WO2012131741A1

WO2012131741A1 - Sun follower with parallel kinematics and process for controlling such follower

Info

Publication number: WO2012131741A1
Application number: PCT/IT2012/000084
Authority: WO
Inventors: Stefano Mauro; Cristina Scarzella; Alessadro BATEZZATO
Original assignee: Politecnico di Torino
Current assignee: Politecnico di Torino
Priority date: 2011-03-25
Filing date: 2012-03-23
Publication date: 2012-10-04
Anticipated expiration: 2013-09-25
Also published as: ITTO20110259A1

Abstract

A sun follower (1) is described, composed of at least one fixed supporting base (3) and of at least one moving structure (5) controlled and adapted to support at least one photovoltaic module, between such fixed supporting base (3) and such moving structure (5) actuating means with parallel kinematics (7) being interposed, adapted to handle such moving structure (5). A process for controlling such sun follower (1) is also described.

Description

SUN FOLLOWER WITH PARALLEL KINEMATICS AND PROCESS FOR CONTROLLING SUCH FOLLOWER

The present invention refers to a sun follower with parallel kinematics and to a process for controlling such follower.

As known, sun followers, and in particular photovoltaic followers, are structures designed for orienting one or more photovoltaic panels towards the Sun and for keeping constantly near zero the angle between the line perpendicular to the plane of the photovoltaic modules and the direction from which the sun light comes.

This function is commonly performed through serial kinematic structures composed of two rotary ■ axes, one with direction perpendicular to the ground and one with direction parallel to the ground .

Arrangements with parallel kinematics are also known where two plates, one fixed and one moving, are mutually connected through some arms with variable length: the adjustment of these lengths through motors allows obtaining the orientation of the moving surface.

The sun follower, in order to be able to ensure the complete exploitation of the available sun radiation, must allow orienting the photovoltaic modules towards the Sun during the whole day. For this purpose, the azimuth angle, namely the rotation around an axis perpendicular to the ground, must be able to change in a range included between ^'±^' 120°, while the zenith angle, namely the rotation around the axis parallel to the ground, must be able to change from 0° to 90°.

Documents US-A1-2009/199846 and WO-A1- 2009/076394 disclose a sun follower according to the preamble of Claim 1.

Therefore, object of the present invention is solving the above prior art problems by providing a follower with parallel kinematics that allows obtaining a high sighting accuracy.

Moreover, an object of the present invention is providing a sun follower with parallel kinematics that allows supporting the photovoltaic module on many abutments.

Another object of the present invention is providing a process for controlling a sun follower with parallel kinematics that allows obtaining a high sighting accuracy.

The above and other objects and advantages of the invention, as will appear from the following description, are obtained with a sun follower with parallel kinematics as described in claim 1.

Moreover, the above and other objects and advantages of the invention are obtained with a process for controlling , a sun follower with parallel kinematics as described in claim 9.

Preferred embodiments and non-trivial variations of the present invention are the subject matter of the dependent claims.

It is intended that the claims are an integral part of the present specification.

. It will be immediately obvious that numerous variations .and modifications (for example related to shape, sizes, arrangements and parts with equivalent functionality) can . me made to what is described, without departing from the scope of the invention as appears from the enclosed claims.

The present invention will be better described by some preferred embodiments thereof, provided as a non-limiting example, with reference to the enclosed drawings, in which: Figure 1 shows a top perspective view of an embodiment of the sun follower with parallel kinematics according to the present invention;

Figure 2 shows a diagram showing the preferred dimensional relationships between . the various components of the sun follower according to the present invention;

Figure 3 shows a block diagram showing some steps of the control process according to the present invention; and

Figure 4 shows a block diagram showing other steps of the control process according to the present invention.

With reference to Figure 1, it is possible to note that the sun follower 1 according to the present invention is composed of at least one fixed supporting . base 3 and of at least one moving structure 5 controlled and adapted to support at least one photovoltaic module (not shown) , between such fixed supporting base 3 and such moving structure 5 actuating means with parallel kinematics 7 being interposed, adapted to handle such moving structure 5, and in particular to orient this latter structure 3 towards the Sun and to keep constantly next to zero the angle between the line perpendicular to the plane of the photovoltaic module and the direction from which the sun light comes. As known, the expression "parallel kinematics" points out the concurrence of movements of the axes of the actuating means whose origin does not depend on the movement of any other axis.

In particular, the actuating means with parallel kinematics 7 of the sun follower 1 according to the present invention are closed- kinematics mechanisms, which have great stiffness due to the presence of many kinematic chains adapted to connect the "end-effector" to the fixed supporting base 3 in addition to reduced positioning errors.

Preferably, both the fixed supporting base 3 and the moving structure 5 are made as plates substantially identical one to the other. In particular, the photovoltaic modules are assembled so that they are co-planar to the plate making the moving structure 5.

According to the invention, the actuating means with parallel kinematics 7 comprise three arms 9 composed of kinematic chains having their respective ends operatively connected to the fixed supporting base 3 and to the moving structure 5, each one of such arms 9 being composed of at least two rods 11, preferably having the same length, mutually connected by interposing at least one first articulating means 13, preferably made, as a ball joint.

The ends of such arms 9 are operatively connected respectively ^' to the fixed supporting base 3 and to the moving structure 5 in fastening points arranged at 120° one to the other; the ends of such arms 9 are operatively connected to the fixed supporting base 3 and to the moving structure 5 by interposing second articulating means 15, preferably composed of hinges.

Moreover, the fixed supporting base 3 and the moving structure 5 are mutually connected through at least one fourth rod 17, whose ends are operatively and respectively connected to such fixed supporting base 3 and to such moving structure 5 by interposing respective third articulating means 19, each one of such third articulating means 19 being preferably composed of a ball joint: alternatively, one of such third articulating means 19 can be a cardan joint.

The above-described moving structure 5 therefore has two degrees of freedom in . rotation, corresponding to the motion along the azimuth and zenith axes.

Moreover, the actuating means with parallel kinematics comprise at least two motors 21. The control of movements along such two axes can be obtained by adjusting, through such motors 21, the slant of the respective two arms 9 composing the kinematic chains. As shown in Figure 1, preferably each motor 21 can have its related drive shaft keyed onto the- axis of the respective lower hinge 15. Alternatively, the motors 21 could be linear motors operating in an intermediate position on the arms 9 whose slant has to be adjusted, and suitably constrained to a frame preferably and functionally integral with the fixed base 3. Possibly, the motors could be keyed-in to the axes of the upper hinges 15.

The geometry of the structure of the actuating means with parallel kinematics 7 can synthetically be described through three dimensional parameters: the distance of the constraint points of the arms 9 of the kinematic chains from the centres of the fixed supporting base 3 and of the moving structure 5, the distance between the same constraint points and the first articulating means 13 and the distance (fixed) between the centres of the fixed supporting base 3 and of the moving structure 5. These quantities are respectively called "base", "arm" and "central rod". The lengths of these components are mutually independent. However, so that the structure can explore the whole working space, required for a sun follower, it is necessary that these quantities keep well-defined relative relationships.

Figure 2 shows a diagram that includes the two-dimensional space defined by the quantities length base , length central rod ,

—-— and —-—= =—— ; the darker space of length _ arm length _ arm the diagram of Figure 2 therefore points out a region so that a follower built with parameters that fall therein allows exploring a working space that comprises an azimuth excursion of at least 240° and a zenith excursion of at least 90°. The abscissa axis contains the value of parameter — len-s—th base

= , while the ordinate axis contains the length _ arm length central rod

values of parameter = = .

length _ arm Consequently, from the diagram in Figure 2, it is possible to note that, preferably, the length base

relationship — computed between the length _ arm distance of the constraint points of the arms 9 of the kinematic chains from the centres of the fixed supporting base 3 and of the moving structure 5 and the, distance between the same constraint point and the first articulating means 13 is included between

0.05 and 0.55, while the relationship length central rod , ,

=—:—:—= computed . between the distance length _arm between the centres of the fixed supporting base 3 and of the moving structure 5 and the distance between the constraint points of the arms 9 of the kinematic chains and the first articulating means 13 is included between 0.6 and 1.8.

Obviously, the sun follower 1 according to the present invention can work only if managed by suitable sensors and by a specific control process based on a dedicated algorithm, implemented by suitable processing means acting on the motors 21.

The sun follower 1 according to the present invention therefore comprises at least one sun alignment sensor and two sensor^'s for detecting the angular positions of the two arms 9, such sensors obviously cooperating with the above processing means.

The sun alignment sensor can be composed of four co-planar photo-diodes, mutually separated by two baffles that are perpendicular one to the other and to the plane of the photo-diodes. In general, the baffles shadow at least one of the photo- diodes: only if the plane on which they lie is perfectly aligned with respect to the Sun, all four photo-diodes are lighted and each one of them provides an active output signal. The alignment error allowed so that all photo-diodes are lighted is determined by the geometric characteristics of the sensor. When at least one of the photo-diodes is lighted and provides a signal, it is possible to determine the direction along which it is necessary to move the sensor to align it with the Sun.

The present invention also deals with a process for controlling the above-described sun follower 1, in particular suitable to orient the structure 3 towards the Sun and to keep constantly next to zero the angle between the line perpendicular to the plane of the photovoltaic module and the direction from which the sun light comes.

In particular, the control process according to the present invention comprises a step of. actively following the sun.

The step of actively following the sun^ requires the_. use of an expressly-devised algorithm whose scheme is included in Figure 3.

In particular, with reference to Figure 3, it is . possible to note that the step of actively following the sun is composed of a closed-loop orientation control that allows, through control signals (ml arid m2) to the motors 21, to orient the moving structure 5 as desired, due to the feedback of the position signals (angles βΐ and β2) coming from the two arms 9 composing the kinematic chains actuated by such motors 21 and by the sun alignment sensor (sun)_,.

In order to describe the step of actively following the sun, it is suitable to point out that the. actual position of the moving structure 5 can be described univocally through the value of the azimuth and zenith angles, namely through the position assumed by the two arms 9 actuated (space of joints) by the motors 21.

In particular, with reference to Figure 4, it is possible to note that the step of actively following the sun comprises a sub-step in which, through a suitable forward kinematic (FWD KIN) function, per se known, . the values of azimuth and zenith angles are determined depending on the position βΐ, β2 of the actuated arms 9 and a sub- step in which, through a suitable inverse kinematic (INV KIN) function, per se known, the positions βΐ, β2 are determined, that the actuated arms 9 must reach so that the azimuth and zenith angles assume certain values.

Moreover, always with reference to Figure 4, it is possible to note that the step of actively following the sun comprises a sub-step that processes, through a suitable function G per se known, the signal Is coming from the sun alignment sensor to determine the direction AAzimuth, AZenith along which the la moving structure 5 must be moved in order to be oriented perpendicular to the line joining the Sun and compute the related displacements. This function G obviously depends on the type of sun alignment sensor being used.

The values processed by the function G in the sub-step related to the step of actively following the sun are displacement values along the zenith and azimuth direction, that can be positive or negative according to the required direction. Their modulus is determined depending on the characteristics of the sun alignment sensor. .

In the step of actively following the sun, the computed displacements are therefore added to the actual zenith and azimuth positions (Zenith, Azimuth) , determined through the forward kinematic function depending on the measured values of the actuated angles βΐ, β2, thereby obtaining the new reference azimuth and zenith positions (Azimuth ref, Zenith ref) .

By processing the reference azimuth and zenith position values (Azimuth ref, Zenith ref) , it is possible to compute, through the inverse kinematic function, the new reference values for the actuated angles and, - by difference with the measured values, the angular displacement Δβΐ, Δβ2 to be obtained, By dividing this value by the amplitude of the single motor-reducer . pitch, the number of control signals (ml, m2) is computed, to be sent to the driver of each motor 21, in addition to the motion direction (dirl, dir2).

After having performed the desired displacement, the step of actively following the sun starts again.

In addition, the process according to the present invention could further comprise other steps common to control processes of prior art sun followers, such as, for example, the following steps :

a) sighting;

b) waiting;

c) safety.

In the sighting step, the process according to the present invention takes care of orienting the moving structure 5 approximately depending on the expected Sun position, determined depending on time, date and geographic location.

In the waiting step, the process according to the present invention placed the sun follower 1 according to the present invention in a "stand-by" position is the Sun is covered.

In the safety step, the process according to the present invention takes care of orienting the moving structure 5 in a parallel position to the ground to provide the minimum resistance, for example during the night or in strong wind situations .

Possible variations are obviously determined by using continuous motors, namely by using alignment sensors of a different type, without thereby departing from the scope of the present invention .

In any way, it is fundamental that the necessary movement to reach the alignment conditions determined depending on the signal provided by the alignment sensor in the azimuth- zenith space is composed with the actual position in the same space, determined by the forward kinematic function depending on angular position values of the actuated arms, in order to determine a new reference position, still in the azimuth- zenith coordinates. It is also fundamental that this reference value is referred to two new reference values in the space of _. the actuated joints through the inverse kinematic function.

Claims

1. Sun follower (1) composed of at least one fixed supporting base (3). and of at least one moving structure (5) controlled and adapted to support at least one photovoltaic module, between said fixed supporting base (3) and said moving structure (5) actuating means with parallel kinematics (7) being interposed, adapted to handle said moving structure (5), characterised in that said actuating means with parallel kinematics (7) comprise three arms (9) composed of kinematic chains having respective ends operatively connected to said fixed supporting base (3) and to said moving structure (5), each one of said arms (9) being composed . of at least two rods (11) mutually connected by interposing at least one first articulating means (13), said ends of said arms. (9) being operatively connected to said fixed supporting base (3) and to said moving structure (5) by. interposing second articulating means (15), and in that said fixed supporting base (3) and said moving structure (5) are mutually connected through at least one fourth rod (17), which ends of said fourth rod (17) are operatively and respectively connected to said fixed supporting base (3) and to said moving structure (5) by interposing a pair of third articulating means (19).

2. Sun follower (1) according to claim 1, characterised in that said actuating means with parallel kinematics (7) are closed-kinematics mechanisms.

3. Sun follower (1) according to claim 1, characterised in that said fixed supporting base (3) and said moving structure (5) are substantially mutually identical plates, said photovoltaic modules being co-planar to said plate that makes said moving structure (5) .

4. Sun follower (1) according to claim 1, characterised in that said first articulating means (13) are a ball joint, said second articulating means (15) are hinges and said third articulating means (19) -are two ball joints or a ball joint and a cardan joint.

5. Sun follower (1) according to claim 1, characterised in that a relationship between a distance of the constraint points of said arms (9) of said kinematic chains . from the centres of said fixed supporting base (3) and of said moving structure (5) and a . distance between said constraint point and said first articulating means (13) is included between 0.05 and 0.55, while a relationship between a distance between the centres of said fixed supporting base (3) and of said moving structure (5) and a distance between said constraint points of said arms (9) of said kinematic chains and said first articulating means (13) is included between 0.6 and 1.8.

6. Sun follower (1) according to claim 1, characterised in that said ends of said arms (9) are operatively and respectively connected to said fixed supporting base (3) and t,o said moving structure (5) in fastening points mutually arranged at 120°.

7. Sun follower (1) according to claim 1, characterised in that said actuating means with parallel kinematics (7) comprise at least two motors (21) _r each one of said motors being adapted to control a slant of a respective one of said arms (9) composing the kinematic chains.

8. Sun follower (1) according to any one of the previous claims, characterised in that it comprises at least one sun alignment sensor and two sensors for detecting the angular positions of two of said arms (9) , said sensors cooperating with processing means acting on said motors (21) .

9. Process for controlling a sun follower (1), preferably according to any one of claims 1 to 8, adapted to orient said structure (3) towards the Sun and keep constantly next to zero the angle between a line perpendicular to the plane of said photovoltaic, module and the direction from which the sun light comes, characterised in that it comprises^' at least one step of actively following the sun comprising a closed-loop orientation control to orient said moving structure (5) through control signals (ml, m2 ) to said motors (21) through feedback of signals (βΐ, β2) coming from the two arms (9) and from said sun alignment sensor (sun) .

10. Process according to claim 9, characterised in that it comprises the sub-step (FWD KIN) in which values of a-zimuth and zenith angles are determined depending on the position (βΐ, β2) of said actuated arms (9) and the sub-step (INV KIN) in which the positions (βΐ, β2 ) are determined that the actuated arms (9) must reach so that the azimuth and zenith angles assume certain values, and in that it comprises the sub-step (G) of processing the signal (Is) coming from said sun alignment sensor to determine the direction (AAzimuth, AZenith) along which said moving structure (5) must be moved in order to be oriented perpendicular to the line joining the_. Sun and compute the related movements, said computed movements being added to the actual zenith and azimuth positions (Zenith, Azimuth) to obtain the new reference azimuth and zenith positions (Azimuth ref, Zenith ref ) , the angular displacement (Δβΐ, Δβ2 ) to be made being computed and the control signals (ml, m2 ) to be sent to each one of said motors (21) and the motion direction (dirl, dir2) being determined.