Note: Descriptions are shown in the official language in which they were submitted.
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WIND TURBINE ALTERNATOR
Description
FIELD OF THE INVENTION
The present invention relates to electricity generating machines. It concerns,
in particular, large diameter
alternators directly driven by wind turbines.
BACKGROUND AND PRIOR ART
Electrical power generators have existed for more than a century and have been
the subject of numerous
inventions since. Commonly, electricity is generated when electrons are
displaced in a conductor moving
transversal to a magnetic field or when electrons are displaced in an
electrical wire coil subjected to a
magnetic field changing intensity.
At the end of the last century, the improvement of the power of permanent
magnets has allowed simplified
models of electricity generators and alternators. Typically, the magnets are
distributed evenly around the
periphery of the power generating apparatus, primarily on the stator, but some
recent designs have included
the permanent magnets on the rotor, in particular, disk shape rotors. The
following United States of America
patents propose some recent designs:
5,696,419 Rakestrw et al.
5,'793,144 Kusase et al.
5,'789,841 Wang
5,'798,591 Lillington et al.
5,!386,378 Caamario
6,037,696 Sromin et al.
6,118,202 Pinkerton
6,177,746 Tupper et al.
6,285,090 Brutsaert et al.
6,404,089 Tomion
2002/0125781 Bales
Though some of these permanent magnet based designs are promising, few address
the specific need to
generate electrical power at low rotational speed, such as for wind turbine
applications, when the power
generator is connected to the blade assembly without speed multiplier
apparatus. Wind turbines also require
a apeed limiting apparatus such that the turbine operates within its optimum
rotational speed window. These
features are rarely inherently built into the power generator apparatus
itself. Rather, rotor speed is limited
u~;ing additional control systems of the blade pitch, blade aerodynamic
breaks, direction of wind turbine
relative to the wind, or load on the power generator.
Wind turbine electricity applications and corresponding power requirements are
numerous and diverse, from
direct current (DC) battery charging to providing alternating current (AC)
power to a grid. Wind turbine
scdutions are usually selected from existing wind turbines available on the
market, based primarily on wind
speeds and the average power density at the selected site during a typical
year. Power density is measured
in watts per square meters (W/m2). The wind turbine selection is also made
based on the estimated energy
consumption requirements, usually measured in kilowatt-hours per year (kWh/y).
The selection of a wind
turbine may therefore result in the best wind turbine available as opposed to
the optimum solution.
The need also exists to produce single phase or polyphase alternating current
power, depending on the
application. In most cases, especially when the quality of the electricity is
critical, converters are used
between the wind turbine electrical power generators and the user or network
connection point. The
capability of a wind turbine alternator to be assembled such that it will
generate single phase or pofyphase
(such as three-phase) electrical power is an essential feature to develop cost
effective alternator.
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Typical power generators require the fast movement of parts at close range.
The air gap between the rotor
heads and stator heads is usually maintained constant. The air gap is part of
the magnetic circuit of the power
generator such that the smaller the air gap, the higher the magnetic flux and
power generated. Therefore,
alternators and generators have massive and rigid assemblies to maintain the
air gap constant and/or to
become part of the magnetic circuit. Generators and alternators are typically
designed as small as possible
for a rated power to reduce weight and cost. However the rotational speed of
the rotor must be high and the
power generator generally require a speed multiplier apparatus.
Also, in typical power generators, the induction elements on the stator or the
rotor, are typically evenly
di:;tributed around the periphery of the stator or rotor for single phase or
polyphase electrical machines for
uniform and continuous operation. While the reasons are numerous and logical,
no patents explore unevenly
di:;tributed induction elements for generating polyphase electrical power.
SUMMARY OF THE INVENTION
A main object of the present invention is the provision of a large size
modular electrical power generator
power that can be directly driven by a wind turbine. The resulting alternator
assembly possibilities facilitate
matching wind energy potential at an installation site with the corresponding
power requirements.
It is also an object of this invention to define an electrical power generator
that produces alternating current.
The present invention is an electrical power generator that has a plurality of
stator units and equal number of
rotor units that are positioned concentrically on a main shaft.
The alternator assembly of the subject invention has modular features to
adjust the power output
characteristics when the alternator is assembled, while keeping the outer
diameter of the alternator the same.
The various power outputs can be accomplished by performing the following,
individually or in any technical
combination possible:
adjust the number of armature winding elements on each stator unit,
adjust the number of pairs of permanent magnets in the magnet holders,
adjust the number of magnetic elements on each rotor unit,
adjust the number of alternators units installed on the main alternator shaft.
It is also an object of the invention that the preferred source of magnetic
flux is provided by permanent
magnets mounted in magnet holders and forming part of the rotor magnetic
elements.
Aa an alternative, the source of magnetic flux in the magnetic elements of the
rotor can also be a coil driven
by direct current (DC) power to create magnetic poles at the end of the
magnetic elements. In this
configuration the rotor assembly needs to be connected to a DC power source
from outside the alternator
casing through brushes, or integrate a DC power generator inside the
alternator assembly.
It is also an object of this invention to create polyphase electrical
currents. The size of the electrical power
generator allows for different configurations of the installation of the
winding elements on the periphery of a
stator unit. Winding elements can be grouped in sectors around the periphery
of the stator, each sector
representing one phase of the electrical power generated. Polyphase electrical
power can be generated when
the sectors of a stator unit are subjected to an angular shift on the
periphery of the stator unit such that the
phases of the power generated the sector are shifted.
As another alternative, polyphase electrical power can also be generated using
multiple alternator units
wherein each alternator unit generates single phase power. In this
configuration, an alternator unit is installed
with angular shift for each phase of the electrical power required. Multiple
alternator units can also be installed
for each phase of power generated.
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As another alternative, each alternator unit installed within the alternator
assembly produces electricity for
different and isolated phase and power levels required for separate
applications.
It is also an object of this invention that the width of the air gap between
the rotor heads and stator heads on
large size alternators changes while in operation, in order to modify the
electrical power capacity of the
alternator under load. The rotor structure, including the magnet holder is
made of material with thermal
conductivity and thermal expansion properties. The rotor structure and magnet
holder material is also non-
magnetically permeable as to not interfere with the magnetic circuit on the
magnetic element. Typically, the
rotor structure is made of aluminum, magnesium, or alloys. The rotor structure
has wing shaped elements on
its periphery to facilitate air movement on, and cooling of the stator winding
elements. The heat extracted will
circulate in the alternator to warm up the rotor structure. Preferably, the
rotor structure is hollow to allow air
circulation within it and accelerating heat transfer. The rotor structure
expands uniformly outwardly under the
effect of heat transfer, therefore reducing the gap between the rotor head and
the stator head such that the
intensity of the magnetic flux increases. As the magnetic flux increases,
forces on the rotor will increase and
tend to limit the speed of the rotor.
In another aspect of the present invention, the alternator casing is made of
material with low thermal
conductivity and thermal expansion properties to reduce heat loss when
operating in cold weather, and to
control the air gap between the rotor heads and the stator heads. The
alternator casing is also made of non
magnetic permeable materials, to avoid interfering with the magnetic fields
inside the alternator. Preferably,
the alternator casing is made of fiber reinforced composite material, making
the alternator also a light weight
assembly. Cast iron covers and non-magnetic permeable stainless steel alloy
outer shell structure are
alternatives given that insulation is added to the assembly.
It is also another object of the invention to modify the alternating current
sinusoidal wave form when
assembling the alternator. This is done by installing rotor heads with
different pole face shapes in the magnet
holders.
In another aspect of the present invention, the resulting large size power
generator allows for the attachment
of a cone to the alternator casing cover to reduce drag on the alternator
assembly when powered by a wind
turbine. In the wind turbine application, a similar cone can also be added to
the face of the turbine blade
system.
BRIEF DESCRIPTION OF THE DRAWINGS
The benefits, advantages and characteristics illustrated in the drawings
described below form part of the
:specification of this invention
figure 1 is a cross-sectional view of the key elements of the alternator.
Figure 2 is a side plan view of the key elements of the alternator. It shows
the arrangement of the rotor poles
and stator winding element ends. In the configuration shown, the winding
elements are distributed evenly
around the periphery of the stator unit.
f=figure 3 is a side plan view of the arrangement of the stator winding
elements in sectors to generate three-
phase power. Angle measurements are shown to demonstrate the phase shift
between each sector.
Figure 4 presents a cross-sectional view of an alternator made of two
alternator units, in a configuration
where the alternator is mounted ahead of the turbine rotor blade assembly. The
figure shows the use of the
hollow alternator shaft.
Figure 5 shows two combinations of alternator and turbine assembly
installations on top on a tower.
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In the basic embodiment of the invention depicted in FIG. 1, the alternator
consists of a single alternator unit
or a plurality of alternator units within a non-magnetic permeable casing. An
alternator unit consists of a rotor
unit and a stator unit. A rotor unit has a main shaft 16 mounted on bearings
3, holding a rotor structure 15
which holds magnetic elements on its periphery. A stator unit has
interconnected winding elements mounted
on ring shaped stator structures. In particular the rotor magnetic elements
and the stator winding elements
form a magnetic circuit 21 that is small relative to the size of the
alternator. Multiple alternator units can be
stacked on a common rotor shaft as shown in FIG. 2.
An alternator casing made of low thermal conductivity material, preferably
fiber-reinforced composite material,
holds the alternator unit or a plurality of alternator units. The casing
consists primarily of 2 rigid covers 1, and
a cylindrical outer shell structure 2. The covers are assembled rigidly to one
another with the outer shell in
between using bolts (not shown) that also hold the stator unit (s) in place.
The covers also hold the bearings 3
of the main shaft of alternator. The length of the main shaft16 varies with
the number of alternator units
mounted inside the alternator. Spacers 20 as shown in FIG. 2 are mounted on
the main shaft 16 to keep the
rotor units aligned with their respective stator units.
Stator units are mounted between the casing covers 1 of the alternator. A
stator unit consists of a plurality of
winding elements mounted rigidly on the periphery of the stator structure 8.
Winding elements are made of
individual U-shaped magnetically permeable laminated cores 6 and coils 7
mounted between flat ring shaped
structures 8. When assembled, the stator poles of the winding elements face
the rotor poles leaving a small
air gap 5 between them.
The said stator winding elements laminated cores 6 are made preferably of thin
silicium iron based plates
separated by non conducting material. This assembly, similar to that of
transformers, prevents losses due to
eddy current losses. The 'U' shaped armature winding elements, when facing the
rotor poles, becomes part of
the magnetic field loop 21. The wiring is such that winding elements are
interconnected in series to increase
the current generated by the alternator.
As an improvement to the intensity of the magnetic flux in the winding element
cores 6 and resulting
increased current in the winding element coils 7, the cross section of the
winding element cores 6 where the
coils 7 are located is smaller than the surface area of the stator ends to
increase the magnetic flux density
where the coil is located.
A rotor unit rigidly mounted and centered to the main shaft 16 of the
alternator holds sources on magnetic
flux, preferably permanent magnets 11 on the periphery of the rotor structure
15. The permanent magnets 11
are disposed, in pairs, on each side of the rotor structure 15, and parallel
to the axis 4 of the main alternator
shaft 16. The permanent magnets 11 face outwardly. The permanent magnets 11
are mounted in cup like
magnet holders 14 fixed on both sides of the rotor structure 15. The pairs of
permanent magnets 11 are linked
with an interconnecting bar 13 to form a magnetic circuit 21 transversal the
direction of the rotation of the rotor
unit. The magnets 11 display the same pole, North or South, on a given side of
the rotor structure 15.
The magnet holders 14 hold the magnetic elements on the periphery of the
rotor. The magnet holders are
made of non-magnetically permeable material, preferably aluminum. A magnetic
element consists of a pair of
rotor heads 12, pairs of permanent magnets 11, and an interconnecting bar 13.
The rotor heads sit firmly in
the cup shaped bottom of the magnet holder and form the poles of the rotor.
The rotor is a separate piece of
magnetically permeable material, preferably made of iron. Rotor poles can also
be shaped permanent
magnets. The permanent magnets 11 are placed in series on top of the rotor
heads 12 in the magnet holders
14 such that a different magnetic pole appears on the other side of the wheel
shaped rotor structure, as
shown in FIG. 1. The permanent magnets 11 are positioned such as the magnetic
poles are the same on a
given side of the rotor structure 15. Magnets 11 from collocated rotor units
have the same pole as shown in
FIG 4.
In another embodiment, the source of magnetic flux in the magnetic elements of
the rotor can be a coil driven
by direct current (DC) power to create magnetic poles at the end of the
magnetic elements. In this
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configuration (not shown), the rotor unit (s) need (s) to be connected to a DC
power source from outside the
alternator casing through brushes, or integrate a DC power generator inside
the alternator assembly.
The periphery of the rotor structure 15 has wing shaped vanes 19 whereby the
heat generated from the stator
laminated cores 6 penetrates in the hollow core of the rotor structure 15
through vent holes 17 on the sides of
the rotor. The heat will warm up and expand uniformly the rotor structure 15
outwardly, therefore reducing the
gap 5 between the rotor head 14 and the stator heads such that the intensity
of the magnetic flux will increase
and the rotational speed of the rotor will be somewhat controlled.
FIG. 2 shows an arrangement of winding elements equally distributed around the
periphery of a stator unit. In
this embodiment, single phase power would be generated, all winding elements
on a stator unit being
interconnected to each other in one 360 degree sector.
FIG. 3 shows the winding elements mounted in angular sectors 35, 36 and 37
covering equal distances
around the periphery of a stator unit, each sector having an equal number of
winding elements depicted by
laminated cores 6. In the embodiment depicted in FIG. 3, each sector is
shifted 1/3 phase as shown by angles
39 and 40 relative to the other sector angle 38. The individual
interconnection of the windings elements within
each sector results in the creation of three-phase electrical current, and
limits the length of the wiring between
winding elements.
In a preferred embodiment, one alternator unit is mounted in the alternator
for each phase of the electrical
power required, wherein each stator unit is installed with an angular shift
equal to the peripheral distance
between winding elements divided by the number of phases required.
FIG. 4 demonstrates the extended capabilities of the alternator in terms of
its assembly ahead of the turbine
blade assembly 30. The turbine blade assembly 30 is somehow mounted to or on
the hollow alternator shaft
16 as shown in FIG.4, with proper spacing between the alternator cover 1, the
wind turbine blade assembly
30, and the tower structure 31. The main shaft16 turns freely on bearings 29.
The alternator unit is supported
by the main shaft 16. The rotation of the alternator casing is prevented by a
rod assembly 28 and 26 held
fixed on the tower structure at one end and to the alternator cover 1 facing
externally at the other end. The
rod 26 passes through the hollow center of the main shaft 16. In this
particular embodiment, the electrical
wires 25 originating from winding elements of the stator unit or units pass
through the alternator cover
opening 24, through the hollow center of the main shaft 16 and then extend to
the tower structure 31 through
an opening 27. Typically, the tower structure will rotate with the direction
of the wind (not shown).
F'IG.S depicts two wind turbine mounted alternator configurations whereby the
alternator can be installed
downwind the turbine blade assembly or upwind. The addition of a cone 45 to
the turbine blade assembly 30
and to the alternator casing provides additional aerodynamic benefits to the
efficiency of the wind turbine and
reduces drag forces on the alternator assembly.
In another aspect of the present invention, the end covers 1 of the alternator
casing structure have a dome
shape such that the air flow around the alternator assembly will be
facilitated.
