, from top disk 9 through bottom disk 10,
to hold the assembly together and maintain rotational alignment of
all stator disks and rotor angle sensors, with four fastener
screws.
[0116] The cross-section view in FIG. 6A shows main elements of a
horizontal axis generator, according to the present invention.
Rotational input power is typically supplied to it by a horizontal
axis wind turbine, having a power output shaft coupled to the
generator shaft 1, by means of a flexible coupling affixed to the
respective shafts; or pedals may be attached at each end of shaft
1, for use in electric vehicles having an exercise option.
[0117] Like its vertical axis version, a plurality of rotor magnet
disks 2 closely fit around shaft 1, aligned therewith preferably by
means of a key-way in shaft 1 and juxtaposed key-way grooves in
each disk 2 inner diameter. Each rotor disk 2 supports a circular
array of alternated pole axial-field magnets 3 attached therein. A
return path, for the magnetic fields of magnets 3, in the disks 2
at each end, is preferably provided by high magnetic permeability
iron disks 4a and 4b attached at each end of rotor disks 2. Rotor
disks 2 are non-magnetic and have low magnetic permeability, to
maximize flux density between the disks 2, which interacts with
stator winding radial segments within stator disks 5. The stator
disks 5 are preferably injection molded with the two stator
windings they hold, and composed of a material that is electrically
non-conductive, which has high thermal conductivity so that heat
generated by current in the stator windings is conducted to the
disk and generator outer surfaces.
[0118] A lighter weight generator assembly embodiment that would
cost more than the preferred embodiments is also contemplated. In
that so called "ironless generator" embodiment, the iron disks 4a
and 4b shown in FIG. 5A-5B would each be implemented by disk
magnets that may have the same physical form as the iron disks.
However, said disk magnets would need to be magnetized with axial
poles aligned with the magnets affixed to the rotor disks. with a
magnetic pattern between said axial poles that transitions between
axial to tangential to axial, and so forth. Said magnetic pattern
would provide a continuous flux path at each end of the rotor disks
that substantially follows the same return flux path as the iron
disks 4a and 4b. Because the two disk magnets are thereby disposed
so they are not required to have high coercive force, they do not
need to be rare earth magnets, which would be difficult to
magnetize in said axial and tangential pattern. However, if thus
magnetizing rare earth magnets such as Neodymium-Iron-Boron is
cost-effective, another contemplated embodiment would include
replacing adjoining rotor magnet disks 2 and iron disks 4a and 4b
by said magnets.
[0119] Like the vertical axis version, preferably 2 phases are
included in the horizontal axis version. One stator winding 6, of
the two, is shown in cross-section FIG. 6A. The second stator
winding axially abuts winding 6, and is disposed relative to
winding 6 an angle of 180 degrees divided by the number of poles.
Note that all rotor magnet disks 2 are identical parts. Note also
that all stator disks 5 are identical pails, including axial
channel 5a for connecting their respective stator windings. Stator
ring 7 holds magnetic field sensors, shown by detail 7a. which
provide substantially sinusoidal rotor angle signals from the
revolving rotor magnets 3. Each sensor is aligned with a radial
segment of a corresponding stator winding 6. Stator rings 7 and 8
facilitate accurate alignment of radially interlocking stator disks
5 and accurate axial clearances with rotor magnet disks 2.
Substantially all the elements described hereabove, and illustrated
in FIG. 5A and FIG. 6A, for respective vertical and horizontal axis
generator versions, are identical.
[0120] Left enclosure disk 9 and right enclosure disk 9a are
preferably a metal such as aluminum. Note that disks 9 and 9a are
identical parts. Disk 9 holds the outer race of deep groove radial
ball bearing 12. Right disk 9a holds the outer race of like ball
bearing 12a. Their inner races support center shaft 1 axially and
radially, while facilitating rotation about its center axis with
minimal friction and drag torque. When assembled, a precise axial
preload is facilitated, by accurate axial hold of the bearing outer
races, cooperative with a wave spring that exerts a prescribed
outward thrust on their inner races. This assembly is supported by
brackets 10 and 10a.
[0121] FIG. 6B illustrates an orthographic projection view of the
horizontal axis generator. It shows exterior views of shaft 1;
stator disk 5 with winding connection channel 5a; stator ring 7
with sensor hold detail 7a; and stator ring 8. It also shows left
disk 9; right disk 9a; and four drilled, tapped, counter-sunk
holes, from disk 9a through disk 9, to hold the assembly together
and maintain rotational alignment of all stator disks and rotor
angle sensors, with four fastener screws. Bracket 10 and 10a
fastening details, and base support attachment, are also shown
here.
[0122] One of a plurality of rotor disks 2, to hold fastened
therein 16 (for example) axially magnetized, preferably
Neodymium-Iron-Boron magnets, samarium-cobalt or other similar
magnet materials, in an alternated pole array, is illustrated by
orthographic projection FIG. 7A. The nearest magnet proximity to
the rotation axis is here denoted 3c; the furthest proximity to the
rotation axis is denoted 3a. Alternate rotor disk embodiment FIG.
7B is an option wherein three (for example) lower cost magnets
constitute each magnetic pole.
[0123] One of the cooperative stator disks 5 is illustrated by the
orthographic projection FIG. 8A. Each stator disk holds two stator
windings. A connection channel 5a is shown, for the winding
terminals. Contiguous space 5b is shown for one of the two
windings, and is partially visible for the second winding. Axial
dimensions of stator disks 5, rings 7 and 8, plus other parts that
determine axial positioning, must maintain adequate clearances
between all rotor and stator parts.
[0124] Two stator windings, 6 and 6a, each preferably formed from
single-strand magnet wire with an insulating coating, having 3
series passes (also known as turns) in some generator embodiments
according to the present invention, are shown in FIG. 8B. Stator
winding radial segments 6r interact with the rotor magnetic field.
Their current path is continued via outer arc segments 6co and
inner arc segments 6ci, and via winding terminals 6t and 6ta. The 2
stator windings are abutted axially, and displaced 11.25 degrees,
relative to each other, in the 16-pole stator disk shown in FIG.
8A. For a prototype generator, said stator disks are machined from
bulk material that is electrically non-conductive; and pre-formed
stator windings are bonded within the recessed space shown. For
production design generators, according to the present invention,
the pre-formed stator windings may be injection-molded within the
space shown, with a thermally conductive resin available
commercially from numerous suppliers.
[0125] With specialized wire-forming equipment, square
cross-section wire would be preferable compared to round magnet
wire, since a square cross-section facilitates more conductor area
and therefore lower stator winding resistance, in an equivalent
stator disk space. FIG. 8B illustrates two very similar stator wire
form candidates. Clearly, the stator windings may have one or any
appropriate number more "turns" and the wire form for each phase
may be identical to one another to minimize the number of different
parts needed for the generator assembly.
[0126] FIG. 9A is a schematic that will be understood by electronic
engineers, of a new circuit for accurately converting, over a very
broad dynamic range (i.e., the variable V ranging from less than 1
millivolt to 2 volts), a feedback signal Vsin(wt)+2.5 v from a
commercially available current sensor, to the absolute value
current feedback 5=V=/sin(wt)/. The absolute value is needed to
control stator winding current by pulse-width-modulation, according
to the present invention. Note the diodes inside the amplifier
feedback loop, which allow only one polarity output and prevent
over-driving amplifiers when negative feedback is blocked. FIG. 9B
achieves a similar and generally more accurate result with fewer
parts; but does not prevent over-driving the amplifier when its
negative feedback is blocked by a diode in series with its output.
So it requires amplifiers with a faster recovery after being
over-driven, to accurately process signals at higher generator
rotational speeds (where signal frequency is correspondingly
higher). Since the signals they process are larger at higher
rotational speeds, the circuit shown by FIG. 9B is preferable.
[0127] FIG. 10A illustrates voltage generated across the respective
2-phase stator windings, approximating V.sub.s=sin(wt) and
V.sub.s=cos(wt). Amplitude V.sub.s is proportional to speed and
(wt) equals the product of said voltage frequency and time.
[0128] FIG. 10B illustrates current controlled by
pulse-width-modulation, approximating I.sub.ssin (wt) and
I.sub.scos (wt) with a time base corresponding to FIG. 10A. For
generator embodiments intended to generate maximum power from wind
turbines, over a broad speed range, amplitude I.sub.s is
proportional to speed squared. Said current is controlled by Power
Electronics 5 shown in FIG. 1, by electronics therein that process
respective maximum signals 2 vsin (A) and 2 vcos (A), denoted 3 and
4 in FIG. 1, which preferably are provided by Hall sensors at
locations 7a in stator rings 7, shown in FIG. 5B and FIG. 6B.
[0129] FIG. 10C illustrates resulting generator output current
components after high-frequency pulse filtering I.sub.s=sin.sup.2
(wt) and I.sub.s=cos.sup.2 (wt), which is equal to I.sub.s having
minimal ripple, with a time base corresponding to FIG. 10A, which
combine to provide DC current I.sub.s fed to a DC voltage bus load.
Said DC current can contain substantially zero ripple components,
without need for large filter capacitors.
[0130] Stator voltage due to generator shaft rotation can be
computed from: V.sub.s(volts per radial
segment)=B.sub.max(weber/m.sup.2)=L (m)=v(m/sec).
[0131] Generator load torque due to stator winding current can be
computed from: Force (newton per radial
segment)=B.sub.max(weber/m.sup.2)=L (m)=I (amperes).
[0132] For a prototype generator according to the present
invention: [0133] B.sub.max=flux density at each radial segment
when centered with a motor magnet [0134] B.sub.max=6000 gauss=0.6
weber/meter.sup.2 [0135] L=length of each wire segment (meters) in
field B.sub.max (see 3a and 3c in FIG. 7A-B) [0136]
L=magnet=R.sub.o-R.sub.i=2.8 inch=0.07 meter (R.sub.o=5.2 inch,
R.sub.i=2.4 inch) [0137] v=average velocity relative to field
(meter/sec) at 1000 rpm shaft speed
[0138] Therefore, at 1000 rpm: [0139]
v=[2pi][(R.sub.o+R.sub.i)/2]/rev[1000 rev/min](min/60 sec)=398
inch/sec=10 m/sec
[0140] Thus, at 1000 rpm: [0141] E.sub.max(volt/segment)=0.6
weber/m.sup.2=0.07 m10 m/sec=0.42 volt
[0142] For 16-pole generator with 3 turns on each of 5 stator
disks: [0143] Total E.sub.max at 1000 rpm=16350.42 volt=100 volts.
[0144] Generated electric power=E.sub.maxI.sub.max=(100 volts)(10
amp)=1-kilowatt.
[0145] For this example, the total for 5 stator disk windings
connected in series, each #12 AWG (which has 0.08 inch diameter,
1.6 olm/1000 ft.), magnet wire length approximates 1000 inches
(about 80 feet). So total stator winding resistance, of 5 windings
connected in series, is about 0.15 ohm. Then, at 10-amp maximum
current per phase, copper loss per phase approximates (10
amp).sup.2(2)(0.15 ohm) which is approximately 7.5 watts.
Therefore, total copper loss in the five stator disks of this
example approximates 15 watts at 10 amperes DC current output. This
loss amounts to 1.5% of shaft (mechanical input) power.
[0146] This stator voltage, power, and loss computation is
important for optimally matching the generator to its intended DC
power bus load voltage, calculating generated power, and for
estimating power conversion efficiency and stator winding heat
dissipation at various loads. Torque load of this 16-pole, 5 stator
disks, 3 turns/disk generator, at 10 amperes DC load=(total forces
on its stator winding radial segments)* (radius from rotational
axis).
Therefore:
[0147] Torque (ntn meter)=0.6 weber/m.sup.2=0.07 m10 amp0.096
m1635=9.6 ntnm. [0148] Mechanical Shaft Power=Torque Speed=(9.6
ntnm)(1000 rev/min)(6.29/rev)(min/60 sec)(1
watt)/(ntn-meter/sec)=1-kilowatt.
[0149] This torque and mechanical power computation is important
for optimally matching the generator to its intended wind turbine
or various other drivers, and for certification testing power
conversion efficiency over the intended operating speed and torque
range. The above simplified electrical and mechanical power
computations do not include any loss factors. So they are equal
here.
[0150] This is the maximum torque, caused by circumferential forces
distributed evenly over each radial stator winding segment of one
stator phase, in the rotor magnet axial field. The torque produced
by the second stator phase is zero, when maximum at the other
phase, because flux density at the second stator phase is then
zero, and current through the second phase is also then zero. As
the rotor spins, the sum of torques from the 2 phases, is constant.
So there is no torque ripple, and no cogging torque (mainly because
the stator disks have no iron core).
[0151] It should be noted from the above detailed generator
geometry and computations, that relatively large generator
diameters are needed, compared to prior art generators driven by
low-speed wind turbines, to obviate need for speed-increase
gearing. Therefore, present invention generator embodiments
intended for horizontal-axis wind turbines will preferably include
an aerodynamic nacelle (a substantially cone shape that minimally
impedes air flow) at each end of the generator. Such nacelles can
additionally provide secure housing for the generator integral
electronics, protected from weather damage such as from rain, dust,
and the like. They can also provide additional shielding to prevent
weather damage, for the ball bearings at each end of the generator
assembly. Note that the design of this generator mechanical
assembly can be sealed, because it does not rely on interior air
flow for cooling, as do many prior art generators.
[0152] Note also the importance of obviating the prior art
generator need for speed-up gearing, and the zero cogging torque of
the present invention generator; At low wind speeds, either said
prior art generator cogging torque, or speed-up gearing stiction
and friction, usually causes wind turbines to stall at low wind
speeds, because torque available at low wind speed is very low.
[0153] Lubrication needs for gears are usually higher and involve
far more periodic maintenance, than lubrication needed by rolling
element bearings. So maintenance costs are correspondingly higher,
for prior art generators, than will be needed by generators
according to the present invention.
[0154] As noted by detailed descriptions herein, of means to
control generator output voltage and current by series
buck-regulator circuits, losses incurred thereby cause lower
generator efficiency, particularly at low wind speeds. Therefore,
it would be very advantageous if turbine shaft speed can be
limited. Variable blade pitch is preferable. Wind diverters are
good options. Sliding brake surface means, whereby braking action
that limits speed is controlled by a centrifugal governor, is also
an option. A shaft disconnect clutch is yet another option; however
no power can be generated unless the turbine and generator are
connected.
[0155] Power available from hydrodynamic sources such as flowing
water is, like wind power, proportional to the third power of
speed. So the same electronics signal processing of the primary
embodiment of the present invention is also applicable to
generators intended to maximize electric energy yields from
variable-velocity water driven turbines.
[0156] Summarizing the hereinabove detailed description and its
associated illustrations, a new wide-speed-range generator, and its
various new subsystems, new element combinations, and new
electronics, provided by the present invention, include: [0157] (1)
Rotor magnets held in rotor disks, to provide an alternating nearly
sinusoidal field pattern to each phase of stator windings held in
coreless stator disks between the magnets, with relative velocity
as the rotor spins producing stator voltage, without magnetically
cycling iron or magnets in their closed magnetic flux paths. Stator
winding current, controlled by integral electronics PWM boost
regulation, to provide usable regulated DC output power having
minimal ripple current, from the generator input mechanical shaft
power, to produce maximum energy yield over a broad speed range.
[0158] (2) Rotor magnet sensors, responsive to rotor angle, each
aligned with a respective stator winding phase, to each provide a
nearly sinusoidal feedback signal responsive to rotor angle,
processed by the integral electronics to control respective stator
conductor current. [0159] (3) Current sensors, to each provide a
current feedback signal, corresponding to respective stator
conductor current, for negative feedback loops that control the PWM
circuits. [0160] (4) Signal processing electronics, responsive to
the rotor magnet sensors and stator current sensors, and to DC
voltage feedback, to control stator current by PWM and thereby
efficiently generate regulated DC current and voltage, from
wide-speed-range rotational power, by boost regulation. PWM
fly-back current pulses are filtered, so the resulting poly-phase
currents combine to minimize ripple components without large
capacitors. [0161] (5) Scalable combinations of the number of rotor
and stator disks, and associated electronics, which facilitate a
wide power range, without need for many different size parts and
the tooling required to manufacture them. [0162] (6) Preferably
iron disks to provide return flux paths for the rotor magnets in
the adjoining rotor disks. A lighter weight generator assembly may
substitute permanent-magnet disks in place of the iron disks (and
possibly also the two adjoining rotor disks) that would
substantially provide equivalent return flux paths. [0163] (7)
Various components in series with the generator load, such as an
inductor to minimize high-frequency pulse current, a relay mainly
to prevent drawing generator electronics quiescent power from the
load, and various EMI shielding means.
[0164] While the foregoing detailed description of the present
invention describes preferred embodiments, no material limitations
to the scope of the claimed invention are intended. It will be
understood that the present invention may have many variations in
addition to those described by example herein, with appropriate
embodiments using constituent elements to best suit a particular
situation, application, or requirement. Further, features and
design alternatives that would be obvious to one of ordinary skill
in the art are considered to be incorporated herein. Accordingly,
it is intended that the claims as set forth hereinafter cover all
such applications, embodiments, and variations thereto within the
true spirit and scope of this invention. I claim as new and an
improvement to the prior art, and desire to secure by Letters
Patent:
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