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an investigation of dual stator winding induction machines

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close to zero, confirming the instability problems observed when operating in the low<br />

speed r<strong>an</strong>ge reported in m<strong>an</strong>y recent publications.<br />

10.7.2 Pole-shift Method<br />

The pole placement method in [10.25] is used to place the poles <strong>of</strong> the full-order<br />

observer. The coefficients <strong>of</strong> the observer are calculated at the base speed ω b so that the<br />

observer poles are shifted to the left by the amount k s with respect to motor poles, that is<br />

o<br />

( b ) = pm(<br />

ωb<br />

) ks<br />

p ω − , with k > 0 .<br />

s<br />

The characteristic equation for <strong>an</strong> <strong>induction</strong> motor is given as:<br />

⎡ p<br />

p ⋅ I − A = ⎢<br />

⎣0<br />

⎡ rsiLri<br />

⎢<br />

− + jωei<br />

0⎤<br />

Di<br />

p<br />

⎥ − ⎢<br />

⎦ ⎢ rriLmi<br />

⎢⎣<br />

Di<br />

rriL<br />

−<br />

Di<br />

rsiLri<br />

p + − jωei<br />

Di<br />

=<br />

rriLmi<br />

−<br />

D<br />

rsiLmi<br />

−<br />

Di<br />

rriLsi<br />

p + − j<br />

D<br />

i<br />

i<br />

si<br />

( ω − ω )<br />

382<br />

ei<br />

rsiL<br />

D<br />

+<br />

j<br />

i<br />

mi<br />

( ω − ω )<br />

ri<br />

ei<br />

ri<br />

⎤<br />

⎥<br />

⎥<br />

⎥<br />

⎥⎦<br />

(10.94)<br />

If E <strong>an</strong>d F are assumed to be the poles <strong>of</strong> the machine, the characteristic equations c<strong>an</strong><br />

be expressed as:<br />

⎛ r L ⎞ ⎛ r L<br />

⎞<br />

si ri<br />

ri si<br />

rsiLmi<br />

rriLmi<br />

⎜ p + − jω<br />

ei p j(<br />

ei ri ) − = ( p − E)<br />

⋅ ( p − F )<br />

D ⎟ ⋅ ⎜ + − ω − ω<br />

i<br />

D<br />

⎟<br />

(10.95)<br />

⎝<br />

⎠ ⎝<br />

i<br />

⎠ Di<br />

Di<br />

If the poles <strong>of</strong> the observer are shifted left with k s , the characteristic equation is<br />

given as:<br />

( p − E + k ) ⋅ ( p − F + k )<br />

λ =<br />

(10.96)<br />

s<br />

Substituting (10.95) into (10.96),<br />

s

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