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an investigation of dual stator winding induction machines

an investigation of dual stator winding induction machines

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zeros <strong>of</strong> the tr<strong>an</strong>sfer function are plotted when the operating rotor speed ch<strong>an</strong>ges from<br />

377 to -377. The slip is kept const<strong>an</strong>t during the speed ch<strong>an</strong>ges <strong>an</strong>d the expression <strong>of</strong> the<br />

slip frequency is given as:<br />

ω = 0 . 05⋅<br />

ω<br />

(10.147)<br />

si<br />

ri<br />

One <strong>of</strong> the reasons to use this kind <strong>of</strong> slip frequency expression is because most <strong>of</strong> the<br />

<strong>induction</strong> <strong>machines</strong> are operated within the slip r<strong>an</strong>ge [− 0.<br />

05,<br />

0.<br />

05]<br />

<strong>an</strong>d the second<br />

reason is that this kind <strong>of</strong> slip definition matches approximately the const<strong>an</strong>t torque<br />

operating condition.<br />

When k i is equal to zero, the pole-zero maps under different rotor speeds with<br />

different const<strong>an</strong>t slip conditions are given in Figure 10.16(a-d). It is found that the poles<br />

<strong>an</strong>d zeros <strong>of</strong> the speed estimator approach the imaginary axis when the rotor speed moves<br />

close to zero no matter the value <strong>of</strong> the operation slip. That might explain why the speed<br />

estimation scheme is always unstable at low speed r<strong>an</strong>ge.<br />

The effects <strong>of</strong> coefficient k i under different rotor speeds <strong>an</strong>d slip frequency<br />

conditions are demonstrated in Figures 10.17 - 10.20.<br />

400

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