Abstract:
An actuating system for controlling the flight of a power wing profile or kite controlled via at least two cables for conversion of wind energy into electrical or mechanical energy, includes a first unit for exerting an action of unwinding-winding of the cables to the same extent, and a second unit set between the power kite and the first unit for providing an action of differential control of the cables. The system employs a single motor or motor/generator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 371 National Phase of PCT International Application No. PCT/IB2011/051364 filed on Mar. 30, 2011, and published in English as WO 2011/121557 A2 on Oct. 6, 2011, which claims priority to Italian Patent Application No. TO2010A000258 filed on Mar. 31, 2010, the entire disclosures of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention regards a first system for implementing the commands of an appropriate control system, whether automatic or manual, of flight of a power wing profile or kite, in particular for conversion of wind energy into electrical or mechanical energy through the flight of the aforesaid power kite connected by means of two cables to conversion devices on the ground. The aforesaid first system for implementing the commands is located on the ground, and the command considered can amount to a difference of length of the two cables. 
     The present invention moreover regards a second system for implementing the commands of an appropriate control system, whether automatic or manual, of flight of a power wing profile or kite, in particular for conversion of wind energy into electrical or mechanical energy through the flight of the aforesaid power kite connected by means of one or more cables to conversion devices on the ground. The aforesaid second system for implementing the commands is set on board the kite, and the command considered can amount to a variation of angle of attack of the kite or else to a variation of the effective area of the kite, or else to a variation of the geometry of the kite such as to generate appropriate aerodynamic forces and momenta on the kite itself, or else to more than one of the aforesaid effects simultaneously. 
     The present invention moreover regards management of lifting off the ground and recall to the ground of the power kites, in particular for the conversion of wind energy into electrical or mechanical energy through the flight of the aforesaid power kite connected by means of at least one cable to conversion devices on the ground. 
     PRIOR ART 
     Known from some prior patents are processes of conversion of wind energy into electrical or mechanical energy by means of devices that are able to convert the mechanical energy generated by the wind source into another form of energy, typically electrical energy, which subtract energy from the wind using power kites connected to said devices by means of cables. For example, the U.S. Pat. No. 4,076,190, U.S. Pat. No. 4,251,040, U.S. Pat. No. 6,254,034 B1, and U.S. Pat. No. 6,914,345 B2, the U.S. patent application No. US 20090072092, the Italian patent application No. TO2003A000945, and the European patent application No. EP 04028646.0 describe systems for converting the kinetic energy of wind currents into electrical energy by means of the control of flight of power kites connected to the ground via one or more cables. Likewise known are systems for converting the kinetic energy of wind currents into electrical energy, in which at least one kite is connected by means of cables to a unit for manoeuvring and generating energy fixed on the ground: in said systems, the kite is carried cyclically through a pulling phase where it ascends pushed by the wind, and during which unwinding of the cables sets in rotation a generator of the unit on the ground designed for generating electrical energy, and a recovery phase in which the kite is recovered and then manoeuvred so as to capture the wind once again. 
     In other known solutions, the energy is converted maintaining the length of the cables fixed and causing the forces exerted on the cables to bring about translation, along a pre-set cyclic path, of a ground unit provided with wheels connected to electric generators. 
     In the past, there have also been proposed various solutions regarding towing of watercraft by means of devices that capture the wind currents via power kites, like the ones described in particular in the British patent No. GB 2.098.951, in the U.S. Pat. No. 5,056,447, in the U.S. Pat. No. 5,435,259, in the international patent No. WO03097448, in the U.S. patent application No. US2004035345, in the U.S. patent application No. US2004200396, in the international patent No. WO2005100147, in the international patent No. WO2005100148, in the international patent No. WO2005100149, and in the German patent application No. DE102004018814. 
     In some of the systems referred to, the kite is constrained with two cables to the ground and is controlled by imposing a difference of length, referred to hereinafter as “differential”, between the two cables. The aforesaid systems use an actuation unit located on the ground, the tasks of which are substantially of two types: unwinding or winding of the two cables to the same extent and imposition of a differential. A modality of imposition of a differential already proposed by the prior art is the one that consists in entrusting with the task of imposing a given value of differential two independent electric motors/generators, each connected to a winch over which the respective cable is run. Another solution is proposed in the international patent application No. WO-2008/072269, which presents an embodiment aimed at decoupling the functions of control of the differential and of winding/unwinding of the cables to the same extent. Said invention is constituted by at least one first actuator motor dedicated to implementing the differential, and by at least one second actuator motor dedicated to unwinding/winding of the cables to the same extent. 
     SUMMARY OF THE INVENTION 
     The present invention proposes improved and more efficient solutions as compared to the known ones, the basic common characteristic of which is defined in claim  1 . 
     In a first embodiment, a single low-power motor is used, and in a second embodiment a single high-power motor/generator is provided flanked by a system for accumulation and transmission of energy. The first solution is devised specifically for generating systems operating with a fixed length of the cables, whilst the second solution is devised specifically for generating systems that exploit cyclic winding and unwinding of the cables. In both types of generators, with fixed cable or variable cable, the present invention is moreover characterized in that it proposes a system for gathering the cables that is able to wind the cables without stratification, with consequent lower wear of the cables and fewer problems of management of winding. 
     Furthermore, there would be considerable advantages in the control of the kite using a second actuation system, in addition to the first actuation system for implementing the differential, which is set on board the kite and is able to give rise to a variation of angle of attack of the kite or else to a variation of the effective area of the kite or else to a variation of the geometry of the kite such as to generate appropriate aerodynamic forces and momenta on the kite itself or else to more than one of the aforesaid effects simultaneously, according to the command calculated by an appropriate automatic-control system or else set by a human operator via an appropriate human-machine interface. In this regard, the present invention proposes a second actuation system, which is set on board the kite and is able to affect the flight of the kite, as described above. 
     Finally, an important aspect in the management of the aforementioned systems of conversion of wind energy into mechanical and electrical energy, via the flight of power kites, regards management of the steps of lift off the ground and of recall to the ground of the power kites. The present invention proposes two possible systems for tackling this type of problem. 
     The present invention hence proposes new and improved solutions as compared to the known ones according to the prior art by providing a first solution for a first system for implementing the differential command, located on the ground, specifically devised for generating systems operating with a fixed length of the cables, a second solution for a first system for implementing the differential command, located on the ground, specifically devised for generating systems operating with a cyclically variable length of the cables, a second system for implementing the commands, located on board the kite, a first possible solution and procedure for lifting off the ground and recall to the ground of rigid or semi-rigid power kites, a second possible solution and procedure for lifting off the ground and recall to the ground of rigid or semi-rigid power kites. 
     Preferred embodiments and original variants of the present invention form the subject of the dependent claims. 
     In the sequel of the description, it will be assumed that at least one kite is connected to the ground by means of at least two cables, with which it is possible to issue a command via differential. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described more fully with reference to some preferred embodiments, provided by way of non-limiting example, with reference to the attached drawings, in which: 
         FIG. 1  is a schematic representation of a first solution for a first system for implementing the control of flight of power wing profiles or kites via differential, devised for generating systems operating with a fixed length of the cables; 
         FIG. 2  is a schematic representation of a second solution for a first system for implementing the control of flight of power wing profiles or kites via differential, devised for generating systems operating with a cyclically variable length of the cables; 
         FIG. 3  is a schematic representation of a preferred embodiment of a second system for implementing the control of flight of power wing profiles or kites, which is located on the kite; 
         FIG. 4  is a schematic representation of a first possible solution and procedure for lifting off the ground and recall to the ground of rigid or semi-rigid power wing profiles or kites; 
         FIG. 5  is a schematic representation of a second possible solution and procedure for lifting off the ground and recall to the ground rigid or semi-rigid power wing profiles or kites. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference then to  FIG. 1 , it may be noted that in the first solution the first system  1  for implementing the control of flight, via differential, of at least one power wing profile or kite according to the present invention comprises: 
     a single actuator motor  3 , which drives, via a gear (not illustrated) and respective racks, two slides  2   a  and  2   b , fixed with respect to which are two return blocks,  4   a  and  4   b  respectively, through which the cables  8  pass after being sent back from the blocks  5   a  and  5   b , the latter being, for example, fixed with respect to the ground or possibly connected to damping systems  14  or in any case not fixed with respect to the slides  2   a  and  2   b;    
     a system  6  designed for tensioning the cables  8 , damping the oscillations of force on the cables  8 , and possibly measuring the forces acting on the cables  8  in the stretch between the return blocks  4   a  and  4   b  and the kite  7 ; 
     a series of pulleys  9 , of a number, diameter, and width appropriately sized according to the diameter and the length of the cables  8 , supported by a shaft  11 ; 
     a series of return pulleys  10 , of a number, diameter and width appropriately sized according to the diameter and the length of the cables  8 , supported by a shaft  12 ; the pulleys  10  and the shaft  12  are located underneath the pulleys  9  and the shaft  11 , and are able to translate vertically, approaching or receding from said elements  9  and  11 ; 
     a system  13  of brake  13   a  and counterweight  13   b , which is applied to the shaft  12  is also able to translate vertically as well as to block, via the brake  13   a , the motion of translation of the shaft  12  with respect to the shaft  11 ; the weight of the counterweight  13   b  is variable, i.e., it can be selectively modulated as a function of the force that is to be obtained on the cables, for example via a water-tank system such as the ones known in the prior art and used for distributing the weights in boats. 
     It may be noted how the movement of the motor  3  gives rise to a difference between the lengths of the two cables  8 , on the side of the kite  7 , through the translatory motion of the slides  2   a  and  2   b . For example, a rotation of the motor  3  in a clockwise direction in the scheme of embodiment illustrated by way of example in  FIG. 1  leads to a shortening of the cable, on the side of the kite  7 , that runs in the block  4   b  and simultaneously leads to a lengthening of the cable, on the side of the kite  7 , that runs in the block  4   a . With an appropriate command of the motor  3  it is consequently possible to issue the desired differential command. It is to be noted that the pulleys  9 , the pulleys  10 , the shaft  11 , and the shaft  12  constitute a multiplication system via which a variation of length of the cables  8  on the side of the kite  7  results in a variation of a smaller amount of the distance between the shaft  12  and the shaft  11 , with a ratio that can be calibrated according to the diameter and to the number of the pulleys  9  and  10 . When the generation system is in normal operating conditions with fixed cable, the shaft  12  is blocked by the brake  13   a  so that the distance from the shaft  11  remains fixed and the cable  8  also remains at a fixed length even under the action of the tensile forces exerted by the kite. When it is necessary to rewind the cables, for example in the case of absence of wind or for maintenance purposes, the kite is manoeuvred so that the tensile forces on the cables are minimal and the system of counterweight  13   a  and brake  13   b  is released, causing recession of the shaft  12  from the shaft  11  and consequent rewinding of the cables. The subsequent unwinding of the cables, to return to the operating conditions, is performed thanks to the pull exerted by the kite in the presence of wind, such as to overcome the friction of the pulleys and the weight of the system of variable brake  13   a  and counterweight  13   b.    
     With reference now to  FIG. 2 , it may be noted that in a second solution specifically devised for generating systems with a cyclically variable length of the cables, the first system  21  for implementing control of flight, via differential, of at least one power wing profile or kite according to the present invention comprises the elements  2   a ,  2   b ,  4   a ,  4   b ,  5   a ,  5   b ,  6 ,  7 ,  8 ,  9 ,  10 ,  11 ,  12 ,  14  similar to the ones described previously with reference to  FIG. 1 , whilst the elements  3  and  13   b  are absent and the elements  15 ,  16 ,  17 ,  18 ,  19 ,  20  are additional. In particular, this second solution presents a system  16  of clutches that is able to connect and disconnect selectively and independently the shafts  11  and  18  to a single motor/generator  15 . The motor/generator  15 , if connected to the shaft  11 , is able to generate power during unwinding of the cables and to supply power in the rewinding step. If connected to the shaft  18 , the motor/generator  15  can moreover drive a system  17  for accumulation of energy, for example of a hydro-pneumatic type. The system  17  can for example be constituted by a compressor and a tank. Once a given pressure is reached, the system of clutches  16  disengages connection between the motor  15  and the shaft  18  until the accumulation of pressure in the system  17  is once again necessary. The system  17  also comprises an actuation system, for example with pneumatic valves, which is able to cause translation of the rack  19 , engaged on the gear  20 , which in turn meshes with the racks of the slides  2   a  and  2   b . It is evident that a translation to the left in  FIG. 2  of the rack  19  causes a clockwise rotation of the gear  20  and consequent increase in length of the left-hand cable and reduction in length of the right-hand cable, on the side of the kite  7 , thus imposing the desired differential. In  FIG. 2 , the systems  16 ,  17 , and  18  are not represented in detail in so far as they can be obtained with known techniques. 
     With reference now to  FIG. 3 , the second system  22  for implementing the control of flight of power wing profiles or kites according to the present invention, illustrated in  FIG. 3  in two different perspective views, comprises: 
     at least two bridles  23 , which are each constrained by the fixing element  30  to one of the two cables  8  and are purposely made so as to be able to run in the blocks  24 . The bridles  23  are moved by the motors  25 . A co-ordinated movement of the motors  25  leads to a variation of the adjustment of the bridles  23 , increasing or reducing the angle of attack of the kite  7  as a function of the direction of rotation of the motors  25 . In this way, it is possible to obtain a variation of the angle of attack of the kite  7 . Furthermore, a rotation of the two motors  25  in opposite directions leads to two different adjustments for the bridles  23  of the kite  7 , thus generating an aerodynamic moment that is able to cause rotation of the kite  7 , thus modifying the trajectory thereof; 
     at least two series of at least two cords  26  each connected at one end to a structural element  27  of the kite  7  and at the other end to one of the at least two motors  28 . The movement of the motors  28  causes winding or unwinding of the cords  26  and consequent approach or recession of the structural elements  27 , leading to a variation of the shape and of the effective area of the kite  7 . It may be noted that with unwinding of the cords  26 , the structural elements  27  recede as a result of the aerodynamic forces acting on the kite  7 . 
     The motors  25 ,  28  and the blocks  24  are appropriately constrained to the kite  7 , for example via fixing to the structural element  29 , which is also referred to as “leading edge”. The leading edge  29  and the structural elements  27  are appropriately provided so as to enable the variation of shape and of effective area of the kite following upon the action of the motors  28 , as described previously. The energy necessary for operation of the motors  28  is supplied by appropriate accumulation systems, possibly flanked by energy-generating systems on board the kite  7 , for example wind microturbines and solar micropanels, as described also hereinafter. 
     With reference now to  FIG. 4 , it may be noted that a first system of lifting off the ground and recall to the ground of power wing profiles or kites is made up of at least one rigid or semi-rigid kite  7  connected to the cables  8  and provided with appropriate supporting systems  31 , such as for example undercarriages with wheels already forming part of the prior art, which will enable the said kite  7  to move over the ground at a high speed with low friction. The kite  7  can be equipped with systems for implementing the commands like the ones described previously and/or be an unmanned aerial vehicle (UAV) according to solutions already present in the prior art. 
     The step of lifting off the ground according to the present invention, represented schematically in  FIG. 4 , starts with the kite  7  on the ground and the cables  8  laid out on the ground ( FIG. 4 a   ). By unwinding the cables  8  at an appropriate rate, for example using systems like the ones envisaged in the two solutions of first system for implementing the commands presented previously, the kite  7  rises as a result of the force of lift that develops at the speed of winding of the cables. During flight ( FIG. 4 b   ), the kite is manoeuvred so as to provide generation of energy according to the modalities envisaged by the generator used, for example with fixed cable or variable cable, according to inventions like the ones cited previously and other solutions forming part of the prior art. In the step of recall ( FIG. 4 c   ), the kite  7  performs a landing whilst the cables  8  are rewound without exerting high tensile forces on the kite so as not to jeopardize landing, with consequent low consumption of energy. The first system for lifting off the ground and recall to the ground of power kites described above differs from the solutions already present in the prior art with just one cable thanks to the presence of two cables  8 . The second cable serves to distribute the forces exerted by the power kite and to implement a command of the power kite via differential, such as for example via the first actuation system described previously in two possible embodiments with reference to  FIG. 1  and to  FIG. 2 ; finally, said second cable provides a higher degree of safety, making possible recovery of the power kite in the event of failure of one of the two cables. 
     With reference now to  FIG. 5 , it may be noted that a second system of lifting off the ground and recall to the ground of power kites is made up of the elements  7 ,  8 ,  31  similar to the ones described previously in the first system of lifting off the ground and recall to the ground of power kites. Furthermore, the second system of lifting off the ground and recall to the ground of power kites is also made up of at least one propeller system  32  connected to an electric motor/generator, used for partial or total thrust during take-off ( FIG. 5 a   ), for generation of energy on board the kite during flight and for thrust of the kite during flight, if necessary ( FIG. 5 b   ), and finally for thrust of the kite during landing, if necessary ( FIG. 5 c   ). 
     Some embodiments of the invention have been described, but of course they may undergo further modifications and variations, all of which fall within the scope of the inventive idea itself.