SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

This coupling can be mitigated by modifying the voltage commands to include decoupling
signals, as shown in Figure 5.32 (this figure replaces the error summing junctions and PI
controllers in Figure 5.30). In addition to the decoupling terms, the q-circuit has a term to offset
the effect of the bEMF. These terms are simply the negative of the corresponding terms in Figure
5.31. Usually when this decoupling controller is shown in the literature ([80, p.689], [107]) a
salient machine is assumed and the inductances in both Figure 5.31 and Figure 5.32 are then d L
and q L , but only a nonsalient machine is considered here, hence L s .
Figure 5.32 – bEMF offset and d-q current decoupling controller in synchronous frame.
The decoupling controller of Figure 5.32 requires as an input the rotor frequency ω. FOC already
requires the rotor position signal and the velocity can be estimated from this. (It should be noted
that this structure is not the same as that in Figure 5.27 or Figure 5.29, wherein the cross-coupling
was internal to the PI controller. Those figures showed the equivalent regulator viewed in
different frames; Figure 5.32 shows a decoupling scheme implemented intentionally, and the
cross-terms are external to the PI controller, as one would normally expect.) The decoupling can
be represented more simply by Figure 5.33, where the signals D
d
terms given by Equation (5.12); these are found directly from Figure 5.32.
i Li
i Li K
D
d s q
D
q s d
E
i and D
i are the decoupling
q
(5.12)
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