SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

Figure 4.33 – SVM overmodulation region: SV locus.
Unlike the SPWM case, one cannot reach six-state squarewave operation by simply increasing the
length of the commanded SV. Instead, the SV will have to be made to linger longer at the corners
of the hexagon until finally it does not trace the hexagon but instead jumps between base SVs as
in regular six-step squarewave mode. As in the SPWM case, there are numerous resources in the
literature concerning the control of a SVM inverter through the overmodulation region and into
six-step squarewave operation. Sometimes the literature will state that the shaded region in Figure
4.34 is what defines the SVM overmodulation region, but what they refer to is the fundamental
produced in overmodulation. Notice that this shaded region in Figure 4.34 is outside the temporal
limit; this shows that it is a representation of the fundamental’s trajectory, not the actual output of
the inverter.
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