Name: Danfoss VLT 5000 Series
Brand: Danfoss
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VLT

5000 SyncPos option

MG.10.J4.02 – VLT is a registered Danfoss trade mark

2. A closed-loop PID control. The PID controller

monitors the difference between the actual

position and the setpoint position. Based on

this information it calculates a control signal to

minimize the position deviance. Thus the

SyncPos option is able to compensate for

changes in load or friction. The PID controller

is also necessary to compensate for any posi-

tion deviance caused by inaccurate setting of

the open-loop feed-forward controller.

In short: The feed-forward control is used to handle

changes in the setpoint reference (especially im-

portant in synchronization applications), while the

PID control is used to handle changes in load con-

ditions or inaccuracies of the feed-forward control.

Proportional factor KPROP (11)

The

Proportional factorProportional factor

Proportional factor is multiplied with the posi-

tion deviance and the result is added to the con-

trol signal (the internal speed-reference to the VLT).

Since the calculated control signal is proportional

to the position deviance (or error) this kind of con-

trol is called proportional control. The behavior of

the proportional control is similar to that of a spring

– the further the spring is extended the stronger

the counter-force it produces.

Influence of the

Proportional factorProportional factor

Proportional factor:

KPROP too small large position deviation due to

non-compensatable load and

frictional moment;

KPROP larger quicker reaction, smaller

steady-state deviation, larger

overshoot, lesser damping;

KPROP too great heavy vibrations, instability.

Derivative factor KDER (12)

The

Derivative factorDerivative factor

Derivative factor is multiplied with the deriva-

tive of the position deviance (the 'velocity' of the

position deviance) and the result is added to the

control signal. The behavior of the derivative con-

trol is similar to that of an absorber – the faster the

absorber is extended the stronger the counter-

force it produces. Thus using the

Derivative factorDerivative factor

Derivative factor

increases damping in your system.

Influence of the

Derivative factorDerivative factor

Derivative factor:

KDER small no effect;

KDER larger better dampening, lesser over-

shoot; if KPROP is increased

simultaneously: faster reaction to

control deviation at the same

level of vibration;

KDER too large heavy vibrations, instability.

Integral factor KINT (13)

The sum of all error is calculated every time the

control signal is updated. The

Integral factor Integral factor

Integral factor is

then multiplied with the sum of all positioning

errors and added to the overall control signal. Thus

in case that steady-state position errors occurs in

your application, make sure you use the integral

part of the controller. Steady-state errors will be

levelled out as the summed error increases over

time until the control signal eventually matches the

load.

It is possible to set a limit for the control signal

generated by the integral part of the controller (anti-

windup).

Influence of the

Integral factorIntegral factor

Integral factor:

KINT very small steady-state position deviance

is very slowly regulated to zero;

KINT larger faster regulation towards zero

steady-state position deviance,

larger overshoot;

KINT too large heavy vibrations, instability.

Integration limit KILIM (21)

The

Integration limitIntegration limit

Integration limit sets a limit for the control sig-

nal generated by the integral part of the controller.

This helps to prevent the so called "wind-up" pro-

blems which typically occurs in applications where

the overall control signal (the internal speed-refe-

rence) is maxed out for long periods of time.

This feature is also very helpful in applications

where the power to the motor is turned off and on

while the option card is controlling the VLT. Cutting

of power to the motor (by setting terminal 27 low)

while little positioning deviance is present in the

controller, could result in an enormous control

signal being generated once the power is turned

back on.

Velocity Feed-forward FFVEL (36)

The

elocity feed-forward elocity feed-forward

elocity feed-forward factor 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 VLT speed reference), and the

speed of the motor. This is indeed the case with

most applications using an asynchronous motor.

Optimizing the PID controller

Brand	Danfoss
Model	VLT 5000 Series
Category	DC Drives
Language	English

Danfoss VLT 5000 Series Manual

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