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SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

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larger than that of the synchronous machines treated in [27]. Nonetheless, this assumption is good<br />

enough to understand the basic principles of motors and will be used throughout this report,<br />

which is concerned with machine analysis not from a design perspective but from the perspective<br />

of basic understanding and control.<br />

Using these assumptions we can trace flux paths through the machine and know that the length or<br />

shape of the path through the stator and rotor steel does not affect the reluctance of that path—<br />

only the length of the path through the effective airgap is important. Since every machine has a<br />

certain cross section that will yield diametrical symmetry it is easiest to trace these flux paths<br />

through the center of the rotor shaft. Finally, this idea allows a basic definition of saliency: when<br />

stator and rotor slotting is ignored a machine is non-salient if all flux paths through the center of<br />

the rotor have the same reluctance; any machine that is not non-salient is salient. The cross<br />

sections of some generalized stators and rotors are shown in Figure 2.7.<br />

18

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