SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

Figure 3.6 – One electrical cycle of unit-amplitude, balanced sinusoidal general quantities.
Now let Figure 3.6 represent the phase currents of a wye-connected stator with an isolated
neutral. As a first example, use the ordinate as a reference line ( 0
) and determine the three
phase currents: IA is equal to 1.0 while IB and IC are both equal to –0.5. Since IA is positive and
unity, its MMF component is exactly that shown in Figure 3.4. Since IB and IC are both negative
and half-unity, their MMF components are of opposite polarity and are half the amplitude of
those shown in Figure 3.4. At this position (zero electrical degrees), the component of MMF in
the airgap due to each phase is shown in Figure 3.7. Also shown is the overall (“total” 12 ) MMF in
the airgap; the peak of the total MMF is coincident with the electrical position of the three-phase
currents (zero electrical degrees).
12 “Resultant” would be a more appropriate term but it is nearly always reserved to describe the
combination of stator and rotor magnetic fields and these will be discussed later.
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