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an investigation of dual stator winding induction machines

an investigation of dual stator winding induction machines

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good steady-state predictions <strong>an</strong>d c<strong>an</strong> be used for the sizing <strong>an</strong>d design optimization <strong>of</strong><br />

the machine. How the time-varying, multi-frequency flux linkages derivable from the<br />

currents flowing in the <strong>stator</strong> <strong>winding</strong>s <strong>an</strong>d rotor bars c<strong>an</strong> be appropriately selected for <strong>an</strong><br />

optimal machine design remains a challenging question. These flux linkages combine<br />

additively in some regions <strong>an</strong>d subtractively in others engendering non-uniform main<br />

flux magnetic saturation.<br />

This chapter reports on a study <strong>of</strong> the effects <strong>of</strong> magnetic saturation on the air-gap<br />

flux linkages <strong>an</strong>d provides for the first time a methodology to include the main air-gap<br />

flux linkage saturation effect in the dynamic modeling <strong>of</strong> the <strong>dual</strong> <strong>winding</strong> <strong>induction</strong><br />

machine. This is achieved by the definition <strong>of</strong> a common reference frame for the defining<br />

differential equations <strong>of</strong> the machine that ensures that the total air gap flux linkage lies on<br />

the d-axis <strong>of</strong> the reference frame. Thus, only the d-axis magnetizing induct<strong>an</strong>ces vary<br />

with the main air-gap flux linkage while the q-axis magnetizing induct<strong>an</strong>ces remain<br />

const<strong>an</strong>t at the unsaturated values. The new dynamic machine model is validated by<br />

computer simulation <strong>an</strong>d experimental results for two operating conditions.<br />

6.2 Main Flux Linkage Saturation Effects<br />

Since the two <strong>stator</strong> <strong>winding</strong>s (ABC <strong>an</strong>d XYZ <strong>winding</strong> sets) have dissimilar pole<br />

numbers, the mutual induct<strong>an</strong>ces between them are zero when the main-flux linkage path<br />

is unsaturated. Possible coupling may be found in the <strong>stator</strong> leakage induct<strong>an</strong>ces.<br />

However, it has been shown in [1.1] that the couplings between the leakage induct<strong>an</strong>ces<br />

do not exist in such a way as to allow the <strong>dual</strong> <strong>stator</strong> <strong>winding</strong> <strong>induction</strong> machine to be<br />

treated (on the fundamental frequency basis) as two independent squirrel-cage <strong>induction</strong><br />

235

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