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SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

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L i <br />

(A.8)<br />

S SS S SR<br />

S SS SR<br />

(A.9)<br />

Since there is only one winding and it is understood to be on the stator, the subscript ‘S’ can be<br />

dropped from the total flux linkage and current. Similarly the first subscript can be dropped from<br />

the self and mutual flux linkages and the two equations simplify to Equations (A.10) and (A.11).<br />

L i <br />

(A.10)<br />

SS R<br />

S R<br />

(A.11)<br />

In Equation (A.11) λ is the total flux linkage of the stator and it has two components: S is the<br />

stator’s self flux linkage due to stator current (shown clearly by Equation A.10) and R is the<br />

stator’s flux linkage due to the flux from the rotor magnets. Each of the components might be<br />

called the stator flux linkage but this would clearly be ambiguous. In this report the total stator<br />

flux linkage will be called the flux linkage. The stator flux linkage due to rotor flux will be called<br />

the rotor-stator flux linkage. Finally, the only inductance of concern is the stator self inductance.<br />

In a wye-connected machine this is the “effective” inductance of the entire machine in operation<br />

(Appendix B) and it is called the synchronous inductance Ls. (The ‘s’ subscript stands for<br />

synchronous, whereas the ‘S’ subscript stands for stator.) With these changes, Equation (A.10) is<br />

written as Equation (A.12).<br />

Li<br />

<br />

(A.12)<br />

s R<br />

To more clearly show that the rotor flux is responsible for the rotor-stator flux linkage, Equation<br />

(A.4) can be rewritten using Equation (A.3).<br />

<br />

NS<br />

S R<br />

N<br />

S S R<br />

Li s NS R<br />

(A.13)<br />

Only nonsalient machines are considered, thus Ls is not a function of rotor position. However, the<br />

stator winding may be a distribution and the rotor flux (as seen from the stator) will always be a<br />

function of rotor position. The interaction of these two to produce the rotor-stator flux linkage and<br />

may require an integral evaluation (Appendix C). Further, as far as motor operation is concerned,<br />

the details of the two are not important—only the rotor-stator flux linkage is required. Therefore<br />

this report will use Equation (A.11) or Equation (A.12).<br />

Li<br />

<br />

<br />

s R S R<br />

271

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