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SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

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Figure 5.8 – Comparison of reference signals under steady state operation.<br />

The figure is now repeated as Figure 5.9 with the exact same commands in the rotor reference<br />

frame (Figure 5.8-a is identical to Figure 5.9-a). However, in Figure 5.9, the rotor was turning at<br />

constant speed as before, but at 60° the rotor was instantaneously locked by an external force that<br />

was applied. The same value of torque is still being produced and the current space vector is still<br />

orthogonal to the rotor flux (as enforced by the PI regulators in the rotor frame; any transient<br />

behavior is not shown). Since the rotor is frozen, the phase values that create the SV are frozen as<br />

well. This should help enforce the visualization that components in the rotor frame do not have<br />

any fixed relationship to those in the stationary frame. This is exactly the point of using the rotor<br />

frame to perform the regulation: the transformations will take care of producing the equivalent<br />

command in the stationary frame.<br />

214

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