CA2404939A1

CA2404939A1 - Wind turbine alternator

Info

Publication number: CA2404939A1
Application number: CA002404939A
Authority: CA
Inventors: Michel J. L. Auclair
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-10-02
Filing date: 2002-10-02
Publication date: 2004-04-02

Abstract

An electrical power generator assembly provides modular power features and directly driven by a wind turbine assembly. The power generator assembly includes a rigid casing with low thermal expansion characteristics holding at least one alternator unit. An alternator unit is composed of a stator unit mounted on the periphery of the alternator casing and a rotor unit mounted on the main shaft of the alternator. A stator unit is composed of a stator structure and a plurality of individual U-shaped armature winding elements than can be mounted in a plurality of sectors. The ends of the winding elements face inwardly. A rotor unit is composed of a thermally expandable rotor structure with a plurality of magnetic elements mounted on its periphery such that the ends of a magnetic element will face the ends of a stator winding element when the main shaft is rotated.

Description

2of8 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.

3of8 WIND TURBINE ALTERNATOR
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.

4of8 WIND TURBINE ALTERNATOR
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 6of8 WIND TURBINE ALTERNATOR
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.

Claims

WIND TURBINE ALTERNATOR
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electrical power generator, comprising:
a casing including end covers, a cylindrical outer shell structure, and a bearing mounted main shaft driven by a blade assembly such that of a wind turbine, a stator unit or a plurality of stator units mounted side by side within the casing, a modular wheel-shaped rotor unit or a plurality of rotor units mounted on the alternator main shaft.

2. The power generator of claim 1, wherein the said outer shell structure is cylindrical in shape and may hold at least one stator unit and at least one rotor unit concentrically installed.

3. The power generator of claim 1, wherein each stator unit comprises a plurality of armature winding elements made of individual U-shaped magnetically permeable laminated cores and interconnected coils.

4. The power generator of claim 1, wherein each rotor unit comprises a plurality magnetic element holders mounted on the rotor structure and holding the magnetic elements on the periphery of the rotor structure, whereby the holders and the rotor structure are of material with thermal expansion and low relative permeability characteristics such as aluminum.

5. The power generator of claim 3, wherein the said winding elements are mounted on flat ring shaped structures mounted inside the cylindrical outer shell structure.

6. The power generator of claim 4, wherein a magnetic element consists primarily of a pair of magnetically permeable poles, permanent magnets stacked in equal numbers in series behind each rotor head, and a magnetically permeable bar joining the back of the permanent magnets, to create a magnetic circuit between the two poles of a magnetic element.

7. The power generator of claim 4, wherein the permanent magnets of the said magnetic elements can be replaced or supplemented by an electrical coil mounted on the interconnecting bars of the magnetic elements.

8. The power generator of claim 3, wherein the said winding elements are mounted in sectors covering equal distances around the periphery of the stator, each angular sector having an equal number of winding elements, and each sector being in phase to create single phase electrical current, or each sector being shifted a fraction of the peripheral distance between winding elements to create polyphase electrical current power.

9. The power generator of claim 6, wherein different magnetically permeable pole shapes can be installed on the rotor without any other change to the alternator to modify the electrical signal wave form of the power generated.

10. The power generator of claim 6, wherein the number of stacked permanent magnets can be changed to modify the intensity of the electrical signal of the power generated.

11. The power generator of claim 1 wherein the main alternator shaft is hollow to allow passage of electrical wires and an inner bar or shaft extending beyond the end of the main shaft that can prevent the casing of the alternator from rotating, and hold a cone against the external cover of the alternator.

WIND TURBINE ALTERNATOR

12. The power generator of claim 1, wherein the heat generated from the stator winding elements penetrates in the hollow core of the rotor structure through wing shaped vanes on the periphery of the a rotor unit structure such that the heat from the stator winding elements will warm up and expand uniformly the rotor structure outwardly, therefore reducing the air gap between the rotor poles and the stator winding element ends.

13. The power generator of claim 1, wherein the end covers of the alternator casing structure have a dome shape such that the air flow around the alternator assembly will be facilitated.

14. The power generator of claim 1, wherein a cone can be added to the alternator casing and to the turbine blade assembly to reduce drag forces on the alternator assembly and to provide additional aerodynamic benefits to the efficiency of the wind turbine.

15. The power generator of claim 1, wherein the alternator can be mounted ahead of the blade assembly.

16. The power generator of claim 1, wherein a plurality of alternators can be mounted on the main rotor shaft.