WO2007048211A2

WO2007048211A2 - Permanent magnet rotor

Info

Publication number: WO2007048211A2
Application number: PCT/BR2006/000218
Authority: WO
Inventors: Mário Célio CONTIN; Carlos Eduardo Guarenti Martins; Valmir Luís STOINSKI; Célia Miwa SIGUIMOTO; Paulo Roberto Lorenzi; Hugo Gustavo Gomez Mello
Original assignee: Weg Equipamentos Eléctricos S.A.
Priority date: 2005-10-25
Filing date: 2006-10-19
Publication date: 2007-05-03
Also published as: WO2007048211A3; BRPI0504776A

Abstract

The present utility patent refers to a rotor with permanent magnets to be used particularly in synchronous motors, being the format of the external part sinusoidal (14). The location and the format of the cross section of the 2permanent magnets (13) are adapted in such a way that the density of the magnetic flux at the air gap, between the stator (11) and the rotor (12), varies substantially in a sinusoidal way Additionally, said rotor (12) comprises holes (22) at the interpolar area which, together with the magnet cavities (17), form bridges (26) to support the shoes (23) serving as barriers to the dispersion of the exciting magnetic flux of the permanent magnets (13).

Description

PERMANENT MAGNET ROTOR

The present invention patent refers to a permanent magnet rotor, to be used particularly in a synchronous motor. Invention History Alternating current motors are used in applications in general because the supply of electrical power is made by alternating current. Among such applications, the main kinds are synchronous and induction motors.

Usually, to obtain constant frequency supply, which is the case of motors supplied directly by electrical power, the synchronous motor works at constant speed.

The induction motor usually works at constant speed, which slightly varies with the mechanical load applied to the shaft. Due to its simplicity, robustness and low cost, it is the most used motor, being adequate for almost all kinds of actuated machines being used today. Nowadays, it is possible to control the speed of induction motors with the help of frequency converters.

Regardless of all the development motors have been through since they were first invented, the costs involved in the manufacturing of synchronous motors still limit them to higher power applications and to applications where it is essential to control speed and torque. However, within this class of motors, a new kind of construction has appeared which, to substitute the wound rotor fed by rings, uses permanent magnets installed in the rotor, thus creating a magnetic field around the rotor, which is the characteristic of synchronous motors. A synchronous motor with permanent magnets is an interesting alternative to drive machines at low speed with no need to use a mechanical speed gearbox. It can also be used to start at high angular speed, for example in air compressors, and it can be coupled directly, without speed increasers. In either case, at low or high speed, it is provided with adequate multiplicity of magnetic poles.

Motors that currently use this technology show drawbacks such as high harmonic content which causes oscillation in the motor torque, and consequently in its rotation. The presence of harmonic components leads to an increase in the loss of iron of the stator and to losses in the iron surface by skin effect, causing the operation temperature to rise and consequent loss of efficiency.

Another problem shown by those motors is low starting torque and instability due to sudden load variations. Aiming at correcting those problems, a rotor with permanent magnets has been developed for synchronous motors which objective is to be simpler, to significantly reduce the harmonic components generated by the rotor magnetic field and low cost.

Another objective of the present invention is a rotor with permanent magnets that allows for the precise control of speed and torque in the motor shaft.

Also an objective of the present invention is a rotor with permanent magnets inserted for synchronous motors, manufactured according to productive processes already known to asynchronous induction machines. To have a clearer view of the present invention rotor with permanent magnets, follow the drawings enclosed which are referred to for better understanding of the detailed description that follows, without excluding any other equivalent construction, where: - figure 1 represents a diagrammatic axial section of a synchronous motor with a rotor provided with permanent magnets, air gaps, a stator and with the magnet in a position orthogonal to the radial direction of the motor shaft; figure 2 represents an enlarged diagrammatic axial section of the rotor with permanent magnets, with the indication of a magnet in a position orthogonal to the radial direction of the rotor shaft; figure 3 represents a diagrammatic axial section of a synchronous motor with a rotor provided with permanent magnets where the magnet is placed in a radial direction in relation to the rotor central shaft;

figure 4 represents a diagrammatic axial section of a synchronous motor with a rotor provided with permanent magnets, the magnets positioned in such a way that they form a "V" pointing to the stator;

figure 5A represents a diagrammatic axial section of the rotor;

figure 5B represents a partial view of the rotor, with the indication of weld fillets done in a longitudinal way to the former;

- figure 6 represents a diagrammatic axial section of air barriers constructed in the rotor and magnet; and

figure 7 represents a diagrammatic axial section of the rotor with permanent magnets, with an indication of damping bars connected among themselves through short rings. Invention Description

The present utility patent refers to a rotor (12) with permanent magnets (13) for a synchronous-type motor, where said rotor is provided with a plurality of permanent magnets (13) which form exciting poles that generate magnetic flux waves of sinusoidal profile. Said motor usually used in applications with switch mode power supply, both of imposed voltage and imposed current, and that allows controlling rotation and/or the position of the shaft motor (31).

The rotor (12) with permanent magnets (13) is provided with poles (23) of sinusoidal profile (14), and cavities (17) with adequate format to house the permanent magnets (13). Said magnets (13) may be comprised of Neodymium- Iron-Boron (NdFeB), Samarium-Cobalt or Ferrite, and are preferably placed in the cavities (17) to prevent them from being displaced by the movement of the rotor (12).

The core of the rotor (12) may be any kind known to a technician, such as ferromagnetic cylindrical core, laminated or solid.

To allow precise control of the rotation and/or of the angular position, the rotor (12) may also contain an auxiliary device which may correspond to a device known as "Resolver" or to a device known as "Encoder" or still to a device known as Hall effect sensor. Said rotation and/or angular position control can also be obtained in a fourth construction, through the feeding of a synchronous motor with permanent magnets by means of a switch mode power supply where there is no need for the motor to have a sensor, which is known to a technician as "sensorless". Figure 1 shows a partial view of a synchronous motor (1) with a rotor (12) provided with permanent magnets (13) and sinusoidal poles (14), with a rotational axis (31), a stator (11) and the rotor (12), which has a reluctance direction of the shaft in quadrature (20) and a reluctance direction of the direct shaft (18); said rotor(12) comprises a sinosoidal geometry (14) that presents a sinosoidal magnetic flux (15) density and longitudinal holes (22) of field dispersion. The rotor (12) has its permanent magnets (13) installed in rectangular cavities (17), and comprises the support bridges (26) of the pole shoes (23). The construction of the rotor (12) is made in a way that the external surface relief has poles with magnetically sinusoidal profiles (14), allowing the permanent magnets (13) to create exciting polar magnetic fluxes (15) with sinusoidal profiles along the polar pitch at the air gap area, assuring a significant reduction of the harmonic components causing harmonic oscillations in the torque and iron losses in the stator (11) armature and surface losses on the rotor (12), improving the performance and efficiency of the motor.

Still, an adequate distribution of coils in the stator (11) armature winding allows for a sharp reduction of the unwanted harmonic components in the magnetic motive force and consequently in the reaction magnetic flux of the stator (11) armature.

Thus, the number of grooves per pole and per phase is made by means of adequate multiplicity so that there is the necessary distribution of coils that comprise the winding of said stator (11) armature. Being the synchronous motor constructed with protruding poles, and using internal permanent magnets (13) in the rotor (12), as described above, the latter now presents magnetization directions of the direct shaft (18) and of the shaft in quadrature (20), and each of these directions (shafts) may have different magnitudes of magnetic reluctance.

This motor (1), with distinct directions of direct and in-quadrature magnetization has magnetic reluctances of both the direct shaft (18) and of the shaft in quadrature (20), producing torque components due to those distinct reluctances. The motor (1) has a torque component originated from mutual inductance of the direct shaft and reluctance torque component due to the differences between the magnetic reluctances of the direct shaft and of the shaft in quadrature.

Due to the magnetic flux in quadrature produced by the armature reaction of the motor (1) statoric winding, which occurs at a phase displacement of 90° in relation to the exciting flux of the direct shaft (18) produced by the permanent magnets (13) of the rotor (12), the rotoric magnetic poles may be saturated as this crossed flux (in quadrature) adds to the direct shaft flux resulting in higher magnetic inductions at the magnetic poles areas. To avoid or soften those crossed fields (fluxes), flux barriers (22) may be used on the rotoric poles at the polar shoes (23) area to produce big magnetic reluctance to the passage of the flow in quadrature of the reaction of the stator (11) armature thus reducing the resulting magnetic reluctance and the correspondent degree of saturation of those rotoric poles. These flux barriers (22), as they are conceived, easily allow the passage of the magnetic flux of the direct shaft (18), and at the same time prevent or make it significantly more difficult for the flux of the shaft in quadrature (20) to pass. Additionally to those flux barriers (22), the sinusoidal air gap, through the variation of the reluctance along the polar pitch, can also be used to soften the traffic of crossed flux of the shaft in quadrature through the polar shoes (23).

The "sinusoidal" air gap is constructed with magnetic reluctance which gradually grows in a sinusoidal way from the center of the pole, on the central line of the direct shaft (18), until the center of the interpoles on the line of the shaft in quadrature (20).

Due to that, the air gap shows a magnetic reluctance relatively bigger to the passage of the lines of the magnetic flux in quadrature, also helping to reduce the saturation of the polar shoes (23). For better performance and efficiency of the motor (1), barriers (24) with low magnetic permeability are foreseen at the interpolar area to avoid the dispersion of the magnetic flux of the permanent magnets (13).

Those barriers (24), when constructed in the appropriate way, besides avoiding that an important part of the fluxes of the direct shaft of the permanent magnets (13) is dispersed through the interpolar areas also promotes a considerable increment in the magnetic reluctance in the direction of the shaft in quadrature(20), especially when associated to the flux barriers (22) on the rotoric poles in the polar shoes area (23), allowing the minimization of the values of the magnetic fluxes in quadrature, reducing the loss of iron at the stator (11) core and at the rotor (12) surface.

Said barriers (24) are of elongated cross section, and are positioned in radial direction to the central shaft (18) of the rotor (12), preferably they are provided with an elliptic cross section.

The format of the relief (14) of the external surface of the rotor ferromagnetic core and the placement of the magnets (13) inside the rotor (12) are adapted so that the profile of the magnetic flux densities along each polar pitch at the air gap area between the stator (11) and the rotor (12) is substantially sinusoidal (14), as shown in figures 1 , 3 and 4.

According to the preferable configuration of the invention, the permanent magnets (13) have a cross section substantially rectangular in shape, and are placed orthogonally to the radial direction of the rotoric shaft.

Figure 5B shows a side view of the rotor (12) which, in this particular example, is comprised of ferromagnetic material plates that can be attached to each other through weld fillets (16) parallel to the rotoric shaft in its external peripheral area (rotor external surface) to form a sufficiently hard rotoric core.

Besides, the weld fillets (16) may function as a winding damper placed at the peripheral part of the rotor (12), being the intensity of that damper proportional to the conductive cross section of each fillet and to the number and position of those fillets (16) in relation to each rotoric pole.

Figure 2 shows a detail of the rotor (12) of the synchronous motor provided with a rotor with permanent magnets (13) and sinusoidal poles (14), where the dispersion flux barriers (22) provided at the interpolar area of the rotor (12) are comprised of preferably rounded holes, with adequate sizes and positions relatively to the cavities (17) for the placing of the permanent magnets (13) so that the dispersion flux of the magnets is minimized.

These flux barriers (22) are characterized by low magnetic permeability of air inside them, and by high magnetic reluctance shown by the bridges (26) that support the polar shoes (23), between the magnets (13) and the flux barriers (22), as shown in figures 1 , 2, 3 and 4.

The magnetic reluctance at those bridges (26), between the magnets

(13) and the flux barriers (22), is increased due to magnetic saturation as the small flux dispersed through those bridges (26) is enough to cause saturation, causing magnetic permeability to be close to the air, thus creating a barrier to the passage of more dispersed flux.

By placing holes, preferably round ones, to provide the dispersion flux barriers (22) at the interpolar areas, as shown in figures 1 , 2, 3 and 4, the reluctance of the magnetic path in quadrature (20) which coincides with the interpolar region becomes relatively high, especially when associated with the barriers (24) on the rotoric poles in the area of the polar shoes (23), minimizing the traffic of the components of the flux in quadrature (20).

By decreasing the flux in quadrature, the saturation effects on the magnetic poles are reduced due to the crossed fields, and iron losses are reduced at the stator (11) core and at the rotor (12) surface, improving the efficiency of the motor.

Also, considering that the air gap itself is constructed with magnetic reluctance which gradually grows in a sinusoidal way from the center of the pole, on the central line of the direct shaft (18), to the center of the interpoles on the line of the shaft in quadrature (20), as shown in figures 1 , 3 and 4, there will be an increment in the reluctance of the shaft in quadrature.

Figure 6 shows barriers (24) of crossed flux that substantially reduce the saturation effects in the polar shoes (23). Those air barriers (24), due to the geometry used, show high magnetic reluctance to the crossed magnetic fluxes originating from the fluxes in quadrature produced by the reaction of the stator (11) armature of the statoric winding, while easily allowing the magnetic flux of the direct shaft originating from the exciting flux provided by the set of permanent magnets (13) inside the rotor (12).

Figure 7 shows an alternative construction of the rotor (12), where it is provided with damping bars (25) interconnected in each outmost part of the rotor (12) by means of rings (27). Those damping bars (25), according to the classic theory, are used to dampen sudden load variations, providing more stability to the operation of the motor (1), besides providing the rotoric winding so that the motor (1) can start as if it were an induction motor.

Those damping bars (25) provide the motor (1) with a squirrel cage that corresponds to a rotoric winding such as that used in induction motors, allowing the synchronous motor (1) with permanent magnets (13) to operate fed by a sinusoidal source or by a switch mode power supply with voltage and frequency control, and no need for a device to control the position of the rotor (12). The stability of the motor (1), in this case, can be obtained by the damping provided by those bars (25) with no need for an additional position control. Figure 3 shows a variation of the position of the magnets (19) in the rotor (12), where they remain placed in radial direction in relation to the shaft (31) of the rotor (12). In this construction, the shaft (31) of the rotor (12) shall be of nonmagnetic material.

Figure 4 represents another variation of the position of the magnets (21a and 21 b) where each pair forms a "V" pointing to the stator (11 ).

A technician will readily observe, from the drawings and the description presented, several ways to carry out the invention without moving away from the scope of the claims enclosed.

Claims

1- ROTOR WITH PERMANENT MAGNETS characterized by comprising a sinusoidal external geometry (14), and permanent magnets (13, 19, 21a, 21b) adapted in such a way that the magnetic flux density curve profile (15) in the air gap, between the stator (11) and the rotor (12), changes substantially with the sinusoidal format (14).

2 - ROTOR WITH PERMANENT MAGNETS according to claim 1 , characterized by the fact that the format of the crossed section of the permanent magnets (13) is substantially rectangular and is positioned orthogonally to the radial direction of the rotor shaft (12).

3 - ROTOR WITH PERMANENT MAGNETS according to claim 1 , characterized by the fact that the rotor (12) is made of ferromagnetic plates connected with weld fillets (16) formed in the outmost circumferential surface of the rotor (12) and parallel to its longitudinal shaft (31). 4 - ROTOR WITH PERMANENT MAGNETS according to claim 3, characterized by the fact that there is at least one weld fillet (16) in each pole of the rotor (12).

5 - ROTOR WITH PERMANENT MAGNETS according to claim 1 , characterized by the fact that the form of the external part of each rotor (12) plate, when flattened, is a substantially sinusoidal (14) curve with maximum amplitudes located at the centers of each rotoric pole of the shaft (18).

6 - ROTOR WITH PERMANENT MAGNETS according to claim 1 , characterized by the fact that the cavities (17) used to introduce and seat the permanent magnets (13, 19, 21a, 21b) are located on the ferromagnetic plates of the rotor (12), and are positioned in such a way that the spatial waves of the magnetic fluxes (15), originated from the permanent magnets (13, 19, 21a, 21 b), have their maximum amplitudes at the air gap area, and are located in such a way as to coincide with the line of the direct shaft (18). 7- ROTOR WITH PERMANENT MAGNETS according to claim 1 , characterized by the fact that the format of the cross section of the permanent magnets (19) is substantially rectangular, and that they are placed in radial direction in relation to the central shaft of the rotor (12) coinciding with the line of the shaft in quadrature (20). 8 - ROTOR WITH PERMANENT MAGNETS according to claim 1 , characterized by the fact that the format of the transversal section of the permanent magnets (21a, 21 b) is substantially rectangular, and that the permanent magnets (13) are tilted in relation to the direct shaft (18) so that each pole of the rotor (12) comprises two permanent magnets (21a, 21 b) arranged in V format, and so that maximum amplitude of the magnetic flux wave (15) produced by those magnets substantially coincides with the line of the direct shaft (18).

9 - ROTOR WITH PERMANENT MAGNETS according to claim 1 , characterized by the fact that in the area of the interpoles, which are centralized on the lines of the shaft in quadrature (20), there are flow barriers (22), preferably round, which correspond to the length of the substantially sinusoidal (14) wave of the shape of the external periphery on the interpolar area.

10 - ROTOR WITH PERMANENT MAGNETS according to claim 1 , characterized by the fact that the support bridges (26) of the polar shoes (23), between the flux barriers (22) and the cavities(17) where the permanent magnets (13) will be placed, are made sufficiently narrow to present a high degree of magnetic saturation with a dispersion magnetic flux of the magnets substantially reduced and, at the same time, sufficiently wide to safely withstand the mechanical efforts due to centrifugal forces on the polar shoes.

11- ROTOR WITH PERMANENT MAGNETS according to claim 1 , characterized by the fact that in the polar shoes (23) area of the rotor (12) there are barriers (24), which are made in a radially elongated way and which are narrow in relation to the rotor shaft (12). 12 - ROTOR WITH PERMANENT MAGNETS according to claim 1 , characterized by the fact that on the polar shoes (23), near the external periphery of the rotor (12), there are damping bars (25) which are short-circuited at both ends that surpass the plates pack by means of short circuit rings (27), forming a squirrel cage that follows the geometric profile of the external circumference of the rotor (12).