116 - 23/May/97
From the above equation, one can derive the power of the electromechanical conversion;
that is, the power flowing through the machine air gap as the consequence of mutual
interaction of the stator and rotor fluxes:
P
e i
e i
e i
I
em
A A
B B
C C
s
i
=
+
+
=
=
−
3
2
2
ω
π
θ
r
r
Ψ
cos( /
)
The electromagnetic torque obtained by dividing the air-gap power with the field frequency:
T
I
em
s
i
=
−
3
2
2
Ψ
r
cos( /
)
π
θ
From (4) and (5), one can conclude that the usage of the motor with the sinusoidal
electromotive force in the regime of sinusoidal current supply gives a shaft torque that does
not possess the torque ripple, inherent to the brushless DC motors with trapezoidal
electromotive force. As can be seen from (5), the torque depends on the amplitude of the
stator current and on the angular displacement between the rotor flux and the stator
magnetomotive force.
The DBM performs control of the torque magnitude through the stator current amplitude Is.
The phase advance
θ
i of the stator current is set to +
π/2
in the cases when it is necessary to
accelerate in the sense of
ω
r. For decelerating (with respect to the sense of rotation shown in
Fig. 1), the phase advance
θ
i of the stator current is set to -
π/2.
Such a choice leads to the
maximum torque for the given stator current; that is, in the maximum Nm/A. In order to
insure maximized torque per amps, the DBM control software is equipped with "Auto
phasing" routine for the drive self-adjustment (see par. 3.2.5).
(4)
(5)
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