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SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

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another and thus could be placed in series to model the circuit is reasonable and familiar. But the<br />

key to understanding this vital aspect is not evident in the circuit theory approach: the flux<br />

produced by the stator winding exists in the same airgap as the rotor flux. As natural as the rotor-<br />

produced airgap flux linkage induces the bEMF 90° ahead, the stator-produced airgap flux<br />

linkage induces a voltage 90°—the standard terminal characteristic of the inductor. This<br />

discussion should cement the meaning of flux linkage provided in the previous chapter: the flux<br />

linkage is the expression that describes the total flux linked by a winding (phase-A in this case).<br />

This should demonstrate why the inductor can be considered an electric circuit element separate<br />

from the bEMF, but both the inductance and bEMF are a result of the resultant airgap flux and<br />

for this reason there are the two distinct (but equivalent) circuit models. Finally, this reinforces<br />

the dependence of bEMF on rotor position.<br />

89

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