Baldor 23H Series Installation & Operating Manual page 137

The brushless motor can be driven by either a DC control
or an AC control. However the torque developed by the
package is different.
The torque developed by a brushless motor depends on the control technology used. The same
motor can be driven by either a DC control or an AC control scheme. However, the torque devel-
oped by the package is different. The following will cover the sine-emf motor when driven by
different methods, and results attained.
Brushless Motors
The winding distribution of a brushless motor is
sinusoidal, and as shown in Figure 1, the result-
ing torque generated is a function of the shaft
angular position. Thus current into a winding
generates a torque which is described by:
T = T x Sin (electrical angle)
pk
^
T = T x Sin (ø)
where T is the instantaneous torque, T
the peak value of torque, and φ is the electrical
angle of the shaft. The electrical angle is different
than the mechanical angle, and these are related
by:
angle elect = N x angle mech
2
where N is the number of poles.
In a three phase system, the windings are shifted
by 120 electrical degrees, and the equations
describing torque per winding are:
^
= T x Sin φ
T
r
^
T = T x Sin (φ+120°)
s
^
T = T x Sin (φ+240°)
T
Energizing winding R while rotor is at a position
of 30 elect degrees (see Figure 2) will result in a
torque being developed forcing the shaft to
rotate. The shaft will rotate to the 180° (elect)
position and stop. However, if when the shaft is
at the 150° (elect) position, the current is
removed from winding R and applied to
winding T, the shaft will continue to rotate. If
Application Notes
Is It DC or AC Brushless
(1)
^
or T is
PK
(2)
(3)
(4)
(5)
Page 17
Figure 1. Sinusoidal - EMF Motor
Figure 2. Energizing Sinusoidal
EMF Motor