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an investigation of dual stator winding induction machines

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should ensure the stability under all the slip values when rotor speed ch<strong>an</strong>ges from -377<br />

rad/s to 377 rad/s.<br />

The methodology for speed estimator design based on D-decomposition method has<br />

been described clearly in this section. A novel error function has been proposed for the<br />

speed estimation, which has been demonstrated by simulation results. The boundary <strong>of</strong><br />

the speed estimator parameters is calculated using D-decomposition method <strong>an</strong>d<br />

simulation results have been shown in Figure 10.23 <strong>an</strong>d Figure 10.24.<br />

It should be noted that the system perform<strong>an</strong>ce is also due to the placements <strong>of</strong> zeros.<br />

When <strong>an</strong>y zero <strong>of</strong> the system tr<strong>an</strong>sfer function has a positive real part (the system is non-<br />

minimum phase), the closed-loop perform<strong>an</strong>ce is compromised as the right half-pl<strong>an</strong>e<br />

zero induces <strong>an</strong> additional phase shift <strong>of</strong> –180 degrees. Hence the designed speed<br />

estimator gains should be substituted back into the tr<strong>an</strong>sfer function to ensure the<br />

minimum-phase system requirement.<br />

10.10 Speed Controller Design<br />

The above <strong>an</strong>alysis focuses only on the parameter design for the speed estimation.<br />

When the estimated speed is used as the feedback for rotor speed control, the tr<strong>an</strong>sfer<br />

function <strong>of</strong> the speed control ch<strong>an</strong>ges so that a new speed controller design process<br />

becomes necessary. The adopted speed controller design strategy is introduced in this<br />

section. The basic idea <strong>of</strong> the controller parameters determination is also based on the<br />

tr<strong>an</strong>sfer function <strong>of</strong> the speed controller <strong>an</strong>d the D-decomposition method.<br />

407

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