WO2019023005A1

WO2019023005A1 - Vertical-axis wind turbine with multi-point bearing support

Info

Publication number: WO2019023005A1
Application number: PCT/US2018/042511
Authority: WO
Inventors: Ian BROWNSTEIN; John DAVIRI
Original assignee: The Board Of Trustees Of The Leland Stanford Junior University
Priority date: 2017-07-24
Filing date: 2018-07-17
Publication date: 2019-01-31

Abstract

A vertical axis wind turbine (VAWT) is provided that includes a vertical tower having a vertical tower axis, a generator, where the generator includes a safety release disposed to enact a free-spin mode when a power output on the generator reaches a threshold, a plurality of bearings disposed concentric to the vertical tower axis, and disposed along the vertical tower, and a rotor having a plurality of rotor arms and plurality of vertical rotor blades, where a proximal end of each the rotor arm is connected radially to the bearing, where a distal end of each blade is connected to rotor arms.

Description

VERTICAL-AXIS WIND TURBINE WITH MULTI-POINT

BEARING SUPPORT

FIELD OF THE INVENTION

The present invention relates generally to wind turbines. More specifically, it relates to structural improvements in vertical axis wind turbines.

BACKGROUND OF THE INVENTION

Vertical Axis Wind Turbines (VAWT), show promise to enable cost-effective operational wind farms, however, shortcomings include reliability due to structural fatigue have been a limitation to their large-scale implantation.

Existing commercially-available VAWT designs are inherently unstable structures. Specifically, the cantilevered rotor structure above the generator induces bending loads on the generator and bearings, especially in high-wind conditions, leading to mechanical failure on time scales much shorter than experienced by the standard three-blade, horizontal-axis wind turbine (HAWT) design. These failures, combined with insufficient mechanisms to shed aerodynamic loads in high winds, makes the current portfolio of VAWT designs too unreliable and too expensive in operations and maintenance to be viable for larger implementation.

What is needed is a VAWT that is capable of sustaining adverse conditions without mechanical failure or material fatigue. SUMMARY OF THE INVENTION

To address the needs in the art, a vertical axis wind turbine (VAWT) is provided that includes a vertical tower having a vertical tower axis, a generator, where the generator includes a safety release disposed to enact a free-spin mode when a power output or rotational rate on the generator reaches a threshold, a plurality of bearings disposed concentric to the vertical tower axis, and disposed along the vertical tower, and a rotor having a plurality of rotor arms and plurality of vertical rotor blades, where a proximal end of each the rotor arm is connected radially to the bearing, where a distal end of each blade is connected to rotor arms.

In one aspect of the invention, the power output or rotational rate threshold is set by the operating limits of the generator to enable a free-spinning mode. In a further aspect of the invention, the generator is disposed concentric with the axis of the vertical tower.

In another aspect, the invention further includes rotor blade containment rings, where the rotor blade containment rings are disposed concentric to the vertical tower axis and connected to a region between the top end and the bottom end of the vertical rotor blade, where the rotor blade containment ring is positioned to limit vertical rotor blade deformation by centripetal acceleration of the vertical blade along the mid-region when the generator is in the free-spin mode. In yet another aspect, the invention further includes sensors, where the sensors include an RPM sensor or torque sensor. Here, the data from the sensor is received by a controller, where the controller engages and disengages the VAWT generator according to measurements by the sensors.

In another aspect, the invention further includes downstream sensors disposed electronically downstream from the generator, where the downstream sensors can be a voltage sensor, an amperage sensor, and power sensor. Here, the data from the downstream sensor(s) is received by a controller, where the controller engages and disengages the VAWT generator according to measurements by the downstream sensors.

According to another aspect, the invention further includes a gearbox, where the gearbox is connected to generator which is not concentric with the vertical towers vertical axis.

BRIEF DESCRIPTION OF THE DRAWINGS

show a perspective view (FIG. 1), and cutaway views (FIGs. 2-4) of different embodiments VAWT's, according to the current invention.

DETAILED DESCRIPTION

The invention provides several vertical axis wind turbine (VAWT) design innovations that are preferably used together but could also be used independently: 1) Multi-point bearing supports at top and bottom, or top, center region and bottom, including a generator at the top or bottom; 2) clamps at ends of blades to restrict blade bending modes; 3) hoops around blades at intermediate positions to prevent blade bending in high centrifugal loads; 4) Simple and efficient rotor release protocol in high winds.

The current invention has various advantages, including: 1) Vastly increased structural stability from currently available VAWT designs; 2) No need for mechanical braking mechanism; 3) Simple and efficient rotor release protocol in high winds.

The invention solves the issues of VAWT reliability by eliminating the primary sources of structural fatigue in existing VAWTs. According to one embodiment, the invention facilitates a rotor release protocol in high winds, instead of conventional electromechanical rotor braking that has proven insufficient for VAWTs. The rotor release protocol for operation in high winds cannot be implemented using existing VAWT designs due to the large bending loads they incur which lead to structural failure.

This vertical-axis wind turbine (VAWT) design can withstand the loads associated power generation and free spin in high wind speeds. When in use, power is generated until the limits of the energy conversion device being used (e.g. permanent magnet generator, water pump, etc.) and then the turbine will be released from producing power into a free spinning condition instead of braking, preventing the highly unbalanced loading which occurs when the turbine is in a braked condition. Embodiments of the current VAWT invention solve the problems with existing VAWT designs by eliminating the primary sources of structural fatigue. This is done using a multi-point bearing support to the tower, including supports at the top and bottom of the rotor. One or more of these bearing supports may be incorporated into the power conversion device, e.g. permanent magnet generator or water pump. This reduces the moments applied to the power conversion device by transferring load low on the tower, resulting in a net zero moment on the rotor structure. Since a portion of the thrust load is applied lower on the tower, the overall moment transferred to the tower is lower, increasing the rated wind speed of the tower foundation. Additionally, the proposed design constrains the blades from bending outward due to the large centrifugal loads when the rotor is spinning at high RPM in high winds. This is done in two ways. First, the ends of the blades are rigidly constrained. In one embodiment, hoops are installed around the blades to prevent bending between these rigid constraints. This forces blade bending to higher frequency modes, which require much larger forces to manifest.

With the implementation of these two aspects to mitigate damage to the rotor, this design can simply be electronically released by disengaging the generator, allowing the rotor to free spin in high winds when the generator would produce power beyond its rated output. When the wind speed reduces sufficiently, the system can be reengaged electronically so that power can again be produced. Some embodiments may include a shaft extending into the tower to the ground where power conversion generator device (e.g. permanent magnet generator, water pump, etc.) can be easily accessed.

The term 'multi -point bearing support' refers to multiple points along the length of tower where the rotating rotor applies load to the tower through a bearing. This invention is meant to include at least one point of connection at each extreme of the rotor. Specifically, FIGs. 1-4 show embodiments of different VAWT's 100 according to the current invention, where shown are two bearing supports 102 points, a rotor system 107 that includes rotor blades 104, and rotor arms 106, and further shown is a generator 108, which houses two internal SKF bearings, shown at the top of the rotor assembly in FIG. 1, where the purpose built 'bearing assembly' is shown at the bottom of the rotor assembly. Also shown is a wind turbine monopole tower 110. The tower 110 mates to all of the bearing supports 102, which transfer loads from the stationary tower to the rotor assembly. In this embodiment, there are two bearing supports: one at the generator 108, which provides the top bearing 102 support and has the potential to generate electricity, and the lower dedicated bearing 102 support designed for this realization, which will be referred to as the bearing assembly. FIG. 2 shows downstream sensors 109 disposed electronically downstream from the generator 108, where the downstream sensors 109 can be a voltage sensor, an amperage sensor, and power sensor.

FIG. 1 and FIG. 2 show a pair of hoops 112, and a single hoop 112, respectively, disposed to support the blades in a manner to reduce deformation under high rotational velocities, where it is understood that any number of hoops can be implemented. A sensor 114 is show in the figures connected to the bottom bearing 102, where the sensor includes an RPM sensor and/or a torque sensor, where it is understood that the sensors can be located at other positions on the VAWT, or located external to the VAWT.

FIG. 4 further shows a gearbox 116, which enables adjustment of a torque imposed on the generator according to an appropriate RPM.

According to embodiments of the invention, the bearing assembly includes:

i. Two-part collar, which adapts the 12-sided tower shape to the inner bearing sleeve.

ii. The inner sleeve, which has a precision cut OD to press onto the ID of the lower bearing.

iii. The lower bearing.

iv. The outer sleeve, which has a precision cut ID to press onto the OD if the lower bearing. This part, along with the outer race of the lower bearing, are the parts of the bearing assembly which rotate with the rotor assembly. In this example, the outer sleeve connects to the rotor through 5- radial holes that the bottom rotor arms bolt into.

v. The bearing cover. This part mates to the stationary two-part collar and reaches over the bearing assembly to prevent contaminates from entering the lower bearing. This helps extend lower bearings lifetime. This cover can have a number of manifestations: providing a labyrinth to complicate the path particulates would need to take to reach the bearing and/ or a sealing ring which presses against the outer sleeve to seal the bearing off from the outside environment.

In one aspect, the rotor assembly includes:

i. The bottom rotor arms, which reach out of the outer sleeve.

ii. The blade block adapters, which transfer the cylindrical top and bottom blade arms shape to the rectangular form of the blade mounting blocks.

iii. The blade mounting blocks, which provide a rigid clamp to the blades on both the top and bottom of the rotor. This constrains blade bending to modes within these two end clamps.

iv. The blades.

v. The hoops, which further constrain blade bending to higher modes than would be possible with just the blade mounting blocks.

vi. The top rotor arms, which connect the top blade mounting blocks to the

generator hub.

vii. The generator hub, which connects the rotor to the generator.

In the embodiment of FIG. 1, the tower 110, bearing assemblies 102, rotor system 107, and generator 108 are all concentric. The tower 110 is preferably made of steel or composite material and all bearing assembly 102 and rotor system 107 components are preferably made of aluminum or composite material except for the bearings 102. The bearings 102, and generator 108 are made of multiple internal components of various materials. There are no practical limitations on the size of this type of turbine compared to commercial wind turbines. The physical ranges used in horizontal-axis turbines, 10W-10MW, are in-line with the current invention.

During operation, the rotor spins under aerodynamic loading. The power is converted to useful energy via at least one generator which converts that energy to useful mechanical or electrical form. In high wind speeds, the turbine can be electronically released (i.e., the rotor assembly is decoupled from the generator), allowing the rotor to free spin in high winds when the generator would produce power beyond its rated output. When the wind speed reduces sufficiently, the system can be re-engaged electronically so that power can again be produced.

The minimum number of bearing connections for this invention is two. As in the case of the embodiment described above, the two bearing connections are at the extremes of the rotor, one at the bottom and one at the top. In this embodiment, the top bearing connection is the generator and the bearings are housed internally. In other embodiments, there could be additional bearing connections between the two bearing connections near the extreme of the rotor. Any of the bearing connections can act as a generator, either mechanical or electrical.

In further embodiments, the invention is configured to convert rotation energy to mechanical power and heat using a generator which uses electro-mechanical forcing to heat a conductive metal which is transferred out of the turbine via working fluid. Alternatively, the rotating turbine can spin a mechanical device to frictionally heat a working fluid.

According to the current invention, integrated power electronics include a control algorithm that accomplishes generator disconnect and reconnect, and optimize the controller to avoid overloading of the generator. An optimized controller is integrated with the VAWT of the current invention, which includes variable frequency AC buses. In one embodiment, the controller is optimized to minimize the number of disconnect and reconnect events under gusting wind conditions, while maximizing power generation and avoiding overloading of the generator.

As mentioned previously, the ability to disconnect the turbine from the load in high winds significantly simplifies the power generation protocol. In particular, the wild three-phase AC power generated by the VAWT is connected to an inverter, which can be included in the generator. When the inverter detects that the generator voltage has reached the maximum that can be accommodated for the associated current draw (i.e. due to rapid rotation in high winds), the inverter is programmed to automatically disconnect the generator from the electrical load (e.g. a central electrical bus). In one embodiment, an electromagnetic RPM sensor on the rotor detects when the turbine has slowed to an acceptable speed again (i.e. after the high-wind event has subsided), at which point the inverter reconnects the generator to the electrical load and power generation resumes.

The present invention has now been described in accordance with several exemplary embodiments, which are intended to be illustrative in all aspects, rather than restrictive. Thus, the present invention is capable of many variations in detailed implementation, which may be derived from the description contained herein by a person of ordinary skill in the art.

All such variations are considered to be within the scope and spirit of the present invention as defined by the following claims and their legal equivalents.

Claims

What is claimed:

1) A vertical axis wind turbine (VAWT) comprising:

a) a vertical tower comprising a vertical tower axis;

b) a generator, wherein said generator comprises a safety release disposed to enact a free-spin mode when a power output on said generator reaches a threshold;

c) a plurality of bearings disposed concentric to said vertical tower axis, and disposed along said vertical tower; and

d) a rotor comprising a plurality of rotor arms and plurality of vertical rotor blades, wherein a proximal end of each said rotor arm is connected radially to said bearing, wherein a distal end of each blade is connected to rotor arms.

2) The VAWT of claim 1, wherein said power threshold is set by the operating limits of said generator or a rotation rate of said rotor.

3) The VAWT of claim 1, wherein said generator is disposed concentric with said axis of said vertical tower.

4) The VAWT of claim 1 further comprises rotor blade containment rings, where said rotor blade containment rings are disposed concentric to said vertical tower axis and connected to a region between said top end and said bottom end of said vertical rotor blade, wherein said rotor blade containment ring is positioned to limit vertical rotor blade deformation by centripetal acceleration of said vertical blade along said mid-region when said generator is in said free-spin mode. 5) The VAWT of claim 1 further comprising sensors, wherein said sensors are selected from the group consisting of an RPM sensor and torque sensor.

6) The VAWT of claim 5, wherein said data from said sensor is received by a controller, where said controller engages and disengages said VAWT generator according to measurements by said sensors.

7) The VAWT of claim 1 further comprising downstream sensors disposed electronically downstream from said generator, wherein said downstream sensors are selected from the group consisting of a voltage sensor, an amperage sensor, and power sensor.

8) The VAWT of claim 7, wherein said data from said downstream sensor is received by a controller, where said controller engages and disengages said VAWT generator according to measurements by said downstream sensors.

9) The VAWT of claim 1 further comprising a gearbox, wherein said gearbox is connected to said generator.