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an investigation of dual stator winding induction machines

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For the current model flux observer, the measured <strong>stator</strong> currents <strong>an</strong>d rotor speed are<br />

used. The influence <strong>of</strong> parameter estimation errors on the estimated flux linkage are<br />

studied using FRF <strong>an</strong>alysis. It is found that under high slip condition, the magnitude <strong>of</strong><br />

rotor flux linkage is sensitive to rotor resist<strong>an</strong>ce while the phase <strong>an</strong>gle <strong>of</strong> the estimated<br />

rotor flux linkage is very insensitive. Both the magnitude <strong>an</strong>d phase <strong>an</strong>gle <strong>of</strong> estimated<br />

rotor flux linkage are sensitive to the rotor resist<strong>an</strong>ce <strong>an</strong>d magnetizing induct<strong>an</strong>ce under<br />

rated slip condition. It should be noted that the accuracy c<strong>an</strong> be affected by the rotor<br />

leakage induct<strong>an</strong>ce under <strong>an</strong>y operating condition.<br />

The measured <strong>stator</strong> voltages <strong>an</strong>d rotor speed are utilized in the full order open loop<br />

flux observer, in which the <strong>stator</strong> currents are estimated as intermediary qu<strong>an</strong>tities. It has<br />

been found that the sensitivity to <strong>stator</strong> resist<strong>an</strong>ce decreases with increasing rotor speed<br />

<strong>an</strong>d the influence <strong>of</strong> leakage induct<strong>an</strong>ce is relatively small <strong>an</strong>d nearly const<strong>an</strong>t. However,<br />

the need for accurately measured <strong>stator</strong> voltages are low <strong>an</strong>d zero speed r<strong>an</strong>ge is a main<br />

limitation <strong>of</strong> this observer.<br />

In addition to these, a c<strong>an</strong>cellation method open loop flux estimator has been<br />

presented, in which <strong>stator</strong> voltages <strong>an</strong>d currents as well as rotor speed are used. The<br />

inherent drawback <strong>of</strong> this observer lies in huge flux estimation error when the rotor speed<br />

is near zero due to the division by rotor speed. In this r<strong>an</strong>ge, the qu<strong>an</strong>tization noise due to<br />

the numerical differentiation will be signific<strong>an</strong>t. Based on the above <strong>an</strong>alysis, <strong>an</strong><br />

improved closed loop Gopinath model for flux estimation has been proposed in [10.14],<br />

in which the voltage model <strong>an</strong>d current model were combined to be a closed loop<br />

observer. A similar flux observer with a generalized <strong>an</strong>alysis method c<strong>an</strong> be found in<br />

[10.15].<br />

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