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an investigation of dual stator winding induction machines

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*<br />

T<br />

*<br />

r<br />

*<br />

I T<br />

λ<br />

current<br />

calculator<br />

*<br />

Iφ<br />

Magnitude<br />

frequency<br />

calculator<br />

ωrm<br />

*<br />

I s<br />

*<br />

ωe<br />

26<br />

current<br />

control<br />

S , S , S<br />

11<br />

21<br />

31<br />

speed<br />

sensor<br />

Inverter<br />

Figure 1.6 The block diagram <strong>of</strong> a scalar torque control system<br />

The reference flux-producing current is calculated as:<br />

m<br />

Motor<br />

*<br />

* λr<br />

Iφ<br />

= (1.2)<br />

L<br />

where, L m is the magnetizing induct<strong>an</strong>ce.<br />

The magnitude <strong>of</strong> the <strong>stator</strong> current is given as:<br />

* * 2<br />

I s IT<br />

= + I<br />

(1.3)<br />

* 2<br />

φ<br />

<strong>an</strong>d the reference frequency <strong>of</strong> the <strong>stator</strong> current is expressed as:<br />

*<br />

* P IT<br />

ωe<br />

= ωrm<br />

+<br />

(1.4)<br />

*<br />

2 τ r Iφ<br />

Lm<br />

where, τ r = is the time const<strong>an</strong>t <strong>of</strong> the rotor.<br />

r<br />

r<br />

The torque developed by the machine is limited by the maximum value <strong>of</strong> current.<br />

Only under tr<strong>an</strong>sient conditions <strong>an</strong>d for a limited time, is a higher th<strong>an</strong> rated current<br />

allowed. The current sensors increase the system cost <strong>an</strong>d the control scheme is more<br />

complicated th<strong>an</strong> the const<strong>an</strong>t V/Hz method.

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