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an investigation of dual stator winding induction machines

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1.2.11 Sensorless Control <strong>of</strong> Induction Machine<br />

After the intensive study all around the world in the past 15 years, the development <strong>of</strong><br />

sensorless <strong>induction</strong> motor drives has become a mature technology. However, a<br />

st<strong>an</strong>dardized solution does not emerge, which indicates that the maturing process <strong>of</strong> this<br />

technology will continue.<br />

The obvious adv<strong>an</strong>tages <strong>of</strong> sensorless drives are system cost reduction <strong>an</strong>d increasing<br />

overall system ruggedness <strong>an</strong>d reliability, especially in hostile environments. Generally<br />

speaking, sensorless control is achieved by the extensive use <strong>of</strong> state observation<br />

techniques, in which the measurements <strong>of</strong> currents <strong>an</strong>d voltages are used to estimate the<br />

flux position or velocity. Several sensorless control techniques have been tried over the<br />

years <strong>an</strong>d the methods c<strong>an</strong> be broadly classified into two categories: equivalent circuit<br />

based methods <strong>an</strong>d magnetic structure based methods [1.11].<br />

For the equivalent circuit based method, well known machine dynamic equations are<br />

used to produce relationships between the measured qu<strong>an</strong>tities <strong>an</strong>d estimated variables.<br />

The voltage model flux estimation method is one <strong>of</strong> the oldest methods. The estimation<br />

method is based on the <strong>stator</strong> voltage equation, in which the rotor speed independent<br />

variables--<strong>stator</strong> voltages <strong>an</strong>d currents are utilized. From the <strong>stator</strong> voltage equation, the<br />

<strong>stator</strong> flux is estimated by the integration as:<br />

pλ = v − r ⋅ i<br />

ˆ (1.6)<br />

s<br />

s<br />

s<br />

s<br />

s<br />

s<br />

s<br />

where, the subscript “s” represents the variables <strong>of</strong> <strong>stator</strong> <strong>an</strong>d the superscript “s”<br />

represents the variables in stationary reference frame; the superscript “ ∧ ” represents the<br />

d<br />

estimated variable; p represents the operator .<br />

dt<br />

30

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