Synchronous machine and a process of manufacturing a synchronous machine

A synchronous machine and a process for manufacturing a synchronous machine having permanent magnets arranged within the rotor such that the leak of magnetic flux generated by the magnets is reduced and having constructive characteristics that maximize the difference in the reluctances of direct axis and quadrature axis while providing the strength necessary for the good functioning of the equipment. Magnet-fixation grooves of the rotor are provided with elongated ends in a curved shape, a first elongated end extending from the first free end to a region adjacent the end of the rotor groove bottom, the first elongated end being configured from an opening in the rotor, forming reluctance-increase channels, a second elongated end of the fixation grooves being configured so as to form the reluctance-increase channel and extending from the respective second free-end portion toward the second free-end portion of the other fixation groove of the pair.

BACKGROUND OF THE INVENTION

The present invention relates to a synchronous machine and to a process of manufacturing a synchronous machine and, more particularly, to a synchronous machine with permanent magnets on the rotor and cage for direct start.

Synchronous machines with permanent magnets are known from the prior art and comprise essentially a stator and a rotor, the rotor being substantially cylindrical in shape, having a surface portion and a rotor nucleus, and the rotor may be provided with a cage positioned on the surface portion, the cage being formed by parallel bars connected at their ends by short-circuit rings. Such a rotor configuration is known as a cage rotor and is useful in the process of starting the machine.

Inside the rotor, one may allocate pairs of permanent magnets in fixation grooves that are positioned longitudinally in the rotor nucleus (or rotor core).

As far as the electric characteristics are concerned, the rotor has a plurality of poles, which varies according to the characteristics and applications of each machine.

The permanent magnets, allocated inside the rotor, have the purpose of generating a machine-magnetization flux.

A common fact found on machines of this type is the flux leak, caused by the magnetic short-circuit of the magnets through the steel bridges formed at the following points: 1) between the grooves for allocation of the magnets of a same pole; 2) between the grooves for allocation of the magnets and the adjacent grooves of the cage 3) between the beak of the rotor grooves and the outer diameter of the rotor. This effect, as well as the flux-loss points can be better understood fromFIG. 6, which shows the magnetic flux lines.

In this regard, it would be ideal be to provide the nucleus totally cut longitudinally with magnets, as can be seen inFIG. 9, since in this way there would be no loss of magnetic flux. The situation is only hypothetical, since in this case the rotor would not have the mechanical stability required for the functioning of electric machine.

One of the solutions of the prior art that discloses the use of the application of permanent magnets is described in document U.S. Pat. No. 6,876,119. According to the teachings of this prior art, one describes a synchronous motor having a rotor provided with V-shaped magnets, through the junction of magnets set to each other. Although this solution is good from the magnetic point of view, it may present problems relating to the mechanical stability (rigidity) of the blade packet, due to the large amount of steel removed during the stamping process. This fact, allied with the fact that significant deformations occur on the steel packet during the injection of aluminum, may cause problems of collision of the rotor, which impairs the reliability of the machine.

Such problems require subsequent treatment of the rotor for reducing the collision, such as grinding, machining or a similar process. The same reference further describes the possibility of configuring the grooves close to the end of the magnets with a greater depth, so that they will approach the magnet and prevent a short-circuit of the magnetic flux from a pole to the other on the same magnet.

This solution minimizes the problems of short-circuit of magnetic flux, but makes the construction of the electric machine difficult, since a cage-rotor groove needs to be especially configured and mounted in an specific manner during the process of manufacturing the machine, requiring differentiated stamping tools, which results in complications of practical and economical nature.

Another characteristic of this reference is the fact that is presents similar reluctances on the direct axis and on the quadrature axis. In this way, however, it is not possible to take advantage of the reluctance torques in the working condition, and this occurs for the following reasons:

The torque generated by a synchronous motor can be divided into two components:(a) synchronous torque: it represents the synchronization torque between the magnet filed and the main spinning filed. It can be calculated by the following formula:

Tsinc=p2·π·f·(V1·EfXsd)·sin⁡(δ)Eq.⁢1
wherein:
p=number of poles
f=frequency [Hz]
V1=feed voltage [V]
Ef=EMF induced by the magnets [V]
Xsd=synchronous reactance of direct axis [Ω]
δ=load anglea) Reluctance torque: it appears due to the difference in reluctance between the direct axis and the quadrature axis. It can be calculated by the following formula:

The total torque generated by the motor in synchronous speed is the sum of Tsync+Trel. In this way, one can observe that the direct-axis reluctance and quadrature-axis reluctance have a great influence on the maximum torque value obtained.

More specifically, the influence of each part of torque and its variation as a function of the motor load angle can be better understood if analyzed graphically, as illustrated inFIG. 1. As shown by the equations, different values of direct axis reluctance and quadrature reluctance may lead to different values of maximum torque generated by the motor.

Taking as a basis a 2-pole motor, one can calculate the magnitude of the maximum torque for each of the configurations below, inFIG. 2a, a situation where the magnitude of the direct axis is substantially equal to that of the quadrature axis (Xd≈Xq); inFIG. 2bone illustrates a situation where the magnitude of the direct axis is smaller than that of the quadrature axis (Xd<Xq), and inFIG. 2cone illustrates a construction where the magnitude of the direct axis is greater than that of the quadrature axis (Xd>Xq).

For each of the alternatives, the Xd and Xq values were obtained by analysis of finite elements. By using the equations 1 and 2, one calculates the value of the total torque as a function of the motor load angle, as shown in the graph ofFIG. 3. As can be seen in the graph, the maximum torque is greater for the case in which Xd<Xq. Most of the gain is due to the drop in direct-axis synchronous reactance, which increases significantly the value of the loss of the part of synchronous torque.

SUMMARY OF THE INVENTION

In order to overcome problems of the prior art, the present invention has the objective of reducing the short-circuit flux close to the ends of the magnets, as well as around the cage-rotor groove, by using grooves in the rotor specifically sized for raising the reluctance to the passage of short-circuit magnetic flux and thus reduce the losses that occur according to the previous techniques. Besides, dynamics problems (collision of the rotor) that occur in the prior-art machines are overcome, whereby the necessary extent of grinding, machining and so on is diminished.

One of the solutions foresees the application of a synchronous machine that has a fixation groove for the permanent magnet, such a groove being specially sized to be provided with an elongated bridge forming a reluctance-increase channel close to the first free end. The first free end is positioned adjacent one of the groves of the rotor cage, and the elongated bridge is formed between the free end of the fixation groove and the internal end of the cage groove.

The elongated end is configured from an opening in the rotor and extends along the rotor and along the fixation groove. Such a configuration can be achieved by stamping during the manufacture of the blades that form the rotor nucleus, or still by perforation when the rotor is already mounted.

Thus, the magnetic flux that tends to leak at the end portions of the magnet is reduced, since with the opening of the channel within the nucleus the reluctance to the short-circuit magnetic flux of the magnets is raised and the losses are minimized.

Another solution of the present invention is to maintain the magnets within the rotor separated from each other and also to provide a reluctance-increase channel close to the other end of the magnet-fixation channel (or close to the second free end). In this case, since the permanent magnets are provided in pairs, the reluctance-increase channel should be configured so that it will, at the same time: (i) prevent short-circuit of the magnetic flux and (ii) maintain the strength of the rotor at levels sufficient for the characteristics of the electric machine not to be impaired when the rotor is moved.

Further, in order to prevent the magnetic flux from being short-circuited outside the rotor groove, according to the present invention one foresees a surface bridge configured through an opening of the nucleus close to the surface portion and the bottom end of the cage groove (or beak of groove), such a bridge extending along the rotor surface.

Thus, by laying bridges close to the ends of the magnet fixation grooves and opening the bridges between the cage grooves and the end surface of the rotor, it is possible to reduce the short-circuit magnetic flux at the magnet ends, and also to reduce the short-circuit magnetic flux around the cage grooves. At the same time, one manages to maintain the mechanical stability of the rotor.

Another objective of the present invention is to generate on the rotor a significant difference in direct-axis reluctance and quadrature-axis reluctance. This is achieved by taking advantage of the grooves for arranging the magnets and elongated bridges that form reluctance-increase channels, which are arranged so as to make the passage of flux towards the direct axis difficult and to facilitate it in the direction of the quadrature axis. With this solution, it is possible to take advantage of the reluctance torque generated so as to maximize the maximum torque working condition.

An objective of the present invention is to provide a synchronous electric machine having permanent magnets and direct start, wherein the leak of magnetic flux generated by the magnets is reduced and, at the same time, a rotor with strength enough for the good functioning of the machine is obtained. Another objective is to achieve an increase in the relationship of rotor reluctances between the direct axis and the quadrature axis.

Such objectives are achieved by means of a synchronous machine comprising a stator and a rotor, the rotor being substantially cylindrical in shape having a surface portion and a rotor nucleus portion, the rotor being provided with a cage positioned at the surface portion, the cage being formed by conductive bars allocated in cage grooves and rings which interconnect the bars at their ends, the rotor further comprising at least one pair of permanent magnets, the permanent magnets being allocated in magnet-fixation grooves, the magnet-fixation grooves being positioned longitudinally on the nucleus of the rotor, the fixation groove having a substantially rectangular section having an engagement region and a first free-end portion and a second free-end portion, the fixation groove extending along the rotor, the permanent magnet being fixedly associated to the rotor in the engagement region, the fixation groove being positioned in a secant manner with respect to the surface portion of the rotor, the fixation groove having a first elongated end configured so as to create a reluctance-increase channel close to the first free-end portion, the elongated end extending from the first free-end portion to a region adjacent the end of the groove bottom, the first elongated end being configured from an opening in the rotor, the opening extending along the rotor and along the fixation groove, the magnet-fixation grooves having displacement limiters adjacent the first free-end portion and the second free-end portion, the displacement limiters being formed by nucleus portions that extend inside the fixation grooves in a direction parallel to the magnet width.

A further objective of the present invention is achieved by means of a synchronous machine comprising a cage rotor, the rotor having a surface portion and a rotor nucleus, the rotor comprising at least one pair of permanent magnets, the permanent magnets allocated in magnet-fixation grooves, the magnet-fixation grooves being positioned longitudinally on the rotor nucleus, the rotor having poles having a central pole region and two end pole regions, a pair of magnet-fixation grooves being positioned symmetrically, having a substantially rectangular section having an engagement region, a first free-end portion and a second free-end portion, the fixation grooves extending along the rotor and being adjacent to each other, the permanent magnets being fixed associated to the rotor in the engaging region, the fixation groove being positioned in a secant manner with respect to the surface portion of the rotor and extending between one of the end pole region and the central pole region, the magnet-fixation grooves being constructed so as to form a reluctance-increase channel close to the first free end, the reluctance increase channel extending parallel to the bottom of the rotor groove, the reluctance-increase channel following the whole or part of the radius of the groove bottom.

Another objective of the present invention is achieved by means of a process of manufacturing a synchronous machine that has a stamping step to form elongated bridges and reluctance-increase channels close to the ends of the magnet-fixation grooves and a stamping step so as to configure a surface bridge through an opening of the nucleus between the surface portion of the rotor and the outer end of the cage grooves adjacent the magnet-fixation grooves.

DETAILED DESCRIPTION OF THE FIGURES

As can be seen fromFIGS. 4 to 7, the synchronous machine according to the teachings of the present invention comprises a stator (not shown) and a rotor10.

The rotor10is substantially cylindrical in shape and has a surface portion14and a rotor nucleus12, the rotor10being provided with grooves15provided on the surface portion of the rotor14, where a cage17is allocated, said cage17being formed by conductive windings or bars16allocated in the grooves15and rings18that interconnect the bars at their ends. The assembly may receive a finish71, as can be seen fromFIG. 10.

Further as can bee seen inFIGS. 4 to 7, which show an embodiment of a 2-pole rotor, in this embodiment the rotor10further comprises at least one pair of permanent magnets22, which are allocated on magnet-fixation grooves20, these magnet-fixation grooves20being positioned longitudinally on the rotor10nucleus. Preferably, the magnet-fixation groove20extends along the rotor10and has a substantially rectangular section having an engagement region REand a first free-end portion25and a second free-end portion26. As can be seen in detail in the figures, each permanent magnet22is fixed associated to the rotor10in the engagement region RE.

The rotor10has poles that extend along a number of cage grooves16, so that for the sake of explanation in the 2-pole configuration one can divide each pole as having a central pole region CPand two end pole regions E.

With regard to the positioning of the magnet-fixation grooves20, they are positioned in a secant manner with respect to the surface portion14of the rotor10and extend between one of the end pole regions EPand the central pole region CP, the fixation grooves coming close to the groove bottom (or beak)15′ of the cage grooves16.

As can be seen in detail inFIG. 6, the fixation groove22has a reluctance-increase channel50near the first free end25, the reluctance-increase channel50being configured so as to form an elongated bridge, built so as to accompany the whole or at least most of the groove bottom15′ of adjacent rotor. This configuration can be seen in greater detail inFIG. 7.

Preferably, one opts for configuring one of the ends of the magnet-fixation groove so as to form a first elongated end101, so that it will extend from the first free-end portion25to the region adjacent the groove-bottom end15′, so as to obtain a reluctance-increase channel50that is as thin as possible. In this way, one preferably opts for configuring the channel walls parallel to the end of the groove bottom15′.

As can be seen inFIG. 7and mainly in detail inFIG. 13, the first elongated end101for a 2-pole motor and the first elongated end103for a four pole motor have a curved or engaging shape which involves substantially the surroundings of the groove-bottom end15′.

This curved or engaging shape as shown inFIGS. 7 and 13, covers not only the groove-bottom end15′, but also the surrounds of it until a linear region of the groove as shown in the embodiment ofFIG. 13. In this case, as already mentioned, the reluctance-increase channel50follows the whole or part of the radius of the groove-bottom15′, accompanying, according to this configuration, a groove flux.

Furthermore, as shown inFIG. 7, the first elongated end101has a reluctance-increase channel50that embraces part of the radius of the groove bottom, thus reducing flux leakage.

The embodiment of the reluctance-increase channel50shown inFIG. 13, due its engaging shape follows the whole radius of the groove-bottom15′ thus embracing a major part of the groove-bottom15′.

Both embodiments of the present invention allow to increase the reluctance of the flux channel and the performance of the motor, when compared to the reluctance channels of the prior art. With these embodiments shown inFIGS. 7 and 13, the present invention result in a construction that is very close to the hypothetical ideal model that is shown inFIG. 9.

A mathematical model of the present invention and its simulation results show that the feature related to the embracing of the part of the radius of the groove bottom offers an improved performance of the motor, since the reluctance torque is increased.

Since the magnet-fixation grooves20are position positioned in “V” and are arranged in pairs, each groove of the pair being positioned symmetrically, extending from the end pole regions EPto the central pole region CP, the fixation groove pair20coming close to and adjacent the central pole region CPand the respective second end portions26remaining adjacent each other. In this case, the magnet-fixation groove is configured so as to form a second elongated end102forming the reluctance-increase channel60extending from the respective second free-end portion26towards the second free-end portion26of the other fixation groove20of the pair, so that this channel will be adjacent the central pole region CP.

As can be seen inFIGS. 6 and 7, each of the permanent magnets22has a rectangular cross section having first and second terminations, and between the pair of fixation grooves20the second elongated end forming the reluctance-increase channel60is configured so as to extend in the radial direction with respect to the geometrical center of the rotor10, in the direction of a direct axis, so as to form a second elongated end102forming a rotor10nucleus12fillet with an extension24in the radial direction that is substantially greater than in the region of the reluctance-increase channel60with respect to a width23of the magnet-fixation groove20.

As can be seen inFIGS. 8 and 11, the reluctance-increase channel, which may be configures so as to have parallel (see reference number60) or non-parallel (see reference number80) side edges, both configuration being made so as to meet simultaneously the motor performance restrictions, as well as the respective strength of the rotor10. In all the cases, one opts for extending the second elongated ends102located in the central pole region CP, so that they will be positioned adjacent the other elongated end of the pair and positioned very close to each other.

In addition, in order to prevent the magnetic flux from the permanent magnets22from propagating through the tips of the cage grooves16close to the free ends of the magnet-fixation grooves20, these cage grooves16are built so as to have a surface bridge70configured through an opening of the nucleus12, this surface bridge70being provided between the surface portion14of the rotor10and the outer end of the outer end of the cage groove16and extending along the surface portion14of the rotor10.

An essential feature of the present invention is related to the use of the surface bridge70configured in a particular way, such as shown inFIG. 7, wherein the opening of the nucleus12is located radially with regard to its respective reluctance-increase channel50.FIG. 7shows the reluctance-increase channel50and its correspondent surface bridge70in order to avoid the flux leakage.

Moreover, as can be seen inFIG. 6, the surface bridge70is applied only radially with regard to its respective reluctance-increase channel and not in all cage grooves such as described in the prior art. The present solution offers an improved mechanical (mechanical stability) and electromagnetic performance, since the surface bridge70(opening) is not distributed in all cage grooves, while the flux has being preserved.

The combination of the surface bridge70(opening) feature with the reluctance-increase channel, according the teachings of the present invention, allows the synchronous motor achieve a optimized solution when compared to the prior art.

The concepts of the present invention are applicable to any number of rotor poles. One can see inFIGS. 12 and 13how the application of this concept for the 4-pole rotor configuration would be.

In this embodiment, one can observe that each fixation groove20extends between an end pole region EPto another subsequent end pole region EP, forming a third elongated end103, which is configured so that the reluctance-increase channel50can be configured close to the groove bottom15′, surrounding it parallel to the respective profile, in the same way as in the first embodiment of the present application, that is to say, close to the first free end25.

Since in the present embodiment the angle between the fixation grooves20is of 90°, one can opt for configuring the inner region of the ends of the fixation grooves100, so that it will have parallel side edges60′ as can be seen in detail fromFIG. 13, or non-parallel (not shown), as shown inFIG. 11that illustrates the other embodiment.

Further, in this configuration one could opt for building a 4-pole machine further having a surface bridge70provided between the surface portion14of the rotor10and the outer end of the cage groove16and extending along the surface portion14of the rotor10, just as in the other configuration described. As already mentioned, one should pay attention to the fact that the mechanical stability should be taken into consideration in order to maintain the rotor10rigid enough for the design conditions.

In view of the need to build machines with a larger number of poles, it is enough to apply combinations of the configurations described in the two configurations above, using the concept of providing the fixation grooves20with elongated bridges that form reluctance-increase channels50, thereby diminishing the short-circuit of the magnetic flux.

Further on the base of the embodiments suggested in the above-described figures, one also presents design alternatives that bring variations that can facilitate the process of manufacturing the rotor and/or guaranteeing the integrity of the motor during its functioning. One of these embodiments is illustrated inFIGS. 14 and 15, which show alternatives for the shape of the ends of the fixation grooves, which can be used for the purpose of facilitating the manufacture process and preventing the displacement of the magnet22during magnetization and/or normal functioning of the machine, the basic principle of these alternative shapes being the use of displacement limiters200,201adjacent the end portions25,26of the magnet, the limiters being formed by nucleus12portions that extend inside the magnet-fixation groove20in a direction parallel to the magnet thickness, forming protrusions that limits its displacement to the sides. In this magnet fixation form one can opt for the configuration illustrated inFIG. 14, where only one of the sides of the groove has displacement limiters200,201.

At each end one may opt for design the limiter coming from one side opposite the groove, or may configure the limiters whenever the came from one side of the groove, or still provided only at one end portions, as can be seen from the configuration illustrated inFIG. 15. The other characteristics of the synchronous machine remain unchanged.

In addition, according to the present invention one provides a process of manufacturing a synchronous machine, which has two stamping steps to form the reluctance-increase channels50and60near the magnet-fixation grooves, as well as comprises a stamping step for making an opening70of the nucleus12between the surface portion and the outer end of a cage groove.

More particularly, this type of stamping process is advantageous when compared to the prior art solutions, because it is possible to manufacture the magnetic fixation grooves and the first101and second102elongated ends during the stamping process, avoiding additional costs related to the use of other materials or elevated development time, such as described in prior art techniques.

Furthermore, as already mentioned, the displacement limiters200,201have been projected on opposite sides, as shown inFIG. 14, in order to maintain the mechanical stability of each magnetic-fixation groove. In addition to that, one can observe that the displacement limiters200,201are positioned at opposite sides of the magnetic poles of the magnet22.

More specifically, one displacement limiter200extends from one side of the pole while the other displacement limiter201extends from the opposite side of the pole and also, as already described, the displacement limiters are provided at the opposite sides of the magnet-fixation groove20itself.

This is particularly advantageous considering the mechanical forces which the magnet22is subjected to during stat-up and also during the magnetization of the synchronous machine as the forces will dislocate the magnet22inside the magnet-fixation groove20, misaligning the magnet22not only with respect to the magnet-fixation groove20itself but also with respect to the first and second elongated ends101,102. The magnetic forces are generated by the electromagnetic field and its interaction as can be seen inFIG. 8,

In addition to that, the displacement limiters200,201, according to the teachings of the present invention are made during the stamping process, such as the first101and second102elongated ends, in order to help the motor manufacturing which can be done in a much simpler process when compared to the prior art, which uses fixation pins, or the like.

In terms of performance, as mentioned before, and when compared with the prior art, the gains of the present invention are significant. The use of the elongated bridges and of the elongated ands guarantees greater utilization of the flux generated. Thus, in comparative terms a motor built according to the teachings of the prior art has flux utilization ranging from 80 to 85%, whereas with a motor built according to the teachings of the present invention the performance ranges from 85 to 90%.

Finally, the simulation results show that the present solution, related to the use of a surface bridge (70) combined with its respective reluctance-increased channel, provides a better flux distribution, or more precisely, a reduction of the flux losses in a range around 7%.

Other results show that the total useful flux has increased from 73% to 87% according to the approach of the present invention.

Preferred embodiments having been described, one should understand that the scope of the present invention embraces other possible variations, being limited only by the contents of the accompanying claims, which include the possible equivalents.