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an investigation of dual stator winding induction machines

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Finite Element Analysis (FEA) is the favored method <strong>of</strong> plotting the steady state<br />

magnetic fields <strong>of</strong> various parts <strong>of</strong> electric <strong>machines</strong>. Using FEA, repeated <strong>an</strong>d time-<br />

consuming simulations are needed to obtain comprehensive perform<strong>an</strong>ce pr<strong>of</strong>iles <strong>of</strong><br />

electric <strong>machines</strong>. Although FEA yields very accurate results, its use to study the<br />

dynamics <strong>of</strong> electric <strong>machines</strong> <strong>an</strong>d <strong>machines</strong> with multiple <strong>winding</strong>s <strong>an</strong>d excitations <strong>of</strong><br />

different frequencies is still a difficult task. With the benefit <strong>of</strong> the <strong>winding</strong> function<br />

approach in which the <strong>winding</strong> distributions are accounted for, <strong>an</strong>d the proposed coupled<br />

circuit model <strong>of</strong> the <strong>dual</strong> <strong>stator</strong> <strong>winding</strong> <strong>machines</strong> which yields currents in <strong>stator</strong> coils <strong>an</strong>d<br />

rotor bars, the air gap flux density c<strong>an</strong> be approximately determined under all operating<br />

conditions. The influence <strong>of</strong> the air gap magnetic saturation is approximated using the B-<br />

H curve <strong>of</strong> the magnetic core material <strong>of</strong> the machine. Both the FEA <strong>an</strong>d the<br />

experimental results on a 3 hp 2/6 <strong>dual</strong> <strong>winding</strong>, squirrel-cage <strong>induction</strong> machine confirm<br />

the accuracy <strong>an</strong>d utility <strong>of</strong> the air gap flux linkage calculation scheme.<br />

The arr<strong>an</strong>gement <strong>of</strong> the chapter is as follows: Some preliminaries are listed in section<br />

3.2. The <strong>winding</strong> function approach used for the calculations <strong>of</strong> the machine induct<strong>an</strong>ces<br />

with a general non-const<strong>an</strong>t air gap length is presented in Section 3.3. Sections 3.4, 3.5,<br />

3.6, respectively outline the calculations <strong>of</strong> the <strong>stator</strong> induct<strong>an</strong>ce, rotor induct<strong>an</strong>ce <strong>an</strong>d<br />

<strong>stator</strong>-rotor mutual induct<strong>an</strong>ce matrices. The <strong>dual</strong> <strong>stator</strong> <strong>winding</strong> <strong>induction</strong> machine<br />

model is presented in section 3.7. A general complex variable tr<strong>an</strong>sformation for n-phase<br />

systems is outlined in Section 3.8 <strong>an</strong>d is utilized to tr<strong>an</strong>sform the phase variable voltage<br />

<strong>an</strong>d electromagnetic torque equations (set forth in Section 3.7) <strong>of</strong> the machine to the rotor<br />

reference frame. This tr<strong>an</strong>sformation retains the space harmonics in the rotor currents <strong>an</strong>d<br />

enables the determination <strong>of</strong> the bar currents. Computer simulation results <strong>of</strong> the <strong>dual</strong><br />

86

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