GB2232305A

GB2232305A - Double coil windings for a switched reluctance motor

Info

Publication number: GB2232305A
Application number: GB9006418A
Authority: GB
Inventors: Charles Micheal Stephens
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1989-03-24
Filing date: 1990-03-22
Publication date: 1990-12-05
Also published as: DE4008446A1; IT9019794A1; DE4008446C2; CA2012233A1; IT9019794A0; GB9006418D0; FR2645685B1; FR2645685A1; IT1240287B; JPH02280643A

Description

1 - W 1 A SWITCHED RELUCTANCE MOTOR AND WINDINGS THEREFOR This invention

relates generally to stator pole coil windings for switched reluctance motors.

RD-18,554 Switched reluctance motors (SRMs) are doubly salient machines; that is, they have multiple poles on both the stator and the rotor. Moreover, there are coil windings on the stator, but no windings or magnets on the rotor. In a SRM, each motor phase comprises at least one pair of diametrically opposite stator poles, each stator pole having a coil winding wound thereon. The stator pole coil windings comprising each motor phase winding are connected in series or in parallel, so that when a phase winding is excited, magnetic flux produced in the corresponding pair(s) of stator poles combines additively. Upon excitation of a motor phase by supplying current to'the corresponding stator pole coil windings, a magnetic force of attraction results between the excited stator pole pair(s) and the nearest rotor poles, thereby causing the rotor to rotate. Current is switched off in the excited motor phase winding before the rotor poles rotate past the aligned position; otherwise, the magnetic force of attraction would produce a negative or braking torque. Continuous rotation of the rotor is achieved by sequentially switching on and off adjacent motor phases. To excite the motor phases, undirectional currenV.pulses synchronized with rotor movement are supplied to the motor phase windings by a converter. niustrative SRM converters are RD-18,554 illustrated in commonly assigned U.S. Patent No. 4,684,867, issued to T.J. E. Miller on August 4, 1987.

In general, during manufacture of a switched reluctance motor, the coil windings are wound as subassemblies and then applied to the stator poles. Disadvantageously, this conventional stator assembly process necessarily leaves unused spaced in each interpole region. That is, in order for a coil being assembled onto a stator pole to be able to clear adjacent windings that have been assembled previously, the width of the coil is restricted. As a result, for a particular SRM, maximum attainable flux, and hence output torque and voltage, are limited.

An embodiment of the present invention seeks to provide stator pole coil windings for a switched reluctance motor which utilize a larger portion of the interpole space than conventional coil windings, thereby enabling production of increased flux per unit of current and, thus, proportionately higher output torque and voltage. 20 Another embodiment of the present invention seeks to provide stator pole coil windings for a switched reluctance motor which result in lower conductor losses per unit of applied power than conventional coil windings. one aspect of the present invention seeks to provide a method of making a coil winding for a switched reluctance motor, which utilizes a larger portion of the interpole space than a conventional coil winding, thus resulting in a more efficient motor. 30 Another aspect of the present invention provides a plural-stage, form-wound coil winding for a switched 1 1 RD-18, 554 reluctance motor. For example, in a two-stage form-wound coil winding, the first stage comprises an inner coil winding which may be rectangular in cross-section and which fits directly, i.e. closely, around a stator pole of the SRM. The second stage comprises an outer coil winding which may also be rectangular in cross-section and which fits directly around the first coil winding. The inner and outer coil windings are form-wound, i.e., separately wound as subassemblies before application to the stator poles.

During SRM stator assembly, each outer coil is assembled around the respective stator pole. After all of the outer coils have been assembled onto the stator, each inner coil is then inserted into the corresponding outer coil. The inner and outer coils on each stator pole are electrically connected so that one coil augments the flux produced by the other. For example, the coils are connected in series with the same general winding direction. Finally, the stator pole coil windings comprising each motor phase winding are connected in series or in parallel.

1 - N_ - 1 RD - 18j554 A better understanding of the present invention will become apparent from the following illustrative description of the invention when read with the accompanying drawings in which: 5 Figure 1 is a cross-sectional view of a conventional switched reluctance motor; Figure 2 is a cross-sectional view of a SRM illustrating the direction of current in an illustrative motor phase winding and further illustrating the direction of magnetic flux resulting therefrom; and Figure 3 is a cross-sectional view of a switched reluctance motor including stator pole coil windings in accordance with the present invention.

4 RD-18, 554 Figure I is a cross-sectional view of a switched reluctance motor (SRM) 10 having conventional stator pole coil windings. By way of example, SRM 10 is illustrated as a three-phase machine, each motor phase comprising one pair of diametrically opposite stator poles. However, it is to be understood that the principles of the present invention apply to SRMs having any number of phases and, thus, any number of stator poles.

As shown, SRM 10 includes a rotor 14 rotatable in either a forward or reverse direction within a stationary stator 15. Rotor 14 has two pairs of diametrically opposite rotor poles 16a-16b and 18a-18b. Stator 15 has three pairs of diametrically opposite stator poles 20a-20b, 22a-22b, and 24a-24b. Conventional stator pole coil windings 26a, 26b, 28a, 28b, 30a and 30b, respectively, are wound on stator poles 20a, 20b, 22a, 22b, 24a and 24b, respectively. The stator pole coil windings on each pair of opposing or companion stator pole pairs are connected in series or parallel to form a motor phase winding. As shown in Figure 2, the current I in each phase produces a magnetic flux linkage by generating flux in the directions indicated by arrows 32 and 34. For example, as shown, windings 26a and 26b are connected in series so that current I flows in the direction indicated.

As hereinabove stated, during manufacture of a typical SRM, the stator pole coil windings are wound as subassemblies, hereinafter designated form-wound coil windings, and thedapplied to the respective stator poles.

The number of turns and type of conductor used to make the coil windings for a particular SRM depend upon the intended application therefor. For windings comprised of a relatively low number of turns of a heavy gauge conductor, the windings are each formed into a predetermined coil shape corresponding RD-18,554 to the size of the respective stator poles, the stiffness of the heavy gauge conductor retaining the shape of.the coil after the conductors have been form-wound. The conductors comprising the form-wound coil are tightly packed. Alternatively, depending upon the SRM and its intended use, a form-wound coil can be wound from many turns of a light gauge conductor, provided that the turns are wrapped around a nonmetallic bobbin to retain the coil shape. In order to apply the form-wound coil windings to 10 the stator poles, as hereinabove described, there is a maximum coil width W1 which allows sufficient clearance for assembly of the adjacent coil windings. Thus, a significant portion of each interpole space 36 is unoccupied by coil windings, as illustrated in Figure 1. This limitation on 15 usable interpole space, in turn, restricts maximum attainable flux and, hence, output torque and voltage. Figure 3 shows a SRM 38 embodying two-stage stator pole coil windings according to the present invention. Each stator pole coil winding comprises an outer coil winding 40a, 20 40b, 42a, 42b, 44a and 44b, respectively, and an inner coil winding 50a, 50b, 52a, 52b, 54a and 54b, respectively. The outer coil winding and inner coil winding comprising each stator pole coil winding are form-wound separately. To maximize use of each interpole space 36, the inner and outer windings each preferably have a substantially rectangular cross-section, as illustrated. Moreover, for equivalentsized SRMs, the width W, of the inner coil winding of the present invention is preferably equal to that of the conventional coil winding shown in Figure 1. Also like the 30 conventional coil winding, the inner coil is sized to fit directly, i.e. closely, around the corresponding stator pole. With the inner coil winding dimensions as hereinabove described, the height H2 of the outer coil winding is required to be less than the height H1 of the inner coil k 1 4 t RD-18, 554 winding, as shown in Figure 3. The outer coil winding is sized to fit directly around the corresponding inner coil winding, and the width W2 of the outer coil winding is limited by the clearance necessary for assembly, to be described hereinafter in detail.

In accordance with the present invention, during SRM stator assembly, outer coil windings 40a, 40b, 42a, 42b, 44a and 44b are applied to stator poles 20a, 20b, 22a, 22b, 24a and 24b, respectively, before any inner coil windings are applied thereto. With each outer coil winding in place about the corresponding stator pole, each inner coil winding 50a, 50b, 52a, 52b, 54a and 54b is inserted into an outer coil winding 40a, 40b, 42a, 42b, 44a and 44b, respectively, while being fitted directly around the corresponding stator pole. Each outer coil winding is then connected in series to the respective inner coil winding to preserve the same general winding direction. Lastly, the diametrically opposite stator pole coil windings are connected in series or parallel, as desired, so that the resulting magnetic flux patterns are similar to those of the conventional SRM, as illustrated in Figure 2.

By utilizing the two-stage stator pole Coil windings of the present invention, magnetic flux production is significantly increased. Hence, torque and voltage output per unit of current are proportionately increased, thereby resulting in a more efficient SRM. Additionally, by employing the two-stage windings according to the present invention, so as to utilize a significantly larger portion of the interpole space, conductor losses per unit of applied power are decreased, thus further enhancing SRM efficiency.

While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will k - is - i RD-18, 554 1 occur to those of skill in the art without departing from the invention herein. For example, a three-stage coil winding comprising an inner coil winding, a first outer coil winding and a second outer coil winding may be constructed in accordance with the present invention. To assemble a stator comprising a three-stage coil winding, the winding stages are applied to the stator poles sequentially as follows: all first outer coil windings; all second outer coil windings; and, lastly, all inner coil windings. In like fashion, the principles of the present invention may be extended to four winding stages and so forth.

1 RD-18, 554

Claims

Claims:-

1. A concentrated stator pole coil winding for a multiphase motor, said motor including a rotor and a stator, said rotor having a plurality of rotor poles, said stator having a plurality of pairs of opposing stator poles, each phase of said motor comprising at least one said pair of opposing stator poles, each pole of said stator having one of said concentrated stator pole coil windings wound thereon, each said stator pole coil winding comprising:

an inner coil winding having a substantially 10, rectangular cross-section and being adapted to fit directly around one of said stator poles; and an outer coil winding having a substantially rectangular cross-section and being adapted to fit around said inner coil winding, said outer coil winding further being electrically connected in series to said inner coil winding. 2. The stator pole coil winding of claim I wherein the height of said outer coil winding is less than the height of said inner coil winding. 20 3. The stator pole coil winding of claim 1 or 2 wherein said outer coil winding fits directly around said inner coil winding. 4. in a multiphase switched reluctance motor having a rotor and a stator, said rotor having a plurality of rotor poles, said stator having a plurality of pairs of opposing stator poles, each phase of said motor comprising at least one said pair of opposing stator poles, each pole of said stator having a concentrated stator pole coil winding wound thereon, each said stator pole coil winding comprising: an inner coil winding having.a substantially rectangular cross-section and being adapted to fit directly around one of said stator poles; and an outer coil winding having a substantially rectangular cross-section and being adapted to fit around said inner coil winding, said outer coil winding further being electrically connected in series to said inner coil winding.

S. The switched reluctance motor of claim 4 wherein the height of said outer coil winding is less than the height of said inner coil winding.

6. The switched reluctance motor of claim 4or 5 wherein said outer coil winding fits directly around said inner coil winding.

7. A method for making a concentrated stator pole coil winding for a switched reluctance motor, said motor including a rotor and a stator, said rotor having a plurality of rotor poles, said stator having a plurality of opposing stator poles, said method comprising:

form-winding an inner coil winding, said inner coil winding having a substantially rectangular cross-section and being adapted to fit directly around one of said stator poles; form-winding an outer coil winding said outer coil winding having a substantially rectangular cross-section and being adapted to fit directly around said inner coil winding; placing said outer coil winding around the corresponding one of said stator poles; inserting said inner coil winding into said outer coil winding; and electrically connecting said inner coil winding and said outer coil winding in series.

8. The method of claim 7 wherein the height of said outer coil winding is less than the height of said inner coil winding.

9. A method for assembling a stator for a multiphase switched reluctance motor, said stator having a RD-18,554 j 1 1 - ( k - 1 RD-18,554 plurality of pairs of opposing stator poles, each pole of said stator having a concentrated stator pole coil winding wound thereon, each phase of said motor comprising at least one said pair of opposing stator poles and the stator pole coil windings wound thereon, said method comprising the steps of:

form-winding a plurality of inner coil windings, each said inner coil winding having a substantially rectangular cross-section and being adapted to fit directly around one of said stator poles; form-winding a plurality of outer coil windings, each said outer coil winding having a substantially -angular cross-section and being adapted to fit around the rect corresponding inner coil winding; placing each of said outer coil windings, respectively, around one of said stator poles, respectively; inserting each of said inner coil windings, respectively, into the corresponding outer coil winding; electrically connecting each of said inner coil windings and the corresponding outer coil winding in series to form the respective stator pole coil winding; and electrically connecting the stator pole coil windings corresponding to each phase of said motor together.

10. The method of claim 9 wherein the height of each of said outer coil windings, respectively, is less than the height of each of said inner coil windings, Xespectively.

11. The method of claim 9 wherein each of said outer coil windings fits directly around the corresponding inner coil winding.

- Q - RD--1 8.v 554 12. A concentrated stator pole coil winding for a multiphase motor, said motor including a rotor and a stator, said rotor having a plurality of rotor poles, said stator having a plurality of pairs of opposing stator poles, each phase of said motor comprising at least one said pair of opposing stator poles, each pole of said stator having one of said concentrated stator pole coil windings wound-thereon, each said stator pole coil winding comprising:

an inner coil winding having a substantially rectangular cross-section and being adapted to fit directly around one of said stator poles; and an outer coil winding having a substantially rectangular cross-section and being adapted to fit around said inner coil winding, said outer coil winding further being electrically connected to said inner coil winding such that the magnetic flux produced by the outer coil winding augments the magnetic flux produced by the inner coil winding.

13. A winding according to claim 12,- wherein the inner and outer windings are connected in-series.

14. A switched reluctance motor substantially as hereinbefore described with reference to Figure 3.

15. A method of making a switched reluctance motor substantially as hereinbefore described with reference to Figure 3.

Published 1990 at The Patent Office. StateHouse.66'71 High Holborn. LondonWClR4TP- Further copies maybe obtainedfrom, The Patent Office Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1/87 c