Danfoss MCO 305 Operating Instructions Manual page 32

MCO 305 Operating Instructions
Run successive test runs until the two velocity profiles shown in the Testrun graph have the same
maximum value.
Velocity Feed-forward is now optimized, save the current value.
4. In systems with large inertia and/or rapid changes in the reference velocity it is a good idea to use and
optimize the Acceleration Feed-forward control (make sure the inertial load is connected when optimi-
zing this parameter):
Execute a Testrun with KPROP=0, KDER=0,
KINT=0, FFACC=0, and FFVEL at the optimized
value found above. Use the highest possible
acceleration setting. If par. 32-81 Shortest
Ramp is adjusted properly an acceleration
value of 100 and a deceleration value of 100
should be sufficient. Start out with a low set-
ting of Acceleration Feed-forward approx. 10.
View the velocity profiles: If during acceleration the actual velocity is constantly lower than the
reference velocity profile, then set a higher value of Acceleration Feed-forward and
again.
Run successive test runs until the two velocity profiles shown in the Testrun graph have similar ramp-
up and ramp-down curves.
Acceleration Feed-forward is now optimized, save the current value.
5. Next step is finding the maximum stable value
of the Proportional Factor in the PID controller.
Execute a Testrun with KPROP=0, KDER=0,
KINT=0. Set FFVEL and FFACC at the optimi-
zed values found above.
View the velocity profile. If the velocity profile
is not oscillating then increase the Proportional
Factor. Run successive test runs until the
actual velocity profile is oscillating mildly.
Decrease this "mildly" unstable Proportional Factor value to about 70 %. Save this new value.
6. In order to dampen the oscillations created by
the Proportional part of the controller, the
Derivative Value should now be optimized.
Start a Testrun with KINT=0 and
KDER=200. Set FFVEL, FFACC and KPROP at
the optimized values found above.
Run successive test runs with increasing
values of the Derivative Value. At first the
oscillations will gradually reduce. Stop in-
creasing Derivative Value when the oscillations
begin to increase.
Save the last value of Derivative.
7. In any system that requires a zero steady-state error, the Integral part of the controller must be used.
Setting this parameter though is a trade-off between achieving zero steady-state error fast (which is
good) and increasing overshoot and oscillations in the system (which is bad).
If you are using the Integral part of the PID controller, remember to reduce the par. 32-63 Limit Value
for Integral Sum as much as possible (without losing the Integral Factor effect of course) in order to
reduce oscillations and overshoot as much as possible.
32
__ Optimizing the PID Controller __
MG.33.K2.02 – VLT is a registered Danfoss trademark
32-60 Proportional
32-61 Derivative
32-62 Integral
32-65 Velocity Feed-
forward
32-66 Acceleration FF
32-60 Proportional
32-61 Derivative
32-62 Integral
32-65 Velocity Feed-
forward
32-66 Acceleration Feed-
forward
32-60 Proportional
Factor
32-61 Derivative
32-62 Integral
32-65 Velocity Feed-
forward
32-66 Acceleration Feed-
forward
KPROP 0
KDER 0
KINT 0
FFVEL result of
step 3
FFACC 10
Start the Testrun
KPROP 0
KDER 0
KINT 0
FFVEL result of
step 3
FFACC result of
step 4
KPROP result of
step 5
KDER 200
KINT 0
FFVEL result of
step 3
FFACC result of
step 4