VLT
®
5000 Series
Relative references can be programmed. A relative
reference is a percentage value (Y) of the sum of
the external references (X). This percentage value
is added to the sum of the external references,
which produces the active reference (X + XY).
See drawing on pages 62 and 63.
If relative references are to be used, parameter 214 is to
be set to Relative [1]. This makes the preset references
relative. Furthermore, Relative reference [4] can be
programmed on terminal 54 and/or 60. If an external
relative reference is selected, the signal on the input will
beapercentagevalueofthefullrangeoftheterminal.
The relative references are added with signs.
NB!:
Terminals that are not in use should preferably
be set to No function [0].
D
ifferentiator gain limit
If there are quick changes in reference or feedback
in a given application - which means that the error
changes swiftly - the differentiator may soon become
too dominant. This is because it reacts to changes in
the error. The quicker the error changes, the stronger
the differentiator gain is. The differentiator gain can
thus be limited to allow setting of the reasonable
differentiation time for slow changes and a suitably
quick gain for quick changes. This is done in parameter
420, Speed PID Differentiator gain limit.
L
owpass filter
If are oscillations of the current/voltage on the
feedback signal, these can be dampened by means
ofalowpassfilter. Setasuitablelowpassfiltertime
constant. This time constant represents the limit
frequency of the ripples occurring on the feedback
signal. If the lowpass filter has been set to 0.1s, the
break frequency will be 10 RAD/sec., corresponding
to (10/2 x π) = 1.6 Hz. This will mean that all
currents/voltages that vary by more than 1.6 oscillations
per second will be removed by the filter.
In other words, control will only be carried out on a
feedback signal that varies by a frequency of less
than 1.6 Hz. Choose a suitable time constant in
parameter 421, Speed PID Lowpass filter.
■ Quick discharge
This function is only available in EB units (extended
with brake) of the following type:
• VLT 5001-5052, 200-240 V
• VLT 5001-5102, 380-500 V
• 5001-5062, 525-600 V
This function is used for discharging the capacitors
in the intermediate circuit after the mains supply
has been interrupted. This is a useful function for
servicing the frequency converter and/or the motor
installation. The motor must be stopped before
quick discharge is activated. If the motor acts as a
generator, quick discharge is not possible.
The quick discharge function can be selected
via parameter 408. The function starts when the
intermediate circuit voltage has dropped to a given
value and the rectifier has stopped.
In order to obtain the possibility of a quick discharge,
the frequency converter requires an external 24 V DC
supply to terminals 35 and 36, as well as a suitable
brake resistor on terminals 81 and 82.
For sizing of the discharge resistor for quick discharge,
see Brake Instructions MI.50.DX.XX.
NB!:
Quick discharge is only possible if the
frequency converter has 24 Volts external
DC supply and if an external brake/discharge
resistor has been connected.
Before servicing the installation (frequency
converter + motor), it must be checked
that the intermediate circuit voltage
is below 60 V DC. This is done by measuring
terminals 88 and 89, load-sharing.
NB!:
The power dissipation during quick discharge
does not form part of the power monitoring
function, parameter 403. When sizing re
sistors,
this fact should be taken into consideration.
MG.51.A9.02 - VLT is a registered Danfoss trademark
92
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