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an investigation of dual stator winding induction machines

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The vector control <strong>of</strong> <strong>an</strong> <strong>induction</strong> machine is based on the synchronous reference<br />

frame tr<strong>an</strong>sformation, in which the state variables in the abc stationary reference frame<br />

are tr<strong>an</strong>sformed into <strong>an</strong> orthogonal q-d reference frame that rotates at the synchronous<br />

speed. One <strong>of</strong> the import<strong>an</strong>t adv<strong>an</strong>tages <strong>of</strong> this tr<strong>an</strong>sformation is that all the state<br />

variables are dc qu<strong>an</strong>tities in steady state after the tr<strong>an</strong>sformation, which greatly<br />

simplifies the controller design so that all the traditional controller design methodologies<br />

applicable to dc signals c<strong>an</strong> be used in ac machine control. The other adv<strong>an</strong>tage gained<br />

from the tr<strong>an</strong>sformation is that the coupling between the <strong>stator</strong> <strong>winding</strong>s is totally<br />

removed because <strong>of</strong> the orthogonality <strong>of</strong> q-d reference frame. The torque equation <strong>of</strong><br />

<strong>induction</strong> machine will be given to explain the similarity between the dc machine control<br />

<strong>an</strong>d vector control <strong>of</strong> <strong>an</strong> <strong>induction</strong> machine. The torque equation <strong>of</strong> <strong>an</strong> <strong>induction</strong> machine<br />

in terms <strong>of</strong> rotor flux linkages <strong>an</strong>d <strong>stator</strong> currents is given as:<br />

3P<br />

L<br />

( λ i − i )<br />

m Te = dr qs λqr<br />

ds<br />

4 Lr<br />

345<br />

(10.2)<br />

where, P is the number <strong>of</strong> poles, L m is the mutual induct<strong>an</strong>ce, L r is the rotor induct<strong>an</strong>ce,<br />

λ qr <strong>an</strong>d λ dr are the q- <strong>an</strong>d d-axis rotor flux linkage respectively, i qs <strong>an</strong>d i ds are the q- <strong>an</strong>d<br />

d-axis <strong>stator</strong> currents respectively. It should be noted that the electromagnetic torque<br />

equation given in (10.2) is satisfactory for <strong>an</strong> arbitrary reference frame, however the<br />

synchronous reference frame tr<strong>an</strong>sformation ensures that all the variables will be dc<br />

qu<strong>an</strong>tities in steady state.<br />

If the rotor flux linkage is aligned with the d-axis, which me<strong>an</strong>s<br />

⎧λdr<br />

= λr<br />

⎨<br />

⎩λqr<br />

= 0<br />

Then the torque equation (10.2) c<strong>an</strong> be simplified as;<br />

(10.3)

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