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an investigation of dual stator winding induction machines

an investigation of dual stator winding induction machines

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The proposed control scheme has also been checked at low speed. The torque<br />

distribution factor K is set to be a negative value when the rotor speed is within a certain<br />

low speed area. The starting process <strong>an</strong>d dynamic response <strong>of</strong> the system are shown in<br />

Figure 10.6 <strong>an</strong>d Figure 10.7. DC bus voltage is 300 V <strong>an</strong>d 2 Nm load torque is added to<br />

the machine at 4.5 second. The rotor speed ramps up from 0 to 37 rad/s during the<br />

starting process. During the dynamic ch<strong>an</strong>ging process, the rotor speed ramps down from<br />

37 rad/s to zero speed <strong>an</strong>d remains there for one second. After that, the rotor speed keeps<br />

decreasing to -37 rad/s, remains there for 2 seconds <strong>an</strong>d ramps up to 37 rad/s. During the<br />

ramping up process, the rotor speed is also kept at zero speed for a while to check the<br />

system perform<strong>an</strong>ce at that particular operating condition. When the absolute value <strong>of</strong><br />

rotor mech<strong>an</strong>ical speed is within 10 rad/s, the torque distribution factor K ch<strong>an</strong>ges from<br />

0.5 to -0.2 so that the ABC <strong>winding</strong> set generates power <strong>an</strong>d output negative torque while<br />

the XYZ <strong>winding</strong> set has to carry the sum <strong>of</strong> the load torque <strong>an</strong>d the negative torque<br />

generated by ABC <strong>winding</strong> set. This operating condition increases the output torque <strong>of</strong><br />

one <strong>winding</strong> set so that the input voltage magnitude <strong>of</strong> the <strong>winding</strong> set is increased. It is<br />

well known that the main difficulty <strong>of</strong> sensorless <strong>induction</strong> machine control is the very<br />

weak input signals at very low speed due to the low input voltage magnitude. By using<br />

the proposed control method, the input voltage <strong>of</strong> one <strong>winding</strong> set is increased so that the<br />

difficulty <strong>of</strong> sensorless control in a single <strong>winding</strong> <strong>induction</strong> machine is overcome<br />

without <strong>an</strong>y hardware or s<strong>of</strong>tware modifications. The actual rotor speed tracks the<br />

comm<strong>an</strong>d rotor speed within the whole speed r<strong>an</strong>ge including zero speed in the computer<br />

simulation results. The simulation results validate the proposed control scheme.<br />

363

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