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SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

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this section torque production is examined in terms of the physical interaction of the space<br />

distributions of stator MMF (FS) and rotor flux density (BR).<br />

It is important to realize that the MMF produced by the stator and the MMF produced by the rotor<br />

will combine in the space of the airgap to produce a resultant MMF; the same can be said of the<br />

other magnetic quantities. Thus the torque can be described in terms of the stator and rotor<br />

components, the stator component and the resultant, or the rotor component and the resultant [27,<br />

p.121].<br />

The developed view of a two pole three-phase motor is shown in Figure 3.13. Whereas the<br />

previous developed views have shown the stator MMF (e.g., Figure 3.7), this view shows only the<br />

rotor flux density distribution; the windings are shown only for positional reference. The rotor is<br />

positioned at 30° and this is only because it is a convenient number—the fact that the peak of the<br />

flux density is collocated with a coilside of phase-B is of no significance.<br />

Figure 3.13 – Developed view of two pole motor showing rotor flux density.<br />

BR is a vector used to represent the peak of the space distribution of flux density due to the rotor.<br />

This vector (BR) and the vector ΦR, which represents the peak of the space distribution of rotor<br />

flux, are always coincident with the rotor axis. Therefore any of these vectors can be used to<br />

denote the position of the rotor and its associated distributions. The cross section of the same<br />

motor with identical rotor position is shown in Figure 3.14.<br />

78

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