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an investigation of dual stator winding induction machines

an investigation of dual stator winding induction machines

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The control parameters <strong>of</strong> a PI controller have to be properly selected to regulate the<br />

error function <strong>of</strong> the Model Reference Adaptive Scheme (MRAS), yield accurate<br />

estimated rotor speed <strong>an</strong>d maintain the stability <strong>of</strong> the whole motor drive. The stability <strong>of</strong><br />

the system in the whole variable speed r<strong>an</strong>ge is the first concern <strong>an</strong>d the condition<br />

required to achieve stability is that all the poles <strong>of</strong> the tr<strong>an</strong>sfer function should be in the<br />

left half s-pl<strong>an</strong>e, which also implies that all the poles should have negative real parts. In<br />

the real applications, from the system noise point <strong>of</strong> view, the real parts <strong>of</strong> the poles<br />

c<strong>an</strong>not be too large. The zeroes <strong>of</strong> the tr<strong>an</strong>sfer function also need to have negative real<br />

parts to ensure that the system is the minimum phase system.<br />

Several approaches have been proposed to select the control parameters <strong>an</strong>d ensure<br />

the stability <strong>of</strong> the system. The Routh criteria is one <strong>of</strong> those methods, in which the<br />

coefficients <strong>of</strong> the tr<strong>an</strong>sfer function are used to build up a Routh table, <strong>an</strong>d the stability<br />

conditions c<strong>an</strong> be found from the Routh table. However, because <strong>of</strong> the complexity <strong>of</strong> the<br />

coefficients, the Routh criteria is not applicable in this case. The D-decomposition is<br />

applied to select the parameters <strong>of</strong> the PI controller. Basically, the boundary <strong>of</strong> the<br />

stability region is found in the control parameters pl<strong>an</strong>e <strong>an</strong>d the parameters within the<br />

stability region are applied to the system. There are two critical conditions that need to be<br />

examined. The first case is the condition in which the poles located at the origin <strong>of</strong> the s-<br />

pl<strong>an</strong>e, which c<strong>an</strong> be expressed as:<br />

p = 0<br />

(10.143)<br />

The second condition is that the poles are located at the imaginary axis <strong>of</strong> s-pl<strong>an</strong>e.<br />

The expression for this case is:<br />

p = ± jω<br />

(10.144)<br />

0<br />

398

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