SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

N e
f A ( ) i
2
N e
f B ( ) i
2
N e
f C ( ) i
2
A
B
C
cos( )
cos( 120
cos( 120
)
)
To further illustrate that the per-phase MMF space distribution is always sinusoidal, Figure 3.5
shows the component of MMF due to phase-A current at different electrical positions ωt=(0°,
60°, 90°, 120°, 180°, 240°, 270°, 300°), assuming i () t 1.0cos( t)
. Each phase’s component
of MMF is a standing wave in space.
Figure 3.5 – Stator MMF distribution of phase-A at various electrical positions in time.
Figure 3.6 shows one complete electrical cycle of unit-amplitude balanced cosinusoidal three-
phase general quantities (notice that the ordinate is not at the far left-hand side). At any given
electrical angular position δ, a vertical reference line will intersect all three phase plots. The
instantaneous value of each phase quantity is that value at the intersection with the reference line.
As a mathematical property, the sum of all instantaneous phase values will always be zero.
A
(3.1)
67