MXPA96001068A - Improvements in commute reluctance machines - Google Patents

Abstract

The present invention relates to a doubly protruding reluctance machine comprising a stator that defines stator poles and a rotor that defines rotor poles, at least a pair of the rotor poles being simultaneously aligned with a corresponding pair of the stator poles when moving the rotor in relation to the stator, and a phase winding arranged in relation to only one of said pair of stator poles, the winding being energizable to produce flow in a magnetic circuit whose trajectory includes the pairs of poles of rotor and stat

Description

MBJORAS BN MAQUINAS DB RELUCTANCIA SWITCHED Inventor: Norman Neilson Fulton, of English nationality, residing at 3 Bir dale Walk, Leeds, LS17 7SX, England Owner: SWITCHED RELUCTANCE DRIVES LIMITED, English national, residing at Springfield House, Hyde Terrace, Leeds, LS2 9LN, England.

Background of the Invention This invention relates to reluctance machines. The invention is particularly applicable to a switched reluctance machine whether operated as a motor or as a generator.

Reluctance machines are electrical machines which produce torsional force by the tendency of a moving component of the machine to take a position in which the reluctance of the magnetic circuit is minimized. Typically, at least one of the stator and rotor members has magnetic prominences which are normally made in the pole shape and project from the member.

The switched reluctance machine (SR) is a particular form of a reluctance machine which has prominent poles on both stator and rotor members. In this way, the machine is referred to as a "double-outgoing" machine. The production of torsional or electric force (depending on whether the machine is run as an engine or as a generator) is controlled by a controller which regulates the period during which the stator winding is electrically connected to a power source.

Switched reluctance machines are manufactured in various ways. In particular, these differ in the number of stator and rotor poles on the stationary and rotating members, respectively, and in the number of independent circuits with which the controller is capable of separately changing the stator windings in and out of the circuit. Each set of windings separately changed in and out of the circuit by the controller constitutes one phase of the machine. The machine may have one or more such phases.

The theory, design and operation of the switched reluctance machines is well documented, for example, in the book "Switched Reluctance Motors and their Control", by T.J.E. Miller, Clarendon Press, 1993 and the article "Characteristics, Design and Applications of Switched Reluctance Engines and Impellers" by Stephenson et al., PCIM 1993, June 21-24, 1993.

Figure 1 shows a known form of a switched reluctance machine. The stator has six poles (A, A ', B, B', C, C) and the rotor has four poles. Each stator pole has a coil around it. Although only two coils on the stator poles A and A 'are shown in FIG. 1 by way of clarity, it will be appreciated that a similar arrangement can be formed with respect to the other pairs of poles. Typically, the coils on the diametrically opposed poles are connected together either in series or in parallel (depending on the nature of the application of the machine) to form a phase of the machine. Therefore, the machine in Figure 1 is a three-phase machine in which the windings of one phase are changed independently of those of the other phases. When the machine is operated, each phase is normally connected to a source of electrical power through one or more electronic switches t as shown in Fig. 2. The method of operation of such machine using the interruption circuit of Fig. 2 It is well known to experts in the art and is documented in the references mentioned above.

In general, the number of poles in a stator is such that each phase has an equal number of coils associated with it. In the example of Figure 1, each of the three phases has two coils, so that the machine has six stator poles. In the example of figure 3 each of the three phases is made up of four coils placed symmetrically around the stator, giving a stator of twelve poles. It will be appreciated that various combinations of rotor pole numbers and stator poles are possible. The selection of a suitable combination is a matter of design choice for a given application.

When a phase of the machine of Figure 1 is energized by a voltage that is applied to the windings of one of the phases, a magnetic field is placed in the machine. This is shown schematically by the dashed lines of arrow in figure 1. The lines are a representation of the magnetic flux lines in the machine when phase A is energized. This field pattern is known as a two-pole field pattern since the magnetic flux crosses the air separation of the machine at the two main locations.

Generally, when a phase of the machine of Figure 3 is energized, a magnetic field is put as represented by the broken lines with arrow. Such an arrangement is known as a four-pole field pattern. By continuing to multiply the number of coils in a phase, field patterns with increasing number of poles can occur. This can be done regardless of the number of phases of the machine.

In a conventional machine having a coil on each pole, the coils are designed so that they can be assembled in turn on the poles without obstruction of each other. The coils and the gaps between the poles in which they are adjusted are generally similar. The coil, when in place, can not extend angularly beyond the midpoint between two adjacent stator poles as it would occupy the available space at the cost of the adjacent coil and would also prevent the insertion of the adjacent coil into its space. Therefore, the cross-sectional area of a coil side must occupy somewhat less than half the total available cross-sectional area between adjacent poles projecting radially. While the machine designer will often want to make the coil larger by increasing the cross-sectional area to reduce the current density and the consequent energy loss in the coil, it is not possible to do this without increasing the overall size of the coil. machine. There are attempts to solve these problems in machines which have a particular phase number or a particular form of rolling (for example GB-A-2240664 and GB-A-2232305) but these are restricted in their applicability.

It is an object of the present invention to provide a reluctance machine structure that allows a larger coil size to be used in relation to a given pole.

It is a further object of the invention to provide a reluctance machine that is easier and cheaper to build than known reluctance machines.

According to the present invention, there is provided a doubly projecting reluctance machine comprising a stator that defines stator poles and a rotor that defines rotor poles, at least a pair of the rotor poles being simultaneously alignable with a corresponding pair of the stator poles when moving the rotor in relation to the stator, and a phase winding arranged in relation to only one of said pair of stator poles, the winding being energizable to produce a magnetic field whose path includes said pairs of rotor poles and stator.

This invention is particularly applicable to switched reluctance machines which have a four-pole field pattern (or four integral multiples) and an uneven number of phases. However, the invention can also be used in other arrangements of reluctance machines including two-phase machines. The invention consists of placing coils on only one stator pole of a pair of poles in the machine. The coils can be designed so that the machine produces the same operation as it would if the conventional design practice of placing a coil on both stator poles in a pair had been adopted. Because only one pole in a pair is arranged with a winding, the motor can be designed so that the poles adjacent to it support the winding and do not have windings associated with them. Therefore, the space available for the winding is substantially increased since each space between the poles can be used exclusively for a single winding.

BRIEF DESCRIPTION OF THE DIBULES The invention can be practiced in several ways, some of which will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic cross section through a conventional reluctance machine; Fig. 2 is a circuit diagram showing the main power management components of a switching circuit for the machine of Fig. 1; Figure 3 is a schematic cross section through a further form of a conventional reluctance machine; Figure 4 is a schematic cross section through a reluctance machine according to a first embodiment of the invention; Y Figure 5 is a schematic cross-section through a reluctance machine according to a further embodiment of the invention.

Detailed Description of the Invention Referring to Figure 4 of the drawings, a doubly projecting reluctance machine comprises a stator 10 defining twelve equiangularly spaced stator poles 12. By way of clarity, an eight-pole rotor is not shown in Figure 4 However, it will be clear to those skilled in the art that such a rotor could be arranged as in Figure 3, to rotate inside the stator 10.

The stator 10 is provided with three phase windings 0A, 0B, 0C comprising pairs of coils 16 embracing the diametrically opposite stator poles 12 so that the alternating stator poles do not have a coil. In this case, the coils 16 in one phase are connected in series between the terminals 18 of the phases 0A, 0B and 0C. In an alternate mode, the coils are connected in parallel.

Each of the phases is shown as ending at terminals 18. For the machine to operate either as a motor or as a generator, these terminals are connected with a switch with a power supply through a controller so that the control The application of a voltage to each of the phases in sequence will produce the required energy flow. It will be apparent to one skilled in the art that the switched reluctance machines use the same circuit to monitor or generate, only the crooming of the changes in voltage pulses to alter the direction of energy flow from / to the supply.

It can be seen from the inspection of Figure 3 that the flow pattern is placed in the circuit of a reluctance machine by means of the magnetomotive force (MMF) produced by the four coils of a conventional four-pole machine. If, say, coil J of figure 3 were to be placed around coil H and coil L was to be placed around coil K, the total of the magnetomotive force being applied to magnetic circuit would not be changed. If then the coils H and J were combined in one coil, with the same number of turns as the coils H and J in total, and also the coils K and L were similarly combined, the machine would have the form shown in figure 4. which is according to the invention. The machine only has the coils on alternating poles of the phase, but substantially the same operation as the machine of figure 3.

Figure 5 shows a doubly protruding reluctance machine according to the invention derived from that of figure 1. A stator 20 defines six stator poles 22 and a rotor 24 defines four rotor poles 26. Again, the torque of coils associated with each of the three phases 0A, 0B, 0C is combined in the coils 28 on a single stator pole of a pair in a two-pole field pattern. The coil in the inventive machine would be arranged to provide the same turn-amps as a conventional machine for substantially the same operation. However, there is a disadvantage in this two-pole field pattern arrangement in the sense that the remaining coils are adjacent to each other.

The present invention can be implemented to better act on switched reluctance machines having an uneven number of phases and a field pattern with an integral multiple of four poles. Due to the geometry of the stator in such a machine, it will be seen that if the coils are placed on the poles according to the invention, the alternating coils in the phases are on alternating poles in the stator. This in turn allows the coils to be considerably larger due to the relieved space constraint. Even when the coils have twice as many turns as they would have on a conventional machine, they can maintain, or even increase the area in cross section per turn. This allows an equivalent machine to operate with at least no performance degradation for the four-pole field pattern. In addition, there are manufacturing advantages since there are half of the coils to be wound, half of the poles to be isolated and half of the phase connections to be made. This leads to both cost reductions and increased reliability through a reduced component current.

It will be appreciated by one skilled in the art that, although the invention is described in relation to rotating machines, it is equally applicable to linear reluctance machines. In a linear machine the movable member is often still referred to as a rotor. The term "rotor", as used herein, is intended to encompass such rotors of linear machines. Again, the space created by the absence of pairs of coils in the same slot between the stator poles can be used with the same advantage. The reduced number of connections, coils and insulating components in the coil array of this invention will reduce manufacturing costs and time.

Although the invention has been described in connection with the illustrative embodiments discussed above, those skilled in the art will recognize that many variations can be made without departing from the present invention. For example, the present invention is applicable to inverted machines in which the stator is in the center of the machine and the rotor is arranged to rotate around the outside of the stator. Therefore, the description mentioned above of various modalities is made by way of example and not for purposes of limitation. The present invention is intended to be limited only by the scope of the following clauses:

Claims (8)

CLAIMS Having described the invention, it is considered as a novelty, and therefore the content of the following clauses is claimed as property:

1. A doubly projecting reluctance machine comprising a stator that defines stator poles and a rotor that defines rotor poles, at least a pair of the rotor poles being simultaneously alignable with a corresponding pair of stator poles when the rotor moves in relation to the stator, and a phase winding arranged in relation to only one of said pair of stator poles, the winding being energizable to produce flow in a magnetic circuit whose path includes the pairs of rotor and stator poles.

2. A machine as claimed in clause 1, characterized in that the poles define a two-pole field pattern, the pair of stator poles being substantially diametrically opposed.

3. A machine as claimed in clause 1, characterized in that the poles define a 2n-pole field pattern (where n is an integer greater than 1) the stator poles 2n of which are aligned with the poles of 2n rotor simultaneously, the stator poles having n windings.

4. A machine as claimed in clause 3, characterized because n = 2.

5. A machine as claimed in any of clauses 1 to 4, characterized in that the phase or each phase of the machine comprises a plurality of pairs of stator poles.

6. A machine as claimed in clause 5, characterized in that the windings are connected together in series.

7. A machine as claimed in clause 5, characterized in that the windings are connected in parallel.

8. A method for constructing a doubly projecting reluctance machine comprising a stator that defines stator poles and a rotor that defines rotor poles, at least a pair of the rotor poles being simultaneously aligned with a corresponding pair of stator poles when moving the rotor in relation to the stator, the method comprises winding a phase winding in relation to only one of said pair of stator poles, so that the winding is energizable to produce flow in a magnetic circuit whose path includes the pairs of rotor and stator pole. In testimony of which I sign this in Mexico, D.F., on March 22, 1996 LIMITED Apo was or SUMMARY A reluctance machine comprising a rotor, which defines rotor poles and a stator that defines stator poles. Each pair of stator poles, creating a flow path through the rotor, includes only one winding mounted on one of the stator poles. The invention is particularly applicable to a machine having a four-pole field pattern and an uneven number of phases. The coils are placed on alternate stator poles so that the space between the stator poles can be used exclusively for a single winding. The single winding becomes larger to compensate for the lack of a winding on its associated pole.