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an investigation of dual stator winding induction machines

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which are superimposed some space harmonics. When the magnetic circuit is saturated,<br />

new saturation induced air-gap flux densities are generated which may link one set <strong>of</strong><br />

<strong>winding</strong>s to the second set. In the case where the pole pair number combination <strong>of</strong> the<br />

two <strong>stator</strong> <strong>winding</strong>s is 1/3, the 2-pole <strong>winding</strong> under main air-gap flux saturation<br />

produces a third harmonic component which is commensurate with the flux linkage<br />

originating from the 6-pole <strong>winding</strong> set. By virtue <strong>of</strong> the phase <strong>an</strong>gle difference between<br />

the flux densities due to the 2 <strong>an</strong>d 6-pole <strong>winding</strong>s, the generated saturation flux linkage<br />

may reduce or enh<strong>an</strong>ce the fundamental air-gap flux linkage due to the 6-pole <strong>stator</strong><br />

<strong>winding</strong> set. An underst<strong>an</strong>ding <strong>of</strong> the consequence <strong>of</strong> the main flux saturation on the air-<br />

gap flux density given in (6.3) is obtained by reviewing Figure 6.1.<br />

Figure 6.1(a) shows the unsaturated <strong>an</strong>d saturated air-gap flux density (at time t = 0)<br />

due to the sum <strong>of</strong> B ( ω e t θ + α ) <strong>an</strong>d ( t θ )<br />

1 cos 1 − P1<br />

237<br />

B2 cos ωe2 − P2<br />

where P 1 = 1 , 2 3 = P ,<br />

B 0.<br />

9 T <strong>an</strong>d 1 . 1 B T <strong>an</strong>d 0 = α is a phase shift <strong>an</strong>gle. The 3-dimensional graph <strong>of</strong><br />

1 =<br />

2 =<br />

the saturated air-gap flux density is given in Figure 6.1(c). The graph <strong>of</strong> the saturated air-<br />

gap flux density is obtained using the effective nonlinear B-H characteristics <strong>of</strong> the air-<br />

gap magnetic flux path. There are 5th <strong>an</strong>d 7th harmonic components shown in Figure<br />

6.1(b) resulting from the magnetic air-gap saturation effect. The fundamental <strong>an</strong>d third<br />

harmonic flux density components reduce from 0.9 T to 0.647 T <strong>an</strong>d 1.1 T to 0.879 T,<br />

respectively. The effect <strong>of</strong> the phase shift <strong>an</strong>gle α on the magnitudes <strong>of</strong> the harmonic<br />

components for the saturated flux density is displayed in Figure 6.2. While the domin<strong>an</strong>t<br />

harmonic components are present under all phase <strong>an</strong>gles, the magnitudes ch<strong>an</strong>ge<br />

cyclically. Apart from the magnitudes <strong>of</strong> the flux densities, the phase <strong>an</strong>gle between them<br />

affects the magnitudes <strong>of</strong> the generated harmonics <strong>an</strong>d fundamental flux densities. For

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