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an investigation of dual stator winding induction machines

an investigation of dual stator winding induction machines

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otating flux vector c<strong>an</strong> be related to the position <strong>an</strong>d the rotor. For example, the<br />

difference <strong>of</strong> the imped<strong>an</strong>ce <strong>of</strong> the motor between the flux axis <strong>an</strong>d the quadrature axis is<br />

measurable at injected high frequency due to the skin effect [10.58]. The flux position<br />

c<strong>an</strong> be estimated from this difference <strong>of</strong> imped<strong>an</strong>ce. A recent speed estimation method<br />

based on high frequency current due to the high frequency injected voltages was found in<br />

[10.59]. Different high frequency injection techniques for sensorless control <strong>of</strong> <strong>induction</strong><br />

machine have been reviewed <strong>an</strong>d experimentally investigated in [10.60]. One <strong>of</strong> the<br />

conclusions <strong>of</strong> this paper is that high frequency injection techniques c<strong>an</strong> outperform<br />

observer-based methods at low speed r<strong>an</strong>ge. The variation <strong>of</strong> the leakage induct<strong>an</strong>ce due<br />

to either saturation or rotor slotting has been used to estimate the flux position by<br />

measuring the zero sequence current in [10.61]. However, <strong>an</strong> appropriate test voltage<br />

needs to be injected <strong>an</strong>d <strong>an</strong> extra sensor is necessary in this application. The low-<br />

frequency signal injection method for sensorless <strong>induction</strong> machine drive has been<br />

proposed in [10.62], in which a zero-sequence voltage component due to the low<br />

frequency injected signal is used to estimate the position <strong>of</strong> the air-gap flux. Another low<br />

frequency current injection method has been proposed to estimate the rotor flux position,<br />

in which <strong>an</strong> oscillation component in back electromotive force (EMF) due to the small<br />

speed oscillation caused by injected current signal is used to form <strong>an</strong> error signal. The<br />

error signal is regulated to be zero. As a result the test signal <strong>an</strong>d rotor flux are aligned<br />

[10.63]. A sensorless position estimation method for double-cage <strong>induction</strong> machine<br />

using the resist<strong>an</strong>ce variation <strong>of</strong> the outer-cage has been proposed in [10.64]. The special<br />

double-cage rotor structure makes this method less attractive for the application.<br />

40

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