Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-08-12
2001-02-27
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S184000, C310S168000, C318S701000
Reexamination Certificate
active
06194804
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to motors, in particular low cost motors, and to improvements to motors usable as general-purpose industrial motors, and furthermore to motors useful as high rotational speed motors in which centrifugal force becoming a problem in terms of rotor strength.
2. Description of the Related Art
When it is necessary to rotate a motor at high speeds, such as the high-speed main shaft of a machine tool in a machining center, the motor's rotor with a diameter of about 100 mm must reach speeds of at least 30,000 rpm. Although induction motors are used for this sort of application, the slots of the rotor are not opened and are often closed to withstand the centrifugal force, and the rotor coil ends are also often reinforced. In any case, the cost increases and a reinforced construction that somewhat sacrifices the motor characteristics is often employed.
Switched reluctance motors, which have high rotor strength, have been researched and some have been put into actual use. A typical example of an actual motor is shown in
FIG. 10. A
rotor
2
is a simple silicon steel plate and extremely strong so as to be suitable for high-speed rotation.
A stator
1
has six salient poles
20
and the width of each salient pole
20
is approximately 30 degrees when converted to the rotor rotational angle. Each salient pole
20
is wound with windings TA
1
, TA
2
, TB
1
, TB
2
, TC
1
, TC
2
, TD
1
, TD
2
, TE
1
, TE
2
, TF
1
, and TF
2
. The rotor
2
has four salient poles
21
and the width of each salient pole
21
is approximately 30 degrees when converted to the rotor rotational angle.
The operation of the switched reluctance motor is described next. For example, when generating a rotational torque in the counterclockwise direction in the state of
FIG. 10
, current is passed through the windings indicated by TC
1
and TC
2
, and TF
1
and TF
2
so that the salient poles
21
of rotor
2
are attracted to generate a rotational torque. At this time, the current flowing through the windings indicated by TC
1
and TC
2
and the current flowing through the windings indicated by TF
1
and TF
2
have opposite directions, and the currents flow so that the generated magnetic flux passes through the rotor
2
. Furthermore, while the rotor
2
rotates in the counterclockwise direction, the rotational torque is not generated when the salient poles
21
of rotor
2
reach the position of the stator pole wound with windings TC
1
and TC
2
. At this time, since the adjacent rotor salient pole in the counterclockwise direction approaches the stator salient pole wound with windings indicated by TE
1
and TE
2
, setting the current in the windings TC
1
and TC
2
to zero, and at the same time passing current in the windings indicated by TE
1
and TE
2
and the windings indicated by TB
1
and TB
2
causes a rotational torque to be generated in the counterclockwise direction. In this manner, passing an appropriate intermittent current in sequence to each stator winding enables a continuous rotational torque to be generated. Simultaneously, when generating a rotational torque in the clockwise direction in the state of
FIG. 10
, current is passed through the windings indicated by TB
1
and TB
2
so that the salient poles of rotor
2
are attracted to generate a rotational torque.
The generated torque is related to the current in the windings and the relative positions of the stator
1
and rotor
2
, and in theory is unrelated to the rotational speed of the rotor.
Characteristics of this switched reluctance motor include a low fabrication cost due to a simple motor construction and a simple winding structure of the stator windings, a relatively short-motor length because the coil ends of the stator windings can be shortened, a durable rotor making it physically possible for high-speed rotation, and a drive circuit that can be simplified since the drive algorithm is simple and only one direction of current is sufficient.
On the other hand, the switched reluctance motor also has a number of shortcomings. When the control algorithm to even the relationship of the supplied electrical energy, the magnetic energy stored in the motor, and the mechanical output energy has not been established, the result is a large torque ripple. One method that has been proposed to solve this is to compensate for the current so as to compensate for torque ripple, thus reducing torque ripple. However, this method introduces other problems, such as the requirement of a complex control method. In addition to torque ripple, the intermittent torque generated by each salient pole also affects in terms of motor strength the stator deformation, and vibration and noise when the motor is driven are large. Furthermore, other problems include the requirement of high-speed current control and the requirement of extremely high-speed current switching for the high-speed rotation of the four-pole motor compared to that for the two-pole motor. Furthermore, there is the problem of the power factor since it is necessary to frequently perform the supply and regeneration of magnetic energy in the motor.
SUMMARY OF THE INVENTION
According to the present invention, a two-pole motor is proposed in which the torque generated at each rotor salient pole is continuous and torque ripple is not generated from the basic algorithm, and in which there is no input or output of magnetic energy in the motor as seen from the drive apparatus. The motor also has low vibration and low noise.
The motor of the present invention includes six stator poles having widths of about 60 degrees, which is less than 60 degrees when converted to the rotor rotational angle.
The excitation windings wound around each stator pole are connected so that adjacent excitation windings are in reverse series. Namely, the excitation windings are wound in opposite directions to each other and then connected in series. The torque windings wound around each stator pole have three phases, where each phase winding comprises a pair on opposite sides with respect to the center of rotor rotation, separated from each other by 180 degrees, and connected in reverse series. In addition, two rotor poles having widths from 60 degrees to 120 degrees when converted to the rotor rotational angle are provided.
Another motor of the present invention is the same as the above-mentioned motor but with common stator windings wound around each stator pole.
A rotor provided with holes or grooves to limit the total magnetic flux of the rotor poles on the outer perimeter of the rotor, or a rotor construction in which air-gaps are provided or non-magnetic materials, such as stainless steel, are provided to limit the total magnetic flux of the rotor poles between electromagnetic steel plates of the rotor laminated along the direction of the rotor shaft are also proposed.
A rotor fabricated from an electromagnetic steel plate with a saturation magnetic flux density lower than the saturation magnetic flux density of the electromagnetic steel plate of the stator is also proposed.
The two-pole rotor, the polarity of which changes according to the position of the rotor, is constructed so that a constant magnetic flux is always present. Therefore, the magnetic energy in the motor can be basically made constant regardless of the rotor rotational position. If the excitation windings are all connected in series and pass excitation current, the magnetic flux of one of the windings decreases during rotation to generate a negative voltage, and at the same time the magnetic flux of one of the other windings increases to generate a positive voltage. Therefore, the total voltage of all the excitation windings connected in series is only a voltage drop of the resistance of the windings, and a voltage is basically not generated from fluctuations in magnetic flux. Therefore, only an extremely simple excitation control for the drive apparatus is sufficient. Regarding the gap between adjacent stator poles, a small gap minimizes any adverse effects, and even if rela
Okuma Corporation
Oliff & Berridg,e PLC
Tamai Karl
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