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an investigation of dual stator winding induction machines

an investigation of dual stator winding induction machines

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3P<br />

L<br />

= (10.4)<br />

m Te λriqs<br />

4 Lr<br />

The torque equation in this form is similar to the one for dc <strong>machines</strong>. So if the rotor<br />

flux linkage λ r is regulated to be const<strong>an</strong>t, the output electromagnetic torque <strong>of</strong> <strong>an</strong><br />

<strong>induction</strong> machine will linearly depend on the q-axis current in the synchronous reference<br />

frame. To achieve good dynamic perform<strong>an</strong>ce, the synchronous reference frame<br />

tr<strong>an</strong>sformation that decouples the state variables, independent control <strong>of</strong> rotor flux<br />

linkages <strong>an</strong>d <strong>stator</strong> currents are the import<strong>an</strong>t issues that need to be dealt with.<br />

The inst<strong>an</strong>t <strong>an</strong>gle for the synchronous reference frame with respect to the stationary<br />

reference frame is the only qu<strong>an</strong>tity needed for the synchronous reference frame<br />

tr<strong>an</strong>sformation. Depending upon the method <strong>of</strong> getting this rotor flux position <strong>an</strong>gle, the<br />

vector control schemes are divided into two categories: direct <strong>an</strong>d indirect vector control.<br />

The rotor flux position <strong>an</strong>gle is determined from the direct flux measurements using flux<br />

sensing techniques in direct vector control while in the indirect vector control scheme the<br />

<strong>an</strong>gle is computed from the measured rotor position <strong>an</strong>d the calculated slip, which is<br />

expressed as:<br />

θe<br />

= θr<br />

+ θ sl<br />

= ∫ r +<br />

( ω ω )<br />

s<br />

dt<br />

where, ω r is the rotor speed <strong>an</strong>d ω s is the slip frequency.<br />

346<br />

(10.5)<br />

Hence the indirect field orientation is basically achieved by controlling the slip<br />

frequency to satisfy the specified slip condition calculated from the <strong>induction</strong> machine<br />

model. Increasing the complexity <strong>of</strong> the system by adding flux sensors or <strong>winding</strong>s to the<br />

<strong>induction</strong> machine not only increases the cost <strong>of</strong> the system but also increases the

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