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SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

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Figure 2.27 – Simulation diagram of general motor.<br />

The figure shows the relationships developed in this chapter. The torque function is the “cascade<br />

connection” and the bEMF function is the “feedback connection” between the electrical portion<br />

and the mechanical portion. The coupling exists via the magnetic medium (rotor-stator flux<br />

linkage). Note that the bEMF acts as a disturbance in the voltage-to-current conversion and the<br />

load torque acts as a disturbance in the electromagnetic-torque-to-velocity conversion. These<br />

relationships are derived from first principles so there is essentially no simpler model of a motor.<br />

That is, the torque production, bEMF generation, and their relationship will exist in any motor in<br />

a way very similar to that shown.<br />

Thus, this model could represent a brush DC motor (in that case the torque and bEMF functions<br />

would be constants). Here, it will be used to represent a single winding in a BPMS motor and it<br />

will be called the “phase model.” If a per-phase model is used for each phase, three of them<br />

combined can be used to represent a three-phase motor; this is called the “phase-variable model”<br />

and is shown in Figure 2.28.<br />

48

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