Patent Publication Number: US-2021167721-A1

Title: Single axis solar tracker with a torsional vibration damping device

Description:
TECHNICAL FIELD 
     The present invention relates in general to a single axis solar tracker with a torsional vibration damping device, and more in particular to a single axis solar tracker having a damping device configured for damping torsional vibrations caused by the wind. 
     STATE OF THE ART 
     Single axis solar trackers are known having a fixed structure and a pivoting assembly. The pivoting assembly has pivoting frame and a solar panel array arranged thereon. The pivoting frame is rigidly attached to a rotating shaft having a longitudinal axis, and the rotating shaft is rotatingly supported on two or more support elements of the fixed structure, thereby the pivoting assembly can rotate together with the rotating shaft about the longitudinal axis. The pivoting assembly is driven by a motor-reducer assembly to rotate with respect to the fixed structure to follow the relative movement of the sun. 
     The motor-reducer assembly is supported on a motor support element pertaining to the support elements and is connected to a motor connection point of the rotating shaft adjacent to the motor support element. The reducer of the motor-reducer assembly is in general irreversible, for example by comprising a worm screw connected to the motor and meshed with a gear wheel connected to the rotating shaft so that the worm screw can rotate the gear wheel but the gear wheel cannot rotate the worm screw. As a result, the motor-reducer assembly provides mechanical retention against torsional vibration of the rotating shaft at the motor connection point. 
     The pivoting assembly, which often has relatively large dimensions, is prone to undergo rotational vibration produced by the wind. As the motor-reducer assembly provides retention against torsional vibration of the rotating shaft at the motor connection point, but the torsional rigidity of the rotating shaft allows an oscillating torsional vibration which rises along the rotating shaft as the distance from the motor connection point increases. 
     The pivoting assembly including the pivoting frame, the solar panels and the rotating shaft has a natural frequency of vibration. When the pivoting assembly vibrates with its own natural frequency, it falls into resonance, meaning that it oscillates with the largest amplitude at the same excitation force, and this can produce damages to the solar tracker. The occurrence of this torsional vibration in resonance is known in the art of solar trackers as “aeroelastic vibration”, “galloping” or “flutter”. 
     Document WO 2017046429 A1 describes a single-axis solar tracker having the above-mentioned features, wherein the reducer of the motor-reducer assembly that drives the rotation of the pivoting assembly has a motor-driven worm screw meshed with a gear wheel coaxially fixed to the rotating shaft, and wherein electrical cables are installed in a hollow interior of the rotating shaft and passed through a central opening of the gear wheel. 
     Document US 20170227080 A1 discloses a torsional damping device for stabilizing a structure exposed to wind such as a solar tracker. The torsional damping device comprises a housing for mounting to a structure experiencing a rotational force such as a pivoting assembly of a single axis solar tracker, an inertial body coupled to the housing so as to rotate about an axis, a biasing mechanism configured to bias the inertial body towards a neutral position, and a damping element configured to damp motion of the inertial body relative to the housing. The damping element can comprise a viscous fluid filling voids between the inertial body and the housing. A drawback of this torsional damping device is that the housing has to be attached to the rotation shaft of the pivoting assembly with the axis of the inertial body coaxial to the axis of the rotation shaft. 
     Document US 2017219045 A1 discloses a magnetic damper for vibration absorbers in machines and installations, particularly wind turbines. The magnetic damper comprises a ring with magnet elements attached thereto and a core slidably inserted into the ring. The damping provided by the magnetic damper occurs by magnetically generated Foucault currents. A simple pendulum is connected to the magnetic dampers and to the installation that is exposed to vibratory forces. 
     Document US 2018013380 A1 discloses a dynamic stabilizer for solar trackers including a damper, such as a gas spring, and an actuator able to lock the damper. The dynamic stabilizer is controlled from an external control unit that receives information from a plurality of sensors including environ sensors that can detect wind speed, wind direction, weather conditions (such as snow prediction), and vibration and/or displacement sensors. The dynamic stabilizer can provide a flexible movement and/or damping state during normal operation of the solar tracker and/or a rigid or locked state whereby the dynamic stabilizer acts as a restraint for the movements of the solar tracker. 
     Document WO 2010084175 A2 describes a method and a device for controlling the translation speed, the rotational speed, and the frequency and/or the amplitude of linear, rotational, and pendulum oscillations of components made of electrically conductive, non-ferromagnetic material by means of magnetic fields. The device comprises components which are guided by at least two magnetic fields. The magnetic fields are arranged one behind the other in the direction of motion of the components and have a constant, opposing polarity, in such a way that the magnetic field lines penetrate the cross-section of the components transversely and opposing voltages are induced in the components by the magnetic field lines. At least three Foucault current fields that lie one behind the other are produced in the components by the mentioned voltages, and Lorentz forces are produced by the interaction of the magnetic fields and the Foucault currents. The translation speed, the rotational speed, or the frequency and/or the amplitude of the linear, rotational, and pendulum oscillations of the components are controlled by the Lorentz forces according to the magnetic field strengths. 
     DISCLOSURE OF THE INVENTION 
     The present invention contributes to solving the problem of aeroelastic vibrations by providing a solar tracker with a torsional vibration damping device, wherein the solar tracker comprises a rotating shaft having a longitudinal axis, a pivoting assembly fixedly connected to the rotating shaft, the pivoting assembly having solar panels arranged to receive solar radiation, a fixed structure including a plurality of support elements rotationally supporting the rotating shaft at a plurality of support points distributed there along, a motor-reducer assembly operatively connected to rotate the rotating shaft about the longitudinal axis so as to track the sun, and a torsional vibration damping device having one moving member rigidly connected to the rotating shaft to move therewith and a stationary member rigidly attached to the fixed structure. 
     The motor-reducer assembly is cinematically connected to the rotating shaft at a motor connection point and has an irreversible reducer which provides retention against torsional vibration of the rotating shaft at the motor connection point. 
     The moving member of the torsional vibration damping device is rigidly connected to the rotating shaft at a damper connection point spaced apart from the motor connection point and arranged to move close to the stationary member without contact. 
     One member selected between the moving member and the stationary member comprises magnetic field-generating elements and the other member selected between the moving member and the stationary member comprises a section made of an electrically conductive, non-ferromagnetic material. Relative movement between the magnetic field-generating elements and the section made of an electrically conductive, non-ferromagnetic material produces a damping torque by Foucault currents effect which is applied to the rotating shaft and dampers the aeroelastic torsional vibration thereof. 
     With this construction, the torsional vibration of the rotating shaft produced by the wind is prevented by the motor-reducer assembly at the motor connection point and dampened by the torsional vibration damping device at the damper connecting point. 
     It will be understood that the further away the damper connecting point is from the motor connection point and the nearer they are to the ends of the rotating shaft, the better is the dampening effect achieved by the torsional vibration damping device. 
     In one embodiment, the motor connection point and the damper connecting point are respectively located at or near to opposite ends of the rotating shaft. In another embodiment, the motor connecting point is located in an intermediate middle section of the rotating shaft and the solar tracker includes two torsional vibration damping devices according to the invention and their respective damper connection points are located at or near to the opposite ends of the rotating shaft. Obviously, the solar tracker can include more than two torsional vibration damping devices if considered necessary. 
     In a preferred embodiment, the motor-reducer assembly is supported on a motor support element of the plurality of support elements, the motor connection point is located adjacent to the motor support element, the stationary member of the or each damping device is supported on a damper support element of the plurality of support elements, and one or more simple support elements of the plurality of support elements are located between the motor support element and the or each damper support element. 
     As far as the torsional vibration damping device is concerned, the stationary member comprises a stationary damper section and the moving member comprises a moving damper section. 
     In one embodiment, the magnetic field-generating elements are attached to the stationary damper section of the stationary member and the section made of an electrically conductive, non-ferromagnetic material is the moving damper section of the moving member. 
     For example, the stationary damper section comprises two opposite walls perpendicular to the longitudinal axis and made of a ferromagnetic material, for example in a non-limitative way, iron, cobalt, nickel or alloys thereof, and the magnetic field-generating elements are permanent magnets attached to one of the opposite walls forming one single arched row or are permanent magnets attached to both opposite walls forming two respective arched rows facing each other. 
     In the case of one single arched row of permanent magnets is provided, the permanent magnets have front surfaces laying in a plane parallel to the opposite walls and a damping gap is provided between the front surfaces of the permanent magnets and the wall opposite thereto. In the case of two facing arched rows of permanent magnets are provided, the permanent magnets of the two arched rows have front surfaces laying in two respective planes parallel to the opposite walls, and a damping gap is provided between the front surfaces of the permanent magnets of the two facing arched rows. In any case, the moving damper section is plate-shaped, has opposite surfaces perpendicular to the longitudinal axis and is inserted so that it can move in the damping gap. 
     Inversely, in another embodiment, the magnetic field-generating elements are permanent magnets attached to the moving damper section of the moving member and the section made of an electrically conductive, non-ferromagnetic material is the stationary damper section of the stationary member. 
     For example, the stationary damper section comprises two opposite walls perpendicular to the longitudinal axis and made of an electrically conductive, non-ferromagnetic material, such as aluminium, cooper, or alloys thereof, and a damping gap is provided between the two opposite walls. The moving damper section is plate-shaped and has opposite surfaces perpendicular to the longitudinal axis, and the magnetic field-generating elements are permanent magnets lodged in openings provided in the moving damper section forming one single arched row or permanent magnets attached to both opposite surfaces of the moving damper section forming two respective arched rows. In any case, the permanent magnets have opposite front surfaces laying in two respective planes parallel to the opposite surfaces of the moving damper section, and the moving damper section with the permanent magnets is inserted so that it can move in the damping gap. 
     In any case, the plate-shaped moving damper section has preferably arched top and bottom edges and the opposite walls of the stationary damper section have respective arched top and bottom edges and are connected to one another by an arched bottom wall. 
     In a preferred embodiment, the moving member has an arm connecting the moving damper section to a shaft fastening element fastened to the rotating shaft, and the stationary member has a base support connecting the stationary damper section to a post fastening element fastened to the damper support element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages will be more fully understood from the following detailed description of merely illustrative and non-limiting embodiments with reference to the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic elevation view of a solar tracker with a torsional vibration damping device according to an embodiment of the present invention; 
         FIG. 2  is a diagrammatic elevation partial view of the torsional vibration damping device included in the solar tracker of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along the plane III-III of  FIG. 2 ; 
         FIG. 4  is a diagrammatic elevation partial view of a torsional vibration damping device according to an alternative embodiment; 
         FIG. 5  is a cross-sectional view taken along the plane V-V of  FIG. 4 ; 
         FIG. 6  is a diagrammatic elevation partial view of a torsional vibration damping device according to another alternative embodiment; 
         FIG. 7  is a cross-sectional view taken along the plane VII-VII of  FIG. 6 ; 
         FIG. 8  is a diagrammatic elevation partial view of a torsional vibration damping device according to still another alternative embodiment; 
         FIG. 9  is a cross-sectional view taken along the plane IX-IX of  FIG. 8 ; 
         FIG. 10  is a diagrammatic elevation view of a solar tracker with a torsional vibration damping device according to an alternative embodiment of the present invention; 
         FIG. 11  is a diagrammatic elevation partial view of a torsional vibration damping device according to another alternative embodiment; and 
         FIG. 12  is a cross-sectional view taken along the plane XI-XI of  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Referring first to  FIG. 1 , reference sign  50  generally designates a solar tracker with a torsional vibration damping device according to an embodiment of the present invention. The solar tracker  50  is a single axis solar tracker comprising a rotating shaft  1  which has a longitudinal axis X. The rotating shaft  1  is rotationally supported at a plurality of support points distributed there along by a plurality of support elements  4 ,  5 ,  6  constituting a fixed structure. A pivoting assembly  2  is fixedly connected to the rotating shaft  1 . The pivoting assembly  2  has one or more pivoting frames  25  attached to the rotating shaft  1  and a plurality of solar panels  3  arranged on the one or more pivoting frames  25  to receive solar radiation. 
     In the shown embodiment, the support elements  4 ,  5 ,  6  are individual support posts anchored to the ground although alternatively they could be part of a base structure anchored to the ground. 
     The rotating shaft  1  extends along the one or more pivoting frames  25  and has opposite ends and an intermediate middle region. The plurality of support elements  4 ,  5 ,  6  comprises a motor support element  4  located at the intermediate middle region of the rotating shaft  1 , two damper support elements located near the opposite ends of the rotating shaft  1 , respectively, and one more simple support element  6  located between the motor support element  4  and each damper support element  5 . 
     A motor-reducer assembly  7  is supported on the motor support element  4 . The motor-reducer assembly  7  comprises an electric motor  23  connected to a reducer  24  which in turn is connected to the rotating shaft  1  at a motor connection point  12  located adjacent to the motor support element  4 , so that the motor-reducer assembly  7  is operatively connected to rotate the rotating shaft  1  about the longitudinal axis X so as to track the sun. The reducer  24  is an irreversible reducer which provides retention against torsional vibration to the rotating shaft  1  at the motor connection point  12 . 
     In the illustrated embodiment, the irreversible reducer  24  comprises a motor-driven worm screw meshed with a gear wheel which is coaxially fixed to the rotating shaft  1 , wherein the worm screw can rotate the gear wheel, but the gear wheel cannot rotate the worm screw. However, other kinds of well-known irreversible reducers and/or other mechanical connections, including for example roller chains, belts, levers or connecting rods, between the reducer and the motor connection point  12  of the rotating shaft  1  will readily occur to one skilled in the art without departing from the scope of the invention. 
     Each damper support element  5  and each simple support element  6  is connected at the upper end thereof to a bearing support  16  carrying a bearing  26  mounted around the rotating shaft  1  for supporting the rotating shaft  1  and guiding rotation thereof. 
     In the embodiment shown in  FIG. 1 , two torsional vibration damping devices  8  are mounted on the damper support elements  5  and connected to the rotating shaft  1  at respective damper connection points  13  adjacent the corresponding damper support elements  5 , so that the damper connection points  13  are located near the opposite ends of the rotating shaft  1  far away from the motor connection point  12 . In an alternative embodiment (not shown) the motor support element  4  with the motor-reducer assembly  7  and the motor connection point  12  are located at or near one end of the rotating shaft  1  and one damper support element  5  with a single torsional vibration damping device  8  and a single damper connection point  13  are located at or near the other end of the rotating shaft  1 . 
     As best shown in  FIGS. 2 and 3 , each torsional vibration damping device  8  comprises a moving member  9  rigidly connected to the rotating shaft  1  and a stationary member  10  rigidly attached to the corresponding damper support element  5 . The moving member  9  has a moving damper section  14  connected by an arm  19  to a shaft fastening element  20 , such as a shaft clamp, which is fastened to the rotating shaft  1  at a damper connection point  13  adjacent the damper support element  5  so that the moving damper section  14  moves with the rotating shaft  1 . The stationary member  10  has a stationary damper section  15  connected to a base support  21  which in turn is connected to a post fastening element  22 , such as a post clamp, fastened to the damper support element  5 , so that stationary damper section  15  remains stationary together with the damper support element  5 . 
     Alternatively, the arm  19  of the moving member  9  can be directly attached to the bearing  26 , which is usually comprised of two complementary solid parts made of a low friction plastic material. The stationary damper section  15  can be alternatively connected to the bearing support  16 . 
     The stationary damper section  15  comprises two opposite walls  17  perpendicular to the longitudinal axis X, which are made of a ferromagnetic material, for example, in a non-limitative way, iron, cobalt, nickel or alloys thereof. The opposite walls  17  have respective arched top and bottom edges and are connected to one another by an arched bottom wall  18 . The moving damper section  14  of the moving member  9  is made of an electrically conductive, non-ferromagnetic material, for example aluminium, cooper, or alloys thereof. The moving damper section  14  is plate-shaped, has opposite surfaces perpendicular to the longitudinal axis X and arched top and bottom edges. 
     The magnetic field-generating elements  11  are permanent magnets  27  attached to both opposite walls  17  of the stationary damper section  15  forming two respective arched rows facing each other and rows having a centre in the longitudinal axis X. Each permanent magnet of one arched row is directly facing a permanent magnet of the other arched row. In an alternative embodiment (not shown), the magnetic field-generating elements  11  are electromagnets  28  energized with electrical current that can be generated for example by the solar panels  3  instead of permanent magnets  27 . 
     As best shown in  FIG. 2 , the permanent magnets  27  of the two arched rows have front surfaces laying in two respective planes parallel to the opposite walls  17  and therefore perpendicular to the longitudinal axis X. Between the front surfaces of the permanent magnets  27  of the two arched rows a damping gap is provided. The moving damper section  14  of the moving member  9  is inserted so that it can move in the damping gap close to the magnetic field-generating elements  11  without contact. 
     Relative movement between the permanent magnets  27  constituting the magnetic field-generating elements  11  and the moving damper section  14  made of an electrically conductive, non-ferromagnetic material produces a damping torque by Foucault currents effect which counteracts the effect of torsional vibration of the pivoting assembly  2  produced by the wind or by other causes. 
       FIGS. 4 and 5  show an alternative embodiment which is a variant of that described above in relation to  FIGS. 2 and 3 . The embodiment shown in  FIGS. 4 and 5  differs from  FIGS. 2 and 3  in that the permanent magnets  27  constituting the magnetic field-generating elements  11  are attached to only one of the opposite walls  17  forming one arched row rows having a centre in the longitudinal axis X. The permanent magnets  27  have front surfaces laying in a plane parallel to the opposite walls  17 , and the damping gap is provided between the front surfaces of the permanent magnets  27  and the wall opposite thereto. The plate-shaped moving damper section  14  of the moving member  9  is inserted so that it can move in the damping gap close to the magnetic field-generating elements  11  without contact. Alternative embodiments shown in  FIGS. 6-7 and 8-9  are inverse constructions to those described above with reference to  FIGS. 2-3 and 4-5 . In the embodiments shown in  FIGS. 6-7 and 8-9  the magnetic field-generating elements  11  are attached to the moving damper section  14  of the moving member  9  and the stationary damper section  15  of the stationary member  10  is made of an electrically conductive, non-ferromagnetic material. 
     In  FIGS. 6 and 7 , the stationary damper section  15  of the stationary member  10  comprises two opposite walls  17  perpendicular to the longitudinal axis X. The opposite walls  17  are made of an electrically conductive, non-ferromagnetic material, such as aluminium, cooper, or alloys thereof. The opposite walls  17  have respective arched top and bottom edges and are connected to one another by an arched bottom wall  18 . A damping gap is provided between the two opposite walls  17 . The stationary damper section  15  is fixedly attached to the damper support element by a post fastening element, such as a post clamp. 
     The moving damper section  14  is plate-shaped and has opposite surfaces perpendicular to the longitudinal axis X and arched top and bottom edges. The moving damper section  14  is made of a ferromagnetic material, for example, iron, cobalt, nickel or alloys thereof. The magnetic field-generating elements  11  are permanent magnets  27  attached to both opposite surfaces of the moving damper section  14  forming two respective opposite arched rows having a centre in the longitudinal axis X. Each permanent magnet of one arched row is directly opposite to a permanent magnet of the other arched row. The permanent magnets  27  have opposite front surfaces laying in two respective planes parallel to the opposite surfaces of the moving damper section  14 . The moving damper section  14  is connected by an arm  19  to a shaft fastening element  20 , such as a shaft clamp, which is fastened to the rotating shaft  1 . The moving damper section  14  with the permanent magnets  27  is inserted so that it can move in the damping gap without contact. 
     The embodiment shown in  FIGS. 8 and 9  is a variant of that described above in relation to  FIGS. 6 and 7 . The embodiment shown in  FIGS. 8 and 9  differs from  FIGS. 6 and 7  in that the permanent magnets  27  constituting the magnetic field-generating elements  11  are lodged in openings formed in the plate-shaped moving damper section  14 . The openings and the permanent magnets  27  form an arched row having a centre in the longitudinal axis X. The permanent magnets  27  have opposite front surfaces laying in two respective planes parallel to the opposite surfaces of the moving damper section  14  at either side of the moving damper section  14 . The moving damper section  14  with the permanent magnets  27  is inserted so that it can move in the damping gap. 
       FIG. 10  shows a solar tracker with a torsional vibration damping device according to an alternative embodiment of the present invention which differs from that described above with reference to  FIG. 1  in that the solar tracker  50  includes one single torsional vibration damping device  8  in cooperation with the motor-reducer assembly  7 . In this embodiment, the rotating shaft  1  has two opposite ends, a motor support element  4  is located at or near to one of the opposite ends of the rotary shaft  1 , one damper support element  5  is located at or near to the other end of the rotary shaft  1 , and two simple support elements  6  are located between the motor support element  4  and the damper support element  5 . 
     The damper support element  5  and each simple support element  6  are connected at the upper end thereof to a bearing support  16  carrying a bearing  26  mounted around the rotating shaft  1 . The motor support element  4  supports a motor-reducer assembly  7  comprising an electric motor  23  connected to an irreversible reducer  24  which in turn is connected to the rotating shaft  1  at a motor connection point  12  located adjacent to the motor support element  4 . The damper support element  5  supports a torsional vibration damping device  8  which is connected to the rotating shaft  1  at a damper connection point  13  adjacent the damper support element  5 . The torsional vibration damping device  8  may be, for example, according to any one of the embodiments described with reference to  FIGS. 2-9 . 
     With this construction, the motor connection point  12  is located at or near to one of the opposite ends of the rotary shaft  1  and the damper connection point  13  is located at or near to the other end of the rotary shaft  1 . 
     It will be understood that in any of the embodiments of the solar tracker  50 , the number of support elements  6  located between the motor support element  4  and the or each damper support element  5  is variable, and that additional torsional vibration damping devices  8  can be associated to one or more of the support elements  6  located between the motor support element  4  and the or each damper support element  5 . 
     The embodiment shown in  FIGS. 11 and 12  refer to an alternative embodiment of the torsional vibration damping device in which the moving member  9  has a moving damper section  14  connected by an arm  19  to the shaft  1  and the stationary member  10  has a stationary damper section  15  connected to a base support  21  which in turn is connected to a post fastening element  22 , as in the previous embodiments of  FIGS. 2 to 9 . 
     As a differential characteristic of this of this embodiment the moving damper section  14  of the moving member  9  comprises permanent magnets  27  and the stationary damper section  15  of the stationary member  10  includes electromagnets  28 , so that a movement of the arm  19  with the permanent magnets  27  as a consequence of the turns of the rotating shaft  1  with regard to the electromagnets  28  that are activated produces an interference between the magnetic fields (permanent magnets  27  and electromagnets  28 ) resulting in a damping torque on the rotating shaft  1 , as the movement of the arm  9  is slowed down counteracting the torsional galloping effect on said rotating shaft  1 . 
     The electromagnets  28  can be feed from an external source under control in a possible embodiment of a control unit which detects the torsional galloping effect on said rotating shaft  1  and proceed to activation of the electromagnets  28 . In an alternative preferred embodiment the electromagnets  28  operate in a bidirectional mode charging an electrical power storage system implemented in a possible embodiment by a capacitor bank (not represented in the drawings) connected to said electromagnets  28  when a torsional galloping occurs at the solar tracker and said electromagnets  28  are later in an automatic way electrically feeded by a discharge of said electrical power storage system when said torsional galloping is higher than a given threshold value, under control for example of the cited control unit. 
     The control method to activate the cited electromagnets  28  can be very diverse, as for example: activation of a DIAC when there is a voltage in the electrical power storage system, a microcontroller with an accelerometer, a microswitch, optical, magnetic switches, inclination switches, etc. 
     In any of the embodiments of the torsional vibration damping device described above, the arched top and bottom edges of the plate-shaped moving damper section  14  as well as the arched top and bottom edges of the opposite walls and the arched bottom wall of the stationary damper section  15  preferably have a centre in the longitudinal axis X. 
     The scope of the invention is defined by the attached claims.