DESCRIPTION

From a general viewpoint, the invention relates to devices exploiting renewable sources for energy generation.

As is known, the theme of renewable energy sources and the use thereof as a replacement for fossil fuels has now become a priority acknowledged worldwide at all levels, whether scientific, technical and institutional.

In fact, in order to cope with global warming and implement the so-called green transition and environment decarbonization, it has now become urgently necessary to reduce the emissions of carbon dioxide and other greenhouse gases, which are typically connected with the combustion of fossil fuels (coal, oil, hydrocarbons, and derivatives thereof).

Renewable sources are also well-known, and the most widespread ones are wind, hydroelectric, photovoltaic, tide and wave motion; other sources may be used as well, depending on the natural resources available in different geographical areas (e.g. geothermal, biomasses, etc.).

The present invention deals, in particular, with the exploitation of wave motion for the generation of electric energy.

Considering, in fact, that seas cover approximately 71% of Earth’s surface, they represent an inexhaustible source of energy, also because of their potential for fulfilling the energy demand of the entire world population, amounting to ca. 32,000 TWh/y.

Therefore, the present invention provides a solution to the need for a device capable of exploiting the wave motion resource for the production of electric energy.

In particular, the invention concerns a novel device which can convert wave force into mechanical energy, which is then used for driving an electric generator, e.g. an alternator, a dynamo, or the like.

Devices of this kind, also referred to as WECs (Wave Energy Converters) or as combinations of said acronym with prefixes or suffixes (e.g. PeWECs, ISWECs, or the like), have been described in scientific and/or patent publications by the present inventors and by other authors, as well as in other prior-art documents available on the Internet and from common patent databases.

In brief, such apparatuses are based on gyroscopic systems supporting suspended masses that can make a pendulum-like oscillatory motion, which rotates a shaft associated with or connected to the rotor of a generator, thereby producing electric energy.

Within the scope of this general principle, different solutions have been conceived.

For example, many devices utilize direct contact between the hydrodynamic force and the power take-off (PTO), in practice, this means that part of the equipment floats or is anyway in contact with the water, with easily imaginable technical and operability contraindications in marine environments (salt corrosion, moisture, vegetable deposits, etc.).

Such devices are referred to as Point Absorber devices.

On the other hand, other solutions install the PTO inside a hull and exploit the physical interaction between the hull and the mechanism to generate a motion that drives the electric generator.

The conversion mechanism may be a gyroscope with a single-gimbal joint, or a pendulum or a cylindrical body hinged at the centre and free to rotate, using different technical solutions (referred to as PeWEC and SeaREV, respectively).

These systems permit capturing energy from limited wave motion directions. Since they are equipped with just a single gyroscope, they cannot operate on two or more waves having different directions and periods.

In practice, these are pitching, hence unidirectional, devices. In particular, the cardanjoint solution (ISWEC) exploits the revolution speed of a gyroscope to generate, along the axis of precession, a motion caused by Coriolis forces. The ISWEC apparatus is unidirectional, and the gyroscope is activated when the axis of precession is aligned with the direction of propagation of the wave.

The PeWEC device is based on the pendulum technology, whereas the SeaREV device is based on the motion of a hinged wheel which, as a result of a relative motion, actuates a hydraulic circuit. Some examples of this type of equipment are described in Italian patent applications T02009A 000422 and T02008A000444, and in United States patent publication US 4352023.

A multidirectional device is also known, which consists of a hull similar to a solid of revolution, generated from an irregular profile. Such a profile allows the hull to make a nutational motion due to the simultaneous presence of a pitching motion about an axis perpendicular to the wave arrival direction and a rolling motion about the axis parallel to the wave. The device consists of a mass hinged along a vertical axis, which utilizes the centrifugal force caused by the motion of the hull for producing energy. This is, therefore, a multidirectional energy converter that exploits the inertial and stiffness coupling given by the variation in the direction of the component perpendicular to the gravity vector.

Some examples of such multidirectional devices are described in international patent applications WO 2010/034888 and WO 2008/119881.

Such solutions are considered to be non-optimal because the dynamics of the internal mechanism cannot be accelerated, being forced to follow the slow dynamics of a hull subject to a nutational motion, resulting in very poor results in terms of power extraction. In light of the above examination, it can be stated that the technical problem at the basis of the invention is to make available a device for converting wave motion into mechanical energy for the production of electric energy, with such structural and operating characteristics as to be able to overcome the above-mentioned limitations and drawbacks of the prior art.

The idea that solves this problem is to create a device that combines gyroscope and pendulum characteristics.

This remedies the problems related to the multidirectionality and multifrequency of wave motion, thus increasing the power production efficiency of the device and maximizing the exploitation of the marine renewable source.

In accordance with a preferred embodiment, the device that comprises the pendulum and the gyroscope is installed aboard an axially symmetrical floating structure, which activates the mechanism through the motion generated by fluid- structure interaction.

Thus, the device does not require a mooring system for aligning the hull, and hence the mechanism, with the incoming wave. The features of the invention are specifically set out in the claims appended hereto; such features will become more apparent in light of the following description of a preferred, but non-limiting, example of embodiment of the invention, as shown in the accompanying illustrative drawings, wherein:

- Fig. 1 is an axonometric view of a pendular gyroscopic device according to the invention;

- Fig. 2 is a front view of the device of Fig. 1;

- Figs. 3 and 4 schematically show a floating installation for a pendular gyroscopic device according to the invention;

- Figs. 5 and 6 are plan views schematically showing the operation of a system according to the invention, for respective directions of the wave front;

- Figs. 7 and 8 show respective block diagrams concerning the adjustment of a power generator system according to the invention.

With reference to the above-listed drawings, numeral 1 (in Figures 5 and 6) designates as a whole a system for the generation of electric energy from wave motion.

The generator system 1 comprises a device or mechanism 2 for converting wave motion energy (more clearly visible in Figures 1 and 2) and a floating structure 3 supporting the device 2 (Figures 3 and 4).

For convenience and clarity, the following will describe such parts 2 and 3 of the system 1 separately; this should not however be understood in a limiting sense, in that the converter device 2 and the floating structure 3 will still provide advantageous features regardless of whether they are considered separately or mutually combined, as will become apparent below.

Therefore, the various components described or shown in this example may be considered as either independent or mutually combined. Likewise, more generally, any reference to a preferred or preferable embodiment thereof should not be understood in a limiting sense or anyway as precluding other alternative solutions conceivable by those skilled in the art.

As can be seen in Figures 1 and 2, the converter device 2 is of the pendular gyroscopic type, and will be hereafter referred to, for brevity’s sake, as “gyropendulum”.

The latter is essentially a gyroscopic converter of energy from wave motion, whose rotor, which lies lower than the axis of precession, is subject to elastic forces that can be exploited for energy generation purposes.

To this end, the device 2 comprises a structure or base 11 from which two columns or uprights 12 extend, which rotatably support an oscillating frame 13 in between; the latter has, preferably, a closed square-like or ring-like configuration, and is externally equipped with two journals or half-shafts 14 protruding from opposite sides along the axis Xi of rotation of the system, also referred to as axis of precession of the gyroscope.

The protruding journals 14 are mounted on respective bearings 15 located at the extremities of the columns 12, and one of them (the left-hand one in Figures 1, 2) is connected to a mechanical reducer 16, which will be described in further detail below.

The bearings 15 along the precession axis Xi are preferably of the radial type, since they mainly perform a supporting function. Due to the low shaft revolution speed (max. 1 rad/s), the loads applied to the bearings are negligible.

The oscillating frame 13 supports, in turn, a pendular mass 17 arranged at a distance L from the base 11, which distance is shorter than that of the axis of precession Xi; the mass 17 is free to rotate about a gyroscopic axis Zi orthogonal to the axis of precession Xi. Several solutions may be adopted for this purpose.

In the example shown in Figures 1 and 2, the mass 17 is fitted onto a shaft 18 idly supported along the axis Zi by the frame 13, which for this reason is made as two substantially C-shaped half-frames 13a, 13b facing each other and mutually connected at their ends by flange assemblies 19; the latter advantageously house bearings (not visible in the drawings) supporting the shaft 18 and allowing it to rotate freely.

These bearings perform a dual function of supporting the flywheel and absorbing the loads that are transferred to the gyroscopic support to induce motion thereof. They may be mounted according to different configurations, considering both axial bearings, which mainly perform a supporting function, and radial bearings, the main task of which is to absorb flywheel-generated loads.

This solution is suitable for large frames 13, but, as aforesaid, other alternatives are also possible, which those skilled in the art will be able to design and set up.

As a matter of fact, the frame 13 may even be designed as one piece, as opposed to two mutually connected half-frames, with a fixed (i.e. not idle) shaft 18 mounted thereto and the mass 17 idly supported on such shaft, like an idle wheel.

Furthermore, the mass 17 is preferably a disk as shown in the drawings, since this promotes the gyroscopic effect and lowers its centre of gravity from the axis of precession Xi, while at the same time limiting, all other conditions being equal, the overall dimensions of the device. The mass 17 may however be configured otherwise, depending on which characteristics are most useful for a specific application of the gyropendulum device 2.

For example, the gyroscopic mass 17 may be spherical, conical, ellipsoidal, or may have a complex profile (e.g. a lobed wheel, a polyhedron, or the like).

In the gyropendulum device 2, the shaft 18 is set in rotation by an electric motor 20, thus rotating the gyroscopic mass 17 fitted thereto, in accordance with the operating principles of this type of mechanism.

The mass 17 acts as a flywheel rotated at high speed by the motor 20, which is positioned at the bottom in Figures 1 and 2, although it may alternatively be installed at the top. This is preferably a permanent-magnet motor or, alternatively, a digital motor (stepper motor). The mass 17 is preferably big in size, for properly performing its dual function, and is located at a certain distance L from the axis of precession Xi. The mass 17 of the flywheel may vary from 5 to 25 tons, resulting in a moment of inertia relative to the polar axis Zi variable from 10 to 30 ton*m ² . The distance L may vary from a minimum value of 0.3 m to a maximum value of 3 m.

In this context, the oscillations of the frame 13 about the axis of precession Xi are transmitted from the reducer 16 to an alternator (not shown in the drawings) for converting mechanical energy into electric energy.

In the illustrated example, the reducer 16 is mounted to a supporting upright 26, adjacent to one of the journals 14 protruding from the frame 13; in this case as well, other mechanically different solutions may alternatively be devised, e.g. belt and pulley transmission systems connecting the journal 14 to the alternator, or gear trains, or the like. With the gyropendulum device 2, output torque values are very high and speed values are low. Therefore, an output torque limiter system is necessary for connecting to commercial electric generators. In particular, the reduction factor may be 5, 10 or 20, depending on the device. The variability of the values indicated herein depends on the site where the device of the invention is to be installed.

Regardless of this, the gyropendulum device 2 is preferably installed on a floating structure 3 anchored to a sea bed in such a way that it can float freely.

According to a preferred embodiment, the floating structure 3 substantially comprises a hull 30 enclosing the gyropendulum 2.

The hull 30 is preferably designed in such a way that its hydrodynamic characteristics are coherent with the frequencies of the externally applied forces on the site of interest.

A hull example is shown in Figures 3 and 4; as can be seen, the shape of the hull may be cylindrical or hemispherical, or parameterized with more complex functions. Its task is to enclose the gyropendulum 2 and, most importantly, to rotate about its own axes in an effective manner to actuate the mechanism 2 inside of it, keeping in mind that the performance of the latter also depend on the kinematics externally imposed by the wave motion.

The mass of the hull 30 may vary depending on the installation site, but is preferably in the range of 10 ³ - 10 ⁴ tons, with a length and a width of 5-10 m.

The hull 30 may be built from sheet metal or made up of mutually assembled floats surrounding a cylindrical body that houses the gyropendulum device 2.

The mooring system can be easily made because, thanks to the characteristics of the generator system 1, wherein a converter device 2 is installed in a floating structure 3, its only function is to anchor the system to prevent it from going adrift.

In particular, the hull 30 is preferably moored using a “multi-leg” system, with a variable number of mooring lines 33 depending on the circumstances. The minimum number recommended to ensure device balance is three lines 33, as shown in Figures 3 and 4, but four or five lines 33 may also be used depending on the characteristics of the installation site (sea bed depth, marine currents, winds, distance from the coast, etc.).

Schematically, the mooring lines comprise anchoring members 35 consisting of masses (e.g. concrete blocks, anchors, or the like) connected to the hull 30 by means of ropes or chains 36.

In accordance with the general principle of operation of the generator device 1, the gyropendulum device 2 is essentially a gyroscope whose rotor, i.e. the gyroscopic mass 17, is located at a predefined distance L from the axis of precession Xi.

Thus, the mass 17 acts as a counterweight in relation to the rotations of the frame 13 about the axis of precession Xi, promoting its oscillation from a condition of equilibrium.

It follows that the converter device 2 is, de facto, a single mechanism capable of operating both as a pendulum and as a gyroscope.

In particular, its functionality varies according to the oscillation imposed by the outside environment, i.e. by the wave motion to which the hull 30 where the gyropendulum device 2 is installed is subjected.

As shown in the drawings, the converter device 2 comprises a flywheel (i.e. the mass 17), which can rotate freely about its own polar axis Zi and which is connected to the gyroscopic support (i.e. the frame 13) through a pair of bearings 19, the frame being allowed to rotate freely about its own axis Xi, which is the axis of precession of the mechanism.

Said axis Xi coincides with, or is connected to, the axis of the electric generator, which, by braking the rotational motion induced on the gyroscopic support 13, extracts electric energy.

The motion of the gyroscopic support 13 may be induced by forces of different nature, depending on the external rotations to which the device 2 is subjected, which forces are transmitted by the hull 30 where the device is installed, which hull is in turn subjected to the wave motion as schematically shown in Figures 3, 4, 5 and 6.

It is assumed herein that the entire gyropendulum device 2 is induced to rotate relative to an XYX inertial reference system as shown in Figure 1.

For simplicity’s sake, it is assumed herein that motion is induced on a single axis, in which case the possible operating conditions will be the following:

- Case wherein the rotation 6 is induced along the inertial axis Y: the gyropendulum 2 acts as a gyroscope because the axis of precession a (coinciding with Xi) is perpendicular to the angular velocity vector <j.

The relation is as follows: (j ₀ )s + J<p8cos£ + Mglsine - T _{p o}

Where Io and Is are the moments of inertia along Xi of the flywheel (mass) 17 and of the support 13, respectively, J is the moment of inertia of the flywheel 17 along the polar axis Zi, M is the mass of the flywheel 17, L is the distance (of the centre of gravity) of the latter from the axis of precession a (or Xi), and g is gravitational acceleration.

Tpto is the torque applied by the generator to extract electric energy from the induced motion of the entire mechanism. The gyropendulum device 2 thus has a kinematics of its own along the axis of precession, which depends on the giroscopic effect JtpScoss .

There is also an elastic component resulting from the flywheel 17 being lower than the axis of precession a.

- Case wherein the rotation 6 is induced along the inertial axis X: the gyropendulum acts as a pendulum because the axis of precession is parallel to the angular velocity vector thereby cancelling the gyroscopic effect.

The forces acting upon the axis of precession are the following:

The motion along the axis of precession is generated by the relative motion generated between the reference systems involved, i.e. the inertial one OXYZ and the one integral with the gyropendulum OX1Y1Z1. In particular, the couplings that occur are of elastic and inertial nature.

A further advantage is obtained from this device in the intermediate operating condition, when the axis of precession lies in the XY plane at a certain angle from the X axis and from the Y axis. In this condition, due to the superposition principle, the gyroscopic effect and the elastic force of the pendulum are both present at the same time, keeping the mechanism always active. Proper angular velocity adjustment is essential for these two effects to be constructive.

The above discussion can be extended assuming that the gyropendulum is forced to rotate and move with six degrees of freedom relative to the OXYZ reference system.

In light of the above explanation and information, it is possible to understand the operation of the system 1 for the generation of electric energy according to the invention. With reference to Figures 5 and 6, considering the axis of precession a or Xi, the degree of freedom of the gyropendulum device 2 coincides with the one about the energy generation axis through which the mechanism is connected to the electric generator.

The following may occur: i) if the wave arrival direction is aligned with the axis a or Xi, (in Figure 5, West and East directions), the hull 30 will be induced to rotate about the Y axis at a certain angular velocity, thereby actuating the gyroscopic effect that will cause the mechanism to rotate about a or Xi; ii) if the wave arrival direction is perpendicular to the axis 8 or Xi (in Figure 6, North and South directions), the hull 30 will be induced to rotate about the X axis at a certain angular velocity, so that the gyropendulum 2 will behave as a pendulum, bringing the revolution speed of the flywheel to 0; iii) if the wave arrival direction lies in an intermediate range between the above-described cases, then the gyropendulum device 2 will behave both as a pendulum and as a gyroscope, suitably adjusting the revolution speed of the mass or flywheel 17.

An electric energy generator system 1 capable of operating in all sea conditions, in the presence of wave motion having frequencies and amplitudes of excitation of the system 1 that may vary from time to time, requires an optimal control strategy or logic that will maximize the electric energy extracted from the system.

Said strategy is preferably managed through the use of electronic processing systems (i.e. computers, servers, and the like) connected to the generator system 1 over telecommunications networks, and will depend from case to case on the installation position of the generator system 1.

For example, satellite or radio TLC networks may be used for off-shore installations, while a wired network may be resorted to for installations near the coast and/or including multiple generator devices.

In this latter case, the cable lines may also be used for transporting the produced electric energy.

The power extracted under a given sea condition is defined as: ?w ~

Therefore, it will depend on the revolution speed of the gyropendulum ^relative to the axis of precession Xi and on the torque applied by the generator T _e .

The device 2 is controlled in such a way as to enhance its characteristics as a function of the descriptive parameters of the incoming wave, such as significant wave height H _s and peak period T _e .

The algorithm that controls the system 1, which may reside either in a local memory of the system 1 or in a remote computer connected to the system 1, is based on the “impedance matching” principle, schematically shown in Figure 7; alternatively, the control algorithm may be based on a model of the gyropendulum device 2, as shown in Figure 8.

In the former case, by using the impedance matching condition it is possible to generate an optimum speed profile by means of the block T by inputting to the system the estimate of the externally applied force f _ex .

Such profile can then be reached by designing a C controller.

Alternatively, an MPC (Model Predictive Control) algorithm may be used, which generates the optimum torque that the electric generator must apply in order to maximize the energy extracted from the device (Fig. 8).

Such an algorithm solves, at every time interval, a constrained optimization for calculating the optimum torque.

The speed of the gyroscopic mass or flywheel 17, which is also a parameter that needs to be managed, is computed as a result of processes of numerical simulation of the gyropendulum device 2.

When the sea is calm, or when an extreme wave is formed, the machine can be switched off.

In light of this description, it can be appreciated that the generator system 1 according to the invention can solve the above-stated technical problem.

In fact, the characteristics of the converted device 2 are partly gyroscopic and partly pendular, and mutually combined.

On the one hand, this makes it possible to obtain rotations of the frame 13 induced by wave motion, in accordance with the normal operation of prior-art gyroscopic devices installed aboard floating structures.

However, the frequency of such oscillations is controlled by means of the pendular behaviour of the device 2, which is given by the mass or flywheel 17 lying at a distance from the axis of precession.

This feature causes the oscillations of the frame 13 to behave periodically, at a frequency that depends, as a first approximation, also on the distance L of the mass 17 from the axis of precession Xi (according to Galileo’s law of the pendulum:

T = 27t IT). g The gyropendulum device 2 can thus be designed as suitably as possible according to the marine conditions in the installation place.

The features of the invention described hereinbefore fall within the scope of the following claims.