Baldor 23H Series Installation & Operating Manual page 139

Thus, the expression for torque, with a floating neutral, becomes:
T = K I
T
φφ I (Torque in N-m, K
T = 0.955 K
E
The back-EMF or voltage constant is measured phase to phase, and current is the DC level thru the
winding.
With the commutation scheme above, the maximum torque developed occurs at 60°, and is:
^
T = T (sin(60)-sin(300))
MAX
^
= T x 1.73
The minimum torque is:
^
T = T x 1.5
MIN
Therefore, theoretical torque ripple in this situation is:
% = MAX - MIN = 1.73 - 1.5 = 13.2%
MAX
Torque ripple depends on the control scheme, and it has to be designed to acceptable application
tolerances.
AC Control
The application of a sinusoidal current:
^
I = I x (Sin φ + φ phase)
is applied to all three windings (see Figure 4), which are sinusoidal:
^
φ sin φ
K = K
T T
When energizing all three windings, the output torque developed is then equal to the sum of the
torques in all three windings:
T = T + T + T
M R S T
Figure 4. AC Control
Application Notes
in v/r/s)
E
1.73
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