The present application claims priority from Japanese application serial No. 2010-178298, filed on Aug. 9, 2010, the content of which is hereby incorporated by reference into this application.
The present invention relates to a permanent magnet rotating machine and, more particularly, to a permanent magnet rotating machine suitable as a rotating machine having a medium or large capacity such as a wind turbine generator or a generator mounted on a vehicle.
As rotating machines have been compact and highly efficient, permanent magnet rotating machines have been used in various fields in recent years. When permanent magnets are used, however, there is a problem in that not only electrical characteristics but also strength characteristics are restricted.
In particular, rotating machines with an output capacity in the several megawatt class, such as generators mounted in railroad vehicles and wind turbine generators, use large quantities of permanent magnets, so restrictions on strength characteristics become prominent. With railroad generators, which are connected directly to engines, vibration and shock caused by the engines and during running are applied to the generators, so high strength characteristics are demanded. With wind turbine generators, the service life of which is assumed to be about 20 years, so long-term durability is demanded.
To respond to this situation, conventional technologies for permanent magnet rotating machines that are compact, highly efficient, and highly reliable are disclosed in Patent Documents 1 to 3.
In Patent Document 1 above, to increase efficiency, gaps between the rotator and stator are increased near parts between magnetic poles, in comparison with a region near the center of the magnetic pole to prevent magnetic flux concentration and reduce harmonic components included in magnetomotive force waveforms.
When the gap between the rotor and stator is increased near parts between magnetic poles, however, the advantage of the salience structure of the rotating machine may be reduced and reluctance torque may also be reduced. The iron core (bridge on the internal diameter side) between two magnet insertion slots provided for one pole is under high stress due to centrifugal force. Therefore, stress exerted on the bridge may not be reduced just by providing a bridge between magnet insertion slots to divide the magnet insertion slots as described in a second embodiment in Patent Document 1, and thus an effect to reduce peak stress may be small.
In Patent Document 2, peak stress is reduced by preventing corners of a magnet embedded in a rotor iron core from being locally brought into contact with the rotor core.
Since the distance between an end of each magnet insertion slot on the external diameter side of the rotor and the outer circumference of the rotor is not constant, however, stress may concentrate at the shortest distance and thereby peak stress may be increased. Furthermore, the magnet insertion slot is shaped so that the corners of the magnet are not brought into contact, the cross sectional area of the iron core (bridge on the external diameter side) between the end of the magnet insertion slot on the external diameter side of the rotor and the outer circumference of the rotor is increased, so leakage magnetic fluxes, which cause a shorting between magnetic fluxes through the bridge on the external diameter side, may be increased and thereby the electrical characteristics may be worsened.
In Patent Document 3, leakage magnetic fluxes of magnets are reduced by restricting directions in which the magnets are magnetized.
When directions in which magnets are magnetized are restricted as in Patent Document 3, however, the magnets are not uniformly magnetized, as in a case in which flat plate magnets are magnetized. To achieve uniform magnetization, a specific mold is needed, resulting in a high cost. It can also be, considered that a magnet cannot be easily inserted into the magnet insertion slot provided in the rotor iron core. An end of each magnet insertion slot on the internal diameter side of the rotor is parallel to the center of the magnetic pole. This shape causes stress concentration on the corners of the magnet insertion slot on the internal diameter side of the rotor, so peak stress may be increased.
An object of the present invention is to provide a permanent magnet rotating machine that can reduce peak stress and leakage magnetic fluxes from magnets, can have superior electrical characteristics, and can reduce stress.
A permanent magnet rotating machine according to the present invention has a stator, in which armature windings are formed in a plurality of slots formed in a stator iron core, and also has a rotor, in which two magnet insertion slots are formed for each pole in a rotor iron core and one permanent magnet is embedded in each magnet insertion slot with polarity alternating for each pole; a wall at an end of the magnet insertion slot on an external diameter side of the rotor is formed so as to be parallel to the outer circumference of the rotor, and a wall at another end of the magnet insertion slot on an internal diameter side is formed in an arc shape.
More specifically, the permanent magnet rotating machine has a stator, in which armature windings are formed in a plurality of slots formed in a stator iron core, and also has a rotor, in which two magnet insertion slots are formed for each pole in an rotor iron core in a V shape when viewed from the outer circumference of the rotor and one permanent magnet is embedded in each magnet insertion slot with polarity alternating for each pole; a wall at an end of the magnet insertion slot on an external diameter side of the rotor is formed with three arcs having different curvatures, one of the three arcs being parallel to the outer circumference of the rotor, and a wall at another end of the magnet insertion slot on an internal diameter side is formed in an arc shape.
The structure described above enables the cross sectional area of the iron core of a bridge on the external diameter side to be reduced, so leakage magnetic fluxes of magnets can be reduced. Furthermore, the width of the bridge on the external diameter side becomes constant, so stress can be distributed, preventing stress concentration and reducing peak stress. On a bridge on the internal diameter side, stress is widely distributed over the entire bridge. Therefore, when the wall at the other end of the magnet insertion slot on the internal diameter side is formed in an arc shape, this stress concentration can be prevented and peak stress can be reduced.
The permanent magnet rotating machine according to the present invention can reduce leakage fluxes from magnets, peak stress and stress, and can also have superior electrical characteristics.
Other objects and features of the present invention will be clarified in the embodiments described below.
Embodiments of the present invention will be described below with reference to the drawings. In the drawings, like elements are denoted by like reference numerals.
As shown in the drawing, a rotor 1, in which permanent magnets are provided, is attached to a shaft 3, and a stator 2 is oppositely disposed with a predetermined distance left between the rotor 1 and stator 2. A coil 4 is embedded in the stator 2.
As shown in
As shown in
Effects in the first embodiment will be described with reference to
Table 1 compares peak stress exerted to rotors having the shapes shown in
Table 2 compares no-load inductive voltage (which is increased when the leakage magnetic flux is small) between shapes in
Accordingly, when compared with the structure shown in
This embodiment can be efficiently used under the conditions described below.
In graphs described below, the peak stress represented in pu takes a value of 1.0 when R2 is equal to R1, W is equal to T, and L is equal to M.
First,
Next,
Next,
Therefore, conditions to efficiently use this embodiment is that R2 is larger than or equal to R1, W is smaller than or equal to T, and L is larger than or equal to M.
Appropriate values of W and T in
The stress in
It is found from
It is found from
Although six poles are shown in the drawing, it will be appreciated that the use of any other number of poles can provide the same effect. The coils in this embodiment are embedded in the stator by distributed winding, but concentrated winding can also provide the same effect.
In this embodiment, a range in which the flat-plate magnet 7 moves in the width direction is narrowed by the step. Accordingly, when the rotor rotates, movement of the flat-plate magnet 7 in the magnet insertion slot 17 can be suppressed, preventing the magnet from being damaged due to vibration and shock. When the flat-plate magnet 7 is inserted into the rotor iron core 16, movement of the flat-plate magnet 7 in the magnet insertion slot 17 can also be suppressed, improving the productivity of the rotor.
Since W is smaller than Wg, however, an angular part C1 is formed in the magnet insertion slot 17, in correspondence to an angular part of the flat-plate magnet 7. Stress exerted to the angular part C1 is then increased. To solve this problem, an end wall 18 of the magnet insertion slot 17 on the internal diameter side may be formed by combining two arcs having different curvatures Ri1 and Ri2.
Then, the stress exerted to the angular part C1 can be distributed to the part having the curvature Ri2, so the stress to the angular part C1 can be reduced, enabling the peak stress over the entire rotor to be reduced. To efficiently reduce stress, Ri1 is preferably larger than Ri2.
Furthermore, a magnet insertion slot 20 may be used, which is hollowed out at a part 19, as shown in
Since the angular part of the magnet insertion slot 20 has a larger curvature than the angular part of the flat-plate magnet 7, the angular part of the magnet does not locally touch the rotor iron core and thereby the peak stress can be reduced.
The positional relationship between the magnet insertion slots 17 and 20 and the rotor iron core 16 and their sizes are the same as in the first embodiment. Although six poles are shown in the drawing, it will be appreciated that the use of any other number of poles can provide the same effect.
In addition to the structures in the first and second embodiments, permanent magnets 22 disposed in a rotor iron core 21 are divided in the width direction as shown in
In addition to the structures in the first to third embodiments, as shown in
In this structure, a duct space 27 is formed by duct pieces 26 provided among rotor iron cores 25 formed by laminating thin steel plates and among stator iron cores formed by laminating thin steel plates, as shown in
Even when the axial duct 23 for draft cooling and duct spaces 27 and 29 are provided, the effects described in the first to third embodiment can be expected.
Although, in this embodiment, two duct pieces 26 are disposed in each of the axial directions of the permanent magnet rotor and stator, any other number of duct pieces 26 may be disposed. Although the duct pieces 26 are disposed for both the rotor 1 and stator 2, they may be disposed only for the stator 2.
A permanent magnet rotating machine 31 having a cantilevered structure, in which a single bearing 30 supports the shaft 3 as shown in
When the permanent magnet rotating machine 31 having a cantilevered structure is connected to an engine 32 through a coupling 33, it is possible to prevent the rotor 1 from being brought into contact with the stator 2 even with the bearing 30 disposed on one side. Furthermore, the number of bearings can be reduced, so the cost and weight of the permanent magnet rotating machine 31 can be reduced.
In addition to the structures in the first to fourth embodiments, cooling ventilation paths 34 are provided between the poles of the rotor 1 as shown in
When the cooling ventilation paths 34 are formed as described above, a cooling area of the rotor 1 is expanded and thereby the temperature of the rotor 1 can be lowered. Cooling air can efficiently flow from the rotor 1 to the stator 2 due to fan action, enabling the temperature in the permanent magnet rotating machine to be leveled. Furthermore, since the harmonic components of fluxes entering the rotor 1 from a part between the poles, eddy currents generated in the magnets can be reduced, efficiency can be increased, and the temperature in the permanent magnet rotating machine can be reduced.
In addition to the structures in the first to fifth embodiments, a plurality of (four) shaft arms 35 are provided between the rotor iron core 5 and the shaft 3, with a predetermined spacing therebetween in the circumferential direction, as shown in
When the shaft arms 35 are disposed as described above, the outer diameter of the shaft 3 can be reduced while maintaining the same strength as when the shaft arms 35 are not provided. Therefore, the entire weight of the rotary electrical machine can be reduced. Although four shaft arms 35 are used in this embodiment, any other number of shaft arms 35 may be used.
The permanent magnet rotating machine 36 described in the first to sixth embodiments is connected directly to an engine 37 and mounted in a power car vehicle. The permanent magnet rotating machine 36 is also connected to an electrical power system 38 through a power converter 39 to generate electrical power. A battery 41 is connected between the electrical power system 38 and power converter 39 through a battery chopper 40.
The permanent magnet rotating machine according to the present invention 36 has improved electrical characteristics, so it is possible to reduce its weight and increase its efficiency in comparison with conventional rotational electrical machines, enabling the fuel efficiency of the entire vehicle system to be increased. It is also possible to operate the permanent magnet rotating machine 36 by using the engine 37 without mounting the battery chopper 40 and battery 41 and to supply power generated by the operation to the electrical power system 38 for an operation.
The permanent magnet rotating machine 42 described in the first to sixth embodiments is connected to a windmill 43 through a speed-up gear 44 and mounted in a nacelle 45. The permanent magnet rotating machine 42 is also connected to an electrical power system 46 through a power converter 47 to generate electrical power. It is also possible to directly interconnect the windmill 43 and permanent magnet rotating machine 42.
The permanent magnet rotating machine 42 has improved electrical characteristics, so it is possible to increase its efficiency in comparison with conventional rotational electrical machines, enabling the efficiency of the power generating system to be increased. Although, in the present invention, wind is used as the power source, a water mill, engine, and turbine can be adequately applied.
Number | Date | Country | Kind |
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2010-178298 | Aug 2010 | JP | national |