WO2018087174A1

WO2018087174A1 - Mini-turbine

Info

Publication number: WO2018087174A1
Application number: PCT/EP2017/078654
Authority: WO
Inventors: Borja POZO LARROCHA; Adriana SERRAS MALILLOS; Erlantz FERNÁNDEZ DE GOROSTIZA LÓPEZ DE VIÑASPRE
Original assignee: Fundación Tekniker
Priority date: 2016-11-10
Filing date: 2017-11-08
Publication date: 2018-05-17
Also published as: ES2667562A1; ES2667562B1

Abstract

A mini-turbine (100) to be installed in gas pipelines in order to harvest electrical power from the kinetic energy of the fluid that passes through it. The mini-turbine (100) has a rotor (130) that has a series of blades (131) between a hub (132) and a closing ring (133). The rotor (130) is a single part.

Description

MINI-TURBINE

Field of the invention

The present invention belongs to the field of electrical power generators/harvesters. More specifically, it belongs to the field of electrical power generators configured to be installed in places with limited and difficult access, in order to provide enough power to a complicated access node.

Background of the invention

There are wind turbines that harvest energy. Examples of these turbines are described by D. A. Howey, A Bansal and A. S. Holmes, in "Design and performance of a centimetre-scale shrouded wind turbine for energy harvesting," Smart Mater. Struct., vol. 20, no. 8, p. 085021 , Aug. 201 1 (hereinafter Howey); or by A. Bansal, D. A. Howey and A. S. Holmes, in "CM-SCALE AIR TURBINE AND GENERATOR FOR ENERGY HARVESTING FROM LOW-SPEED FLOWS", Department of Electrical and Electronic Engineering, Imperial College, London SW7 2AZ, UK," pp. 529-532, 2009 (hereinafter Bansal).

A. S. Holmes, D. A. Howey, A. Bansal and D. C. Yates describes, in "Self- Powered Wireless Sensor for Duct Monitoring," Proc. Int. Work. Micro Nanotechnol. Power Gener. Energy Convers. Appl., pp. 1 15-1 18, 2010, an application of these turbines as a self-powered wireless sensor for monitoring the flow of fluid that flows through a duct (hereinafter Holmes).

Indeed, to obtain the final geometry of the blades, the state of the art (Howey) proposes to manufacture the blades initially with a constant pitch angle along the entire length of the blade and then twist the blade to achieve the desired variation of pitch angle as the radius of the rotor increases. Howey also proposes a coating on the blade to give it rigidity, since the blades are initially too flexible. This coating first requires a layer of copper in order to then place a layer of nickel on the layer of copper, making it necessary to secure the blade in an auxiliary support to carry out these coating operations. Lastly, once each of the rotor components (known in the state of the art) have been manufactured, they must be assembled to obtain the rotor mounted as a single subset.

Furthermore, although aluminum magnet carrier rings are known (Howey), plastic is a material that has a lower magnetic permeability than aluminum, meaning that fewer eddy current losses are generated in a turbine where the magnet carrier ring is made of plastic as compared to in a turbine where the magnet carrier ring is made of aluminum. The magnet carrier rings are discs that house a plurality of magnets such that when the rotor rotates, a variable magnetic flux is generated on the stator. In addition, specifically the blades described in Howey have a nickel coating which is a material with an elevated magnetic permeability, which is contrary to the reduction of the losses by eddy currents.

Taking into account the teachings of Howey with respect to the formation of the rotor (several parts manufactured by means of different processes and then assembled together to form the rotor), as well as the magnetic permeability of the materials that make up the parts that form the rotor (materials such as nickel with magnetic permeability that do not reduce the formation of eddy currents) and as can be seen, the known turbines have several drawbacks. One the one hand, since the turbines are made of metal, there are eddy currents inside of them. On the other hand, the rotor of these turbines is composed of an elevated number of parts, which makes it difficult to manufacture them with precision and reduces efficiency when mounting the system, since it complicates the assembly of all components that form the turbine. Given this number of parts, these turbines are also more likely to malfunction or have limitations under the operating conditions; for example, the maximum rotational speed of the mini-turbine may be limited by the occurrence of vibrations due to the smallest mechanical misalignments that lead to an imbalanced rotor.

Description of the invention

The present invention provides an energy harvesting turbine (sometimes called "mini-turbine" throughout this text due to its small dimensions), the operation of which is based on taking advantage of the rotation of the rotor of the turbine to create a variable magnetic field.

The term "mini" applied to the mini-turbine refers to the reduced size of the turbine. Indeed, the mini-turbine has this reduced size because the interference thereof in the flow of the duct where it is installed is intended to be as small as possible. In turbines of this size, specific operating conditions are provided that do not make it possible to directly use the conclusions that can be made from turbines of more common sizes as disclosed by Howey. Therefore, it is important to clarify the order of magnitude of the mini-turbine of the invention. In the context of the present invention, a mini-turbine is a turbine with a maximum outer diameter that is less than 100 mm.

The existence of a variable electromagnetic field induces an electrical current in a static generator (stator) that comprises a printed circuit board (PCB) comprising a series of coils that can be made of copper. The electrical current harvested in the PCB through the movement of the rotor of the mini-turbine can be used in various ways, such as powering devices. Some of the devices that can be powered by the mini-turbine include wireless communication devices and temperature sensors. The mini-turbine comprises a body of the mini-turbine and a generator built into the mini-turbine itself.

Possible applications of the device of the invention include the installation of the device in the gas pipelines of a residence or any building that has a gas installation, such that the user can remotely consult the gas consumption values of their home or building by using an application. Since the gas pipelines are in a place of limited and difficult access, the device resolves the problem of powering the device due to the fact that a battery change is not necessary, thus converting the system into a permanent or semi-permanent system since it is a self-powered device. Another advantage of the device of the invention is that energy harvesting and the measurement of consumption are carried out with the same device, the mini-turbine.

Another possible application of the device is as an energy harvester for environments with gas flows (chimneys, transportation, etc.) which supplies power to a sensor network. For example, by adding an energy harvester to a sensor that may be situated on a duct of a refinery, the residual energy of the fluid flow in the environment of the monitoring point is used to power the sensor and extend the battery life of the sensor by years or even prevent dependence on a battery.

In a first aspect of the invention, a mini-turbine configured to be installed in ducts of a fluid, such as a gas, is provided to generate electrical energy from the kinetic energy of the fluid that passes through the mini-turbine. The mini- turbine comprises a single-part rotor that comprises a plurality of blades between a hub and a closing ring.

As indicated, one aspect of the invention relates to a mini-turbine to generate electrical energy from the kinetic energy of the fluid that passes through the mini-turbine, wherein the mini-turbine comprises:

a rotor that comprises a plurality of blades between a hub and a closing ring; a stator facing the rotor;

wherein:

an extension of the closing ring forms a first magnet carrier ring integrated in the closing ring, wherein the first magnet carrier ring comprises a plurality of magnets configured to generate a variable magnetic flux on the stator when rotated;

the blades have a first end integrated in the hub and a second end integrated in the closing ring to form a single-part rotor structure.

According to the defined configuration of the rotor, the magnet carrier ring forms a circular crown with an inner diameter that coincides with the outer diameter of the rotor, in other words, with the closing ring. This means that there are no joints between the different parts that make up the subset, but instead the rotor is a single part that has a shape wherein different areas can be identified according to the function of each of these areas: thus, the hub is the area of the rotor configured to couple the rotor to the rotation shaft that is going to be pulled by the rotor; the blades are the elements of the rotor that transform the kinetic energy of the fluid that passes through the mini-turbine in a pair that rotates the rotor coupled to the rotation shaft; the closing ring is the area of the rotor that reinforces the structure of the rotor, especially the blades, that faces a rotor with blades with a free end, wherein there may be problems of bending and vibration of the blades.

In other words, the rotor is a single part that integrates the hub, which has the first end of the blade, the blade and the closing ring, wherein it is connected to the second end of the blades. This single-part configuration of the rotor enables a simplified manufacturing process of the rotor with respect to the process of other known rotors, wherein each of these parts that make up the rotor are manufactured separately. Therefore, by means of the single-part rotor, first, the number of manufacturing processes needed to obtain the final product are reduced, and second, the number of operations needed to obtain the blades are also reduced. Indeed, the number of processes are reduced since one manufacturing method for each component of the rotor does not exist, but rather there is a single process for the entire rotor. The machine used to manufacture the single-part rotor preferably has 5 axes to be able to machine the blades inwardly. One possible manufacturing method is the following: The rotor is the most complex part, and first, the block of material (in one possible embodiment, polyether ether ketone (PEEK)) is machined on both sides. Next, once the inner part is finished, a false shaft is made to be able to secure the rotor and cut the outer piece that defines an external perimeter slot in the shape of a circular crown.

Furthermore, the number of operations is also reduced since a series of successive operations on the same component are not needed to obtain the final geometry thereof, as was the case in conventional proposals, such as that of Howey. On the other hand, the rotor of the invention, by being a single part, no only simplifies the manufacturing process thereof, but also obviates the assembly operation. In addition, the single-part rotor also makes it possible to obtain greater accuracy than the known multi-part rotor, since it prevents the accumulation of tolerances needed for mounting and deviations of the measurements of each of the parts. Another result of the greater accuracy obtained with the single-part rotor of the invention is a better-balanced rotor, which reduces vibrations during the rotation thereof, allowing the mini-turbine to operate at higher rotational speeds, and therefore, be able to obtain greater power.

Due to the light weight of the single-part rotor, blades and magnet carrier rings, the small resistance to the rotation of the shaft and bearings, the tolerance of a maximum of 50000 rpm and the constant distance between the PCB and the magnet carrier rings in the rotations, very high rotational speed levels are reached with the mini-turbine of the invention. The rotational speeds (rpm) that are reached with an electrical load that hardly limits the pair of magnets, in other words, very similar to the open circuit, is possible with the configuration in which higher rotational speeds (rpm) can be reached, but this is not a real situation. Given the rotational speeds that are reached with the mini-turbine of the invention, the state of the art, for example Howey, has a maximum limit on the rotational speed of 4000 rpm, given the vibrations due to mechanical imbalances in the rotor.

Due to the fact that the mini-turbine reaches high rotational speeds, the magnetic field that is generated and the energy that is subsequently harvested is much greater in the mini-turbine of the invention that in the turbine of Howey. The differences can be observed in the following table A:

Table A: Comparison of results of the mini-turbine of the invention and Howey.

In one possible implementation of the invention, in which the fluid is air, the mini-turbine operates at an air speed between 1 m/s and 12m/s. The electrical signal generated cannot be detected below 1 m/s, since a sufficient magnetic field is not created due to the low rotational speed of the blades and magnet carrier ring caused by the low air speed that passes through the mini-turbine. However, the mini-turbine does not stop; it continues to rotate as long as there is an air flow, however low the speed thereof may be; in other words, the starting resistance that allows the turbine to begin to rotate is very low. This means that the starting torque of the turbine is very low. The upper limit of 12m/s is due to the tolerance of the bearings, since they have an operational limit of 50000rpm. At 10m/s, with little load, the mini-turbine rotates at 39062.5rpm; since the system is linear, exceeding 12m/s would reach 50000rpm, such that there exists the risk of breakage.

As can be seen, the invention makes it possible to obtain a much higher level of energy with each fluid velocity, multiplying the maximum power by 77. This is due to the absence of any anomaly such as vibrations, mechanical friction between elements with relative movement between each other and the light weight of the rotor. All of these improvements increase efficiency in the transfer of kinetic energy of the fluid to the rotational energy of the rotor. The system is capable of rotating at high rotational speeds (rpm). This has been proven for up to nearly 40000rpm, being able to ensure a maximum speed of 50000rpm. However, known turbines can only reach up to 4000rpm due to problems with vibrations.

Furthermore, when the fluid is air, the range of the incident wind speed in the mini-turbine of the invention goes from 1 and 1 2m/s, while the operating range of the known turbines goes from 3 to 10m/s.

In accordance with other features of the invention:

In a possible embodiment, the magnet carrier ring is made of a plastic material. The magnet carrier ring, which has a circular crown shape, comprises a plurality of housings configured to house the magnets in said housings. The configuration of the magnet carrier ring enables the magnets to generate a variable magnetic flux on the stator when the rotor rotates. The plastic material may be made of PEEK. Some parts of the mini-turbine may be made of PEEK and others may be made of polyamide, where both PEEK and polyamide are plastic materials. In another possible embodiment of the invention, the magnet carrier ring comprises:

- A cage provided with housings to contain the magnets which, in one embodiment, on one side, is an extension of the rotor and, on the other side, it has the shape of an outer bushing that couples to the extension of the rotor.

The magnets integrated in the housings or cavities

- A lid-type collar of the cage that works with the magnets in channeling the magnetic field and with the cage in securing the magnets.

As mentioned above, it is important to reduce losses due to eddy currents in order to maximize the electrical energy generated. To do so, an attempt is made so that the materials of all components that may distort the electromagnetic field generated from the magnets towards the coils are magnetically inert, in other words, they are not ferromagnetic materials. In this embodiment, the cage of the magnet carrier ring is made of plastic (PEEK in one embodiment of the invention).

According to another possible embodiment, the mini-turbine comprises a casing configured to place the stator with respect to the rotor, wherein the casing is made of plastic; the plastic may be made of PEEK.

In another embodiment, the mini-turbine comprises a second part that forms a fairing to channel a flow of fluid that passes through the mini-turbine, wherein the second part is made of plastic. The second part may be made of polyamide or PEEK.

As mentioned above, in order to increase the performance of the mini- turbine, losses in the energy generated must be minimized. One way of minimizing these losses is by reducing the eddy currents. To do so, non- ferromagnetic materials must be used in all components susceptible to allowing the generation of Eddy currents. The invention envisages that the rotor as well as the casing are made of plastic. The rotor as well as the casing may be made of PEEK.

According to another embodiment of the mini-turbine, the extension of the closing ring forms two magnet carrier rings comprising a plurality of magnets, wherein said first and second magnet carrier rings are arranged in two rotational circular crowns that have an inner diameter coinciding with an outer diameter of the rotor determined by the closing ring; an outer diameter larger than the outer diameter of the rotor; said first and second magnet carrier rings being separated axially by a distance configured to house the stator, wherein the stator has the shape of a static circular crown comprised between the two magnet carrier rings, the stator comprising a printed circuit board PCB and a plurality of coils; wherein the magnets and the coils are configured so that, during a rotation of the rotor, an electrical current is induced in the coils by the magnets in motion.

In this embodiment of the invention, as in all the preceding embodiments, the rotor continues to be a single part. In other words, the rotor, although it may have a more or less complex geometry, in this case with an extension of the closing ring in two magnet carrier rings, continues to be made up of a single part wherein the different areas that can be identified are presented continuously. The single part is manufactured, for example, by the 5-axis machining technique to be able to machine the blades inwardly.

According to another embodiment, the mini-turbine comprises fastening means configured to ensure the stator in an interchangeable way.

According to one embodiment, the coils are arranged in single-phase and three-phase configuration.

The configuration of the interchangeable stator makes it possible to generate energy in a single-phase or three-phase way by only interchanging the stator in the mini-turbine.

According to one possible embodiment, the magnet carrier rings have dimensions selected from:

an inner diameter less than 40mm, preferably less than 35mm and more preferably less than 30mm;

an outer diameter less than 45mm, preferably less than 40mm and more preferably less than 35mm;

a thickness less than 2mm, preferably less than 1 .5mm and more preferably less than 1 .3mm;

a plurality of housings with a housing diameter less than 2.3mm, preferably less than 2.2mm and more preferably less than 2.1 mm;

and combinations thereof.

According to another embodiment, the mini-turbine has a maximum outer diameter less than 100mm, preferably less than 50mm, more preferably less than 45mm and even more preferably less than 40mm. In one embodiment of the invention, the mini-turbine has an inner diameter of 22.7mm; an outer diameter of 27.7mm; a thickness of 1 mm; 32 housings for magnets of a housing diameter of 2mm; a maximum outer diameter of 32mm.

According to another embodiment of the invention, the magnets have dimensions selected from:

a magnetic diameter less than 8mm, preferably less than 6mm and more preferably less than 4mm;

a length less than 4mm, preferably less than 3mm and more preferably less than 2mm;

In one possible embodiment, the mini-turbine is configured to be installed in gas ducts.

Another feature of the mini-turbine of the invention is that it comprises a single-phase or a three-phase generator. Furthermore, the mini-turbine comprises means for easily mounting/dismounting the generator. Thus, maintenance tasks such as repairs and even changing from one type of a generator to another (single-phase or three-phase) are significantly facilitated.

The device of the invention can: provide enough energy to power a node of a sensor network; increase the lifespan of a battery in a node of the sensor network or not have to change the battery of a node of the sensor network; increase the functions of a node of a sensor network with respect to the energy that other types of harvesters supply; enable an easy and miniaturized installation of an energy harvester of the wind turbine type.

In the mini-turbine of the invention, the parts that make up the rotor have been reduced in number, optimizing the design and manufacture thereof. The reduction in the number of elements that make up the device provides greater accuracy in manufacturing and efficiency in mounting the device, resulting in a more robust device that can work at higher rotational speeds and with greater fluid flows that pass through the turbine.

As can be seen, the mini-turbine has two fields of application: on one hand, it can be used as an energy harvester in a windy atmosphere in order to power nodes of a sensor network, for example, and on the other hand, when it is installed in a pipeline or in a conduit, it can act as an energy harvester for other uses.

Further advantages and features of the invention will become apparent from the detailed description that follows and will be particularly indicated in the attached claims.

Brief description of the figures

As a complement to the description, and for the purpose of helping to make the features of the invention more readily understandable, in accordance with a practical embodiment thereof, said description is accompanied by a set of figures constituting an integral part thereof, which by way of illustration and not limitation represent the following:

Figure 1 shows an exploded view of the mini-turbine according to a possible embodiment of the invention.

Figure 2 shows an axial cross section of a mini-turbine according to a possible embodiment of the invention.

Figure 3 shows a view of the assembly formed by a rotor with an integrated cage to house the magnets and another cage configured to be coupled to said rotor-cage assembly.

Figure 4A shows a perspective view of the rotor of Figure 3 with an integrated cage to house the magnets.

Figure 4B shows a perspective view of the cage of Figure 3.

Figures 5A and 5B show a rear and front perspective view, respectively, of the mini-turbine of Figures 1 and 2.

Figure 6A shows the magnet carrier rings and the printed circuit board PCB placed between the magnet carrier rings.

Figure 6B shows a detailed view of Figure 6A that shows the coils in the printed circuit board PCB placed between the magnet carrier rings.

Figure 7A shows the magnet carrier rings that contain the magnets in the cages and the collars.

Figure 7B shows the arrangement of the magnets in the magnet carrier rings.

Figures 8A and 8B shows the effect of the steel sheet collar of the magnet carrier rings in the magnetic field.

Figures 9A and 9B show the phases and the magnetic poles. Figure 9C shows the three phases generated.

Figures 10A and 10B respectively show a single-phase generator and a detailed view of the representation of the coil.

Figures 1 1 A and 1 1 B respectively show a three-phase generator and a detailed view of the connection of the coils.

Figures 12A and 12B show the equivalent single-phase and three-phase electronic model, respectively, of the generator.

Figure 13A shows a simulation of the density of the magnetic flux (B) generated by the magnets of the magnet carrier rings.

Figure 13B shows the arrangement of the magnets and the coils to analyze the density of the induced and harvested magnetic flux.

Figure 14 shows the voltage values that are obtained at different rotational speeds of the rotor by using the mathematical and electronic model of the single- phase generator.

Figure 15 shows a frequency analysis by using the mathematical and electronic model of the single-phase generator.

Figure 1 6 shows the voltage values that are obtained with different rotational speeds of the rotor by using the mathematical and electronic model of the three- phase generator. The legends of the voltage graphs indicate the rotational speed of the rotor that is obtained in each graph.

Figure 17 shows a frequency analysis by using the mathematical and electronic model of the three-phase generator.

Figure 18 is a detailed view of the coils of the single-phase generator. Figure 19 is a detailed view of the coils of the three-phase generator.

Figure 20 shows the wave shapes obtained in trials carried out with the single-phase generator with an incident wind speed of 5m/s.

Figure 21 shows the wave shapes obtained in trials carried out with the single-phase generator with an incident wind speed of 10m/s.

Figure 22 shows the load resonance of the mini-turbine and the importance of impedance matching for greater performance when obtaining power with a single-phase generator.

Figure 23 shows the power obtained with different loads and wind speeds with the single-phase generator.

Figure 24 shows the frequencies obtained and the linearity thereof with different loads and wind speeds with the single-phase generator. The legends of the frequency graphs indicate the load that is obtained in each graph.

Figure 25 shows the wave shapes obtained in trials carried out with the three-phase generator with an incident wind speed of 5m/s.

Figure 26 shows the wave shapes obtained in trials carried out with the three-phase generator with an incident wind speed of 10m/s.

Figure 27 shows the load resonance of the mini-turbine and the importance of impedance matching for greater performance when obtaining power with a three-phase generator.

Figure 28 shows the power obtained with different loads and wind speeds with the three-phase generator.

Figure 29 shows the frequencies obtained and the linearity thereof with different loads and wind speeds with the three-phase generator. The legends of the frequency graphs indicate the load that is obtained in each graph.

Figure 30 shows the different maximum rotational speeds of the rotor in revolutions per minute (rpm) as a function of the incident wind speed.

Figure 31 A shows a side view of a mini-turbine.

Figure 31 B shows a side view of a mini-turbine.

The mini-turbine comprises the elements listed below:

100 Mini-turbine

1 Rotation shaft

2 Bearings

3 Thrust thread

4 Thrust and alignment piece

5 Cage

6 Magnets

7 Collar

8 Alignment pins

9 Casings

10 Connection elements

1 10 First aerodynamic piece

12 Inlet body

14 Outlet body

120 Second aerodynamic piece or nacelle or fairing

1 1 First body

13 Second body

15 Printed circuit board, PCB

15' Coils

1 6 Clamp

17 Fairing screws D Maximum outer diameter of the mini-turbine

130 Rotor

131 Blades

132 Hub

133 Closing ring

140 Magnet carrier ring

Di Inner diameter of the magnet carrier ring

De Outer diameter of the magnet carrier ring

e Thickness of the magnet carrier ring

Da Diameter of the housing

Dm Magnetic diameter or diameter of the magnets

L Length of the magnets

Description of an embodiment of the invention

Figure 1 shows an axial cross section of the mini-turbine 100 of the invention. Figures 5A and 5B show a rear and front perspective view, respectively, of the mini-turbine 100 of the invention. The mini-turbine 100 is formed by a mini-turbine body and an electromagnetic generator of the mini- turbine.

The mini-turbine 100 comprises several elements, which are shown in figures 1 and 2. A first aerodynamic piece 1 10 comprises two bodies 12, 14 and is arranged along a rotation shaft 1 . The inlet body 12 is arranged in the front portion of the rotation shaft 1 , while the outlet body 14 is arranged in the rear portion of the rotation shaft 1 . The cross section of the outlet body 14 reduces as it moves further away from the rotation shaft 1 until it essentially ends in a point. Hence the definition of the first piece 1 10 formed by the bodies 12, 14 as "aerodynamic". The rounded outer shape of the inlet body 12 also makes the first piece 1 10 aerodynamic. The rotation shaft 1 is mounted on two bearings 2 (one bearing 2 is at one end of the rotation shaft 1 in which the inlet body 12 is located, and another bearing 2 is at the opposite end of the rotation shaft, in which the outlet body is located 14). A thrust and alignment piece 4 is connected to each bearing 2; the thrust and alignment piece 4 is adjusted by means of the thrust thread 3; the thrust thread 3 is positioned after the thrust and alignment pieces 4 on both sides of the rotation shaft 1 and it is accessible when the inlet body 12 and the outlet body 14 are disassembled. The bearings 2 enable the rotor 130 to rotate, that is, the rotation of the rotation shaft 1 with respect to the support points thereof, when the rotor 130 is driven by the flow of fluid that passes through the mini-turbine 100. The thrust threads 3 and the thrust and alignment pieces 4 enable the support points of the rotation shaft to withstand an axial thrust exerted thereon by the flow incident on the rotor 130. The thrust and alignment pieces 4 also enable the rotor 130 to be aligned, through the rotation shaft 1 , with the nacelle, or second aerodynamic piece 120.

The second aerodynamic piece 120 (nacelle or fairing) of the mini-turbine 100 comprises a first front body 1 1 and a second rear body 13. The second piece 120 is substantially cylinder shaped, open at the ends thereof in order to enable an inlet and outlet of fluid that passes through mini-turbine 100. The longitudinal axis of the second piece 120 coincides with the rotation shaft 1 . The second rear body 13 has a thickness that reduces as it moves further from the first front body 1 1 , such that the rear end of the second rear body 13 (the end furthest from the first front body 1 1 ) is tapered. That is, at the rear end thereof, the thickness of the second rear body 13 reduces such that the end of the inner surface joins to the end of the outer surface, thus forming a duct with an increasing transverse cross section in the direction of the flow, that is, that forms a divergent duct. Hence the definition of the piece 120 formed by the bodies 1 1 , 13 as "aerodynamic". The rounded outer shape of the first front body 1 1 also makes the piece 120 aerodynamic.

The mini-turbine 100 comprises a series of bearing elements that constitute, along with the rotation shaft 1 , the resistant components of the mini-turbine 100. These bearing elements form a block that serves to connect other components of the mini-turbine 100. The elements that form the block are the following: discshaped connection elements 10, mounted on casings 9, which are substantially cylinder shaped. The casings 9, arranged one after the other in an axial direction, house the printed circuit board (PCB) between them. Auxiliary elements work with the connection elements 10 and the casings 9 to maintain the cohesion of the package. These auxiliary elements are clamps 1 6 that exert axial compression between the connection elements 10 to ensure the compactness of the package in which the casings 9 are compressed by the connection elements 10 due to the effect of the clamps 1 6. Other auxiliary elements, the alignment pins 8, help correct the positioning of the elements to subsequently secure them together due to the clamps 1 6. That is, the clamps 1 6 provide the frame with axial rigidity and the alignment pins 8 enable different components of the frame to be axially aligned.

It can be said that these bearing elements comprising connection elements 10, casings 9, clamps 1 6 and alignments pins 8 make up the central core of the second aerodynamic piece 120, given that they are located in the portion of the mini-turbine 100 that surrounds the rotor 130. In fact, as can be seen in figures 1 , 5A, 5B and 31 A, the contour of the connection elements 10, casings 9, clamps 1 6 and alignment pins 8 is exposed to the fluid current where the mini-turbine 100 is installed (the clamps 1 6 and alignment pins 8 on the outer surface of the second aerodynamic piece 120).

Inside the bearing block, the casings 9 join or assemble the first aerodynamic piece 1 10 with the second aerodynamic piece 120. In this way, the casings 9 establish the relation between the first piece 1 10 and the second piece 120, which are kept fastened to each other by means of connection elements 10.

Moreover, the connection elements 10 are fastened to the casings 9 by one face opposing the casings 9. On the opposite face, the connection element 10 positioned towards the inlet of the mini-turbine 100 comprises fastening means to support the first body 1 10 while the connection element 10 positioned towards the outlet of the mini-turbine 100 comprises fastening means to support the second body 13.

Likewise, the casing 9 positioned towards the inlet of the mini-turbine 100 comprises, in the central area corresponding to the rotation shaft 1 , fastening means to support the inlet body 10, while the casing 9 positioned towards the outlet of the mini-turbine 100 comprises, in the central area corresponding to the rotation shaft 1 , fastening means to support the outlet body 12.

The aforementioned elements form the body of the mini-turbine 100. The mini-turbine 100 further comprises a generator. The generator comprises a plurality of magnets 6 and a printed circuit board or PCB 15, shown in figures 1 , 6A and 6B. In a possible, non-limitative embodiment, the generator comprises 64 magnets 6. Coils 15' configured to conduct electricity are integrated or implemented on the printed circuit board or PCB 15. The coils 15' are preferably made of copper. Copper is the best material to use due to its good features for harvesting a magnetic field and its common use in manufacturing. However, another material could also be used, such as silver, which is a better electrical conductor, but more difficult to manufacture. Continuing with the explanation of the generator, the elements involved in generating a current intensity originating from the rotation of the rotor 130 are the magnets 6, which rotate when the rotor 130 rotates, and the coils 15', which are static on the printed circuit board or PCB 15 and the collar 7 that is joined to the magnets 6.

Preferably, the printed circuit board or PCB 15 is positioned equidistant between the two cages 5 (where the magnets 6 are housed) in the vicinity of the magnetic field. The electric current induced in the PCB 15, specifically the coils 15', generated by the movement of the rotor 130, can be used in various ways, such as powering wireless communication devices, temperature sensors, etc.

Having seen the basic configuration of the generator, the basic configuration of the mini-turbine 100 is detailed below. The operation of the mini-turbine 100 is based on using the rotating movement of the rotor 1 30 in order to create a variable magnetic field. Specifically, in the operation of the mini-turbine 100, when the rotor 130 is rotating, it creates the rotating movement of the magnet carrier rings 140 given that the magnet carrier rings 140 are arranged in the periphery of the rotor 130 as can be seen in figure 1 . When the magnet carrier rings 140 rotate, it creates a variable magnetic field. The magnetic field generated is variable because the magnet carrier rings 140 have the magnets 6 of the generator arranged in the most peripheral portion thereof, that is, in the portion thereof furthest from the shaft 1 . These magnets 6 describe a circular movement as it forms part of the rotor 130 that is rotated by the flow of a fluid that passes through the mini-turbine 100 (the fluid can be a gas, which can be the gas supply to a home or the air of an air conditioning duct). The existence of a variable electromagnetic field induces an electric current in the coils 15' arranged in the printed circuit board PCB 15 of the stator. As previously stated, the printed circuit board PCB 15 is positioned equidistant between the magnet carrier rings 140 in the vicinity of the magnetic field.

In order to maximise the energy generated, the losses that can be caused in several ways must be minimised: (i) friction caused by relative movement between elements, (ii) reluctance in the magnetic circuit caused by the air mass between the magnets 6 and the coils 15' and (iii) eddy currents (or Foucault current) that can negatively affect the electrical current generated in the coils 15'. The structure of the mini-turbine 100 seeks the best balance between maximisation of the energy generated and viability in terms of manufacturing, assembly and installation of the mini-turbine 100. The electromagnetic generator of the mini-turbine 100 is described below in accordance with a possible embodiment of the invention. The electromagnetic generator comprises the following main elements: two magnet carrier rings 140 respectively, configured to generate a variable magnetic flux/field and a printed circuit board (PCB) 15 that has a plurality of coils 15', preferably made of copper, configured to generate an electric current induced by the variable magnetic field. Figure 6A and 6B show several of these components.

As has been stated, the magnet carrier rings 140 are integral to the rotors 130, form a circular crown on the periphery of the rotor 130, and house a plurality of magnets 6 that, when rotated, generate a variable magnetic flux on the stator where the printed circuit board PCB 15 is positioned. The arrangement of the magnets 6 is presented below and it is also shown in figures 7A and 7B:

- The light grey and dark grey magnets 6 have opposite polarity in order to generate an alternate magnetic flux when rotated.

- The magnets 6 facing each other in the two magnet carrier rings 140 have the same polarity so as not to nullify the magnetic field in the center.

The magnet carrier rings 140 comprise three elements: magnets 6, cages 5 and collars 7. Figures 7A and 7B show part of the structure of the magnet carrier rings 140 respectively: the magnets 6, cages 5 and collars 7 are shown in light grey and dark grey.

The collar 7 is configured to ensure the magnets 6 remain in the cavities thereof of the cages 5, which is very important at high rotational speeds, to the order of 10,000 rpm, whilst also maintaining ease of disassembly/assembly in the event that the magnets 6 must be changed.

A prototype of the mini-turbine 100 has been designed with the following features:

The cages 5 have an outer diameter De of 27.7 mm, an inner diameter D1 of 22.7 mm, a thickness e of 1 mm and has 32 housings of 2 mm in housing diameter Da. The mini-turbine 100 has a maximum outer diameter D of 32 mm. The housings are distributed equidistantly, and located in the average diameter of the magnet carrier rings 140.

The mini-turbine 100 comprises a total of 32 magnets 6 (therefore 16 poles) that can be NdFeB (50H grade) for each cage 5. The magnets 6 are cylinder or disc shaped. The magnets 6 have a lower magnetic diameter Dm of 8 mm, preferably lower than 6 mm, more preferably lower than 4 mm. In the prototype of the invention, the diameter is 2 mm. With regards to the length, the magnets have a length smaller than 4 mm, preferably less than 3 mm, more preferably less than 2 mm, and even more preferably less than 1 .4 mm. According to a possible embodiment, the length of the magnets is 1 mm.

Although a greater magnetic field is generated with longer magnets (2 mm) and, therefore, a greater electric flux in the coils 15', increasing the total length of the mini-turbine 100 can cause problems with the rigidity thereof. The embodiment described seeks balance between the size of the magnets 6 and the generation of a magnetic field.

The cages 5 are the mechanical element of the magnet carrier rings 140 that comprises a disc with holes to house the magnets 6. The cages 5 respectively must be made of a non-magnetic material so that there are no magnetic losses due to hysteresis and induced currents, that is, due to eddy currents. Although a magnetic material can provide value when the field is to be specifically directed, in the case of the invention, the magnets 6 along with the collar 7 are responsible for channeling said magnetic flux in the axial direction of the mini-turbine 100. Figure 8 A shows the effect of the collar 7 on the magnetic field compared to an embodiment without the collar shown in figure 8B.

In the printed circuit board PCB 15:

- The overall geometry of the printed circuit board PCB 15 is conditioned by the overall design of the mini-turbine 100.

- The printed circuit board PCB can comprise two materials: an insulator (FR4) and a conductor (Cu).

- The generation of electric energy depends on the design of the printed circuit board PCB 15: material thickness, both of the insulator material and the conductor material, space between the coils 15', structure/arrangement/shape of the coils 15', type of connection between the coils 15' to form a single-phase circuit or a three-phase circuit.

- The dimensions of the printed circuit board PCB 1 5 are defined with the aim of achieving the integration of the mechanical portion with the printed circuit board PCB 15, as well as obtaining the maximum energy possible from the electromagnetic field generated by the magnet carrier rings 140.

The number of coils 15' in each one of the faces of the printed circuit board PCB 15 is defined by the number of magnets 6 according to the 3 to 2 ratio (3 phases, 2 magnetic poles), which means that the total number of coils in each one of the faces in an embodiment of the invention is 48. Figures 9A and 9B show the phases with blank circles and the magnetic poles with solid circles. Figure 9A shows the 3 to 2 ratio (3 phases, 2 magnetic poles). Figure 9B shows an area of the mini-turbine 100 that shows a plurality of phases and magnetic poles. Figure 9C shows the three phases generated.

In accordance with an embodiment of the invention, the generator is single- phase. The single-phase generator comprises winding coils 15' as shown in figure 10B. The coils 15' are connected in series to each other and the two sides of the generator are connected to the outside, which means that this design is easier and cheaper to manufacture. Figures 10A and 10B respectively show a single-phase generator and a detailed view of the representation of a winding coil 15'.

In accordance with another embodiment of the invention, the generator is three-phase. The three-phase generator contains spiral square coils 15', which make this configuration more complex but much more efficient. The coils 15' are connected in series on the same face and in parallel with those of the other face of the generator. In addition, the coils 15' are connected three by three in order to obtain the three phases of the signal. Figures 1 1 A and 1 1 B respectively show a three-phase generator and a detailed view of the connection of the rectangular spiral coils.

With respect to the applicability of the system, with the single-phase generator a more economic, although less efficient, mini-turbine 100 is obtained, while with the three-phase a more expensive but more efficient mini-turbine 100 is obtained. Therefore, it is preferable to use one or the other (the single-phase generator mini-turbine or the three-phase turbine) depending on the application.

The invention also relates to a mathematical and electronic model. The mathematical modelling of the printed circuit board PCB 15 serves to simulate the results of the energy that can be generated through the generator of the invention. The model comprises:

- A mathematical model, in turn comprising a model of the single-phase generator and a model of the three-phase generator;

- A simulation of the energy generation through the single-phase generator and a simulation of the energy generation through the three-phase generator. The two models comprise one generator (single-phase case) and three generators (three-phase case), an equivalent coil, an equivalent resistor and an equivalent condenser. The coil corresponds to all the coils (or inductances) of the generator (single-phase case) or of the phase (in the case of the three-phase). The resistance is determined by the resistance of the conductor, in the embodiment chosen for the model, copper. The condenser represents the capacity that is generated between the tracks that form the coils.

The method for obtaining the values of the different elements that make up the model is detailed below.

Firstly, the voltage and frequency values of the generators are obtained for each established rotational speed.

A magnetic simulation is carried out with the configurations described in the section on the magnet carrier rings 140 and description of the generator. To do so, a magnetic simulation is carried out of the density of the magnetic flux (B) on the surface of the printed circuit board PCB 15 and the electromotive force induced in the coils 15'. This gives both the field generated by the magnets 6 based on the rotational speed of the rotor 130 and the energy generated in the coils 15'. Figures 13A and 13B show images of the magnetic simulation carried out: figure 13A shows a simulation of the density of the magnetic flux (B) on the surface of the printed circuit board PCB 15 and figure 13B shows the electromotive force induced in the coils 15'.

Table B below summarises the induced voltage values obtained based on the simulation of a pair of coils, and calculated for each phase for different rotational speeds. The value shown is the rms value.

Table B: Summary of the induced voltage values obtained with magnetic simulation.

The necessary values, such as resistance, capacity and inductance, are obtained for the model of the generator based on the following equations. In order to carry out calculations and obtain the model of the generator, it is essential to define the length of the conductor and the material (for example, copper) of the coils since the equivalent resistance, capacity and inductance depend on the amount of conductor and the material.

The resistance of the generator is calculated using the following equation:

The equivalent capacity of the circuit is obtained using the following equation:

In the case of the equivalent inductance, the model thereof is different depending on the generator used, either single-phase or three-phase (shape of the coil, number of phases and type of connection between the phases).

The equations necessary for a single-phase generator with winding coils are the following:

The equations necessary for a three-phase generator with square coils are the following:

Taking into account the size, mechanical design and the electronic properties of the generator of the invention, the results of the model are obtained with which the preliminary results with respect to the real ones are obtained.

For the single-phase generator, the voltage results and frequency analysis are the following:

Figure 14 shows the voltage values that are obtained at different rotational speeds of the rotor 130 by using the mathematical and electronic model of the single-phase generator. Figure 14 shows that both the voltage and the frequency increase when the rotational speed is increased.

There is the possibility that the coils 15' of the generator act as a filter after a frequency or at a/some certain frequency/ies. The critical frequency for the single-phase generator can be obtained through the model, which can be seen in figure 15, which shows the frequency analysis by using the mathematical and electronic model of the single-phase generator.

The critical frequency is at 60 MHz, which translated to the rotational speed in rpm of the rotor 130 (rpm= (f^*60)/(1 6^*3)), is 75- 10⁶ rpm. Therefore, the single- phase generator of the invention never acts as a filter, since it is impossible for the rotor 130 to reach this rotational speed.

For the three-phase generator, the model results are the following:

Figure 1 6 shows the voltage values that are obtained with different rotational speeds of the rotor 130 by using the mathematical and electronic model of the three-phase generator.

In the case of the three-phase generator, the critical frequency changes, since the model and the resistance R, capacity C and inductance L values also vary with respect to the single-phase generator.

The critical frequency for the three-phase generator is at 2.5 MHz, as can be seen in figure 17, which translated to the rotational speed in rpm of the rotor 130 (rpm= (f^*60)/(1 6^*3)), would be 3.125- 10⁶ rpm. Therefore, the three-phase generator of the invention never acts as a filter, since it is impossible for the rotor 130 to reach this rotational speed.

Having explained the operation of the generation, a breakdown is provided below of the main components that make up the turbine and the important features of these components with regards to mechanical criteria.

(i) Firstly, considering the high performance that the elements must meet in order to withstand the working conditions, for example, in gas conduits for domestic and/or industrial use. In these installations, a possible application of the turbine of the invention is as a gas consumption meter.

The elements in this first group comprise:

- On the one hand, the rotation shaft 1 , bearings 2 and thrust thread and alignment pieces 3 and 4: The imbalance of the rotation shaft 1 of the turbine 100 can cause the generation of additional forces that oppose the rotation of the blades.

- On the other hand, the magnet carrier rings 140: The insertion of the printed circuit board PCB 15, with a substantially circular crown shape between the two magnet carrier rings 140, adds possible accuracy errors compared to the behaviour shown by a single piece fulfilling the same function. Therefore, the structure comprising the two magnet carrier rings 140 is optimized in order to obtain a simple and robust assembly once assembled and operating (the rotational speeds of the rotor 13 can be to the order of 10,000 rpm).

(ii) Secondly, the optimal maximum distance between the magnets 6 and coils 15' must be controlled in order to prevent excessive insulation caused by the air mass between the magnets 6 and coils 15'.

The elements in this second group comprise:

- The casings 9, clamps 1 6 and alignment pins 8, since it is critical to accurately ensure the distance between the printed circuit board PCB 15, positioned between the opposing inner faces of the magnet carrier ring 140, and these opposing inner faces of the magnet carrier rings 140. The casings 9, clamps 1 6 and alignment pins 8 make up a structure that guarantees that the printed circuit board PCB 15 is secured, keeping it static, while the rotor 130, which comprises the rotation shaft 1 , and the magnet carrier rings 140, rotate with respect to the stator, creating a variable magnetic field.

The alignment pins 8 are responsible for keeping the printed circuit board PCB 15 joined to the casings 9, while the clamps 16 are responsible for keeping the join/closure between the casings 9; the casings 9 and the clamps 16 are configured and manufactured to exactly maintain the thickness of the printed circuit board PCB 15.

(iii) Thirdly, the eddy currents must be minimized. In order to minimize the losses due to these eddy currents, the mini-turbine 100 would ideally be integrally built in a material that is "inert" to the electromagnetic field generated. However, in order to fulfil other operation criteria, some components of the mini-turbine 100 are made of materials that are "non-inert" to the electromagnetic field. Therefore, those elements whose operation requirements allows it, are made of a plastic material, which also fulfils other additional requirements, more related to the particular application for which the mini-turbine 100 is intended. In the specific case of measuring gas (natural gas in the case of domestic use), a material inert to humidity and other chemical compounds is used. The material used can be PEEK.

PEEKs are a thermoplastic with special features. The good mechanical resistance of the aromatic semicrystalline polymer is retained even at high temperatures. Furthermore, these materials have good resistance to impacts at low temperatures, high resistance to fatigue, low creep tendency, as well as good slip and wear properties. Its resistance to chemical agents is also excellent. Due to its excellent properties, polyether ether is used in applications where demanding loads are required.

With the exception of the rotation shaft 1 , bearings 2, alignment pins 8, collars 7 of the magnet carrier rings 140, fairing screws 17 and, naturally the magnets 6, the elements inside this third group of material that is inert to the electromagnetic field comprise: the thrust threading 3, alignment piece 4, cages 5, casings 9, clamps 1 6, inlet body 12, first body 1 1 , outlet body 14 and the second body 13.

After having broken down the components of the mini-turbine 100 taking into account the different functions they carry out, the manufacturing method of the mini-turbine 100 is explained below in accordance with a possible embodiment of the invention.

The rotor 130 is the most complex piece of the turbine 100. In accordance with an embodiment of the invention, the rotor 130 is obtained by machining with a 5-axis machine in order to be able to shape the blades and obtain finishes with the required accuracy.

- First the source block of the rotor 130 is machined on the front face, that is, the side of the fluid inlet, and on the rear face, that is, the side of the fluid outlet;

- Then the blades are machined;

- A false shaft is made in order to secure the rotor 130, which enables the perimeter slot to be carried out, which is configured to enable the rotation of the magnet carrier rings 140 on the printed circuit board PCB 15 and the housings of the magnets 6 in the opposing faces of the magnet carrier rings 140.

The manufacturing of the rest of the elements that are inert to the electromagnetic field is carried out by means of 3D printing technology, Selective Laser Melting (SLM), using a polyamide, due to the fact that it provides sufficient accuracy in non-critical pieces for the operation of the overall assembly. The manufacturing process of the mini-turbine can also be carried out by means of polymer injection molding in order to reduce costs and manufacturing time.

One embodiment of the invention has been carried out using polyamide, which is a material used with the SLM manufacturing technology. However, taking into account the operating conditions of the mini-turbine 100, working with gas, at a certain temperature and humidity, it may be more appropriate for the pieces to be made of PEEK, given its good mechanical properties. The pieces made of PEEK can be manufactured by 5-axis machining. In addition to having very good thermal stability, the pieces made of PEEK have mechanical properties required in the critical pieces, such as the casing, rotor and cages.

For large-scale manufacturing, pieces can be obtained by injection molding, rather than by machining the plastic. In the case of manufacturing by injection molding, instead of machining the plastic, the metal mold is machined, to subsequently inject PEEK material (available for use in injection molding processes) and obtain the injection molded pieces (a very cost-effective process for manufacturing large batches).

Having described the manufacturing methods of the different components of the mini-turbine 100, the manner in which the mini-turbine 100 is assembled is described below, where it can be seen how simple it is to assemble the turbine using the components thereof.

- The connection between the casings 9 and the connection elements 10 is carried out by assembly; that is, that the casings 9 and the connection elements 10 match to each other in order to enable coupling and fastening to each other.

- On the one hand, the connection between the first body 1 1 and the connection elements 10 and, on the other hand, the connection between the second body 13 and the connection elements 10 is carried out by means of fairing screws 17.

- The connection between the casings 9 and the printed circuit board PCB 15 arranged between the casings 9 is carried out by means of the pins 8 and clamps 7.

The assembled mini-turbine 100 is shown in figures 31 A and 31 B. As can be seen, the assembly process of the mini-turbine 100 does not require expert knowledge or tools that are complicated to handle, thus facilitating the assembly operations of the mini-turbine 100, reducing the time necessary for the assembly and the qualification required by the operator responsible for the assembly. Furthermore, the structure of the mini-turbine 100 enables the generator to be easily changed, such that repair, maintenance or modification (for example, changing a single-phase generator to a three-phase generator and vice versa) operations are envisaged in the structure of the mini-turbine 100 so that such tasks can be carried out without the need for complicated auxiliary operations.

In a particular embodiment of the invention, the mini-turbine 100 has a maximum outer diameter D of 32 mm.

The configuration of the components of the mini-turbine 100 enables rotational speeds of the rotor of 50,000 rpm to be reached.

With regards to the single-phase generator, manufacturing is carried out by means of machining a "sandwich" material (Cu-FR4-Cu) by means of a picosecond ultra-fast laser. On the one hand, this manufacturing method enables the dimensional tolerances of the printed circuit board PCB 15 to be achieved and, on the other hand, achieve the required configuration for the coils 15'. Figure 10A shows a view of the printed circuit board PCB 1 5 comprising the coils 15'. Figure 10B is a detail view of the coils 15'.

Figures 20 and 21 show the wave shapes obtained in trials carried out with the single-phase generator of the invention with an incident wind speed of 5m/s and 10m/s on the mini-turbine. These figures show the increase in voltage and frequency as the speed of the incident air increases.

Impedance matching must be carried out in order to obtain the greatest amount of power at the outlet. To do so, different resistive loads have been placed at the outlet and with different wind speeds. The results can be seen in the graph of figure 22 and the suitable resistance can be seen to obtain maximum power at the outlet. In this case it is 30Ω due to the addition of the resistive and reactive parts that make up the sum of the coils.

The results obtained with the single-phase generator of the invention, rotating with different incident wind speeds and with a load of 30Ω are included below (Table C):

Table C: Summary of the maximum power values obtained in the tests with the single-phase generator.

It is important to know the power results obtained with other loads since perfect impedance matching can be impossible to obtain. Therefore, figure 23 shows the different power values obtained with different loads at different incident speeds.

Another aspect to analyse is the linearity of the results, both for power and frequency. A relative linearity must be maintained in order to ensure that the results are correct since a generator that depends on the wind must linearly increase the amount of power generated as the speed of the incident wind rises. Both figures 23 and 24 show the linearity of the system.

With regards to the three-phase generator, it is manufactured as a traditional PCB, but with highly accurate details. The small distance between the tracks (50μm), the small width of the tracks (80μm) and the interconnection of the 3 phases through the inner layers made the manufacturing process of this PCB very complex. On the one hand, this manufacturing method enables the dimensional tolerances of the printed circuit board PCB 15 to be achieved and, on the other hand, achieve the required configuration for the coils 15'. Figure 1 1 A shows a view of the printed circuit board PCB 15 comprising the coils 15'. Figures 1 1 B and 10 are a detailed view of these coils 15'.

As with the single-phase generator, the equivalent data has been carried out and obtained for the three-phase generator.

Figures 25 and 26 show the wave shapes obtained in trials carried out with the single-phase generator of the invention with an incident wind speed of 5m/s and 10m/s on the mini-turbine. These figures show the increase in voltage and frequency as the speed of the incident air increases.

As has been stated above, impedance matching must be carried out in order to obtain the greatest amount of power at the outlet. To do so, different resistive loads have been placed at the outlet and with different wind speeds. The results can be seen in the graph of figure 27 and the suitable resistance can be seen to obtain maximum power at the outlet. In this case it is 27Ω due to the addition of the resistive and reactive parts that make up the sum of the coils.

The results obtained with the three-phase generator of the invention, rotating with different incident wind speeds and with a load of 27Ω are included below (Table D):

Table D: Summary of the maximum power values obtained in the tests with the three-phase generator.

The results to find out the impedance matching can be seen in figure 28. There are different power values obtained with different loads at different incident speeds. In this case, as it is a three-phase generator, the calculation of the power is carried

out using the following formula:

The linearity is still an important aspect, it is independent from the type of generator, which means that linearity results for the three-phase generator in terms of power and frequency have been obtained. Figures 28 and 29 show the linearity of the system.

Table E shows the maximum power difference obtained with each one of the generators:

Table E: Difference of the maximum power values obtained with each type of generator.

It can be seen that the results obtained with the three-phase generator are substantially better. However, this does not exclude the use of the single-phase generator for applications that require less energy since this generator is simpler to manufacture.

In this text, the word "comprises" and its variants (such as "comprising", etc.) should not be understood in an exclusive sense, i.e. they do not exclude the possibility of that which is described including other elements, steps, etc.

Also, the invention is not limited to the specific embodiments described herein, but rather encompasses the variations that one skilled in the art could make (e.g. in terms of choice of materials, dimensions, components, design, etc.), within the scope of what may be deduced from the claims.

Claims

1 . Mini-turbine (100) to generate electrical energy from the kinetic energy of a fluid that passes through the mini-turbine (100), wherein the mini-turbine (100) comprises:

a rotor (130) comprising a plurality of blades (131 ) between a hub (132) and a closing ring (133);

a stator (15, 15') facing the rotor (130);

wherein an extension of the closing ring (133) forms a first magnet carrier ring (140) integrated in the closing ring (133), wherein the first magnet carrier ring

(140) comprises a plurality of magnets (6) configured to generate a variable magnetic flux on the stator (15, 15') when rotated;

characterized in that:

the blades (131 ) have a first end integrated in the hub (132) and a second end integrated in the closing ring (133) to form a single-part rotor structure (130).

2. Mini-turbine (100) according to claim 1 , characterized in that the magnet carrier ring (140) configured to house a plurality of magnets (6) is made of plastic. 3. Mini-turbine (100) according to any of claims 1 -2, characterized in that it comprises a casing (9) configured to locate the stator (15, 15') with respect to the rotor (130), wherein the casing (9) is made of plastic.

4. Mini-turbine (100) according to any of claims 1 -3, characterized in that it comprises a second piece (120) that forms a fairing to channel a flow of fluid that passes through the mini-turbine (100), wherein the second piece (120) is made of plastic.

5. Mini-turbine (100) according to any of the claims 1 -4, characterized in that the extension of the closing ring (133) forms a second magnet carrier ring

(140) comprising a plurality of magnets, wherein said first and second magnet carrier rings (140) are arranged in two rotational circular crowns that have an inner diameter (Di) coinciding with an outer diameter of the rotor (130) determined by the closing ring (133); an outer diameter (De) larger than the outer diameter of the rotor (130); said first and second magnet carrier rings (140) being separated axially by a distance configured to house the stator (15, 15'), wherein the stator (15, 15') has the shape of a static circular crown comprised between the two magnet carrier rings (140), the stator (15, 15') comprising a printed circuit board PCB (15) and a plurality of coils (15'); wherein the magnets (6) and the coils (15') are configured so that, during a rotation of the rotor (130), an electrical current is induced in the coils (15') by the magnets (6) in motion.

6. Mini-turbine (100) according to any of the claims 1 -5, characterized in that it comprises fastening means (8, 9) configured to ensure the stator (15, 15') in an interchangeable way.

7. Mini-turbine (100) according to any of the claims 5-6, characterized in that the coils (15') are arranged in single-phase or three-phase configuration. 8. Mini-turbine (100) according to any of the claims 5-7, characterized in that the magnet carrier rings (140) have dimensions selected from:

an inner diameter (Di) less than 40mm, preferably less than 35mm and more preferably less than 30mm;

an outer diameter (De) less than 45mm, preferably less than 40mm and more preferably less than 35mm;

a thickness (e) less than 2mm, preferably less than 1 .5mm and more preferably less than 1 .3mm;

a plurality of housings with a housing diameter (Da) less than 2.3mm, preferably less than 2.2mm and more preferably less than 2.1 mm;

and combinations thereof.

9. Mini-turbine (100) according to any of the claims 5-8, characterized in that it has a maximum outer diameter less than 50mm, preferably less than 45mm and more preferably less than 40mm.

10. Mini-turbine (100) according to the claims 8 and 9, characterized in that the magnet carrier rings (140) have an inner diameter (Di) of 22.7mm; an outer diameter (De) of 27.7mm; a thickness (e) of 1 mm; 32 housings with a housing diameter (Da) of 2mm; a maximum outer diameter (D) of 32mm.

1 1 . Mini-turbine (100) according to any of the claims 8-10, characterized in that the magnets (6) have dimensions selected from:

a magnetic diameter (Dm) less than 8mm, preferably less than 6mm and more preferably less than 4mm;

a length (L) less than 4mm, preferably less than 3mm and more preferably less than 2mm;

12. Mini-turbine (100) according to any of the claims 1 -1 1 , characterized in that it is configured to be installed in gas pipelines.

13. Mini-turbine (100) according to any of the claims 1 -12, characterized in that it comprises a single-phase or a three-phase generator.