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an investigation of dual stator winding induction machines

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additional torque generated by the one-rotor circuit model during the tr<strong>an</strong>sient process as<br />

shown in Figure 5.2(c). Greater oscillatory torque is observed in the results from the one<br />

rotor circuit model which is absent in two independent rotor circuit model as shown in<br />

Figure 5.2(d-f). It follows that the pulsating torque is due to the interaction <strong>of</strong> the two<br />

<strong>stator</strong> <strong>winding</strong>s through a common rotor current. The power consumption distribution<br />

between the two <strong>stator</strong> <strong>winding</strong> sets (represented by the electromagnetic torques due to<br />

each <strong>winding</strong> set in Figure 5.2(e-f)) ch<strong>an</strong>ges; however the total developed<br />

electromagnetic torque is const<strong>an</strong>t as the load torque remains the same.<br />

When the same operating equal slip frequency condition (5.116) as enforced in the<br />

computer simulation in Figure 5.2 is applied to a 2hp laboratory <strong>dual</strong> <strong>winding</strong> squirrel-<br />

cage <strong>induction</strong> machine, the experimental results are shown in Figure 5.3. The two <strong>stator</strong><br />

<strong>winding</strong> sets are fed with two voltage source PWM inverters using the space vector PWM<br />

modulation scheme. The rotor speed is measured by a shaft mounted encoder. The open-<br />

loop control algorithm in (5.116) is implemented using a TI DSP TMS320LF2407 EVM<br />

board to determine the frequency <strong>of</strong> the XYZ <strong>winding</strong> set. The motor under load is<br />

initially running under steady state condition with a const<strong>an</strong>t Volt/Hz operating condition<br />

at frequencies <strong>of</strong> 30 <strong>an</strong>d 90 Hz for the ABC <strong>an</strong>d XYZ <strong>winding</strong> sets respectively. Then the<br />

measured rotor speed is used to adjust the frequency <strong>of</strong> the XYZ <strong>winding</strong> set (the<br />

frequency <strong>of</strong> the ABC <strong>winding</strong> set is kept const<strong>an</strong>t at 30 Hz) to force the values <strong>of</strong> slip<br />

frequency <strong>of</strong> the two <strong>winding</strong>s to be equal. The rotor speed drops <strong>an</strong>d the power drawn<br />

by the ABC <strong>winding</strong> set <strong>an</strong>d the phase “A” current increases while the power drawn by<br />

the XYZ <strong>winding</strong> set <strong>an</strong>d the phase X current decreases, validating the trends in the<br />

computer simulation results in Figure 5.3.<br />

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