WO2021119670A1

WO2021119670A1 - Wind turbine protections

Info

Publication number: WO2021119670A1
Application number: PCT/US2020/070908
Authority: WO
Inventors: Jason Day
Original assignee: Star Wind Turbines, Llc
Priority date: 2019-12-13
Filing date: 2020-12-14
Publication date: 2021-06-17

Abstract

In order to protect a wind turbine system from over-voltage/rpm, power surges, excess temperature, and/or vibration, one or more of the following improvements is provided: a passive pitch mechanism that causes blades to pitch backwards, slowing increases in rpm; a selective, incremental stator-inverter engagement system; an enhanced air cooling system; and a vibration damping system. Stator assemblies have dedicated, power-matched inverters in order to produce power when certain wind availability thresholds are met. Enhanced air cooling includes air inputs on the front plate behind the cone and in rotor plates and paddles or paddle shaped portions of magnets on rotors assist to move air through and around generator components. Vibration reduction is achieved by reducing the power pulse by shifting the stator coils to offset the phase of magnetic engagement, and/or vibration dampers are used to isolate the stators.

Description

WIND TURBINE PROTECTIONS

FIELD OF THE INVENTION

[0001] The present invention generally relates to wind turbines. In particular, the present invention is directed to a system that includes protection mechanisms for protecting a wind turbine system from one or more of the following: over-voltage/rpm, power surges, excess temperature, and vibration.

BACKGROUND

[0002] A common type of wind turbine is a horizontal axis wind turbine, which typically uses several blades coupled together on a hub that rotates in response to a lifting force created by the wind. As used herein, the term “wind rotor” denotes the assembly that comprises a blade hub and a plurality of blades (also called airfoils). Generally, the wind rotor converts wind energy into the rotational energy that drives a generator. The hub is connected to a shaft that is connected to the generator, which supplies power to a load (e.g., electrical grid, residence, etc.). For certain wind turbines, a gearbox converts the rotation of the blades into a speed usable by the generator to produce electricity at a frequency that is proper for the load.

[0003] Generally, wind turbines are designed for a maximum revolution per minute (rpm) and as such, in high winds, the wind turbine needs a mechanism to protect itself from over-rotation of the rotor and blades. If the rotor blades go over the maximum rpm, damage can happen in the form of:

1) over-voltage/power to the generator and electrical components that can cause thermal and electrical destruction, and 2) an excess of centrifugal force that can damage the blades or hub.

[0004] Pitching the blades, a means by which wind force that would otherwise turn the blades is shed due to a smaller exposed blade surface, is a common method of protecting a wind turbine from over-rotation of the rotor. Large wind turbines typically use electromechanical systems that can, for example, include independent digital step motors on geared slewing bearings, rpm sensors, and controllers to control and move the blades into a pitch position. When the rpm sensors sense that the blades are rotating at a predefined limit, the step motors pitch the blades so as to reduce the surface area exposed to the wind. This change increases the ratio of flat plate drag to lift/rotational force and thus slows or minimizes increases in the rotation of the rotor. [0005] However, electrical/electromechanical pitch mechanisms are expensive and unreliable. These types of mechanisms are vulnerable to electronic failure due to, among other things, wear, lightning strike, temperature, semiconductor failure, and corrosion. The sensors, motors, controllers, and other electronics involved make a durable, reliable electro/mechanical pitch control expensive and risky, especially for smaller wind turbine manufacturers.

[0006] There are non-electrical and electromechanical pitch mechanisms. For example, one mechanical mechanism uses rod-shaped weights that rotate the blades forward upon experiencing sufficient centrifugal force. The forward rotation of the blades (i.e., making the blades perpendicular to the wind direction) reduces the pitch angle to the air foil to the point that it reduces lift and the rotational force on the blade. These systems still have too many components, require significant space within the hub, and significant tower infrastructure to combat the forces of the wind on the blades. Also, the perpendicular position of the blades can cause an excess bending stress when the wind is high, which can result in structural failures.

[0007] Although gear-driven wind turbines are still being made and used, direct-drive wind turbines are becoming more prevalent largely due to advances in systems for controlling this type of wind turbine. As its name implies, direct-drive wind turbines do not include a gearbox, but rather have a direct mechanical coupling between the wind rotor and generator so that the wind drives the wind rotor and the rotor within the generator together as a unit. Direct-drive wind turbines have an important advantage in lessened complexity, which typically results in direct-drive wind turbines being more reliable, and having longer life spans and lower costs of operation than their gear-driven counterparts.

[0008] Current wind turbine designs are focused on developing maximum power. As the generator produces more power, however, coils in the generator produce more heat, and the heat increases the temperature on wires, which causes the wires to have greater resistance. Therefore, as the heat builds up, the generator becomes less efficient. Also, permanent magnets in the generator may have a temperature limit at which their magnetism can be lost.

[0009] In addition, generally the stators in the generator are of the same number of windings and are mounted on a stator assembly so as to line up in the same phase pattern, in which case an amplified power pulse may be created by all of the stator coil legs generating power at the same time. This power pulse transmits throughout the wind turbine structure which can result in excess vibration and sound, and in extreme cases can damage turbine components.

[0010] Further, power generated by wind turbines is often converted from direct current to alternating current (so as to supply power to an electrical grid), which requires inverters. Conventional inverters do not support high power solutions for single phase above 5-10kW in power, yet higher power rated inverters diminish the ability to generate power at lower wind conditions. Splitting the power from a generator to multiple inverters poses a risk since it can cause power surges and transient voltages that can damage the electronics of the system.

SUMMARY OF THE DISCLOSURE

[0011] A passive wind turbine pitch mechanism for a wind turbine with a plurality of blades that includes a push/pull tube including a piston and a return spring coupled to the piston. A plurality of bearings is coupled to a corresponding respective one of the plurality of blades, and the piston is coupled to the plurality of blades such that the blades move in unison with movement of the piston. As a wind speed increases, the plurality of blades rotate and move backward from an initial position and the piston moves within the push/pull tube against the return spring.

[0012] Additionally or alternatively, each of the plurality of blades have an initial position that is forward tilted and lagging tilted so as to create a moment arm for a wind force to move the plurality of blades backwards.

[0013] Additionally or alternatively, the piston is coupled to each of the plurality of blades via a respective lever and a linkage.

[0014] Additionally or alteratively, as a wind speed increases, the return spring resists movement of the piston and the plurality of blades are pitched into a feathered state.

[0015] Additionally or alternatively, a hydraulic damper is configured to counteract movement of the return spring and thereby limit a rate of pitch changes.

[0016] In another aspect of the invention, a wind turbine generator includes a plurality of rotor assemblies, wherein each of the plurality of rotor assemblies includes a rotor plate and a magnet and wherein the magnet is shaped such that upon rotation the magnet assists in creating airflow through the generator, and a plurality of stator assemblies, each of the plurality of stator assemblies having a respective corresponding one of the plurality of rotor assemblies, wherein the plurality of stator assemblies are stacked from a front to a back of the generator such that a space is provided between each of the plurality of stator assemblies and each of the respective corresponding one of the plurality of rotor assemblies. A housing includes a front plate and a rear section, wherein the front plate includes a plurality of holes configured to allow air to flow into the generator. A diffuser is attached to the rear section of the housing, wherein the diffuser is tapered such that a front portion has a larger profile than a back portion.

[0017] Additionally or alternatively, the generator does not include a shaft such that air flows through a center of the generator.

[0018] Additionally or alternatively, a plurality of paddle-like assemblies are positioned between each of the plurality of rotor assemblies and stator assemblies and configured to move air through the generator from the front to the back of the generator when rotating.

[0019] Additionally or alternatively, each of the plurality of rotor assemblies include one or more magnets and wherein each of the magnets include a paddle-shaped portion configured to move air through the generator from the front to the back of the generator as a rotor plate rotates.

[0020] In another aspect of the invention, a wind turbine generator includes a housing, a plurality of rotor assemblies, wherein each of the plurality of rotor assemblies includes a magnet, and a plurality of stator assemblies, wherein each of the plurality of stator assemblies corresponding to a respective one of the plurality of rotor assemblies, wherein each of the plurality of stator assemblies includes a stator coil, and wherein each stator coil is offset sufficiently along a circumference traversed by the plurality of rotor assemblies with respect to another stator coil on an adjacent stator coil assembly such that, when the plurality of rotor assemblies rotate, magnet/stator coil engagement will not occur simultaneously at each stator coil.

[0021] Additionally or alternatively, a plurality of vibration dampers are included, wherein at least one of the plurality of vibration dampers is between each of the plurality of stator assemblies and the housing. [0022] In another aspect of the invention, a wind turbine system for producing electrical energy includes a wind turbine generator including a plurality of stator assemblies and a plurality of inverters, wherein each of the plurality of inverters is connected to a dedicated one of each of the plurality of stator assemblies forming a plurality of stator-inverter subsystems, wherein each one of the plurality of stator-inverter subsystems is engaged at a different wind availability threshold.

[0023] In another aspect of the invention, a wind turbine generator includes a plurality of rotor assemblies, the rotor assemblies each including a magnet and configured to rotate about an axis such that the magnet travels along a circumference, and a plurality of stator assemblies having a stator coil, wherein each stator coil is positioned to be engaged by a corresponding one of the magnets and is offset along the circumference with respect to a counterpart stator coil on an adjacent stator assembly such that engagement of the offset stator coil and the counterpart stator coil by respective corresponding magnets is offset in time.

[0024] In another aspect of the invention, a method of incremental wind turbine generator engagement includes determining a wind availability, engaging a first stator-inverter subsystem if the wind availability is above a first stator-inverter subsystem threshold, disengaging the first stator- inverter subsystem if the wind availability is below the first stator-inverter subsystem threshold, engaging a second stator-inverter subsystem if the wind availability is above a second stator-inverter subsystem threshold, wherein the second stator-inverter subsystem threshold is greater than the first stator-inverter subsystem threshold, and disengaging the second stator-inverter subsystem if the wind availability is below the first stator-inverter subsystem threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 is an elevated isometric view of a prior art wind turbine;

FIG. 2 is a side elevated isometric view of the wind turbine of FIG. 1;

FIG. 3 is a cutaway view of a portion of a wind turbine showing a passive pitch mechanism (PPM) according to an embodiment of the present invention; FIG. 4 is another cutaway view of a portion of a wind turbine showing a PPM according to an embodiment of the present invention;

FIG. 5 is a perspective view illustrating the movement of a wind turbine blade in response to wind forces according to an embodiment of the present invention;

FIG. 6 is a side view of a portion of a wind turbine showing the blades in a forward tilt position according to an embodiment of the present invention;

FIG. 7 is a front view of a portion of a wind turbine showing the blades in a lagging tilt position according to an embodiment of the present invention;

FIG. 8 is a chart of wind speed versus force as experienced by a wind turbine made according to an embodiment of the present invention;

FIG. 9 is a cutaway view of a portion of a wind turbine showing a passive pitch mechanism (PPM) according to an embodiment of the present invention;

FIG. 10 is a cutaway plan view of a permanent magnet wind turbine generator according to another embodiment of the present invention;

FIG. 11 is a perspective, partially cut-away view of a wind turbine generator in accordance with an embodiment of the present invention;

FIG. 12 is a perspective, partially cut-away view of the wind turbine generator of FIG. 11 including an airflow indicator;

FIG. 13 is a partially exploded side view of a portion of a wind turbine generator in accordance with an aspect of the present invention;

FIG. 14 is a partially exploded perspective view of the portion of a wind turbine generator of FIG.

13;

FIG. 15 is side view of an uncovered wind turbine generator connected to a shaft and blades in accordance with another embodiment of the present invention; FIG. 16 is a perspective view of a portion of a wind turbine generator showing stators and rotors in accordance with an embodiment of the present invention;

FIG. 17A is detail view of a portion of FIG. 16 with some components not shown for clarity;

FIG. 17B shows the portion of FIG. 17A in which the rotors have rotated counterclockwise;

FIG. 17C shows the portion of FIG. 17A in which the rotors have rotated further counterclockwise;

FIG. 18 is a schematic diagram of a prior art single-stator wind turbine generator system;

FIG. 19 is a schematic diagram of a multi-stator wind turbine generator system in accordance with another embodiment of the present invention; and

FIG. 20 is a process diagram for a wind turbine with multi-stator/inverter subsystems in accordance with another aspect of the present invention.

DESCRIPTION OF THE DISCLOSURE

[0026] Turning first to FIGS. 1 and 2 there is shown a direct-drive, wind turbine 100. Wind turbine 100 generally includes a wind rotor 104 and a tower 112. Wind rotor 104 includes a rotor hub 116, a plurality of blades 120, and a shaft (not shown). Blades 120 are coupled to rotor hub 116 and extend generally radially outward from a rotational axis. Rotor hub 116 is coupled to the shaft, which is coupled to portions of the generator (also not shown). Blades 120 include a profile that assists in generating lift forces on the blade so that rotor hub 116 rotates. Wind turbine 100 may also include a pitch control mechanism (discussed in more detail below) that would facilitate the altering of the attack angle of blades 120 so as to produce energy efficiently at varying wind speeds or to preserve the integrity of the wind turbine. While the blades may be made of any suitable material, typically a fiberglass reinforced vinyl ester or epoxy is used to reduce weight while still providing the mechanical strength required to withstand wind loads. During operation of wind turbine 100, wind rotor 104 is driven by the wind to rotate and supply a useful torque through rotor hub 116 to the generator via the shaft.

[0027] Wind rotor 104 may be positioned above the ground by a tower 112 having a height suitable for the intended application. Considerations in selecting the height of tower 112 include, among other things, the distance from the tips of blades 120 to their rotational axis and the proximity and characteristics of surrounding structures, geographic features or the like, that may affect the wind impinging upon wind rotor 104. For example, tower 112 is a tapered tubular steel structure that is constructed in sections to facilitate the transportation and assembly of the tower at its point of use. Alternatively, the tower may be made from a lattice structure or from concrete sections. Tower 112 may also include a lift assembly 132 that allows the tower to be raised and lowered for maintenance. Lift assembly 132 may be a hydraulic lift assembly that allows tower 112 and wind rotor 104 to move from a substantially horizontal orientation to a substantially vertical orientation.

[0028] Wind rotor 104 may be supported on tower 112 via a nacelle 136 that may be rotatably attached to the tower by a yaw bearing assembly (not shown) that allows the nacelle and wind rotor to rotate toward the prevailing winds (or away from the prevailing winds in the case of a desired shut-down or reduced power operation). As seen in FIG. 2, wind rotor 104 also typically includes a nose cone 140 that is secured to rotor hub 116 and/or one or more of blades 120. Nacelle 136 is typically sized to enclose generator (not shown) and other components of wind turbine 100, such as, but not limited to, power converters, control systems, etc.

[0029] Turning now to FIGS. 3 to 5, and first with respect to FIGS. 3 and 4, there is shown a cutaway view of an internal portion of a wind turbine 200 (which may be similar in most respects to the internal portion of wind turbine 100 described above) including a PPM 204 according to an embodiment of the present disclosure. At a high level, PPM 204 is a durable, non-electrified blade pitch mechanism that is not vulnerable to the electrical failures, temperature changes, or corrosion issues that plague electromechanical pitch mechanisms. In an embodiment, PPM 204 includes a push/pull tube 208 and a piston 212 that connects to each blade 236 (FIG. 5) via a respective lever 216 and a linkage 220 (both best seen in FIG. 4). Each blade 236 is mounted on a bearing 224, which allows the blade to swivel in response to pressure from wind forces or from piston 212. The use of piston 212 in combination with lever 216 and linkage 220 allows the blades to pitch together in unison as piston 212 moves within push/pull tube 208. Push/pull tube 208 also includes a return spring 228. Return spring 228 resists the movement of piston 212 as blades 236 are pitched into a feathered state and provides the return force necessary to move the piston forward so as to reduce the pitch of the blades.

[0030] In relation to the plane of bearing 224, the blades are set in a tilt-forward position opposite to the wind direction and set in a lagging rotational tilt behind the perpendicular axis of the blade (the forward tilt and lag tilt are shown in FIGS. 6 and 7 respectively). The lagging tilt and forward tilt make a lever moment for air pressure to push against. Thus, in operation, as the wind speed increases or decreases, the piston moves forward or backward in response to changes in the relative wind speed, e.g., the faster the wind speed the further “backward” the piston moves. The impact of these forces on the blade is shown in FIG. 5. As shown, in response to increased force from the oncoming wind, blade 236 moves “back” relative to its initial position and rotates so as to pitch the blade out of the wind.

[0031] As a blade rotates backward, e.g., increasing in pitch angle from about 7 degrees to about 70 degrees (shown in FIG. 5), the flat-plated drag increases and the aerodynamic lift or rotational force decreases, causing the rotor to curb increases in its rotation. Because the flat-plated drag increases faster than the aerodynamic lift or rotational force of the blade, the rotor is prevented from going into over-rotation and potentially being damaged or causing damage to other components. Placing blades 236 into an increasing flat plate drag position, instead of forward as found in prior art systems, generates a stall using only the blades to catch the wind forces. When the wind decreases, return spring 228 pushes piston 212 back, and the blades are reduced in pitch.

[0032] In an embodiment, PPM 204 also includes a hydraulic damper 232 (FIGS. 3 and 4) to limit the rate of pitch changes, otherwise the blades could oscillate and potentially become unstable. Hydraulic damper 232 counteracts the movement of return spring 228.

[0033] A constant, regulated rotation of the wind rotor in response to the wind speed is a preferred outcome for wind turbine operation. The desired rpm range of a wind turbine can be effectively determined by size and configuration of the blades, the amount of lagging tilt, the amount of forward tilt (the combination of lagging tilt and forward tilt creating the moment arm that the wind can press against), and the spring constant of return spring 228. In particular, with respect to return spring 228, the return spring is designed to compress until the compressed load is equal to the aerodynamic lift force and the drag force at a specific wind velocity and/or rpm. Once this point is reached, the blade will pitch back rapidly and slow down the rotation.

[0034] FIG. 8 shows a chart 300 of wind speed vs. force (both lift and drag forces 304 and compressive force 308). For this example, a return spring 228 with a spring constant of 1501bs./inch, when compressed 9 inches, will result in 1,350 lbs. of compressive force. In this example, at this compressive force, the blades will remain unpitched when the wind speed is less than 14 to 15 mph and rotating at less than 36 rpm. This stage is referred to herein as the “equilibrium point” 312. However, after equilibrium point 312 is exceeded, the combination of lift and drag forces 304 increases faster than the 1501bs./inch of compressive force 308. Accordingly, this combination of forces causes the blades to pitch backwards, slowing increases in rpm. In other words, while it took l,3501bs. of force to hold the blades at 0 degrees of movement, after 14 mph of wind force, the blades will start to pitch when additional lift and drag force is applied because the wind lift force increases exponentially with wind speed and is much greater after equilibrium point 312. In another example, in an embodiment, return spring is preloaded with 600 lbs. of compressive force (which can be accomplished by adjusting loading mechanism 238 that can, in certain embodiments be a screw that extends into push/pull tube 208 so as to engage return spring 228 and compress it). In this embodiment, the preloaded compression results in only a small increase, e.g., 79 lbs./inch, to pitch the blades significantly. Thus, in this embodiment, the blades are held at 0 degrees of movement until the wind turbine blades begin to rotate at about 36 rpm, at which time blades exert a force on the piston that exerts the remaining 79 lbs./inch force required to move the return spring 228 and the blades are pitched about 70 degrees.

[0035] Returning now to FIG. 3, in certain embodiments, PPM 204 may include a backup system 240. In an embodiment, backup system 240 is an electro-mechanical system 244 that is powered by an electric motor 248. Electro-mechanical system 244 has the capability to override the return spring 228 and put blades 236 in to feathered/fully pitched position in the event of an emergency or for service. Electro-mechanical system 244 acts as a regulator and has the capability to change the flat pitch setting in operation and to relieve spring pressure if needed, for example, in the event of a severe wind gust. By setting a flat pitch stop 252 at a higher pitch, system 244 has the capability to limit the rpm of the wind turbine. This rpm limiting is for the purpose of either limiting generator output in the event of high generator temperatures or to reduce noise output. Return spring 228 acts simultaneously with the electro-mechanical system 244.

[0036] In FIG. 9, a cutaway view is shown of a portion of a wind turbine showing a passive pitch mechanism 400 that includes a blade bearing 404, a blade arm and linkage 408, a hydraulic dampener/speed limiter 412, a main bearing 416, a return spring pre-load adjustment 420, a return spring 424, a push-pull tube 428, a push-pull tube flat stop 432, a worm drive 463, and a pitch motor 440. Passive pitch mechanism functions similarly to the passive pitch mechanism shown in FIG. 3 as described above.

[0037] In addition to the above-described passive pitch mechanism, the present invention may also provide a wind turbine generator that has improved operation at lower wind speeds, reduced vibration, and improved air cooling of generator components. Turning now to FIG. 10, there is shown an exemplary wind turbine generator 508 suitable for use with wind turbines, such as wind turbine 100. In an exemplary embodiment, generator 508 is a permanent magnet generator that includes a housing (not shown), a shaft 524, a plurality of rotor assemblies 544 and a plurality of stator assemblies 548. Rotor assemblies 544 are shown in two forms in FIG. 10, rotor assemblies 544 A and rotor assemblies 544B. Rotor assemblies 544 each include a rotor plate 552 and a plurality of permanent magnets 556 embedded therein. Rotor assemblies 544B include a yoke 550 and a plurality of permanent magnets 556 affixed thereon. Each stator assembly 548 includes a stator plate 560 and a plurality of stator coils 564.

[0038] In the embodiment shown in FIG. 10, generator 508 is made of an alternating assembly of alternating rotor assemblies 544 and stator assemblies 548, which in certain embodiments may be coupled to shaft 524, or may be configured so as to be part of a shaftless assembly. Each rotor plate 552 and yoke 550 supports a circular array of alternated pole axial-field permanent magnets 556 attached thereon. Yokes 550 also provide a return path for the magnetic fields of permanent magnets 556 and can be formed of high magnetic permeability materials. Rotor plates 552 are typically nonmagnetic and have low magnetic permeability so as to maximize flux density between the rotor plates. The stator plates 560 can be molded with the stator coils 564 and composed of a material that is electrically non-conductive and that has high thermal conductivity so that heat generated by current in the stator coils is conducted to the stator plate.

[0039] In an embodiment of generator 508, permanent magnets 556 on adjacent rotors are set in an opposing relationship.

[0040] In general, the number of rotor assemblies 544 and stator assemblies 548 affects the electrical generation capacity of generator 508, i.e., the more assemblies there are, the more power will be generated by generator 508 at a given wind rotor angular speed. Concomitantly, an increase in the number of rotor assemblies 544 and stator assemblies 548 also requires increased torque transmitted by the wind rotor in order to achieve a given wind rotor angular speed. Accordingly, the number of stages (e.g., a set of rotor assemblies 544 and stator assemblies 548) selected for use in generator 508 (which can be any number) and/or the number of stator coils 564 and permanent magnets 556 can be chosen so as to maximize the power output for a desired wind rotor 504 speed, also referred to herein as “tuned”.

[0041] With increased power output, however, comes an increase in heat produced within the generator, and the need to remove heat. Turning to FIGS. 11-14, in an embodiment, a wind turbine generator, such as wind turbine generator 608, includes an improved air-cooling system. A partial cutaway view of generator 608, as seen in FIGS. 11 and 12, shows the improved air-cooling system that allows for cooling of copper coils and generator components generally by including a plurality of air inputs 612 (e.g., 612a-612g as seen in FIG.14), which reside in a front plate 616 of housing 610 behind cone 620, as well as a spaced-apart struts 622. The plurality of stator assemblies 648 are stacked from front to back, which allows for spaces between each stator assembly and its corresponding rotor assembly 644. Additionally, generator 608 is shaftless, thereby allowing for air to ingress into the center area of generator 608. Air, which is pulled in through inputs 612 and area 618, can flow through and between stator assemblies 648 and rotor assemblies 644 and exit out spaces 650 that are between struts 622. This flow is aided by paddles or paddle-like assemblies 624, which are positioned between rotor assemblies 644 and stator assemblies 648 and configured to move air through generator 608 from a front 645 to a back 647 of generator 608. Additionally, magnets 156, when mounted on the surface of their respective rotor assemblies 644, act as paddles as well. Thus, as the shaft turns and rotor assemblies 644 and paddle assemblies 624 spin, cool air is pulled in to generator 608 and flows across components to cool them. Alteratively, magnets 156 may include paddle-shaped portions 625 (as shown in FIG. 12) to similarly aid in air flow as rotor plate rotates. As shown in FIGS. 12 and 14, air flows in through inputs 612 and through each rotor assembly 644 and passes each stator assembly 648. Paddle assemblies 624 (and/or magnet portions 625) facilitate this flow and also push air to the inside perimeter of generator 608, where the air flowing through enters a diffuser 628 (discussed in more detail below) exits to the side of generator 608 thereby allowing air flow through and around internal portions of generator 608 and cooling of generator 608. [0042] FIGS. 13-14 show a portion 609 of generator 608. An exploded side view is shown in FIG. 13 and an exploded perspective view is shown in FIG. 14. In conjunction with air input holes 612 in front plate 616, in each rotor plate 652 includes a plurality of apertures 632 (e.g., 632a-632b, which can be seen in FIG. 14) to aid in the air flow through generator 608. Additionally, a large air passage through generator 608 is included to further assist with air flow. In addition to aiding in air flow through the components, paddle assemblies and/or magnet paddles 625 may be designed to create a flow perpendicular to the shaft when rotating as well as some turbulent flow to assist with more even cooling of components from front to back.

[0043] Diffuser 628 (shown in FIGS. 11 and 12) on the rear of generator 608 is designed to assist with air flow through generator 608 by increasing pressure on air around front portion 616 and by creating a differential pressure at a rear 636 of diffuser 628 to assist with causing the air to flow through generator 608. Diffuser 628 tapers to a smaller profile toward rear 636, which causes air passing around the exterior of diffuser 628 (i.e., air moving past the wind turbine) to speed up as it moves toward rear 636. The difference in speed from front to back results in a pressure difference in which there is greater pressure at the front than at the rear of diffuser 628, further facilitating air flow through generator 608. Optionally, an electric fan (not shown) may be located in diffuser 628 to blow air out when generator 608 reaches a set temperature. In an embodiment, generator 608 can experience a 30% reduction in heat due to the configuration that allows for air-flow throughout generator 608. This reduction in heat also results in improved power output and efficiency of the generator.

[0044] In addition to requiring cooling, wind turbine generators can produce vibration and sound when power is being produced. A common design of axial generators is to position stator coils on each respective stator assembly such that each of the stator coils is magnetically impacted by the magnets on the rotors at the same points during rotation of the rotors. In such a configuration, an amplified power pulse may be created by all of the stator coil legs generating power at the same time. Such power pulses are transmitted throughout the wind turbine structure, which can result in significant vibration and sound as well as require additional infrastructure, e.g., more robust tower structures, to absorb the vibration. To reduce the vibration and sound caused by a power pulse (which can especially be amplified in a hollow tower), in an embodiment the power pulse is broken up by shifting the stators (in particular, the stator coils) and thereby shifting the phase of power generated by a respective stator assembly such that each stator is magnetically impacted at different points in the rotor motion. In addition, or in the alterative, stators are suspended and isolated with rubber vibration dampers.

[0045] In an embodiment, a wind turbine generator, such as generator 308 as shown in FIG. 15, is attached to wind rotor 703. Generator 708 includes a plurality of rubber isolation dampers 706 (discussed further below) to reduce vibration. In addition, stator assemblies 748 are rotated with respect to each other in order to offset the phases, thereby reducing the incidence of power pulses, which also reduces vibration. The legs of the multiple stator coils do not generate power simultaneously, resulting in a finer frequency vibration. Energy produced at each stator assembly 748 is then DC rectified and combined (either before or after reaching the inverters).

[0046] The shifting of stators may be illustrated by the following example in which there are six stator assemblies 748 (as in FIG. 15) and the “stator shift” will be one third of the phase on the six stators assemblies. To achieve this phase shift, stators are rotated such that they are offset by a distance equal to half the distance between each phase divided by three. In other words, in this example, if the distance between each phase is six inches (i.e., the arc length the rotors must traverse to engage with (i.e., magnetically impact) a stator coil is six inches), then the stator coils on a respective stator plate would be rotated one inch (along the circumference of the path the rotor magnets traverse) with respect to the previous adjacent stator plate. In another embodiment, if the desired stator shift is one sixth of the phase on the six stator assemblies and the distance between each phase is six inches, then each stator coil on a respective stator plate would be rotated/shifted ½ inch with respect to the stator coils on the previous adjacent stator plate. In this way, magnets on rotor assemblies will not simultaneously magnetically impact each stator coil; rather, when a magnet is aligned with and engaging a given stator coil on a given stator assembly, the magnet on an adjacent rotor assembly will not be aligned with and engaging a stator coil on an adjacent stator assembly because that stator coil is offset with respect to the circumferential path through which the rotor assembly magnets travel. Therefore, the stator coil on one stator assembly will be engaged by a rotor magnet before (or after) the nearest stator coil on the adjacent stator assembly.

[0047] In FIG. 16, a portion 711 of generator 708 is shown for clarity, which includes six stator assemblies 748 are matched with six rotor assemblies 744. As can be seen, stator coils 724 of adjacent stator assemblies 748 are shifted with respect to each other such that as each respective magnet 756 of rotor assemblies 744 rotates, the coil/magnet pairing alignments will not occur simultaneously. For example, magnet 756f is aligned with and magnetically impacting stator coil 724f at the point of rotation shown of rotor assembly 744f in FIG. 16, while magnets 756a-756e are not aligned with counterpart stator coils 724a-724e. For clarity, FIGS. 17A-17C depict only one magnet on each stacked rotor assembly and one stator coil on each stator assembly to illustrate the offset of stator coils 724. As can be seen, as the rotor assemblies rotate (counterclockwise as shown in FIGS. 17A-17C), adjacent magnets on respective rotor assemblies are offset as they pass by adjacent stator coils on respective stator assemblies, thereby reducing the impulse associated with simultaneous alignment.

[0048] In the alternative or, in a preferred embodiment, in addition, each of the plurality stator assemblies 748 can be suspended or isolated via a vibration damper 706 (e.g., 706a-706f in FIG. 15) placed between each stator plate and housing 704. Vibration dampers 706 can be made of any suitable material such as rubber and will reduce high frequency vibrations. However, vibration dampers may not have an appreciable effect on low frequency power pulses. Therefore, vibration dampers and stator shifting may both be used in a complementary manner to reduce overall vibration and noise.

[0049] In another embodiment, a generator is provided with incremental engagement of stator- inverter subsystems in order to increase the overall energy output in many wind environments (e.g., light wind conditions). Typically, high performance transformerless single phase inverters are designed to accommodate 1-7 kW of electrical power. These inverters are primarily designed for a solar photovoltaic (PV) systems that have a DC input that matches the rating of the inverter. For example, a 5kW panel would drive a 5kW inverter. While solar PV systems can have a larger array that produces total power outputs greater than 5 kW, each group of 5 kW panels will have its own 5kW inverter. However, a single-phase power output wind turbine producing more than 7 kW cannot divide its output amongst multiple inverters because there is a single generator. One solution is to stack multiple inverters in parallel and sharing the power input from the wind turbine generator. However, this shared input makes the stack of inverters tussle over DC levels, which results in voltage transients, input current imbalances, damage/failure of the inverters, and potentially the injection of DC current into the grid. Therefore, wind turbines capable of generating a higher (10- 70kW), single phase power, typically employ three-phase inverters. [0050] To avoid using three-phase inverters, a wind turbine generator in another embodiment of the present invention is used to generate higher power by incrementally engaging each of a plurality of stators, each of which is isolated with a dedicated inverter. The rating/size of the dedicated inverters can be any suitable power, preferably ranging from 1-10kW. Each inverter is coupled with a stator of roughly equal power. In this arrangement, none of the inverters is sharing the output of its dedicated stator with any other inverter. In this way, the wind turbine can begin generating power at lower wind speeds and ramp up power output as wind speed increases, while also being able to scale back down as wind speed diminishes. This may be accomplished by switching on each successive stator assembly as more power becomes available and then off as less power is available.

[0051] Alternatively, each inverter can be programmed so as to achieve the highest output voltage available at a given turbine rotation without slowing down the turbine.

[0052] In prior art arrangements, as depicted in FIG. 18, a single stator 10kW generator 800 is connected to a DC rectifier 804, which is then connected to a 5kW master inverter 808 and a 5kW slave inverter 812. In this arrangement a wind turbine generator cannot begin producing power until sufficient wind speed causes the turbines to spin enough to generate 10kW because as a turbine accelerates, the voltage rises rapidly causing the inverter to respond to the rising voltage by harvesting more power, but that causes the turbine voltage to drop, and the inverter momentarily over-taxes the turbine, thereby slowing the turbine down and causing the voltage to drop again. This problem is exacerbated at wind turbine start up, causing greater than desired wind speeds to be available before the wind turbine can maintain rotation.

[0053] Multiple single phase stators can be managed by programming independent engagement windows that turn on and off as the wind force increases and decreases, thus providing a ramped up power curve that matches the electrical power generation. A programable input power curve (voltage input vs. power output) may also be used to make the power curve. In this way, the rotors are prevented from being overloaded and can “spool up” exponentially with the horizontal wind force. In an exemplary embodiment, and as shown in FIG. 19, an incrementally engaged generator system, such as system 900, has a plurality of separated stator/rotor assemblies 904 (e.g., 904a, 904b) that are each connected to a dedicated DC rectifier 908 (e.g., 908a, 908b), which are in turn connected to a dedicated inverter 912 (e.g., 912a, 912b) that is matched in power to its respective assembly 904. Output from inverters 912 can be combined and sent to an AC grid 916, for example. With this arrangement, electrical connections between each stator portion of assembly 904 and inverter 912 pairing can be switched on or off (i.e., engaged or disengaged) as needed depending on the current wind speed such that the total amount of stator/inverter power available is appropriate for the current wind speed (in consideration of other factors such as number and size of blades, etc.).

[0054] In operation, an incrementally engaged generator as described above preferably maintains the engagement of at least one stator-inverter subsystem and determines whether to engage or disengage additional stator-inverter subsystems based on the current wind conditions. The current wind conditions may be determined in any suitable way, including based on one or more parameters such as wind speed, torque, and rotor hub rotation speed. Each successive stator-inverter subsystem has a wind power threshold value, which is the value at which the next stator-inverter subsystem is engaged. The threshold value is primarily dependent upon rotor diameter and inverter size. In an embodiment, relays and contactors are configured to engage/disengage once a predetermined voltage/rpm is achieved. In addition, when the determined wind availability falls below the threshold value for a given stator-inverter subsystem, that stator-inverter subsystem is disengaged. For example, as shown in FIG. 20, in an incremental wind turbine generator engagement process such as process 1000, wind availability is determined at step 1004. If the wind availability (WA) is above the threshold value for stator-inverter subsystem 2 at step 1006, stator-inverter subsystem 2 is engaged at step 1008. If the wind power is below the threshold value for stator- inverter subsystem 2, stator-inverter subsystem 2 is disengaged at step 1012. It will be understood that if a subsystem is already engaged or disengaged, then no action need be taken as the case may be, i.e., an engaged subsystem will remain engaged if the threshold is met and will remain unengaged if the threshold remains unmet. If the threshold for threshold value for stator-inverter subsystem 2 is met, in addition to engaging subsystem 2, it is determined whether threshold value for stator-inverter subsystem 3 is met at step 1016. If the wind availability is above the threshold value for stator-inverter subsystem 3, stator-inverter subsystem 3 is engaged at step 1020. If the wind availability is below the threshold value for stator-inverter subsystem 3, stator-inverter subsystem 3 is disengaged at step 1024. In any case, a new wind availability determination is made at step 1004 at an appropriate frequency so that the system is updated appropriately. It will be understood that this process may be expanded to as many stator-inverter subsystems as may be desired for a given wind turbine generator. [0055] In this way, the total power generated by the wind turbine is essentially divided into multiple stator-inverter subsystems, allowing more total power to be produced while at the same time allowing lower power to be generated at lower wind speeds that can still be converted to AC power that can be sent into an AC grid or other load.

[0056] In an alternative embodiment, instead of using relays and contactors to incrementally engage/disengage stator/rotor assemblies and their respective inverters, each inverter has been designed and configured such that the inverter power harvesting amount is proportional to the voltage output of the wind turbine at a given rate of rotation (i.e., stator/rotor assembly power output) such that the inverter does not over-tax the turbine and slow it down or cause it not to start at slower wind speeds. In this way, the wind turbine can start rotating at relatively low wind speeds, produce power at those wind speeds, and output single phase power.

[0057] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention

Claims

What is claimed is:

1. A passive wind turbine pitch mechanism for a wind turbine with a plurality of blades comprising: a push/pull tube including a piston and a return spring coupled to the piston; and a plurality of bearings coupled to a corresponding respective one of the plurality of blades, wherein the piston is coupled to the plurality of blades such that the blades move in unison with movement of the piston, and wherein as a wind speed increases, the plurality of blades rotate and move backward from an initial position and the piston moves within the push/pull tube against the return spring.

2. The passive wind turbine pitch mechanism according to claim 1 , wherein each of the plurality of blades have an initial position that is forward tilted and lagging tilted so as to create a moment arm for a wind force to move the plurality of blades backwards.

3. The passive wind turbine pitch mechanism according to claim 1 , wherein the piston is coupled to each of the plurality of blades via a respective lever and a linkage.

4. The passive wind turbine pitch mechanism according to claim 1 , wherein, as the wind speed increases, the return spring resists movement of the piston and the plurality of blades are pitched into a feathered state.

5. The passive wind turbine pitch mechanism according to claim 1 , further including a hydraulic damper configured to counteract movement of the return spring and thereby limit a rate of pitch changes.

6. A wind turbine generator comprising: a plurality of rotor assemblies, wherein each of the plurality of rotor assemblies includes a rotor plate and a magnet and wherein the magnet is shaped such that upon rotation the magnet assists in creating airflow through the generator; a plurality of stator assemblies, each of the plurality of stator assemblies having a respective corresponding one of the plurality of rotor assemblies, wherein the plurality of stator assemblies are stacked from a front to a back of the generator such that a space is provided between each of the plurality of stator assemblies and each of the respective corresponding one of the plurality of rotor assemblies; a housing including a front plate and a rear section, wherein the front plate includes a plurality of holes configured to allow air to flow into the generator; and a diffuser attached to the rear section of the housing, wherein the diffuser is tapered such that a front portion has a larger profile than a back portion.

7. The wind generator of claim 6, wherein the generator does not include a shaft such that air flows through a center of the generator.

8. The wind generator of claim 6, further including a plurality of paddle-like assemblies positioned between each of the plurality of rotor assemblies and corresponding ones of the plurality of stator assemblies and configured to move air through the generator from the front to the back of the generator when rotating.

9. The wind generator of claim 6, wherein each of the plurality of rotor assemblies include one or more magnets and wherein each of the magnets include a paddle-shaped portion configured to move air through the generator from the front to the back of the generator as a rotor plate rotates.

10. A wind turbine generator comprising: a housing; a plurality of rotor assemblies, wherein each of the plurality of rotor assemblies includes a magnet; and a plurality of stator assemblies, wherein each of the plurality of stator assemblies corresponding to a respective one of the plurality of rotor assemblies, wherein each of the plurality of stator assemblies includes a stator coil, and wherein each stator coil is offset sufficiently along a circumference traversed by the plurality of rotor assemblies with respect to another stator coil on an adjacent stator coil assembly such that, when the plurality of rotor assemblies rotate, magnet/stator coil engagement will not occur simultaneously at each stator coil.

11. The wind turbine generator according to claim 10, further including a plurality of vibration dampers, wherein at least one of the plurality of vibration dampers is between each of the plurality of stator assemblies and the housing.

12. A wind turbine system for producing electrical energy comprising: a wind turbine generator including a plurality of stator assemblies; and a plurality of inverters, wherein each of the plurality of inverters is connected to a dedicated one of each of the plurality of stator assemblies forming a plurality of stator-inverter subsystems, wherein each one of the plurality of stator-inverter subsystems is engaged at a different wind availability threshold.

13. A wind turbine generator comprising: a plurality of rotor assemblies, each of the plurality of rotor assemblies including a magnet and configured to rotate about an axis such that the magnet travels along a circumference; and a plurality of stator assemblies, each of the plurality of stator assemblies having a stator plate and a stator coil, wherein each stator coil is positioned to be engaged by a corresponding one of the magnets and is offset along the circumference with respect to a counterpart stator coil on an adjacent one of the plurality of stator assemblies such that engagement of an offset stator coil by a respective corresponding magnet is offset in time with respect to engagement of the counterpart stator coil by another respective corresponding magnet.

14. A method of incremental wind turbine generator engagement comprising: determining a wind availability; engaging a first stator-inverter subsystem if the wind availability is above a first stator- inverter subsystem threshold; disengaging the first stator-inverter subsystem if the wind availability is below the first stator-inverter subsystem threshold; engaging a second stator-inverter subsystem if the wind availability is above a second stator-inverter subsystem threshold, wherein the second stator-inverter subsystem threshold is greater than the first stator-inverter subsystem threshold; and disengaging the second stator-inverter subsystem if the wind availability is below the first stator-inverter subsystem threshold.