Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1999-03-29
2000-10-31
Ramirez, Nestor
Electrical generator or motor structure
Dynamoelectric
Rotary
310168, 310162, 310261, 310 68R, 318138, 318166, 318254, H02K 1700
Patent
active
061407291
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to electrical machines, and is concerned more particularly, but not exclusively, with electrical motors.
DESCRIPTION OF THE RELATED ART INCLUDING INFORMATION DISCLOSED UNDER 37 CFR
1.97 AND 1.98
FIG. 1 shows a conventional two-phase variable reluctance motor comprising a stator 2 having two pairs 3, 4 of oppositely disposed inwardly directed salient poles provided with two pairs 5, 6 of energising windings corresponding to the two phases, and a rotor 7 having a single pair 8 of oppositely disposed outwardly directed salient poles without windings. Each of the four energising windings is wound about its corresponding pole, as indicated by the symbols Y--Y denoting two diametrically opposite portions of each winding of the winding pair 6 and the symbols X--X denoting two diametrically opposite portions of each winding of the winding pair 5. An excitation circuit (not shown) is provided for rotating the rotor 7 within the stator 2 by energising the stator windings in synchronism with rotation of the rotor so that torque is developed by the tendency of the rotor 7 to arrange itself in a position of minimum reluctance within the magnetic field produced by the windings, as will be described in more detail below. Such a variable reluctance motor offers the advantage over a conventional wound rotor motor that commutator brushes, which are wearing parts, are not required for supply of current to the rotor. Furthermore the fact that there are no conductors on the rotor and that high-cost permanent magnets are not required provides other advantages.
The symbols + and - in diagrams (a) and (b) in FIG. 1 show the directions of current flow in the windings in the two modes of excitation in which the rotor 7 is attracted either to the horizontal position or to the vertical position as viewed in the figure. It will be appreciated that rotation of the rotor 7 requires alternate energisation of the winding pairs 5 and 6, preferably with only one winding pair 5 or 6 being energised at a time, and with the current usually being supplied to each winding pair 5 or 6 in one direction during such energisation. However the windings can only be energised for a maximum of half the time per revolution if useful torque is to be produced, so that highly efficient utilization of the magnetic circuit is not possible with such a motor.
By contrast a fully pitched two-phase variable reluctance motor, as described by J. D. Wale and C. Pollock, "Novel Converter Topologies for a Two-Phase Switched Reluctance Motor with Fully Pitched Windings", IEEE Power Electronics Specialists Conference, Braveno, June 1996, pp. 1798-1803 and as shown in FIG. 2 (in which the same reference numerals are used to denote like parts as in FIG. 1), comprises two windings 10 and 11 having a pitch which is twice the pole pitch of the motor, that is 180.degree. in the example illustrated, and disposed at 90.degree. to one another. The winding 11 may be wound so that one part of the winding on one side of the rotor 7 fills a stator slot 12 defined between adjacent poles of the pole pairs 3, 4, and another part of the winding 11 on the diametrically opposite side of the rotor 7 fills a stator slot 13 defined between two further adjacent poles of the pole pairs 3, 4. The winding 10 has corresponding parts filling diametrically opposed stator slots 14 and 15. Thus the two windings 10 and 11 span the width of the motor with the axes of the windings 10, 11 being at right angles to one another.
Furthermore two modes of excitation of such a motor corresponding to the horizontal and vertical positions of the rotor 7 are shown in diagrams (a) and (b) of FIG. 2 from which it will be appreciated that both windings 10, 11 are energised in both modes of excitation, but that, whereas the direction of current flow in the winding 10 is the same in both modes, the direction of current flow in the winding 11 changes between the two modes. Since current is supplied to both phase windings 10, 11 in both modes and since each winding 10 or
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Barnes Mike
Pollock Charles
Wale John David
Lam Thanh
Ramirez Nestor
University of Warwick
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