LOW-NOISE, HIGH ROTOR POLE SWITCHED RELUCTANCE MOTOR

Abstract

The present embodiment is a high rotor pole switched reluctance machine (HRSRM) which provides a plurality of combinations of the number of rotor poles R.sub.n and number of stator poles S.sub.n utilizing a numerical relationship defined by a mathematical formula, R.sub.n=2S.sub.nF.sub.p, when S.sub.n=mF.sub.p, wherein F.sub.p is the maximum number of independent flux paths in the stator when stator and rotor poles are fully aligned, and m is the number of phases. The mathematical formulation provides an improved noise performance and design flexibility to the machine. The mathematical formulation further provides a specific number of stator and rotor poles for a chosen m and Fp. The HRSRM can be designed with varying number of phases. The HRSRM provides a smoother torque profile due to a high number of strokes per revolution.

Claims

1. A high rotor pole switched reluctance machine (HRSRM) comprising: a stator including a plurality of stator poles; and a rotor including a plurality of rotor poles; wherein the plurality of rotor poles is in a numerical relationship with the plurality of stator poles and provides a plurality of combinations of the stator poles and rotor poles utilizing the numerical relationship defined by a mathematical formula:
R.sub.n=2S.sub.nF.sub.p, such that S.sub.n=mF.sub.p, F.sub.p>2, m>1 and m and F.sub.p are independent variables, wherein R.sub.n is the number of rotor poles, S.sub.n is the number of stator poles, F.sub.p is the maximum number of independent flux paths in the stator when stator and rotor poles are fully aligned, and m is the number of phases, the number of phases and the number of independent flux paths determines the plurality of combinations of the stator poles and rotor poles.

2. The HRSRM according to claim 1 further comprising a varying number of phases.

3. The HRSRM according to claim 1 wherein the mathematical formulation provides a specific number of stator and rotor poles for a chosen m and Fp.

4. (canceled)

5. (canceled)

6. (canceled)

7. (canceled)

8. The HRSRM according to claim 1 wherein the rotor is external to the stator.

9. The HRSRM according to claim 1 wherein each rotor pole constitutes a plurality of flux guides which serve to bend the flux in the stator pole around a periphery of the rotor pole.

10. (canceled)

11. A high rotor pole switched reluctance machine (HRSRM), comprising: a stator including a plurality of stator poles and a rotor including a plurality of rotor poles, the HRSRM providing a plurality of combinations of the rotor poles and stator poles utilizing a numerical relationship defined by a mathematical formula:
R.sub.n=2S.sub.nF.sub.p; such that S.sub.n=mF.sub.p, F.sub.p>2, m>1 and m and F.sub.p are independent variables wherein Rn is the number of rotor poles, S.sub.n is the number of stator poles, F.sub.p is the maximum number of independent flux paths in the stator when stator and rotor poles are fully aligned, and m is the number of phases, the number of phases and the number of independent flux paths determines the plurality of combinations of the stator poles and rotor poles.

12. The HRSRM according to claim 11 further providing a high rate of change of inductance with respect to rotor position, which can improve torque quality of the machine.

13. The HRSRM according to claim 11 further comprising a varying number of phases.

14. The HRSRM according to claim 11 wherein the mathematical formulation provides a specific number of stator and rotor poles for a chosen m and Fp.

15. (canceled)

16. (canceled)

17. (canceled)

18. (canceled)

19. The HRSRM according to claim 11 wherein the rotor is external to the stator.

20. The HRSRM according to claim 11 wherein each rotor pole constitutes a plurality of flux guides which serve to bend the flux in the stator pole around a periphery of the rotor pole.

21. (canceled)

22. The HRSRM according to claim 11 wherein the stator poles facilitate a high fill factor.

23. A method for estimating number of rotor poles for a high rotor pole switched reluctance machine (HRSRM) comprising a rotor including a plurality of rotor poles and a stator including a plurality of stator poles each having a plurality of windings, and providing a plurality of combinations of the rotor poles and stator poles, the method comprising the steps of: (a) energizing at least one stator pole, wherein each of the windings of a remainder of stator poles is in an open circuit state; (b) applying current to the at least one stator pole; (c) inducing a magnetic flux, the magnetic flux following a path through the plurality of stator poles; (d) storing a maximum number of independent flux paths (F.sub.p) in the stator when stator and rotor poles are fully aligned; (e) calculating a number of phases (m); (f) determining a number of stator poles (S.sub.n) utilizing a mathematical formula:
S.sub.n=mF.sub.p, wherein F.sub.p>2, m>1, m and F.sub.p are independent variables, the number of phases and the number of independent flux paths determines the plurality of combinations of the stator poles and rotor poles; and (g) estimating the number of rotor poles (R.sub.n) utilizing a mathematical formula:
R.sub.n=2S.sub.n=F.sub.p

24. (canceled)

25. The method of claim 23 providing a high rate of change of inductance with respect to rotor position, which can improve torque quality of the machine.

26. The method of claim 23 enabling a switched reluctance machine with varying number of phases.

27. The method of claim 23 wherein the mathematical formulation provides improved noise performance and design flexibility to the switched reluctance machine.

28. The method of claim 23 wherein the switched reluctance machine exhibits a smoothed torque profile due to a high number of strokes per revolution.

29. The method of claim 23 wherein the stator poles facilitate a high fill factor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Elements in the figures have not necessarily been drawn to scale in order to enhance their clarity and improve understanding of these various elements and embodiments of the invention. Furthermore, elements that are known to be common and well understood to those in the industry are not depicted in order to provide a clear view of the various embodiments of the invention. Thus, the drawings are generalized in form in the interest of clarity and conciseness.

[0020] The foregoing aspects and many of the attendant advantages of the invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the attached charts and figures, wherein:

[0021] FIG. 1 illustrates a cross-sectional view of a switched reluctance motor;

[0022] FIG. 2 illustrates a 16/28 SRM as an example of the proposed formulation;

[0023] FIG. 3 is a 3-D view of the 16/28 SRM as an example of the proposed formulation;

[0024] FIG. 4A illustrates 16 stator poles of the 16/28 SRM without coils and rotor assembly in accordance with the preferred embodiment of the present invention;

[0025] FIG. 4B illustrates 28 rotor poles for the 16/28 SRM without stator assembly in accordance with the preferred embodiment of the present invention;

[0026] FIGS. 5A and 5B show the coil configuration in the 16/28 SRM that can be modified to allow four independent short-flux paths;

[0027] FIG. 5C shows a finite element analysis simulation of 16/28 SRM showing an alternate winding combination; and

[0028] FIG. 6 is a flowchart that illustrates a method for estimating number of rotor poles for a high rotor pole switched reluctance machine (HRSRM).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0029] In the following discussion that addresses a number of embodiments and applications of the present invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustrating specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and changes may be made without departing from the scope of the present invention.

[0030] Various inventive features are described below that can each be used independently of one another or in combination with other features. However, any single inventive feature may not address any of the problems discussed above or only address one or more of the problems discussed above. Further, one or more of the problems discussed above may not be fully addressed by any of the features described below. The invention will now be described with reference to the accompanying drawing which does not limit the scope and the ambit of the invention. In the following discussion that addresses a number of embodiments and applications of the present invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustrating specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and changes may be made without departing from the scope of the present invention.

[0031] The present invention rovides a plurality of combinations of the rotor poles and stator poles utilizing a numerical relationship defined by a mathematical formula:

R.sub.n=2S.sub.nF.sub.p;

Where S.sub.n=mF.sub.p, F.sub.p>2, m>1 and m and F.sub.p are independent variables, R.sub.n is the number of rotor poles, S.sub.n is the number of stator poles, F.sub.p represents the maximum number of independent flux paths in the stator when stator and rotor poles are fully aligned AND F.sub.p>2, m is the number of phases AND m>1 and m and F.sub.p are independent variables.

[0032] Turning first to FIG. 1, a cross-sectional view of a switched reluctance motor 100 is illustrated. The switched reluctance motor 100 includes a stator 102 and a rotor 104 that rotates inside the stator 102. The stator 102 includes a plurality of stator poles 106 and the rotor 104 includes a plurality of rotor poles 108. As the rotor 104 rotates, an airgap 110 separates stator poles 106 from rotor poles 108. The switched reluctance motor 100 shown in FIG. 1 is referred to as an 8/6 SRM since stator 102 includes eight stator poles 106 and rotor 104 includes six rotor poles 108. Other viable combinations of the stator poles and rotor poles of the switched reluctance motor 100, and may benefit from the teachings of the invention. A winding 112, for example a copper winding, is wound around each stator pole 16. The windings 112 on diametrically opposite pairs of the stator poles 106 are connected in series or in parallel. Phase currents are sent through the windings 112 on pairs of stator poles 106 connected in series or in parallel, and are turned on and off based on the angular position of the rotor 104 with respect to the stator 102.

[0033] Electromagnetic torque is produced in switched reluctance motor 100 by the attraction of rotor pole(s) 108 to the excited stator pole(s) 106. For example, exciting the stator poles 106 by turning on a current through the windings 112 on stator poles 106 creates an electromagnetic force density in air gaps 110. Due to a tangential component of this electromagnetic force density, a rotor pole 108 near stator pole 106 is attracted to the stator pole 106. Likewise, the diametrically opposite rotor pole 108 near the stator pole 106 is attracted to, and attempts to align itself with, the stator pole 106. Thus, an electromagnetic torque force is produced, turning the rotor 104 counter-clockwise.

[0034] FIG. 2 illustrates a 16/28 SRM as an example of the proposed formulation with 16 concentrated stator coil-stator poles 106 and 28 rotor poles 108. FIG. 3 illustrates a 3-D view of 16/28 SRM as an example of the proposed formulation showing rotor and stator with 16 concentrated stator coil-stator poles 106 and 28 rotor poles 108.

[0035] FIG. 4A shows 16 stator poles 106 of the 16/28 SRM without coils and rotor assembly in accordance with the preferred embodiment of the present invention. FIG. 4B shows 28 rotor poles 108 for the 16/28 SRM without stator assembly in accordance with the preferred embodiment of the present invention.

[0036] FIGS. 5A and 5B show the coil configuration in the 16/28 SRM that can be modified to allow four independent short-flux paths 140A-140D. FIG. 5A shows a finite element analysis simulation of 16/28 SRM showing two independent flux paths 140A and 140B, second quadrant 132 and fourth quadrant 136 in the machine. FIG. 5B shows a finite element analysis simulation of 16/28 SRM showing two other independent flux paths 140C and 140D, first quadrant 130 and third quadrant 134 in the machine. FIG. 5C shows a finite element analysis simulation of 16/28 SRM showing an alternate winding combination, also leading to four independent flux paths 140E, 140F, 140G and 140H in the machine. In yet another embodiment, the SRM is of the external-rotor internal-stator design.

[0037] As shown in FIG. 6, a method for estimating number of rotor poles for a high rotor pole switched reluctance machine (HRSRM) comprising a rotor including a plurality of rotor poles and a stator including a plurality of stator poles each having a plurality of windings is disclosed. A first step at FIG. 6 involves providing the HRSRM comprising a rotor including a plurality of rotor poles and a stator including a plurality of stator poles each having a plurality of windings as shown in block 152. Then, energizing at least one stator pole, wherein each of the windings of the remainder of the stator poles is in an open circuit state as illustrated in block 154. Current is applied to the at least one stator pole as illustrated in block 156. Next, inducing a magnetic flux, the magnetic flux follows a path through the plurality of stator poles as shown in block 158. Storing a maximum number of independent flux paths (F.sub.p) in the stator when stator and rotor poles are fully aligned as illustrated in block 160. Then, calculating a number of phases (m) as illustrated in block 162. Finally, determining a number of stator poles (S.sub.n) utilizing a mathematical formula, S.sub.n=mF.sub.p, wherein F.sub.p>2, m>1, m and F.sub.p are independent variables is illustrated in block 164. Thus, estimating the number of rotor poles (R.sub.n) utilizing a mathematical formula, R.sub.n=2S.sub.nF.sub.p is accomplished as illustrated in block 166.

[0038] The present invention relates to a switched reluctance machine (SRM) in which noise and vibration generated can be reduced through an improvement of the rotor pole/stator pole configuration. The improved configuration provides a higher rate of change of inductance with respect to rotor position, which can improve the torque quality of the machine. The system provides a switched reluctance machine having salient rotor poles and stator poles in a numerical relationship. The proposed formulation presents a mathematical formulation, with a specific number of stator and rotor poles for a chosen m and Fp, which provides improved noise performance and design flexibility. In one example, when m=4, a machine with four phases and Fp=4 a machine with four possible independent flux paths, a 16/28 SRM results. Table 1: Some, but not all viable combinations of stator poles and rotor poles using the proposed formulation with m=4 are as follows:

TABLE-US-00001 TABLE 1 Number of phases (m) 4 F.sub.p S.sub.n R.sub.n 3 12 21 4 16 28 5 20 35 6 24 42 7 28 49 8 32 56 9 36 63 10 40 70 11 44 77 12 48 84 13 52 91 14 56 98 15 60 105 16 64 112 17 68 119 18 72 126 19 76 133 20 80 140

[0039] The embodiment of this formulation can be described by several other viable combinations of stator poles and rotor poles. Utilizing the proposed formulation, it is possible to design machines with varying number of phases and stator/rotor configurations. The present invention provides an SRM with applications for both rotary or linear designs, and which comprises a relationship between the number of stator poles and rotor poles so as to provide an SRM with a minimal amount of torque ripple and acoustic noise while providing improved power density and torque production. In particular, the present invention provides an SRM having a salient rotor and stator pole numerical relationship of number of stator poles Sn, and number of rotor poles Rn, which can be expressed as R.sub.n=2S.sub.nF.sub.p, such as an S.sub.n/R.sub.n pole count in a 16/28 configuration. The present invention provides an SRM, whether operated as a motor, generator, or both. The proposed topologies have the highest inductance when aligned and the lowest at unaligned positions, much like a conventional SRM. All conventional power electronic converters and control strategies adopted for conventional SRMs can be applied to the proposed SRM. The proposed SRM exhibits a smoother torque profile due to the higher number of strokes per revolution. This offers better peak and average torque profiles relative to conventional SRMs. The narrower stator pole facilitates a larger fill factor i.e. more windings, which considerably improves the winding resistance and the thermal limits of the phase windings.

[0040] The foregoing description of the preferred embodiment of the present invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teachings. It is intended that the scope of the present invention not be limited by this detailed description, but by the claims and the equivalents to the claims appended hereto.