Danfoss MCO 305 Operating Instructions Manual page 30

MCO 305 Operating Instructions
Velocity Feed-forward: FFVEL
The par. 32-65 Velocity Feed-forward is a scaling factor that is multiplied with the derivative of the setpoint
position (the velocity of the setpoint). The result of this operation is added to the overall control signal. This
feature is especially useful in applications where there is a good correlation between the control signal (the
FC 300 speed reference), and the speed of the motor. This is indeed the case with most applications.
NB!:
The scaling of the FFVEL parameter is dependent on the correct setting of the Maximum Reference
(par. 3-03) as well as the parameters 32-80 Maximum Velocity and 32-01 Incremental Resolution.
Acceleration Feed-forward: FFACC
The par. 32-66 Acceleration Feed-forward is multiplied with the 2nd derivative of the setpoint position (the
acceleration of the setpoint) and the result is added to the control signal. This feature should be used to
compensate for the torque used to accelerate/decelerate the system inertia.
NB!:
Scaling of the Acceleration Feed-forward factor is depending on the setting of the Shortest Ramp.
You should therefore increase the par. 32-66 Acceleration Feed-forward accordingly when
decreasing par. 32-81 Shortest Ramp and vice versa.
Sampling Time for PID Control: TIMER
For particularly slow systems you can slow down the entire control system by entering multiples of 1 ms as
the sampling time. However, it is important to remember that such a change influences all the control
parameters!
Therefore, normally you should not deviate from the value of 1 ms in par. 32-69 Sampling Time for PID
control.
PID Bandwidth
A Bandwidth of 1000 means that the set value is being executed 100%, thus Derivative, Proportional and
Integral Factors are effective as defined.
But if you are operating a system which could be jeopardized by vibrations, for example, a crane with a
heavy load then you can limit the bandwidth in which the PID controller should function. Par. 32-64 PID
Bandwidth of 300 makes a limitation of 30% possible. The build-up of a vibration is thus prevented since
the control is only moved to with 30% of the calculated set value.
However, then it is necessary also to use the feed-forward part of the controller in order to achieve the
corresponding control.
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__ Optimizing the PID Controller __
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