Pole-amplitude modulation, pole-changing electric motors and generators
AssigneeNational Research Development Corporation
InventorsAlexander R. W. Broadway, Gordon H. Rawcliffe, deceased, by Caroline S. Rawcliffe, executrix
Life of this patent
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Abstract
A pole-amplitude modulation (P.A.M.) three-phase, pole-number changing machine having star-connected and delta-connected stator winding components, thereby providing additional means for reducing m.m.f. harmonics in the resultant three-phase field. Pole-number changing is effected by reversing the star-connected winding component relatively to the delta-connected component. A design method defines relationships between alternative pole-numbers and stator slot number, and slot-spacing between star- and delta-connected components.
Claims6
A pole-amplitude modulation, pole-number changing electric machine having a three-phase stator winding comprising three phase-winding sections in delta connection and three other phase-winding sections in star connection, coils of the delta-connected phase-windings and coils of the star-connected phase-windings following each other regularly and alternately around the winding periphery and pole-amplitude modulation of the combined stator winding being effected by reversal, in current-carrying sense of the series-connected phase windings relatively to the delta-connected phase-windings.
A method for designing a pole-amplitude modulation, pole-number changing electric machine having a three-phase stator winding comprising star-connected and delta-connected winding sections, comprising the steps of:
- selecting a slot-number "S" for a three-phase winding element where S=12 slots or a multiple thereof;
- selecting a pole-number "P1" for the first of the alternative pole-numbers required;
- designing a first three-phase winding for P1-poles in 1/2S slots;
- designing a second and similar three-phase winding for P1-poles in 1/2S slots having coils with substantially 1/.sqroot.3 times the number of turns and conductors of substantially .sqroot.3 times the cross-section area of the coils of the first winding;
- combining the said first three-phase winding with said second three-phase winding in the S slots of the winding element using a phase band of each winding in a regular and alternate sequence throughout the winding section;
- ensuring that the slot-spacing of corresponding phase-bands of the first and second windings corresponds substantially to 30.degree. electrical spacing at the first pole-number, P1;
- selecting one pole-number from the alternatives (P1+S)-poles and (P1-S)-poles to be the second alternative pole-number;
- selecting a stator slot-number equal to NS slots, where N is a small even integer;
- combining 1/2N pairs of said winding elements in the NS slots of the stator with such slot-spacing that the m.m.f. component of the other one of the said pole-number alternatives (P1+S)-poles and (P1-S)-poles, whichever one was not selected for the said second alternative pole-number, is most completely eliminated;
- selecting a coil-pitch for the combined winding;
- connecting the said first three phase-windings in delta-connection and connecting the second three phase-windings, at one end of each, to the delta terminals of the first windings;
- and
- providing six control leads from the delta terminals and the other ends of the second windings for providing parallel-(star/delta) and series-(star/delta) switching of the combined stator winding for providing said first pole-number and said second pole-number, respectively.
Dependencies are inferred from the claim text.