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an investigation of dual stator winding induction machines

an investigation of dual stator winding induction machines

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<strong>machines</strong> coupling through the rotor circuit. The magneto-motive forces (MMFs)<br />

resulting in the air-gap flux linkage is the sum <strong>of</strong> the MMFs due to the currents flowing<br />

in the two <strong>stator</strong> <strong>winding</strong> sets <strong>an</strong>d the MMFs arising from the induced rotor bar currents.<br />

If only the fundamental <strong>stator</strong> currents <strong>an</strong>d their induced harmonic-rich rotor currents are<br />

considered, the air-gap flux density therefore has four components given as:<br />

B = B<br />

+<br />

+<br />

1s<br />

∑<br />

k<br />

∑<br />

k<br />

cos<br />

B<br />

B<br />

1rk<br />

2rk<br />

( ωe1t<br />

− P1θ<br />

) + B2s<br />

cos(<br />

ωe2t<br />

− P2θ<br />

+ α1<br />

)<br />

cos(<br />

ω t + ( k − P ) ω t − kθ<br />

+ α )<br />

cos<br />

e1<br />

( ω t + ( k − P ) ω t − P θ + α )<br />

e2<br />

1<br />

2<br />

r<br />

r<br />

2<br />

2k<br />

3k<br />

236<br />

(6.1)<br />

where, B1 s <strong>an</strong>d B2 s are the peak values <strong>of</strong> the air gap flux densities contributed by the<br />

<strong>stator</strong> ABC <strong>an</strong>d XYZ <strong>winding</strong> sets, respectively. B1 rk <strong>an</strong>d B2 rk are the flux densities due<br />

to the<br />

th<br />

k harmonic MMFs <strong>of</strong> rotor currents.<br />

The <strong>dual</strong> <strong>stator</strong> <strong>winding</strong> squirrel-cage <strong>induction</strong> <strong>machines</strong> operate in the asynchronous<br />

mode for the development <strong>of</strong> torque components usually found in the single <strong>winding</strong><br />

three-phase squirrel-cage <strong>induction</strong> machine, however additional average torque<br />

components c<strong>an</strong> be produced during the tr<strong>an</strong>sient process when the absolute values <strong>of</strong> the<br />

slip frequencies relative to the two <strong>stator</strong> <strong>winding</strong>s are equal as shown in previous<br />

chapter; i.e<br />

ω<br />

m ω<br />

e1<br />

e2<br />

ω r = (6.2)<br />

P1<br />

m P2<br />

B = B<br />

1s<br />

+ B<br />

1rp1<br />

cos<br />

( ω t − Pθ<br />

) + B cos(<br />

ω t − P θ + α )<br />

cos<br />

e1<br />

( ω t − Pθ<br />

+ α ) + B cos(<br />

ω t − P θ + α )<br />

e1<br />

1<br />

1<br />

2s<br />

2 p1<br />

e2<br />

2rp2<br />

2<br />

e2<br />

1<br />

2<br />

3p<br />

2<br />

(6.3)<br />

When the speed constraint in (6.2) is implemented in (6.1), the resulting fundamental<br />

air-gap flux density is given in (6.3), comprising <strong>of</strong> components <strong>of</strong> 1<br />

P <strong>an</strong>d 2<br />

P poles upon

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