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B.2.3 Torque controller and feedback
The torque controller, shown in Figure 56, is a PI controller. Gains are set using the Mint
keywords KIPROP and KIINT. The torque demand is scaled into a current demand. This is
compared with the measured current, obtained from the current sensors, and the error is fed
into the PI control calculation. The resulting value forms the PWM signal that is fed through
the power stage into the motor windings. The gain values KIPROP and KINT must be tuned
for a specific motor. This is performed automatically by the Commissioning Wizard.
The feedback device (e.g. an encoder or resolver) is used to determine motor position and
speed. Motor speed can be filtered to reduce measurement noise if necessary. The time
constant of this filter is specified using the keyword KVTIME. By default the filter is turned off
(KVTIME = 0). Note that introducing a filter on measured speed tends to reduce the stability
of the speed controller. This can make the tuning of the speed controller gains difficult if large
values of KVTIME are used.
Torque demand
Internal
scaling
Measured speed (VEL)
Measured position (POS)
B-8 Control System
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Proportional gain term
KIPROP
Integral gain term
Current
demand
+
dt
-
Filter
(KVTIME)
Figure 56 - Torque control system
PWM value
+
(EFFORT)
KIINT
+
Measured current
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Feedback
device
(e.g. encoder,
resolver)
Power
Motor
stage
Current
Feedback
sensors
interface
MN1902
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