Sectionalized electromechanical machines having low torque ripple and low cogging torque characteristics
View Patent ↗A method and apparatus for reducing or eliminating the effects of torque ripple and cogging torque and otherwise improving performance in an electromechanical machine such as a motor or generator. The rotor and/or stator is conceptually sectionalized and the sections spaced apart by amount sufficient to alleviate deleterious aspects of cogging torque and torque ripple. Positioning of the stator teeth or rotor magnets is determined based on the calculated spacing. Conceptual sections may be formed as physically individual segments. Unwound teeth may be disposed in end spaces between sections occupying less than the entire area of the end space.
1. An electromechanical machine having rotor poles and stator poles that cooperate to generate electricity from rotation or convert electricity to rotation, comprising inner and outer structures, at least one of said structures rotating relative to the other of said structures with the rotor poles disposed on the rotating structure and the stator poles disposed on the other structure, at least one of said structures including a plurality of sections, wherein:
the poles of said structure including the plurality of sections are arranged in sets of wound poles formed on teeth having a depth;
a set of said poles is disposed in each one of said plurality of sections and each set has two end poles, one at each section end;
the end poles are spaced from the section ends by an end space at each section end, the end space having a width of approximately the distance from the end pole winding to the section end, and a depth of approximately the depth of the wound pole teeth to define an end space area; and
an unwound tooth is disposed in each said end space, the unwound teeth occupying not more than 90% of said end space area.
2. An electromechanical machine according to claim 1 , wherein the unwound teeth occupy approximately 55 -80% of the end space area.
3. An electromechanical machine according to claim 1 , wherein the unwound teeth have a depth of approximately 90 -98% of the wound pole teeth.
4. An electromechanical machine according to claim 1 , wherein the unwound teeth have a trapezoidal shape.
5. An electromechanical machine according to claim 1 , wherein the unwound teeth have a substantially rectangular shape and a depth less than the wound pole teeth depth.
6. An electromechanical machine according to claim 1 , wherein the unwound teeth have a substantially rectangular shape and a width less than the end space width.
7. An electromechanical machine according to claim 1 , wherein the end spaces of adjacent sections are occupied by a single unwound tooth.
8. An electromechanical machine according to claim 1 , wherein the end spaces of adjacent sections are occupied by separate unwound teeth.
9. An electromechanical machine according to claim 1 , wherein:
each said section has as a section pole pitch (PPs), the section pole pitch being the same within each section;
wound teeth of adjacent sections are spaced by a boundary pole pitch (PPb); and
the end space has a size equal to the boundary pole pitch minus the section pole pitch (PPb−PPs).
10. An electromechanical machine according to claim 9 , wherein the boundary pole pitch is defined by the function:
PPb
=
(
360
-
(
P
×
PPs
)
N
)
+
PPs
where:
PPb is the boundary pole pitch;
PPs is the section pole pitch;
P is the number of poles; and
N is the number sections.
11. An electromechanical machine according to claim 10 , wherein the section pole pitch is defined by the function:
PPs
=
360
P
×
(
1
-
N
×
Ph
×
X
H
×
P
)
where:
PPs is the section pole pitch;
P is the number of poles;
Ph is the number of phases;
H is the harmonic number corresponding to a torque ripple harmonic to be reduced or eliminated in the operation of the machine;
N is the number of sections; and
X is a factor in the range of greater than zero to one corresponding to a selected amount of torque ripple reduction.
12. A stator for an electromechanical machine, comprising wound stator poles formed on teeth having a depth, wherein:
the wound poles are arranged a plurality of sections each comprising a set of wound poles with two wound end poles, one at each section end;
the wound end poles are spaced from the section ends by an end space at each section end, the end space having a width of approximately the distance from the end pole winding to the section end, and a depth of approximately the depth of the wound pole teeth to define an end space area; and
at least one unwound tooth is disposed in the end spaces defined by adjacent section end, the unwound teeth occupying not more than 90% of the total end space area of the adjacent sections.
13. An electromechanical machine according to claim 12 , wherein said at least one unwound tooth has a trapezoidal shape.
14. An electromechanical machine according to claim 12 , wherein said at least one unwound tooth has a substantially rectangular shape and at least one of a depth less than the wound pole teeth depth and a width less than the total end space width.
15. An electromechanical machine according to claim 12 , wherein the sections are formed as physically separate segments and said at least one unwound tooth comprises two adjacent unwound teeth.
16. A method for arranging wound stator poles in an electromechanical machine to reduce torque ripple, the wound poles being formed on teeth having a depth, the method comprising:
conceptually dividing the stator poles into a plurality of sections to provide a sectionalized stator with each section having ends adjacent a next section;
arranging the poles of the sectionalized stator in a plurality of sets of poles, each set disposed within one said section and having two end poles, one at each section end; and
positioning the poles within each set at a section pole pitch, the section pole pitch being a function of the frequency of the torque ripple harmonic to be at least reduced in operation of the machine;
positioning the end poles of adjacent sections at a boundary pole pitch, the boundary pole pitch being a function of the section pole pitch;
spacing the end poles from the section ends by an end space at each section end, the end space having a width of approximately the distance from the end pole winding to the section end, and a depth of approximately the depth of the wound pole teeth to define an end space area; and
disposing an unwound tooth in each said end space, the unwound teeth occupying not more than 90% of said end space area.
17. The method according to claim 16 , wherein the section end is disposed at a distance from the end pole center of approximately half the boundary pole pitch.
18. The method according to claim 16 , wherein a single unwound tooth is positioned within the end spaces of adjacent sections.
19. The method according to claim 16 , further comprising providing the conceptual sections as physically separate segments wherein separate unwound teeth are positioned within the end spaces of adjacent sections.
20. The method according to claim 16 , further comprising sizing the unwound teeth to have a depth of approximately 90 -98% of the wound pole teeth.
21. The method according to claim 16 , wherein the unwound teeth have a trapezoidal shape.
22. The method according to claim 16 , wherein the unwound teeth have a substantially rectangular shape and a depth less than the wound pole teeth depth.
23. The method according to claim 16 , wherein the unwound teeth have a substantially rectangular shape and a width less than the end space width.
24. The method according to claim 16 , wherein said section pole pitch function is:
PPs
=
360
P
×
(
1
-
N
×
Ph
×
X
H
×
P
)
where:
PPs is the section pole pitch;
P is the number of poles;
Ph is the number of phases;
H is the harmonic number corresponding to a torque ripple harmonic to be reduced or eliminated in the operation of the machine;
N is the number of sections; and
X is a factor in the range of greater than zero to one corresponding to a selected amount of torque ripple reduction.
25. The method according to claim 24 , wherein said pole pitch function is:
PPb
=
(
360
-
(
P
×
PPs
)
N
)
+
PPs
where:
PPb is the boundary pole pitch;
PPs is the section pole pitch;
P is the number of poles; and
N is the number of sections.