Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-10-03
2004-04-13
Ponomarenko, Nicholas (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S254100, C310S261100
Reexamination Certificate
active
06720686
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to dynamoelectric machines, and more particularly to dynamoelectric machines having a characteristic of decreased noise while operating.
2. Relation to Prior Art
Dynamoelectric machines are well known in the art. One such dynamoelectric machine is a reluctance machine. In general, a reluctance machine is an electric machine in which torque is produced by the tendency of a movable part to move to a position where the inductance of an excited winding is maximized (i.e., the reluctance is minimized).
In one type of reluctance machine, the phase windings are energized at a controlled frequency. This type of reluctance machine is generally referred to as a synchronous reluctance machine. In another type of reluctance machine, circuitry is provided to determine or estimate the position of the machine's rotor, and the windings of a phase are energized as a function of rotor position. This type of reluctance machine is generally referred to as a switched reluctance machine. Although the description of the current invention is in the context of a switched reluctance motor, the present invention is applicable to all forms of reluctance machines, including synchronous and switched reluctance motors, reluctance generators, and to other machines that have phase winding arrangements similar to those of switched reluctance machines.
Generally, the stator of a switched reluctance motor includes a ring of inwardly extending stator poles about which are positioned one or more phase windings. The energization of such a phase winding tends to cause the rotor to move into a position where the inductance of an excited winding is maximized. The energization of such a phase winding will also tend to deform the stator by drawing certain stator poles associated with the energized phase winding towards the rotor poles. In general, as a rotor pole comes into alignment with a stator pole, the forces tending to draw the stator pole towards the rotor pole (i.e., the normal forces) will generally begin to increase, will reach a maximum at full alignment, and will decrease thereafter.
FIG. 1A
generally illustrates an exemplary rotor pole
1
as it rotates into and then past alignment with a stator pole
3
, surrounded by a phase coil
5
. The current profile supplied to the stator pole
3
is shown in FIG.
1
B. The current profile presented is idealized, and actual currents will have characteristics different from those represented in FIG.
1
B. Particular apparatus for generating the illustrated currents as a function of the angular position of the rotor is omitted, and the construction of such apparatus will be apparent to one of ordinary skill in the art.
The exemplary current in
FIG. 1B
supplied to coil
5
surrounding stator pole
1
is shown in relation to the angular position of a rotor pole
1
. The current typically involves a ramp increase to energize the stator pole. Then, the current is maintained at a substantially constant level to bring the rotor pole into minimum reluctance relation to the stator pole. Once the rotor pole has aligned with approximately 50 % of the stator pole (corresponding to the position identified by the dashed line in FIGS.
1
A-
1
C), the current undergoes a cutoff, and begins to decrease in accordance with traditional energization schemes. The rotor pole reaches minimum reluctance as it aligns 100% with the stator pole and then passes out of relation to the stator pole.
As the rotor pole
1
moves in relation to stator pole
3
, the inductance between the poles changes. The change in inductance produces torque in the rotor, which causes angular displacement of the rotor. The torque has a tangential and normal component due to the magnet flux path that passes through the radially opposed pole pairs, the rotor and the stator. The tangential component will tend to cause the rotor to rotate. The normal component will tend to cause the stator pole to move towards the rotor pole.
FIG. 1C
generally illustrates the normal forces exerted on the stator pole as a function of the angular position of the rotor for the illustrated current waveform. As illustrated, the normal forces will begin to increase near the point where the rotor pole begins to overlap the stator pole. In
FIG. 1C
, the normal force increases as the rotor pole aligns with stator pole until a maximum force is reached at the point where the rotor pole is fully aligned with the stator pole. This point of full alignment also generally corresponds to the minimum reluctance point. The normal force then decreases steadily as the poles pass out of alignment. As illustrated in
FIGS. 1A-1C
, for traditional reluctance machines energized in the traditional manner, the normal force curve has a continuous, uniform profile for the electrical interaction of the two uniform faced poles as they pass in relation to one another.
The establishment of the normal forces described above tends to result in an “ovalizing” of the stator as normal forces attempt to collapse the air gap between the rotor poles and the stator poles associated with the energized phase winding. These radially opposed normal forces tend to distort the stator yoke from its generally circular configuration and force it out of round. Upon de-energization of the stator poles, the stator returns to its original circular configuration. Even though the deflection during energization is extremely slight, under continuous operation the distortion produces a noticeable whining noise.
Traditional switched reluctance machines have rotor and stator constructions that result in the establishment of normal forces such that each of the stator poles in the machine experiences the same normal forces, although not necessarily at the same point in time.
FIGS. 2A-2B
generally and schematically illustrate the types of “deflection modes” that are established in reluctance machines having two and four normal forces acting on the stator. As used herein, the number of deflection modes that a reluctance machine may have corresponds to the number of localized areas where normal forces are generated in the machine during energization of one of the machine's phase windings. Typically, the number of deflection modes for a given machine will correspond to the number of stator poles encircled by each phase winding in the machine. Although the present discussion describes reluctance machines with 2 and 4-modes of deflection, it is to be understood that additional modes exist beyond those depicted. Furthermore, 3-mode deflection (i.e. odd-mode deflection) cannot occur in an electromagnetically balanced motor.
Referring to
FIGS. 2A-2B
, the identified figures include arrows
8
representing the normal forces acting on the stator poles associated with an exemplary energized phase winding at a specific point in time. As noted in the Figures, the normal forces
8
acting on the various stator poles associated with the given energized phase winding are, at each point in time, substantially equal.
In
FIG. 2A
, the equal and opposite normal forces
8
tend to ovalize the stator
6
. This represents a two-mode deflection since there are two localized areas where normal forces
8
are generated during energization of phase A windings. Also,
FIG. 2B
represents a four-mode deflection since there are four localized areas where normal forces
8
are generated during energization of phase A windings. Higher ordered modes of deflection are also possible beyond four modes.
In addition to establishing normal forces that are equal with respect to an energization of a given phase winding, traditional reluctance machines are constructed so that the normal forces established by the energization of another phase winding are the same in profile (although physically displaced) as the normal forces established upon energization of the given or another phase at a later point in time. In other words, in typical reluctance machines, the normal forces that are exerted on the stator poles associated with the energization
Emerson Electric Co.
Perez Guillermo
Ponomarenko Nicholas
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