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an investigation of dual stator winding induction machines

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10.6 Full-order Flux Observer<br />

The control scheme for <strong>dual</strong> <strong>stator</strong> <strong>winding</strong> <strong>induction</strong> machine with a speed sensor<br />

has been derived <strong>an</strong>d simulated in the previous section. The existence <strong>of</strong> the speed sensor<br />

not only increases the cost but also decreases the reliability <strong>of</strong> the whole system. For<br />

example, in the power train application, the environment for encoder is normally hostile<br />

so that more th<strong>an</strong> one encoder will need to be installed in the system. At <strong>an</strong>y point in<br />

time, only one <strong>of</strong> the encoders is working while the others are the backup <strong>of</strong> the primary<br />

one in case <strong>an</strong>y failure is found in the primary encoder. Industrial drive applications<br />

require the sensorless technique rather th<strong>an</strong> the use <strong>of</strong> encoder. Generally speaking, two<br />

techniques have been proposed. One <strong>of</strong> them is machine model based methods <strong>an</strong>d the<br />

other one is magnetic structure based methods. A brief introduction <strong>of</strong> the sensorless<br />

control <strong>of</strong> <strong>induction</strong> machine has been given in chapter 1.<br />

From the review <strong>of</strong> the previous work on the full-order observers, some import<strong>an</strong>t<br />

issues related to the selection <strong>of</strong> observer gains <strong>an</strong>d the determination <strong>of</strong> speed estimator<br />

parameters have not been clearly <strong>an</strong>d adequately addressed. A relatively comprehensive<br />

methodology for the design <strong>of</strong> full-order flux observer <strong>an</strong>d the speed adaptive mech<strong>an</strong>ism<br />

are defined [10.39]. The observer gains are designed based on the Butterworth<br />

polynomials. The tr<strong>an</strong>sfer function between the estimated speed <strong>an</strong>d actual speed is<br />

derived in the synchronous reference frame, which are used to select appropriate PI<br />

controller parameters for the speed estimation. The D-decomposition method is applied to<br />

determine the stable <strong>an</strong>d unstable regions <strong>of</strong> the tr<strong>an</strong>sfer function. However, the designed<br />

system parameters have only been checked for a particular rotor speed with variable slip<br />

frequencies so that stability within the whole operating speed r<strong>an</strong>ge c<strong>an</strong>not be guar<strong>an</strong>teed.<br />

367

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