WO1998024167A1

WO1998024167A1 - Switched reluctance electric motor

Info

Publication number: WO1998024167A1
Application number: PCT/SI1997/000031
Authority: WO
Inventors: Franc Tasner
Original assignee: Franc Tasner
Priority date: 1996-11-29
Filing date: 1997-11-17
Publication date: 1998-06-04
Also published as: SI9600355A

Abstract

Within a switched reluctance electric motor stator, poles (4A, 1, 3A, 6, 2A, 5, ...) are arranged so that two by two adjacent stator poles are magnetically joined to a stator pole pair (4A, 1; 3A, 6; 2A, 5; ...). The value of the ratio of a central angle (ζ3) corresponding to a distance between adjacent pole pairs to a central angle (ζ1) corresponding to a distance between poles belonging to a pole pair is between 0.09 and 0.99. This ratio value changes from the value 0.09 at a switched reluctance electric motor having four stator pole pairs and six motor poles to the value 0.99 when the number of the stator pole pairs increases. A junction of two by two adjacent stator poles to stator pole pairs makes possible that the distance between stator poles in a pole pair differs from the distance between stator poles belonging to two adjacent pole pairs. Thereby a simultaneous excitation of several stator poles is made possible, which also makes possible a larger torque as well as a larger power of the motor of the invention.

Description

SWITCHED RELUCTANCE ELECTRIC MOTOR

The invention concerns a switched reluctance electric motor and more precisely an electric motor of said type in which two by two adjacent stator poles are magnetically joined to a pole pair and distances between poles belonging to a pole pair differ in length from distances between poles of two adjacent pole pairs.

With respect to deficiencies of hitherto known switched reluctance electric motors the technical problem of the present invention is how to construct an electric motor of said type so that during the operation of the electric motor of the invention, already when being equipped with the lowest number of poles at any given ratio of a rotor pole number to a stator pole number, two or more pairs of coils facing each other in diametrically opposite stator pole pairs could be fed at the same time.

In switched reluctance electric motors a stator and a rotor are made of a ferromagnetic material. They comprise an even number exceeding two of stator poles and any even number of rotor poles. The distance between adjacent stator poles is the same throughout the circumference (P.J.Lawrenson, A brief review of switched reluctance drives, European Power Electronics and Drive Journal, 2, pp. 133-144 /October 1992/; E.Hopper, Projektierung von Switched-Reluctance-Antrieben, Antriebstech- nik, 35, pp. 29-31). Attracting forces between the electromagnets of two diametrically opposite poles of the stator or the rotor and the ferromagnetic material of two adjacent rotor and stator poles, respectively, create a torque driving the rotor. The stator poles are formed individually and therefore they must be connected by a ferromagnetic ring armature. Moreover, permanent magnets cannot be mounted on the rotor. Thus some energy is consumed for the rotor pole excitation and no repelling forces between the stator and rotor poles can appear. Among the disadvantages of the known switched reluctance electric motors there is a moderate torque since only two diametrical stator coils can be fed at the same time.

The said technical problem is solved by a switched reluctance electric motor of the invention, which motor is characterized in that stator poles are arranged so that two by two adjacent ones are magnetically joined to a stator pole pair and that the value of the ratio of a central angle corresponding to a distance between adjacent pole pairs to a central angle corresponding to a distance between poles belonging to a pole pair is between 0.09 and 0.99 and this ratio value changes from the value 0.09 at a switched reluctance electric motor having four stator pole pairs and six rotor poles towards the value 0.99 when the number of the stator pole pairs increases.

A magnetic junction of two by two adjacent stator poles to stator pole pairs within a switched reluctance electric motor of the invention advantageously makes possible that the distance between the stator poles in a pole pair differs from the distance between the stator poles belonging to two adjacent pole pairs. Thereby a simultaneous excitation of several stator poles and hence also a larger torque and a larger power of the motor of the invention are made possible.

The invention will now be described in detail by way of example and with reference to the accompanying drawing showing in the single figure a switched reluctance electric motor of the invention represented in a section accros its axis.

The switched reluctance electric motor of the invention is a DC motor having all stator poles 4A, 1, 3A, 6, 2A, 5, ... equipped with coils. Rotor poles 1', 2', ..., however, can be made of permanent magnets (represented) - their poles are designated by designations N (north) and S (south) - or from a ferromagnetic material and in the latter case every second pole is equipped with an exciting coil (not represented). The motor comprises four, six, eight, ... stator pole pairs and six, ten, fourteen, ... rotor poles. These numbers of poles can be multiplied by an arbitrary factor. In the drawing the switched reluctance electric motor is represented as having six stator pole pairs 4A, 1; 3A, 6; 2A, 5; ...; 5A, 2 and ten rotor poles 1', 2', ..., 10'. The switched reluctance electric motor of the invention is characterized in that the stator poles 4A, 1, 3A, 6, 2A, 5, ... are arranged so that two by two adjacent ones form stator pole pair 4A, 1; 3A, 6; 2A, 5; ..., i.e. they are magnetically joined to stator pole pairs 4A, 1; 3A, 6; 2A, 5; ... The stator pole pairs are fastened to a stator ring armature. The motor of the invention can have a stator ring armature made also of a non- ferromagnetic material, e.g. of aluminium.

The switched reluctance electric motor of the invention is further characterized in that the value of the ratio of a central angle φ3, which corresponds to the distance between adjacent pole pairs, to a central angle φl, which corresponds to the distance between poles belonging to a pole pair, changes from the value 0.09 at a switched reluctance electric motor having four stator pole pairs and six rotor poles to the value 0.99 when the number of either kind of poles is very high.

For the represented embodiment it has been found out by experiment that it is suitable if the angular width φl, the angular width φ2 of the stator pole and the angular width 3 are related to each other as follows: φl = 1.06 φR, φl = 0.94 φR, φR being equal to the angle 360° divided by a double number of rotor poles. Herefrom the following ratio results: φ3 : φl = 0.37.

The coils of the stator poles are connected as follows. The opposite coils mounted on diametrically opposite stator pole pairs 1, 1A; 2, 2A; ... and 6, 6A are connected either in series or in parallel and are connected to voltage sources Ul, U2, ... and U6, respectively, so that in the switching moment these poles appear as south poles (S); obviously, it could be arranged so that they would appear as north poles (N). As the voltage sources Ul, U2, ..., U6 rectifiers controlled in a specific sequence may be applied.

In the following the operation of the switched reluctance electric motor of the invention is described.

First the voltage sources Ul and U2 are switched on. The stator poles 1, 1A, 2, 2A become south poles (S) and the stator poles 4, 4A, 5, 5A become north poles (N). Eight pairs of poles mutually attract each other: the stator poles 1/S, 1A/S, 2/S, 2A S, 4/N, 4A/N, 5/N, 5A/N and the rotor poles l'/N, 5'/N, 9'/N, 3'/N, 6'/S, 10'/S, 4'/S and 8'/S, respectively. The rotor is driven by the torque in the negative sense, i.e. in the clockwise direction.

Thereafter the voltage sorce U3 is switched on. The stator poles 3 and 3A become south poles (S) and the stator poles 6 and 6A become north poles (N). After a short time delay the voltage source Ul is switched off whereas the voltage source U2 continues to be switched on. Four pairs of poles mutually repel each other: the stator poles 3/S, 3A/S, 6 N and 6A/N and the rotor poles 8'/S, 2'/S, 3'/N and 7'/N, respectively. After the angle φ3 rotation the attractive force on four rotor poles 7'/N, l'/N, 2'/S and 6'/S appears. Eight stator poles and eight rotor poles mutually attract each other again since the voltage source U2 is still switched on and therefore the attractive force between the stator poles 2/S, 2A/S, 5 N, 5A/N and the rotor poles 9'/N, 3'/N, 4'/S and 8'/S, respectively, continues to act. The rotor is rotated in the negative sense for the angle 2/3 φR, i.e. for 12°.

The voltage source U4 is switched on and between four stator poles and four rotor poles a repelling force appears and after the angle φ3 rotation of the rotor the attractive force between four stator poles and the following four rotor poles appears. After a short time delay after the voltage source U4 has been switched on, the voltage source U2 is switched off. The voltage source U3 continues to be switched on and therefore four stator poles and four rotor poles continue to mutually attract each other. The rotor has been rotated for the angle 2/3 φR again, i.e. for 12°.

The voltage source U5 is switched on and between four stator poles and four rotor poles a repelling force appears and after the angle φ3 rotation the attractive force between four stator poles and the following four rotor poles appears. With a short time delay after the voltage source U5 has been switched on, the voltage source U3 is switched off. The voltage source U4 continues to be switched on and four stator poles and four rotor poles continue to mutually attract each other. The rotor has been rotated for the angle 2/3 φR again, i.e. for 12°.

The voltage source U6 is switched on and the voltage source U4 is switched off. The voltage source U5 continues to be switched on. The rotor has been rotated for the angle 2/3 φR again.

The voltage source Ul is switched on again and the voltage source U5 is switched off. The voltage source U6 continues to be switched on. The rotor has been rotated for the angle 2/3 φR again.

The voltage source U2 also is switched on again and the voltage source U6 is switched off whereas the voltage source Ul continues to be switched on. The situation which existed soon after connecting the electric motor to the voltage sources Ul and U2 is repeated, however, the rotor pole 9' is now next to the stator pole 1.

One cycle comprises six steps which consist in connecting the voltage sources Ul, U2, ..., U6 to the stator coils successively in the positive sense whereat the rotor is rotated in the negative sense for the angle 6 x 2/3 x φR = 4 x φR = 72°.

Claims

1. Switched reluctance electric motor, characterized in that rotor poles (1', 2', ...) act as magnets.

2. Switched reluctance electric motor as recited in claim 1, characterized in that the rotor poles (1', 2', ...) are permanent magnets.

3. Switched reluctance electric motor as recited in claim 1, characterized in that every second rotor pole (1', 2', ...) is equipped with an exciting coil.

4. Switched reluctance electric motor as recited in claim 2 or 3, characterized in that stator poles (4A, 1, 3A, 6, 2A, 5, ...) are arranged so that two by two adjacent ones are magnetically joined into a stator pole pair (4A, 1; 3A, 6; 2A, 5; ...) and that the value of the ratio of a central angle (φ3) corresponding to the distance between adjacent pole pairs to a central angle (φl) corresponding to the distance between poles belonging to a pole pair is between 0.09 and 0.99 and this ratio value changes from the value 0.09 at a switched reluctance electric motor having four stator pole pairs and six rotor poles towards the value 0.99 when the number of the stator pole pairs increases.

AMENDED CLAIMS

[received by the International Bureau on 30 April 1998 (30.04.98); original claims 1-4 replaced by amended claims 1-2 (1 page)]

1. Switched reluctance electric motor, its rotor poles (1', 2', ...) acting as magnets and the number of stator pole pairs (4A, 1; 3A, 6; 2A, 5; ...) being equal to any of the following numbers: 4, 6, 8, ..., characterized in that the number of the rotor poles (1', 2', ...) equals any of the following numbers: 6, 10, 14, ... and that two by two adjacent rotor poles (1', 2', ...) magnetized in radial direction, are oriented in opposite sense.

2. Switched reluctance electric motor as recited in claim 1, characterized in that stator poles (4A, 1, 3A, 6, 2A, 5, ...) are arranged so that two by two adjacent ones are magnetically joined into a stator pole pair (4A, 1; 3A, 6; 2A, 5; ...) and that the value of the ratio of a central angle (φ3) corresponding to the distance between adjacent pole pairs to a central angle (φl) corresponding to the distance between poles belonging to a pole pair is between 0.09 and 0.99 and this ratio value changes from the value 0.09 at a switched reluctance electric motor having four stator pole pairs and six rotor poles towards the value 0.99 when the number of the stator pole pairs increases.

STATEMENT UNDER ARTICLE 19

Claim 1 has been amended since the novelty of its feature has been anticipated by the cited patent US 5 304 882 A and other documents.

The distinctive features of the amended claim 1 are disclosed on page 2, lines 30 and 31, and on page 2, line 28 (cf. Figure).

For the same reason claims 2 and 3 have been cancelled and the former claim 4 is now claim 2.

The description of the invention will be amended accordingly after the written opinion drawn up by the International Preliminary Examining Authority has been received.