Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-09-13
2002-01-29
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S156550, C310S156570, C310S166000, C310S216006, C310S261100, C310S156070
Reexamination Certificate
active
06342745
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reluctance type rotating machine equipped with permanent magnets, which is compact with a high output and which is capable of rotating in a wide range by its adoption of a new pole structure.
2. Description of the Related Art
As shown in
FIG. 1
, an earlier reluctance type rotating machine comprises a stator
1
having armature windings
2
and a salient-pole rotor
3
having an uneven core
4
since the rotating machine does not require coils for forming a field system about the rotor
3
. Therefore, the reluctance type rotating machine is simple in structure and low in price.
We now describe a principle of producing the output of the reluctance type rotating machine. Because of unevenness about the rotor, the reluctance type rotating machine exhibits small magnetic reluctance at protrusions of the rotor and large magnetic reluctance at recesses of the rotor. That is, there is a difference of stored magnetic energy between a gap over the protrusion and another gap over the recess. The output of the reluctance type rotating machine comes from the change in magnetic energy. Note, the protrusions and recesses may be provided by a configuration allowing the unevenness to be formed not only geometrically but magnetically, in other words, the configuration where the magnetic reluctance and distribution of magnetic flux density vary depending on the position of the rotor.
As another high-performance rotating machine, there is a permanent magnet type rotating machine. In the rotating machine, a plurality of permanent magnets are arranged on the substantial whole periphery of the rotor core although the armature windings of the machine is similar to the armature windings of an induction machine, the same windings of the reluctance type rotating machine, etc.
Due to the unevenness about the core surface, the reluctance type rotating machine has different magnetic reluctance which depends on the rotational position of the rotor. This change in magnetic reluctance causes the magnetic energy to be varied thereby to produce an output of the rotor.
In the conventional reluctance type rotating machine, however, the increasing of currents causes a local magnetic saturation to be enlarged at the protrusions of the rotor
4
. Thus, the enlarged magnetic saturation also causes magnetic flux leaking to the recesses between poles to be increased, so that effective fluxes are decreased while lowering the output power.
On the other hand, as another high-powered rotating machine, there is a permanent magnet type rotating machine using “rare-earth metal” permanent magnets having high magnetic energy products. Owing to the arrangement of the permanent magnets on the surface of the rotor core, when the permanent magnets of high energy are employed to form a magnetic field, the permanent magnet type rotating machine is capable of forming an intense magnetic field in an air-gap of the machine, providing a compact and high-powered rotating machine.
Nevertheless, it should be noted that a voltage induced in the armature windings gets larger in proportional to the rotating speed of the rotor since the magnetic flux of each magnet is constant. Therefore, if the machine is required to operate at a wide range of variable speeds up to the high-speed rotation, it is difficult to carry out the “rated-output” operation of the machine at a rotating speed twice or more as large as the base speed under constant current and voltage.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a reluctance type rotating machine which is compact in spite of high output and which is capable of operating at a wide range of variable speeds.
To achieve the object of the present invention described above, from the 1st aspect of the invention, there is provided a reluctance type rotating machine comprising:
a stator having armature windings;
a rotor having a rotor core, the rotor being provided, in a circumferential direction thereof, with a magnetic unevenness;
a plurality of permanent magnets arranged in the rotor core, for negating the armature windings' flux passing between adjoining poles defined in the rotor, each of the permanent magnets being magnetized in a direction different from a direction to facilitate the rotor's magnetization; and
wherein a magnetic portion is ensured in the rotor core so that, when the armature windings are not excited, more than 30% (percent) of the permanent magnets' flux is distributed in the rotor and also that, when the machine is loaded, the permanent magnets' interlinkage flux is more than 10% of composite interlinkage flux composed of current and the permanent magnets.
It is noted that the above composite interlinkage flux is changed by a phase difference between the flux vector of current and the flux vector of permanent magnets. Therefore, we now define the amount of composite interlinkage flux when both phases exerting no influence on each other are on the crossing condition at a right angles, as the above composite interlinkage flux of the invention.
As the magnetic unevenness is formed about the rotor core, a magnetic protrusion of the unevenness constitutes a pole of a reluctance motor, while a magnetic recess does an interpole (i.e. a part between the adjoining poles) of the motor. Namely, the magnetic protrusion corresponds to a “easy-magnetizing” direction to facilitate the rotor's magnetization, while the magnetic recess corresponds to a “hard-magnetizing” direction where it is difficult to magnetize the rotor.
According to the invention, the permanent magnets are arranged in the magnetic recesses in the rotor core. Additionally, in the rotor core, there is provided a magnetic portion for closing the permanent magnets' flux in a short circuit so that, when the armature windings are not excited, more than 30% (percent) of the permanent magnets' flux is distributed in the rotor. With this structure, it is possible to reduce an induced voltage generating at the rotor's rotating to 0 to 70% of the rated voltage for the rotating machine. For example, under condition that the induced voltage is set to 33%, even if rotating the rotating machine at high speed of three times as fast as the base speed, there would be no possibility to apply an excessive current to an electric circuit.
Next, when the machine is loaded, the above magnetic portion is intensely subjected to the magnetic saturation by the flux due to the load current. Consequently, the permanent magnets' flux distributing between the poles does increase. According to the invention, the magnetic portion between the poles constitutes a magnetic path so that a part of permanent magnets' flux is distributed in the direction of the center-axis of interpole. Additionally, the magnetic portion is adapted in a manner that, when the machine is loaded, the permanent magnets' interlinkage flux is more than 10% of composite interlinkage flux composed of armature current and the permanent magnets.
The flux of each permanent magnet has an action to repulse the armature current flux entering along the center-axis direction of the interpole and increase the magnetic reluctance in the direction of the magnet since the relative permeability of the magnet is generally equal to zero. Thus, since the permanent magnets' flux and the armature flux in the opposite direction cancel each other, the composite flux along the center-axis direction of the interpole gets fewer or flows in a direction opposite to the armature current when the armature current is small.
Therefore, since the interlinkage flux along the center-axis direction of the interpole gets smaller, a change within the magnetic unevenness about the rotor is so enhanced that the output of the machine does increase. On the other hand, the armature flux has a tendency of distribution to pass through the magnetic protrusions of the rotor core in concentration. Consequently, as the unevenness of flux density about th
Arata Masanori
Hashidate Yoshio
Kurosawa Ryoichi
Nakazawa Yosuke
Sakai Kazuto
Kabushiki Kaisha Toshiba
Mullins Burton S.
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