SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

obviously a change in perspective. For the former controllers, one might imagine having a phase-
locked loop keeping a set of sinusoidal currents locked 90° ahead of the rotor position. In the
rotor frame controller the reference generated is a DC value. Figure 5.5 is now redrawn from the
rotor reference frame perspective as Figure 5.7. There is no longer any attempt to create a rotating
reference SV that is 90° ahead of another rotating quantity. In fact, although it is tempting to
think about generating the current SV to be 90° of the rotor-stator flux linkage (which is
stationary), it is better to think only about controlling the components of the SV in the rotor
frame.
Figure 5.7 – SV diagram for most efficient torque production; rotor frame.
It is important to note that the signals in Figure 5.8-b and Figure 5.8-c have the relationship
shown for all time (recall that since 0 one of the phase variable signals is simply a linear
combination of the other two). On the contrary, the signals in Figure 5.8-a have no relationship to
the others in the figure unless r is known. The relationship between the signals of Figure 5.8-a
and those of (Figure 5.8-b and Figure 5.8-c) is shown for a constant rotor speed.
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