Vertical axis wind turbine

Abstract

A vertical axis wind turbine (VAWT) comprising a central shaft 2, radially extending rotor arms 3, a respective rotor blade 4 mounted at the outer end of each arm, and a controller is disclosed. The c

Description

1. This invention pertains generally to the field of vertical axis wind turbines, and is concerned particularly, although not exclusively, with controlling vertical axis wind turbines to maximise power output. 2. There are two main types of wind turbines, a Horizontal Axis Wind Turbine (HAWT) and a Vertical Axis Wind Turbine (VAWT). Typically, a HAWT has high efficiencies, but also high costs of materials, transportation, installation and maintenance. HAWTs have also proven to be unsuitable for urban environments where they struggle to capture the turbulent airflow that is common in built-up areas. In contrast, a VAWT has lower efficiency, but lower costs of materials, transportation, installation and maintenance. VAWTs are a type of cyclorotor, and tend to offer a subtler design with less environmental impact. VAWTs tend to offer a renewable energy source with reduced shadow flicker, which is when the sun shines through the rotating blades, causing a nuisance to landowners within the vicinity. They also reduce the likelihood of bird strike, where birds collide with the rotating blades, and cause less noise pollution. However, due to the lower efficiency of a VAWT, it is not usually an economically sound method of producing renewable energy. 3. A VAWT typically comprises a plurality of rotor blades mounted to a central shaft, and arranged around a central rotation axis. Each rotor blade comprises a spanwise axis parallel to the axis of rotation. The motion of the rotor blades creates lift forces as they travel through the air. By varying the pitch angle of the blades during this rotation, the resultant lift forces created by each rotor blade can be coordinated to provide an overall force that drives the central shaft. The pitch of the rotor blades is varied throughout rotation in response to the wind direction and the position of the rotor blades in the rotation cycle. In this way the position of the rotor blades can be optimised in response to the wind incident upon the VAWT at any time. 4. VAWTs are subjected to downwash which greatly affects their efficiency. The rotor blades in a typical VAWT experience both lift and drag, with both forces driving them to rotate, thereby rotating the rotor arm assembly, and therefore rotating the central shaft. Downwash is an opposing horizontal force, in a downward direction, experienced by the rotor blades. This downwash affects the following blades. Downwash is the velocity component in the downward direction of a rotor blade. This downwash velocity is created by the angle of attack of the rotor blades and the presence of tip vortices. The power required to induce downwash is typically expressed in terms of induced drag. The value of downwash at any given time is extremely challenging to calculate. Downwash also readily changes. Therefore, it is difficult to configure a VAWT to be able to compensate for this. 5. There is a need to increase the efficiency of a VAWT to be close to that of a HAWT without sacrificing the cost savings. There is a need to harness the energy from the wind in an efficient yet economical way, whilst minimising the environmental impact. There is a need to be responsive to ever changing, localised, wind conditions. 6. The prior art shows a number of devices which attempt to address these needs in various ways. 7. WO 2019 002 549 (Agile Wind Power AG) discloses a vertical axis wind turbine with improved efficiency and service life, where the wings of the turbine are attached independently of one another to a vertical wing axis. The angular positions of the blades can be optimised at any given moment, taking into account varying system conditions such as wind speed, wind direction, rotor rotation and power output. At least one wind speed sensor and / or at least one wind direction sensor is arranged in the area of at least one of the pitch motors, or in the area of the motor hub. The at least one wind speed sensor or wind direction sensor is connected to a signal transmitter to transmit a signal to a control device for determining a set point value of the pitch angle. 8. CN 102 678 467 (Harbin Engineering) discloses a variable pitch vertical axis wind turbine that comprises a main shaft encoder to collect instantaneous position readings of the wind wheels. An anemoscope and an anemometer are mounted above the main shaft encoder to take a reading for wind speed and wind direction. 9. WO 2014 147 423 (Switft TG Energy Ltd) discloses a controller for a vertical axis wind turbine, whereby the controller is configured to control the pitch of each blade in dependence on at least one azimuthal position of that blade, fluid speed, fluid velocity, blade speed, blade velocity and tip speed ratio. The controller is configured to select a control mode from at least two stored control modes. 10. Whilst the prior art appears to address the issue of controlling a VAWT to optimise performance by taking measurements of wind speed and direction, and altering the pitch of the rotor blades accordingly, and even providing a closed loop feedback system to provide incremental performance improvements, these documents do not address the issue of downwash. The prior art adjusts rotor blade pitch angle in response to various conditions through trial and error, by making an adjustment and checking RPM to indicate whether the change was effective. The rotor blades pitch to an optimum angle with respect to apparent wind speed to give an optimum torque in the direction of rotation, but neglect the additional forces at play on the different rotor blades that make up the VAWT. Deflected air from a leading rotor blade will alter wind direction on a trailing blade, so a predetermined pitch angle for this trailing blade may not be correctly adjusted. 11. Preferred embodiments of the present invention aim to provide a selflearning control system for a VAWT that makes incremental adjustments over a long period of time to the pitch angle of each of the rotor blades that make up the system, taking into account rotor blade position, wind speed and wind direction at any one time, and, where possible, referring to a data store to optimise rotor blade pitch angle from historical data. 12. According to a first aspect of the present invention there is provided a vertical axis wind turbine (VAWT) comprising: a vertical, central shaft, mounted for rotation about a vertical axis of the turbine; a plurality of rotor arms extending radially from the central shaft, for rotation with the shaft; a respective rotor blade mounted at the outer end of each of the rotor arms, each rotor blade being rotatable about a vertical axis; a respective drive arranged to drive each of the rotor blades in rotation about its vertical axis; at least one wind sensor arranged to sense wind speed and direction; at least one shaft sensor arranged to sense speed of rotation and position of the central shaft; a controller arranged to receive data from the wind and shaft sensors and to send control data to said drives to adjust the angular positions of the rotor blades: wherein the controller is arranged to: set each of the rotor blades in a respective angular position, in response to data from the wind and shaft sensors; adjust the angular position of at least one of the rotor blades; detect whether the speed of rotation of the central shaft increases or decreases in response to the adjustment of angular position of the respective rotor blade(s); and continually adjust the angular position of the rotor blades to achieve a maximum speed of rotation of the central shaft. 13. Preferably, each of said drives may comprise a respective motor mounted at or adjacent the respective rotor blade. 14. Preferably, each of said motors may be mounted at or adjacent the respective rotor blade. 15. Preferably, each of said motors may be a stepper motor. 16. Each of said drives may comprise gearing between the respective motor and rotor blade. 17. Preferably, the controller may comprise a master controller mounted adjacent the central shaft and a respective slave controller at or adjacent each of said drives. 18. Each of the rotor blades may be provided with an endplate to inhibit wingtip vortices. 19. Preferably, a pair of said rotor blades may be mounted at the outer end of each of the rotor arms, one of the rotor blades of the pair being above the rotor arm and the other of the rotor blades of the pair being below the rotor arm, both of the rotor blades of the pair being rotatable in unison about the same vertical axis. 20. The vertical axis wind turbine may comprise three of said aforementioned rotor arms. 21. According to a further aspect of the present invention there is provided a vertical axis wind turbine further comprising: a store arranged to store a table of data from the wind and shaft sensors along with angular position data of the rotor blades: wherein the controller is arranged to look up data from the table that indicates optimum angular positions of the rotor blades for given data from the wind and shaft sensors; and to control the drives to place the rotor blades in those respective optimum angular positions: and after controlling the drives to place the rotor blades in respective optimum angular positions, the controller continues to: adjust the angular position of at least one of the rotor blades; detect whether the speed of rotation of the central shaft increases or decreases in response to the adjustment of angular position of the respective rotor blade(s); and continually adjust the angular position of the rotor blades to achieve a maximum speed of rotation of the central shaft. 22. According to yet a further aspect of the present invention there is provided a vertical axis wind turbine further comprising a mechanical or electro-mechanical brake arranged to stop rotation of the central shaft. 23. For a better understanding of the invention and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: 24. Figure 1 shows one embodiment of a vertical axis wind turbine or VAWT showing a central shaft provided with three horizontal rotor arms and a pair of rotor blades rotatably mounted to a blade shaft at the end of each arm; 25. Figure 2 shows the VAWT of Figure 1, showing an axis of the central shaft being substantially vertical, and axes of the blade shafts being substantially vertical, with arrows to show the directions of movement of the rotor arms about the central shaft, and the rotor blades about the blade shafts; 26. Figure 3 shows an enlarged view of a drive mounted to the blade shaft between each pair of rotor blades; T1. Figure 4A shows a section through the VAWT of Figure 1, with Figure 4B showing an enlargement of Circle D with one embodiment of a controller for controlling a pitch angle of the rotor blades, the controller comprising a motor within a motor housing; 28. Figure 5A shows a section through the rotor arms and rotor blades in a horizontal plane, with Figure 5B showing an enlarged view of Circle E, showing one embodiment of drive to alter the pitch angle of the rotor blades; 29. Figure 6A shows a side view of the VAWT of Figure 1 and Section A:A taken along the vertical axis of the drive shaft, with Figure 6B showing an enlargement of Circle B and one possible arrangement of controller within the drive shaft; and 30. Figure 7A shows a section through the rotor arms and rotor blades in a horizontal plane, with Figure 7B show an enlargement of Circle J and one possible arrangement of drive for driving the rotor shaft. 31. In the figures like references denote like or corresponding parts. 32. It is to be understood that the various features that are described in the following and / or illustrated in the drawings are preferred but not essential. Combinations of features described and / or illustrated are not considered to be the only possible combinations. Unless stated to the contrary, individual features may be omitted, varied or combined in different combinations, where practical. 33. Figure 1 shows one possible embodiment of a vertical axis wind turbine (VAWT) 1 comprising a vertical housing 2A, within which a central shaft 2 is mounted for rotation about a vertical axis of the VAWT 1. The vertical housing 2A and / or the central shaft 2 may incorporate various devices for engaging with a surface, such as brackets or similar projections, at the ground engaging end. The VAWT 1 comprises a plurality of rotor arms 3 that extend radially from the central shaft 2, and are configured to rotate with the central shaft 2. Mounted to the end of the rotor arms 3 is at least one rotor blade 4, whereby each rotor blade 4 is rotatable about a vertical axis. Figure 1 shows an identical pair of rotor blades 4 at the end of each rotor arm 3, mounted one above another. 34. The VAWT 1 may comprise any number of rotor arms 3, and rotor blades 4 mounted to these rotor arms 3, the key limiting factor being the diameter of the VAWT 1 and the chord of the rotor blades 4 to allow full rotations of the rotor blade 4 relative to the incident flow. The rotor blades 4 may have a substantially symmetrical profile or a cambered profile. 35. The rotor blades 4 may be mounted to rotor arms 3, where the rotor arms 3 comprise a mounting element for mounting each end of each rotor blade 4 securely. The rotor blades 4 may be connected to the rotor arms 3 through bearings, not shown. The mounting elements may be provided on a disc that projects from the central shaft 2, or on one or more spokes projecting from the central shaft 2. The central shaft 2 may be mechanically connected to a generator, not shown. 36. The rotor blades 4 at the end of each rotor arm 3 are mounted to the same blade shaft 11. A drive 5 is arranged at the end of each rotor arm 3 to drive the blade shaft 11 and therefore the rotor blades 4 about the vertical axis. 37. The VAWT 1 incorporates at least one sensor for sensing various conditions. The VAWT 1 shown incorporates a wind direction sensor 6 and wind speed sensor 7 to sense wind speed and direction. The wind direction sensor 6 and wind speed sensor 7 is shown mounted to the very top of the VAWT 1 above the rotor blades 4 such that an accurate reading of wind speed and wind direction can be obtained. The wind direction sensor 6 and wind speed sensor 7 may be combined in a single unit or provided as discrete units. 38. The VAWT 1 comprises a master controller 8 that receives the data obtained from the at least one sensor, such as the wind direction sensor 6 and wind speed sensor 7, and a shaft sensor, not shown, arranged to sense speed of rotation and position of the central shaft 2. The master controller 8 sends this control data to the drives 5 along the rotor arms 3 to adjust a pitch angle of each of the rotor blades 4 according to the specific sensed conditions at any one time. The master controller 8 communicates with a slave controller 10 through wires which run along the rotor arms 3. Each of the rotor arms 3 comprises its own slave controller 10 for controlling the drive 5. 39. The shaft sensor may comprise a speed of rotation sensor and a position sensor combined in a single unit or provided as discrete units. It is a requirement to know the delta angle between the wind direction and the rotor arms 3. Having the shaft sensor as a position sensor means the system knows the location of the central shaft 2 relative to a chosen point and therefore knows the location of the rotor arms 3, as they are fixed to the rotating shaft 2. Another option for sensing position is to have magnetometers on the rotor arms 3 that would sense an angle relative to North, thereby sensing position. 40. Figure 2 shows the direction of rotation of the rotor arms 3 and central shaft 2, about a vertical axis 9A. Also shown is the direction of rotation of the rotor blades 4, about vertical axes 9B. 41. Figure 3 shows an enlarged view of the drive 5 configured towards the end, or at the end, of each of the rotor arms 3. The drive 5 controls the rotor blades 4 through the blade shaft 11. The slave controller 10 controls the drive 5 in response to data received from the master controller 8 in response to data from the VAWT mounted sensors. The drive 5 varies the pitch angle of each of the rotor blades 4 by incremental amounts, and on an ongoing basis, in response to ever changing conditions. The master controller 8 controls each of the slave controllers 10 to control the drive 5 to set each of the rotor blades 4 in a respective angular position, in response to data received from the wind direction sensor 6 and wind speed sensor 7 and the shaft sensor, not shown. The wind direction sensor 6, wind speed sensor 7 and shaft sensor are continuously reading local conditions for the VAWT 1 and the master controller 8 is interpreting this data to make further adjustments to the angular position of at least one of the rotor blades 4, or to each pair of rotor blades 4 mounted at the end of the rotor arm 3. The master controller 8 detects any change in the speed of rotation of the central shaft 2 in response to this change in pitch angle of the rotor blades 4, and either maintains pitch angle of the rotor blades 4 if an optimum condition at any given time has been reached, or makes further adjustments to the pitch angle of the rotor blades 4 to achieve a maximum speed of rotation of the central shaft 2. 42. By continuously monitoring external conditions such as wind speed and direction, and continuously monitoring performance of the VAWT 1, the master controller 8 can make use of the data obtained, and any historical data that may be contained within memory, to improve the efficiency of the VAWT 1. The master controller 8 may be operatively connected, or wirelessly connected, to a store of data obtained from the wind direction sensor 6 and wind speed sensor 7 and any shaft sensors, along with data from the slave controllers 10 relaying the angular position data of the rotor blades 4, and the performance of the VAWT 1 for different combinations of this data. The master controller 8 is therefore arranged to look up this store or table of data, to obtain the best pitch angle for rotor blades 4 for any given combination of data, and controls the slave controllers 10 to control the drives 5 to place the rotor blades 4 at the optimum pitch angle for specific local wind conditions. 43. The master controller 8 is configured to continue to adjust pitch angle of the rotor blades 4 on an ongoing basis through the slave controllers 10. The master controller 8 may adjust each of the rotor blades 4 to a different pitch angle to the other rotor blades 4, or each pair of rotor blades 4 mounted to the end of each rotor arm 3, to a different pitch angle to the rotor blades 4 at the ends of the other rotor arms 3. 44. Figure 4A shows the VAWT 1 in side view with circle D about the area between a pair of rotor blades 4 and the drive 5 configured to adjust pitch angle of these rotor blades 4, controlled by the slave controller 10. Figure 4B shows an enlargement of circle D which shows one possible embodiment of the drive 5 configured to alter the angle of the rotor blades 4. The enlarged view shows a common blade shaft 11 that connects the pair of rotor blades 4. The blade shaft 11 is operatively connected to a motor 12 that may comprise an electric motor. In some embodiments the motors may be stepper motors, DC servomotors or the like. The motor 12 is contained within a motor housing 13. 45. The motor 12 may be connected directly to the rotor blade 4 or may be connected via a suitable gearing arrangement. An example of such a gearing arrangement is shown, where the motor 12 drives a small cog 15, which drives a belt 17 and a large cog 16, where the drive is relayed to the blade shaft 11. This arrangement of cogs and belt drive provides gearing to increase torque of the motor 12. The motor 12 is controlled by the slave controller 10 in response to instructions from the master controller 8. Power to the motors 12 along each rotor arm 3 may be supplied via slip rings. 46. The drive 5 is operatively connected to an encoder 14. This shaft encoder 14 comprises an electro-mechanical device for converting the angular position or motion of the blade shaft 11 into an output signal for relaying to the master controller 8 through the slave controller 10. The encoder 14 indicates the current blade shaft 11 position at any given moment in time and therefore provides information about the motion of the shaft. This information can be processed by the master controller 8 into performance data for the rotor blades 4. The encoder 14 may comprise a rotary encoder, or rotation sensor, such that the motion of the rotor blades 4 can be synchronised with rotation of the central shaft 2. 47. Each rotor blade 4 may be moved to a positive pitch angle with respect to the direction of local wind or desired thrust to maximise the output RPM of the central shaft 2. The pitch angle of each rotor blade 4 may be adjusted to produce optimum positive lift, negative lift or drag depending on the position of the rotor blade 4 and its rotation cycle. The optimum pitch angle may be determined by the lift characteristics of the blade, or through machine learning, and an algorithm that feeds from data contained within a memory or store. 48. Figure 5A shows a further section through the rotor arms 3 and central shaft 2, showing one possible embodiment of arrangement of drive 5 for the rotor blades 4. One of the rotor arms 3 is shown to be connected to a brake 20 that comprises a brake calliper and brake pads for contacting the brake disk when operated. The brake 20 reduces the speed of rotation when this exceeds a predetermined value. The brake 20 is operated by an hydraulic pump 21, that is mounted adjacent to the brake calliper. One end of the rotor arm 3 in circle E is shown enlarged in Figure 5B. The drive 5 is shown mounted to a mounting plate 18 which supports the various components that make up the drive 5 and the slave controller 10 is mounted to this mounting plate 18. The drive 5 includes the small cog 15 and large cog 16 connected by a belt 17. Also shown is the rotor blade 4 with an endplate 19. The endplate 19 inhibits wingtip vortices from occurring. These wingtip vortices comprise circular patterns of rotating air left behind the rotor blade 4 as it generates lift. Wingtip vortices are often associated with induced drag, and the imparting of downwash, and therefore the endplate 19 helps to prevent this from occurring. 49. The central shaft 2 may comprise a slip ring 22 that is configured to pass power and signals from the master controller 8 to the slave controllers 10 and from the motor 12 to the master controller 8 and a power system, not shown. The slip ring 22 is an electromechanical device that allows the transmission of power and electrical signals from stationary to rotating structures. 50. Figure 6A shows the VAWT 1 in side profile whilst also showing section A:A through the VAWT 1. Figure 6B is an enlargement of circle B taken from the section view, showing the location of the master controller 8 in relation to the slip ring 22. Also shown is part of a pole 25 at the top of which the wind direction sensor 6 and wind speed sensor 7 are mounted. Signals from these sensors pass down the pole 25 and through the slip ring 22 to the master controller 8. Also incorporated adjacent to the central shaft 2 is a proximity sensor 23 that monitors the speed of rotation of the central shaft 2, and therefore the turbine RPM. 51. Figure 7A is an underside view of a section through the VAWT 1 showing the wind direction sensor 6 and wind speed sensor 7 mounted to the top of pole 25, and a brake 21 that is operatively connected to the master controller 8 for providing safety braking. The central shaft 2 incorporates a gear system 24 for increasing the RPM of the VAWT 1 to the appropriate RPM for the attached generator, not shown. 52. Figure 7B shows an enlarged view of circle J in Figure 7A, showing a section view of one of the rotor blades 4. The rotor blade 4 typically comprises a symmetrical aerofoil shape for facilitating lift generation in both directions, regardless of rotor blade orientation. The drive 5 by belt 17 between small cog 15 and large cog 16 makes incremental changes to the pitch angle of the rotor blade 4, or to both rotor blades 4 cojoined by blade shaft 11. 53. In this specification, the verb "comprise" has its normal dictionary meaning, to denote non-exclusive inclusion. That is, use of the word "comprise" (or any of its derivatives) to include one feature or more, does not exclude the possibility of also including further features. The word "preferable" (or any of its derivatives) indicates one feature or more that is preferred but not essential. 54. All or any of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all or any of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. 55. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 56. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A vertical axis wind turbine (VAWT) comprising:a vertical, central shaft, mounted for rotation about a vertical axis of the turbine;a plurality of rotor arms extending radially from the central shaft, for rotation with the shaft;a respective rotor blade mounted at the outer end of each of the rotor arms, each rotor blade being rotatable about a vertical axis;a respective drive arranged to drive each of the rotor blades in rotation about its vertical axis;at least one wind sensor arranged to sense wind speed and direction;at least one shaft sensor arranged to sense speed of rotation and position of the central shaft;a controller arranged to receive data from the wind and shaft sensors and to send control data to said drives to adjust the angular positions of the rotor blades:wherein the controller is arranged to:set each of the rotor blades in a respective angular position, in response to data from the wind and shaft sensors;adjust the angular position of at least one of the rotor blades;detect whether the speed of rotation of the central shaft increases or decreases in response to the adjustment of angular position of the respective rotor blade(s); andcontinually adjust the angular position of the rotor blades to achieve a maximum speed of rotation of the central shaft.

2. A vertical axis wind turbine according to claim 1, wherein each of said drives comprises a respective motor mounted at or adjacent the respective rotor blade.

3. A vertical axis wind turbine according to claim 2, wherein each of said motors is a stepper motor.

4. A vertical axis wind turbine according to claim 2 or 3, wherein each of said drives comprises gearing between the respective motor and rotor blade.

5. A vertical axis wind turbine according to any of the preceding claims, wherein the controller comprises a master controller mounted adjacent the central shaft and a respective slave controller at or adjacent each of said drives.

6. A vertical axis wind turbine according to any of the preceding claims, wherein each of the rotor blades is provided with an endplate to inhibit wingtip vortices.

7. A vertical axis wind turbine according to any of the preceding claims,wherein a pair of said rotor blades is mounted at the outer end of each of the rotor arms, one of the rotor blades of the pair being above the rotor arm and the other of the rotor blades of the pair being below the rotor arm, both of the rotor blades of the pair being rotatable in unison about the same vertical axis.

8. A vertical axis wind turbine according to any of the preceding claims, comprising three said rotor arms.

9. A vertical axis wind turbine according to any of the preceding claims, further comprising:a store arranged to store a table of data from the wind and shaft sensors along with angular position data of the rotor blades:wherein the controller is arranged to look up data from the table that indicates optimum angular positions of the rotor blades for given data from the wind and shaft sensors; and to control the drives to place the rotor blades in those respective optimum angular positions: andafter controlling the drives to place the rotor blades in respective optimum angular positions, the controller continues to:adjust the angular position of at least one of the rotor blades;detect whether the speed of rotation of the central shaft increases or decreases in response to the adjustment of angular position of the respective rotor blade(s); andcontinually adjust the angular position of the rotor blades to achieve a maximum speed of rotation of the central shaft.

10. A vertical axis wind turbine according to any of the preceding claims, further comprising a mechanical or electro-mechanical brake arranged to stop rotation of the central shaft.

Images