DESCRIPTION

Technical field

The present invention is generally applicable to the technical field of the energy storage. In particular, the object of the invention is a dynamic energy-storage device.

State of the art

In the last decades, the increasing need for energy in many sectors of the human activity led to the constant search for efficient methods for reasonably use of the energy produced by power plants.

To that end, dynamic storage systems of mechanical-kinetic kind exist and are known in which, typically, the energy is stored in the form of rotational mechanical energy of a rotor that is rotatable in a stator. These mechanical systems offer peculiar features in terms of storing, use and lifetime, rendering them particularly suited to be used in industrial fields where, typically, there is the need for very high powers for short periods of time. In fact, the kinetic storage allows to storage a relatively high amount of energy and to quickly return such energy at a high power.

However, the above mentioned storage systems have such costs that they turn out to be unsuited to be used in other fields, for example domestic fields.

The high costs derive form several factors, among which the most significant are the need for managing high powers, the need for stabilizing and managing the motion of the masses, and the high cost of the systems for suspending the rotor and limiting the friction. Other non-negligible factors are the cost of the safety devices, that are needed in the above mentioned storage systems due to the high energy at stake, and also the cost of the materials, that are required to have extreme mechanical properties.

At present, the devices that are most common in the market and that allow to minimize the frictions are of dynamic kind, in which a rotor is suspended to a stator through cooled superconductors and through a system of magnetic bearings. For the dynamic devices of the kind just mentioned, the well-known Earnshaw theorem applies. A corollary of the theorem states that a system of stationary magnets, including the above mentioned magnetic bearings systems, can't have any stable-equilibrium configuration, hence it always tends to instability.

Clearly, due to the theorem just mentioned, it is impossible to stabilize the rotor in the above mentioned dynamic storage devices merely by making use of permanent magnets: in fact, due to the high rotational regime of the rotor, the instability that would arise would render the device unusable. For that reason, in a dynamic storage device of known kind the magnetic suspension of the rotor is obtained by using, possibly in combination with permanent magnets, electromagnets that are actively controlled by electronic systems that identify and suppress instability by generating suitable stabilizing magnetic forces.

The above mentioned active-control systems have the drawback that they need a constant power supply, that brings significant operating costs, also due to the necessary redundancy that such systems must implement.

Presentation of the invention

The present invention intends to overcome at least in part the drawbacks of the above mentioned prior art.

In particular, it is an aim of the invention to provide a dynamic energy-storage device that has a lower cost compared to that of the dynamic storage devices of known kind.

A further aim of the invention is to provide a dynamic storage device allowing to achieve an optimal control on the rotational and translational speed of the system.

Last but not least, it is another aim to provide a dynamic storage device structurally simple, that can be manufactured through the usual and known plants. the above mentioned aims are achieved by a dynamic storage device according to the main claim.

Further details of the invention are specified in the respective dependent claims.

Advantageously, due to its limited cost the storage system of the invention is particularly suited for domestic storage uses and, potentially, also in other fields of similar energy demand.

The aforementioned aims and advantages, together with further of them hereinafter mentioned, will be made apparent from the following description of some preferred embodiments of the invention, that are explained by way of non-limiting examples with reference to the attached drawings.

Brief description of the drawings

Fig. 1 represents the dynamic storage device of the invention, in lateral cross- sectional view according to a section plane comprising the longitudinal axis.

Fig. 2 schematically represents the configuration of some magnets belonging to the device of Fig. 1 , in axonometric view.

Figs. 3 and 4 schematically represent two further configurations of the magnets belonging to the device of Fig. 1 , according to respective variant embodiments of the invention, in axonometric view.

Detailed description of some preferred embodiments

The dynamic storage device of the invention, identified in its entirety in Fig. 1 with 1 , comprises a stator 3 having generally cylindrical shape that defines a longitudinal axis X, and a rotor 2, having a shape that is, as well, generally cylindrical and that is substantially coaxial to the stator.

The rotor 2 is magnetically constrained to the stator 3 through a magnetic suspension system that, besides allowing the rotation of the rotor 2 according to the longitudinal axis X, at the same time dynamically stabilizes the rotor 2 during its rotation around the longitudinal axis X.

The device 1 is configured to operate with the longitudinal axis X arranged horizontally. Therefore, the following description shall be construed with implicit reference to an operating condition in which the longitudinal axis X has horizontal orientation.

Moreover, hereinafter in the description it will be assumed that, at least in normal operating conditions, the rotation axis of the rotor 2 coincides with the longitudinal axis X. In fact, despite the fact that the rotational constraint of the rotor 2 to the stator 3 is magnetic, thus the position of the rotor 2 with respect to the longitudinal axis X is subjected to small oscillations in a direction orthogonal to the longitudinal axis X, nevertheless, the above oscillations are, in practice, entirely negligible.

The above mentioned magnetic suspension system comprises first magnetic means 15a, 15b, 22a, 22b to magnetically constraining the rotor 2 to the stator 3 according to a direction that is orthogonal to the longitudinal axis X. In particular, the first magnetic means 15a, 15b, 22a, 22b are configured so that their mutual interaction generates, in its whole, a sustaining force on the rotor 2 that is substantially orthogonal to the longitudinal axis X, and that is suited to compensate the weight of the rotor 2 during its rotation around the same axis so as to sustain it.

The magnetic suspension system also comprises second magnetic means 13a, 13b, 21a, 21b to magnetically constrain the rotor 2 to the stator 3 according to the direction of the longitudinal axis X, allowing it a limited axial movement. In particular, the second magnetic means 13a, 13b, 21a, 21b are configured so that their mutual interaction generates, in its whole, a stabilizing force on the rotor 2 that is substantially parallel to the longitudinal axis X, i.e. horizontal in operating conditions.

Both the above mentioned sustaining and stabilizing forces constantly operate to prevent the contact between the rotor 2 and the stator 3. Nevertheless, the two above mentioned forces have mutually different features, as will be explained more in detail hereinafter.

In particular, the first magnetic means 15a, 15b, 22a, 22b are configured so that the sustaining force defines, for the rotor 2, a position of stability in a direction orthogonal to the longitudinal axis X. The above mentioned position of stability coincides with the particular position of the rotor in which the module of the sustaining force has a value that coincides with the weight of the rotor. The above mentioned position is made stable due to the fact that the sustaining force increases, or respectively decreases, compared to the above mentioned value, as a consequence of the movement of rotor below, or respectively above, the position of stability, so as to exert on the rotor 2 a feedback tending to bring it back to the position of stability. In the normal operating conditions, the sustaining force is constantly directed upwards. Moreover, the sustaining force remains preferably constant, or substantially constant, during each rotation of the rotor around the longitudinal axis X. It is hereby specified that the wording "a rotation" is to be construed to indicate a 360° turn of the rotor 2 around the longitudinal axis X. Moreover, the wording "substantially costant" referred to the sustaining force is to be construed to indicate that the changes in the force during each rotation of the rotor are negligible compared to the mean value of the same force, and, anyway, those changes do not induce instability in the motion of the rotor.

Concerning the second magnetic means 13a, 13b, 21a, 21b, they comprise a plurality of first permanent magnets 13a, 13b belonging to the stator 3 and a plurality of third permanent magnets 21a, 21b belonging to the rotor 2. In particular, the above mentioned first permanent magnets 13a, 13b and third permanent magnets 21a, 21b are configured so that the stabilizing force is subject to a cyclical inversion of its direction during each rotation of the rotor 2 around the longitudinal axis X.

It can be noticed that the stabilizing force does not define, for the rotor 2, a stability position in the strict sense: in fact, in operating conditions that force is subject to continuous inversion of its direction as a consequence of the rotation of the rotor, hence it impart an oscillatory motion on the rotor 2 according to the longitudinal axis X, yet having limited entity and high frequency. Nevertheless, it is precisely the above variability of the force that allows to reach a condition of dynamic stability for the rotor 2. The reason of that dynamic stability is to be found in the fact that the variability of the stabilizing force allows to overcome the limitation posed by the aforementioned Earnshaw theorem, that is applicable only to the case of stationary magnetic forces.

It it hence possible to constrain the rotor 2 to the stator 3 exclusively through the use of permanent magnets, i.e. in a passive way, at the same time avoiding instability. Therefore, it is reached the aim of reducing the cost of the dynamic energy-storage device compared to the devices of known kind. In fact, the cost of a passive system based on permanent magnets is lower than that of an active system based on electromagnets, both because the permanent magnets themselves have a lower cost compared to the electromagnets, and because they don't require a control system analogous of that which is needed for the electromagnets.

As a consequence, advantageously, the above mentioned device 1 is particularly suited to be used in the application field of domestic storing, as well as in other fields of similar energy demand.

Preferably, the stator 3 is provided with two first flanges 5, 6 that are arranged mutually facing according to the direction of the longitudinal axis X, to which the first permanent magnets 13a, 13b belong. Similarly, the rotor 2 is provided with two second flanges 17, 18 to which the third permanent magnets 21a, 21b belong, and configured so that each one of them faces a corresponding one of the above mentioned first flanges 5, 6 during rotation of the rotor 2.

Preferably, at least a part 13a of the first permanent magnets belongs to a corresponding first flange 5 and at least a part 21a of the third permanent magnets belongs to the second flange 17 facing to the above mentioned first flange 5, so that the above mentioned permanent magnets 13a, 21a are mutually facing in order to magnetically interact with one another.

Still preferably, the first permanent magnets 13a and the third permanent magnets 21a just mentioned are configured in such a way that the overall magnetic force between the first flange 5 and the second flange 17 generated by the mutual interaction between the above mentioned magnets 13a, 21a is repulsive during a first portion of each rotation of the rotor 2, and attractive during a second portion of the above mentioned rotation.

Still preferably, the above mentioned permanent magnets 13a and 21a are so configured as such to define a succession of several first portions and second portions of the kind above described, in order to obtain a succession of inversions of the above mentioned overall force between the two flanges 5 and 17 during each rotation of the rotor 2.

Preferably, a remaining part of the first permanent magnets 13b and a remaining part of the third permanent magnets 21b belong to the other first flange 6 and to the other second flange 18, respectively. Still preferably, the configuration of the latter permanent magnets 13b, 21b is similar to that of the permanent magnets 13a, 21a above described. Still preferably, these latter permanent magnets 13b, 21b are angularly displaced with respect to the permanent magnets 13a, 21a in such a way that, for any angular position of the rotor 2, their mutual magnetic interaction generates, between flange 5 and flange 17, an overall force that is opposite to the force generated between flange 6 and flange 18. What has been just described is to be construed as meaning that, if, for a given angular position of the rotor 2, the force acting between flanges 5 and 17 is attractive, the force acting between the flanges 6 and 18 is repulsive, and vice-versa.

Fig. 2 represents a possible configuration of the first permanent magnets 13a,

13b and third permanent magnets 21a, 21b in the embodiment just described. For the sake of simplicity, that figure only shows the parts of rotor 2 and of stator 3 that support the above mentioned magnets 13a, 13b and 21a, 21b. In particular, for the stator 3, only the surfaces of the first flanges 5, 6 facing to the rotor 2 are represented, while the rotor 2 is represented in a simplified way as a cylinder that is delimited at the opposite ends by the surfaces of the second flanges 17, 18. Fig. 2 only represents the mutually-interacting magnetic polarities belonging to magnets 13a, 13b, 21a, 21b, hence it is not intended to limit in any way the actual geometrical configuration of the magnets themselves.

Preferably, the arrangement of the first permanent magnets 13a, 13b is such as to define, on each first flange 5, 6, corresponding successions of alternate polarities, that are arranged according to corresponding annuli and at uniform angular intervals around the longitudinal axis X. The above mentioned annuli are represented in Fig. 2 by dash-dot lines. Similarly, the third permanent magnets 21a, 21b are arranged on each of the second flanges 17, 18 so as to define corresponding successions of same polarities arranged according to corresponding annuli at uniform angular intervals around the longitudinal axis X. Preferably, the angular intervals of the annuli of the second flanges 17, 18 are twice as wide as the angular intervals of the annuli of the first flanges 5, 6. Still preferably, the polarities of the annulus of the first flange 5 are angularly displaced with respect of those of the annulus of the other first flange 6 by an angle equal to the angular interval between two successive polarities in the same annulus, while, on the other hand, the polarities of the annuli of the two second flanges 17, 18 are mutually in phase. This means that, each polarity belonging to the annulus of the first flange 5 is aligned with a polarity of opposite sign belonging to the annulus of the other first flange 6, according to the direction of the longitudinal axis X, while the polarities belonging to the annuli o the two second flanges 17, 18 are mutually aligned according to the longitudinal axis X. Accordingly, when magnets 13a, 21a belonging to the two flanges 5-17 are aligned so as to mutually repel, the magnets 13b, 21b belonging to the other two flanges 6-18 are aligned so as to mutually attract, and vice-versa, as it may be clearly seen in Fig. 2.

In a variant of the above mentioned embodiment, the third permanent magnets 21a define a succession of alternate polarities arranged at uniform angular intervals along an annulus that is coaxial to the longitudinal axis X, while the first permanent magnets 13a define a succession of polarities having the same sign, arranged at uniform angular intervals along an annulus coaxial to axis X, the angular intervals being twice as wide as the intervals in the annulus defined by the third permanent magnets 21a.

In a third variant of the above mentioned embodiment, each succession of the first permanent magnets 13a and of the third permanent magnets 21a is arranged according to a respective annuli and with polarities in alternate succession.

The three variant embodiments just described are those that allow, advantageously, to achieve the better stability of the rotor 2. Nevertheless, the advantages of the invention can be achieved through further variant embodiments.

One of the above further variants, schematically represented in Fig. 3, is identical to the first variant above described, except that the polarities of the two second flanges 17, 18 are mutually angularly displaced by a predefined displacement angle. Preferably, the polarities between the two first flanges 5, 6 are displaced by an angle equal to the sum of the displacement of the previous variant and the above mentioned displacement angle. In such a way, it is possible to achieve the same effect of simultaneous attraction on one side of the rotor, and repulsion on the other side, as described in the previous variant embodiment.

According to a further variant embodiment of the invention, the magnets are configured so that the interaction between each of the flange pairs 5-17 and 6-18 during each rotation of the rotor 2 are all repulsive, or all attractive. In this variant embodiment, an example of which is depicted in Fig. 4, the condition of cyclical inversion of the stabilizing force can be achieved by arranging the permanent magnets 13a, 21a of the flange pair 5-17 so that they are angularly displaced with respect to the permanent magnets 13b, 21b of the other flange pair 6-18 so that, during each rotation of the rotor 2, the forces act, in alternative succession, between the flanges 5-17 or between the flanges 6-18.

A different embodiment of the invention differs from the previous one in that the first permanent magnets 13a and the third permanent magnets 21a are provided only on the flange pair 5-17, while the said magnets are absent in the flanges 6-18 of the other pair. In this latter embodiment, the cyclical inversion of the stabilizing force can be achieved by arranging the first permanent magnets 13a and/or the third permanent magnets 21a according to an annulus around the longitudinal axis X so as to define corresponding successions of polarities having alternate signs.

In a first variant of this second embodiment, the first permanent magnets 13a can be arranged so as to define a succession of polarities having alternate signs, arranged at uniform angular intervals along an annulus that is coaxial to the longitudinal axis X, while the third permanent magnets 21a can be arranged so as to define a succession of polarities having the same sign at uniform angular intervals along an annulus coaxial to the axis X, the latter intervals being twice as width compared to the intervals of the annulus formed by the first permanent magnets 13a.

The configuration just described is similar to that depicted in Fig. 2, when only the magnets 13a, 21a of the flange pair 5-17 are taken into consideration and the magnets 13b, 21b of the other flange pairs 6-18 are ignored, since, as above mentioned, the latter magnets are absent in this embodiment.

In the above described variant embodiments, the permanent magnets 13a-21a and 13fo-21b belonging to each pair of mutually facing flanges 5-17 and 6-18 are arranged so that the corresponding poles define, on the two flanges of the pair, two respective annuli around the longitudinal axis X, the two annuli being arranged mutually facing according to the direction of the axis X, and having substantially equal diameters.

Anyway, a variant embodiment of the invention may envisage that the permanent magnets belonging to the two flanges of a pair, or of each pair, are arranged so that the corresponding poles define two or more of the above mentioned annuli, the annuli having mutually different diameters.

Clearly, the variants and the embodiments above described can be combined in order to achieve the cyclical inversion of the stabilizing force.

It is also clear that the number of first magnets 13a, 13b and third magnets 21a, 21b indicated in Figs. 2-4 is purely exemplary, and that, in variant embodiments of the invention, can be any number.

Preferably, in all of the variant embodiments above described, each of the first permanent magnets 13a, 13b and third permanent magnets 21a, 21b is arranged so that their two poles are aligned according to a direction parallel to the longitudinal axis X. Advantageously, the configuration just described allows to achieve a stabilizing force having a particularly precise orientation according to the longitudinal axis X, in order to avoid unwanted oscillations of the rotor 2.

Still preferably, each of the first permanent magnets 13a, 13b and third permanent magnets 21a, 21b is a corresponding bar that develops with uniform cross section, e.g. circular, according to a direction parallel to the longitudinal axis X.

Concerning in more detail the stator 3, preferably it comprises an inert containment casing 4 that, in turn, comprises a tubular metallic shell 7 whose ends are sealingly associated to, respectively, the two first flanges 5, 6.

Still preferably, the above mentioned containment casing 4 comprises a first outer layer 16 made in massive material arranged outside of the tubular metallic shell 7 and that, advantageously, allows to achieve a restraint on the movement of the rotor 2 in case of breakdown. Still preferably, the first outer layer 18 and the tubular metallic shell 7 define a gap containing a substance, such as for example viscous oil or sand, that, in case of breakdown, can penetrate in the sealed chamber so as to contribute dissipating the kinetic energy of the rotor 2 The cases in which this may occur comprise possible extreme instability, e.g. earthquakes, impact damages, etc., as well as system breaking due to possible manufacturing defects.

Concerning in more detail the first flanges S, 6 of the stator 3, preferably they have corresponding holes 8a, 8b in which respective safety bearings 9a, 9b are housed that are provided with corresponding seats. Moreover, the rotor 2 comprises two end portions 12a, 12b that are mutually opposite according to the direction of the longitudinal axis X and are coaxial thereto. The end portions 12a, 12b are housed with play, respectively, in the above mentioned seats so as to avoid contact between the end portions 12a, 12b and the seats in the normal operating conditions of the device 1, thus preventing also the consequent friction. The above mentioned contact may occasionally occur during an instability event and/or during transients - acceleration and deceleration - of the rotor 2, thus advantageously limiting the misalignment of the rotor 2 so as to prevent contact between the rotor 2 and the stator 3, that would consequently cause damages to the device 1.

Still preferably, the above mentioned end portions 12a, 12b have corresponding sharped ends. Moreover, the holes 8a, 8b of the stator 3 house corresponding safety capsules 11a, 11b in which the above mentioned sharp ends may stick in case of excessive displacement of the rotor 2 with respect of the stator 3 that may follow serious instability events. Advantageously, when one of the sharp ends sticks in the corresponding safety capsule 11a, 11b, it establishes a mechanical constraint between the rotor 2 and the stator 3, that is suited to reduce the number of degrees of freedom of the rotor itself, in order to enhance the containment action of the safety bearings 9a, 9b so as to prevent potentially disruptive circumstances.

Concerning in more detail the rotor 2, preferably it comprises a cylindrical connecting tube 19 whose ends are associated, respectively, to the second flanges 17, 18. Still preferably, the rotor 2 comprises a covering 20 in composite material that increases the peripheral mass and the energy storing capacity of the rotor 2, as well as its mechanical strength to centrifugal stress.

Preferably, the rotor 2 is further covered with an outer shell in fiberglass.

Still preferably, the rotor 2 comprises a shaft 10 whose main function is to carry, at its corresponding ends, the above mentioned end portions 12a, 12b. The shaft 10 is not subjected to a noticeable kinetic mechanical stress, hence it may be made in steel alloy.

On the contrary, the second flanges 17, 18 of the rotor 2 are subjected to high mechanical stress, mainly cause by centrifugal forces, therefore their dimensions and materials shall be defined based on the rotational speed of the system, hence on the required energy storing capacity. A material that is typically employed for the second flanges 17, 18 is the aluminum alloy known as Ergal.

Concerning the first magnetic means 15a, 15b, 22a, 22b originating the sustaining force, preferably they define a first ring 15a, 15b belonging to the stator 3 and being coaxial to the longitudinal axis X, and a second ring 22a, 22b belonging to the rotor 2 and concentric to the first ring. The two rings are configured in such a way that their corresponding mutually facing surfaces have the same magnetic polarities, so that the mutual interaction between the two rings is always repulsive in any of their angular positions. Moreover, the first ring comprises a plurality of portions having the same angular widths that exert, on the second ring, respective magnetic forces having mutually different magnitudes, so that the resulting overall force between the two rings compensate for the weight of the rotor 2 when the longitudinal axis X is arranged horizontally.

Preferably, the first ring is defined by a plurality of second permanent magnets

15a, 15b belonging to the two first flanges 5, 6 of the stator 3, arranged around the longitudinal axis X, preferably at uniform angular intervals. Similarly, the second ring is preferably defined by a plurality of fourth permanent magnets 22a, 22b belonging to the two second flanges 17, 18 of the rotor 2, and arranged at uniform angular intervals around the longitudinal axis X. Preferably, the magnetic forces produced by the second permanent magnets 15a, 15b have mutually different magnitudes, i.e. bigger for the magnets arranged at the base of the first ring and smaller for the magnets arranged on top of the first ring. According to a variant embodiment, the forces of the second permanent magnets 15a, 15b have all the same magnitudes, but the magnets are arranged at nonuniform angular intervals around the longitudinal axis X, that are narrower at the base of the first ring and wider towards its top.

On the contrary, the magnetic forces of all of the fourth permanent magnets 22a, 22b have, preferably, the same magnitudes.

Still preferably, the stator 3 comprises a plurality of coils 14a, 14b to induce the rotary motion on the rotor 2, arranged in a ring around the longitudinal axis X, preferably farther from the axis that with respect to the first permanent magnets 13a, 13b.

Moreover, the rotor 2 comprises fifth permanent magnets 23a, 23b, that are also arranged in a succession of alternate polarities around the longitudinal axis X to define a ring that is concentric to the ring defined by coils 14a, 14b, in order to be faced to the above mentioned coils 14a, 14b. The coils 14a, 14b are being operated by a control unit, that is not represented in the drawings but that is per se known, so as to interact with the fifth permanent magnets 23a, 23b to impart the rotation to the rotor 2, in a way similar as in a brushless motor of known kind.

Preferably, a first group of coils 14a belongs to the first flange 5 and the remaining group of coils 14b belongs to the other first flange 6. Similarly, a first group of fifth permanent magnets 23a belongs to the second flange 17 and the remaining group 23b belongs to the other second flange 18. The control unit is configured to operate each one of the two groups of coils 14a, 14b differently than the other group, thus allowing, to advantage, the active compensation of possible instabilities on the rotor 2, in particular during critical conditions such as acceleration, deceleration and possible breakdowns.

Preferably, the device 1 also comprises a detecting device to detect the position of the rotor 2 with respect to the stator 3 according to the longitudinal axis X, while the above mentioned control unit is configured to perform the above mentioned differentiated operation two groups of coils 14a, 14b based on the reading of the detecting device.

Preferably, the detecting device is configured to measure the reluctance induced by the fifth permanent magnets 23a, 23b on the coils 14a, 14b during rotation of the rotor 2. In variant embodiments of the invention, the detecting device may detect the position of rotor 2 through other magnetic and/or optic systems of known kind.

More generally, the geometries of the rotor 2 and/or of the stator 3 are preferably symmetrical according to a plane perpendicular to the longitudinal axis X.

Still preferably, all of the permanent magnets 13a, 13b, 15a, 15b, 21a, 21b, 22a, 22b and the coils 14a, 14b above described are fixed to the corresponding flanges 5, 6, 17, 18. More preferably, the above mentioned magnets and coils are housed in corresponding seats made in the above mentioned flanges.

Still preferably, the first flanges 5, 6 of the stator 3 have corresponding central parts projecting towards the rotor 2, and that house the first permanent magnets 13a, 13b, the coils 14a, 14b, and the second permanent magnets 15a, 15b. On the other hand, the second flanges 17, 18 of the rotor 2 have corresponding central recesses that house the central parts of the first flanges 5, 6, the third permanent magnets 21a, 21b, the fourth permanent magnets 22a, 22b, and the fifth permanent magnets 23a, 23b.

In particular, the acting poles of the second permanent magnets 15a, 15b are all oriented towards the outside of the stator 3, with the consequence that the active poles of the fourth permanent magnets 22a, 22b, that face the above mentioned poles, are all oriented towards the inside of the rotor 2. A similar configuration also applies to the coils 14a, 14b of the stator 3 and the fifth permanent magnets 23a, 23b of the rotor 2, respectively.

However, it is clear that, in variant embodiments of the invention not depicted in the drawings, the configuration may be switched with respect to the above description, meaning that the first flanges 5, 6 may have corresponding central recesses in which corresponding central parts of the second flanges 17, 18 are housed.

The device 1 may be associated with further electric, electronic and mechanical system, among with, for example, control systems and energy static- conversion systems, that, for the sake of simplicity, are not described hereby, nor depicted in the drawings, but that are per se known.

For example, the above mentioned systems may comprise an energy static- conversion device from AC to DC, a device for controlling the static conversion, a device for controlling the brushless motor, an energy-withdrawal device for converting kinetic energy into DC electric energy, a device to convert energy from DC to AC, synchronized with the user network, and a device for controlling and managing the whole system, provided with a user interface.

In particular, since the dynamic energy-storage device is intended to be used mainly for domestic consumers, like households, small enterprises, etc., it is necessary to manage the operations of charging, discharging, and retention of the stored energy.

In substance, the different components of energy-conversion management are devoted to manage the withdrawal and the storing of the energy from the AC electric network, through a conversion into DC that is needed by the system, as per any other storing system based on usual batteries.

Practically, the operation of the device comprises a startup phase to bring the, initially stationary, rotor 2 to a rotational regime of “minimum charge”, in which the values of the energy parameters for tension, current, frequency, and so on, are sufficient to allow connecting the system to the electric network in energy-exchange regime, and to reach a stable rotational regime for the rotor.

The startup phase is carried out by withdrawing energy from the network through capacitive-charge stages in pulsed regime (PWM).

Afterwards, the energy is withdrawn from the capacitors and transferred to coils 14a, 14b, so that a torque is imparted to the rotor 2. The distribution of the torque among the two ends of the rotor 2 also allows to achieve some control of the axial translational motion of the rotor, so as to maintain it in a configuration of equilibrium until reaching the rotational speed required to obtain a passive stability, i.e. without using the controlling action of the coils.

Hence, the system can store energy from generator plants, and transfer the energy to the coils as above explained in order to convert it into kinetic energy of the rotor.

When needed, the kinetic energy is withdrawn from the rotor through the withdrawal device to be converted into DC synchronized with the consumer network.

In the device heretofore described, it has been provided a passive suspension system, which is stabilized dynamically yet passively. In particular, an assembly of permanent magnets induce on the rotor an axially limited oscillation, that is also controlled around a position of equilibrium which, in practice, becomes a stable position.

Therefore, the rotation of the rotor, together with the adoption of the permanent magnets, allow to passively stabilize and suspend the rotor for a wide range of rotational speeds.

At very low speeds, that is during the system startup and turn off, the stability may be achieved either through bearings, or through the intervention of the coils.

It is clear that the above mentioned control devices may cooperate with an active system for suppressing abnormal oscillations that might compromise the system integrity.

From the above description, it is understood that the dynamic energy-storage device reaches the intended aims.

In particular, the use, for the rotor, of a magnetic suspension system of a passive kind, i.e. exclusively based on permanent magnets, allows to provide a dynamic energy storage device having lower cost compared to that of the similar devices of known kind. Consequently, the device of the invention is particularly suited to be used for domestic storing, or for uses that have similar requirements.

At the same time, the above mentioned passive magnetic suspension system, cooperating with the coils for the induction of the motion, distributed on both sides of the stator and operable in a mutually different way, allow to achieve optimal control on the rotational speed and on the translation of the system.

Moreover, the device of the invention employs the same components that are typically used in the dynamic energy storage devices of known kind, hence can be manufactured in a simple way through the usual and known plants.

The invention is susceptible of modifications and variants, all falling within the inventive concept expressed in the attached claims. In particular, the elements of the invention may be replaced by other technically-equivaient elements.

Moreover, the materials may be choose based on the requirements, yet without departing from the scope of the invention.

Moreover, one or more elements belonging to a specific embodiment of the invention and technically compatible with another specific embodiment of the invention may be introduced in the latter embodiment in addition to, or in replacement of, elements of the latter embodiment.

Where technical elements specified in the claims are followed by reference signs, those reference signs are included at the sole purpose to improve the understanding of the invention, hence they do not imply any limitation of the scope of protection as claimed.