Patent Description:
Wind turbines are manufactured, which comprises an electric generator having a stator assembly having an inner frame structure and an outer frame structure, which surrounds the inner frame structure and which supports the conducting coils of the electric generator. Examples of such a stator assembly are disclosed in <CIT>, <CIT>, <CIT> and <CIT>.

Such an assembly may be significantly heavy in construction, complicated to build and expensive. For large turbines such an assembly is often at the limit of manufacturability and transportation.

Therefore, it is desirable to replace such a structure with another one that is lighter and easier to manufacture.

This objective may be met by the subject matter according to the independent claim. According to the invention there is provided a stator assembly for an electric generator, as defined in claim <NUM>, in particular an electric generator for a wind turbine is provided. The stator comprises an inner frame structure having an annular shape formed around a rotational axis of the electric generator; and an outer frame structure formed around the center axis and surrounding the inner frame structure, the outer frame structure being radially distanced from the inner frame structure. The stator comprises a plurality of spokes distributed around the center axis and connecting the inner frame structure and the outer frame structure.

The described spoked stator assembly permits achieving a lighter structure with respect to the prior art. The spokes radially extend between the inner and the outer frame structure providing the required structural mechanical properties to the stator with a lower weight with respect to the prior art.

According to the invention, the outer frame structure comprises two outer rings coaxial with the rotational axis. The inner frame structure comprises an inner ring coaxial with the rotational axis Y. In such embodiments, each spoke provides a structural connection between the inner rings and the two outer rings. The use of rings permits to minimize also the weight of both the inner frame structure and the outer frame structure.

According to the invention, each spoke has a divergent shape extending from a vertex fixed to the inner ring and diverging towards the two outer rings. This provides a simple, light and effective geometry for connecting the inner ring with the outer rings.

According to embodiments of the invention, the stator further comprises an intermediate frame structure attached to at least a portion of the plurality of spokes, the intermediate frame structure being radially comprised between the inner frame structure and the outer frame structure. The intermediate frame structure may include an annular flange at least partially surrounding the inner frame structure around the rotational axis. The intermediate frame structure provides a support for attaching components of the stator, for example:.

The invention will be described in more detail hereinafter with reference to examples of embodiment, however the invention is solely defined by the appended claims.

The illustration in the drawing is schematic. It is noted that in different figures, similar or identical elements or features are provided with the same reference signs. In order to avoid unnecessary repetitions elements or features which have already been elucidated with respect to a previously described embodiment are not elucidated again at a later position of the description.

<FIG> shows a wind turbine <NUM> according to the invention. The wind turbine <NUM> comprises a tower <NUM>, which is mounted on a non-depicted foundation. A nacelle <NUM> is arranged on top of the tower <NUM>. The wind turbine <NUM> further comprises a wind rotor <NUM> having at least one blade <NUM> (in the embodiment of <FIG>, the wind rotor comprises three blades <NUM>, of which only two blades <NUM> are visible). The wind rotor <NUM> is rotatable around a rotational axis Y. The blades <NUM> extend substantially radially with respect to the rotational axis Y and along a respective longitudinal axis X. In general, when not differently specified, the terms axial, radial and circumferential in the following are made with reference to the rotational axis Y. The wind turbine <NUM> comprises an electric generator <NUM>, including a stator <NUM> and a rotor <NUM>. The rotor <NUM> is rotatable with respect to the stator <NUM> about the rotational axis Y. The wind rotor <NUM> is rotationally coupled with the electric generator <NUM> either directly, e.g. direct drive or by means of a rotatable main shaft <NUM> and/or through a gear box (not shown in <FIG>). A schematically depicted bearing assembly <NUM> is provided in order to hold in place the main shaft <NUM> and the rotor <NUM>. The rotatable main shaft <NUM> extends along the rotational axis Y. In order to provide an AC power signal being matched with a utility grid the electric output of the electric generator <NUM> is electrically connected to a power converter <NUM> provided in the nacelle <NUM>. Such converter may however also be placed outside the nacelle, e.g. within or even outside the tower <NUM>.

<FIG> show in more detail a partial representation of the electric generator <NUM>.

The stator <NUM> comprises an inner frame structure <NUM> having an annular shape formed around the rotational axis Y. According to the exemplary embodiment here described the inner frame structure is realized by means of an internal ring <NUM> coaxial with the rotational axis Y. According to other embodiments (not shown in the attached figures) the inner frame structure is realized by means of other annular structures.

The stator <NUM> comprises an outer frame structure formed around the center axis Y and surrounding the inner frame structure <NUM>, the outer frame structure being radially distanced from the inner frame structure <NUM>. According to the exemplary embodiment here described the outer frame structure is realized by means of two outer rings <NUM>, <NUM> coaxial with the rotational axis Y and having the same diameter, which is greater than the diameter of the internal ring <NUM>. The two outer rings <NUM>, <NUM> are distanced from one another along the longitudinal axis Y. The stator <NUM> further comprises a plurality of stator segments <NUM> (only one stator segment is shown in the attached figure), each comprising at least one conductor coil <NUM> in which during normal operation of the electric generator <NUM> magnetic induction takes place. According to the exemplary embodiment here described each of the stator segments <NUM> is fixed to both of the two outer rings <NUM>, <NUM>, for example by means of a plurality of bolts.

The stator <NUM> further comprises a plurality of spokes <NUM> distributed around the longitudinal axis Y and connecting the inner frame structure <NUM> and the outer frame structure <NUM>, <NUM>. The plurality of spokes <NUM> may be regularly distributed around the longitudinal axis Y. According to the exemplary embodiment here described each of the plurality of spokes <NUM> is fixed to the internal ring <NUM> and to the outer rings <NUM>, <NUM>, for example by means of respective pluralities of bolts or by welding. Each spoke <NUM> has a flat shape, basically lying along a respective radial plane including the longitudinal axis Y. Each spoke <NUM> has a divergent shape extending from a first vertex <NUM> and diverging radially outward up to a second and a third vertex <NUM>, <NUM>. At the first vertex <NUM>, each spoke <NUM> comprises two curved internal fins <NUM>, which are coaxial with the longitudinal axis Y. The two internal fins <NUM> are fixed to the internal ring <NUM>, by means of respective pluralities of bolts or by welding. At each of the second and third vertexes <NUM>, <NUM>, each spoke <NUM> comprises a curved outer fin <NUM>, which is coaxial with the longitudinal axis Y. The two outer fins <NUM> of each spoke <NUM> are respectively fixed to the two outer rings <NUM>, <NUM>. Each spoke <NUM> may comprise one or more holes <NUM> (two holes <NUM> are provided for each spoke <NUM> in the exemplary embodiment of the attached figures), for reducing the weight of the each spoke <NUM> and therefore of the stator <NUM>. According to another exemplary embodiment (not shown) of the invention each spoke may have on open configuration, extending according to a "V" shape between the first vertex <NUM> and the second and third vertexes <NUM>, <NUM>. According to another exemplary embodiment (not shown) of the invention each spoke may have a simple close triangular configuration having three vertexes <NUM>, <NUM>, <NUM>. According to another exemplary embodiment (not shown) of the invention each spoke may a simpler linear and pure radial configuration connecting the inner frame structure and the outer frame structure <NUM>, <NUM>. In the latter embodiment the outer frame structure may still comprise two rings <NUM>, <NUM>, connected to each other by means of other elements parallel to the longitudinal axis Y.

<FIG> further show an annular device <NUM> which is fixed to the rotor <NUM> (not further represented and described). The annular device <NUM> is an annular planar flange extending for <NUM>° around the longitudinal axis Y, between the inner frame structure <NUM> and the outer frame structure <NUM>, <NUM>. The annular planar flange <NUM> is therefore basically lying on plane orthogonal to the rotational axis Y. The annular device <NUM> comprises a toothed profile <NUM> provided on a circular edge facing the outer frame structure <NUM>, <NUM>. The annular device <NUM> is used for rotating the rotor <NUM> in a controlled manner, e.g. for mounting and maintenance procedures up to an angular desired position about the rotational axis Y and for slowing down a rotational movement of the rotor <NUM> in a controlled manner.

The stator <NUM> further comprises an intermediate frame structure <NUM> attached to a portion of the plurality of spokes <NUM>. According to another exemplary embodiment (not shown) the intermediate frame structure <NUM> is attached to all the spokes <NUM>. The intermediate frame structure <NUM> is radially comprised between the inner frame structure <NUM> and the outer frame structure <NUM>, <NUM>. According to the exemplary embodiment here described the intermediate frame structure <NUM> is a planar annular flange partially surrounding the inner frame structure <NUM> around the rotational axis Y, i.e. the planar annular flange circumferentially extends for less than <NUM>° around the longitudinal axis Y. The annular planar flange <NUM> is basically lying on plane orthogonal to the rotational axis Y. The stator <NUM> further comprises on or more turning devices <NUM> (five turning devices <NUM> are shown in <FIG>) attached to the stator intermediate frame structure <NUM>. Each turning device <NUM> includes an actuator <NUM> and a toothed wheel <NUM>. Each toothed wheel <NUM> is drivable by the actuator <NUM> and is engaged with the toothed profile <NUM> for turning the rotor <NUM> in a controlled manner. The turning devices <NUM> can cause the rotor <NUM> to move in a controlled manner such that it will be brought into a predetermined angular position. At the predetermined angular position, the movement of the rotor assembly will be stopped by stopping the operation of the turning device. This can be achieved simply by stopping the operation of the actuator. Additionally, a brake system and/or a mechanical blocking system may be used in order to maintain a proper angular position of the rotor assembly. The brake system is provided by means of one or more brake calipers <NUM> attached to the intermediate frame structure <NUM>. Each brake caliper is active on the annular device <NUM> for slowing the rotation of the rotor <NUM> around the rotational axis Y. The brake calipers, when activated, may also be used to prevent movement of the rotor <NUM> once brought to a stop.

Claim 1:
A stator (<NUM>) for an electric generator (<NUM>), in particular for a wind turbine (<NUM>), the stator (<NUM>) comprising:
an inner frame structure (<NUM>) having an annular shape formed around a rotational axis (Y) of the electric generator (<NUM>), the inner frame structure (<NUM>) comprising an inner ring coaxial with the rotational axis (Y); and
an outer frame structure (<NUM>, <NUM>) formed around the rotational axis (Y) and surrounding the inner frame structure (<NUM>), the outer frame structure (<NUM>, <NUM>) being radially distanced from the inner frame structure (<NUM>) and comprising two outer rings (<NUM>, <NUM>), which are distanced from one another along the rotational axis (Y),
wherein the stator (<NUM>) comprises a plurality of spokes (<NUM>) distributed around the rotational axis (Y) and connecting the inner frame structure (<NUM>) and the outer frame structure (<NUM>, <NUM>),
wherein the plurality of spokes (<NUM>) are fixed to the internal ring (<NUM>) and to the outer rings (<NUM>, <NUM>),
characterized in that
each spoke (<NUM>) has a divergent shape extending from a vertex (<NUM>) fixed to the inner ring (<NUM>) and diverges towards the two outer rings (<NUM>, <NUM>).