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SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

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Appendix B - Phase-Variable BPMS Motor Model<br />

This appendix derives the phase-variable model of a BPMS motor. Particular attention is given to<br />

the concepts of magnetizing, leakage, and synchronous inductance of a three-phase machine and<br />

the influence wye connection on the phase-variable model.<br />

Appendix A considered the total flux produced as having two components: that produced by the<br />

rotor and that produced by the stator. This separation is still considered but the stator-produced<br />

flux is studied more carefully. Figure B.1 shows the general paths taken by flux produced by the<br />

stator.<br />

Figure B.1 – Magnetizing and leakage paths of stator flux.<br />

Magnetizing flux ( mag ) is that which crosses the airgap and links both the rotor and stator steel<br />

(shaded regions). The leakage flux ( ) shown is produced by stator current but it does not link<br />

the rotor. In addition additional leakage flux is associated with end turns and harmonic slot<br />

leakage, but there is no disadvantage to grouping them together. The leakage flux cannot<br />

contribute to torque production but it does contribute to the electrical inductance of the winding.<br />

There is also rotor leakage but the only consequence of it is that the rotor flux profile will not be<br />

ideal; the rotor-stator flux linkage ψR already takes this into account. In other words the formulae<br />

cannot distinguish between the ideal and actual rotor flux, whereas we can always separate those<br />

two components in the stator.<br />

272

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