SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

Figure 2.28 – Phase-variable simulation diagram of general motor.
Clearly, each phase contributes to the overall torque production, thus torque production of a
three-phase motor cannot be investigated unless all three phases are considered. Additionally,
each winding has mutual inductive coupling with the other windings. The duality between torque
and bEMF would then suggest that the circuit of each phase could not be investigated unless all
three phases are considered. This is true but for a wye-connected motor it turns out that this
coupling can be removed by replacing the simple inductance with the “synchronous inductance”
Ls (Appendix B). Thus, the phase-variable model shows that torque is produced by all three
phases but the electrical circuits are not coupled. However, it is vital to note that the applied
voltages are the line-neutral voltages (this directly follows from the previous electrical model;
combining three models (such as that shown in Figure 2.18) the “ vt () ” is by definition the line-
neutral voltage). This means that the model is correct only for applied three-phase voltages that
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