VLT
®
5000 Series
Special
functions
quick gain for quick changes. This is done in parameter
443, Process PID Differentiator gain limit.
L
owpass filter
If there are oscillations of the current/voltage feedback
signal, these can be dampened by means of a lowpass
filter. Set a suitable lowpass filter time constant. This
time constant represents the limitfrequency of the
ripples occurring on the feedback signal. If the lowpass
filter has been set to 0.1s, the limit 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 444, Process PID Lowpass filter.
O
ptimisation of the process controller
The basic settings have now been made; all that needs
to be done is to optimise the proportional gain, the
integration time and the differentiation time (parameters
440, 441, 442). In most processes, this can be done
by following the guidelines given below.
1. Start the motor
2. Set parameter 440 (proportional gain) to 0.3 and
increase it until the feedback signal again begins
to vary continuously. Then reduce the value until
the feedback signal has stabilised. Now lower
the proportional gain by 40-60%.
3. Set parameter 441 (integration time) to 20s
and reduce the value until the feedback signal
again begins to vary continuously. Increase the
integration time until the feedback signal stabilises,
followed by an increase of 15-50%.
4. Only use parameter 442 for very fast-acting
systems only (differentiation time). The typical
value is four times the set integration time. The
differentiator should only be used when the
setting of the proportional gain and the integration
time has been fully optimised.
NB!:
If necessary, start/stop can be activated
a number of times in order to provoke a
variation of the feedback signal.
See also the examples of connection given
in the Design Guide.
■ PID for speed control
F
eedback
Use the list below to decide which terminal to use for
the feedback signal and which parameters to program.
Feedback type Terminal Parameters
Pulse 32 306
Pulse 33 307
Feedback
pulse/rev.
329
Voltage 53 308, 309, 310
Current 60 314, 315, 316
Furthermore, the minimum and maximu
m feedback
(parameters 414 and 415) are to be set to values in the
process unit that correspond to the actual minimum
and maximum process feed
back values and units.
The minimum feedback cannot be set to a value
lower than 0. Choose unit in parameter 416.
R
eference
Aminimumandamaxi
mum reference can be set (204
and 205) which limit the sum of all references. The
reference range cannot exceed the feedback range.
If one or several p
reset references are required,
the simplest way of doing this is by setting such
references directly in parameters 215 to 218. Choose
between the
preset references by connecting terminals
16,17,29,32 and/or 33 to terminal 12. Which of them
that are to be used depends on the choice in the
parame
ters of the terminals in question (parameters
300, 301, 305, 306 and/or 307). The table below
can be used to select the preset references.
Preset ref. msb Preset ref. lsb
Preset ref. 1
(par. 215)
00
Preset ref. 2
(par. 216)
01
Preset ref. 3
(par. 217)
10
Preset ref. 4
(par. 218)
11
If an external reference is required, this can either by an
analogue reference or a pulse reference. If current is
used as a feedback signal, voltage can be used as an
analogue reference. Use the list below to decide which
terminal to use and which parameters to program.
Reference type Terminal Parameters
Pulse 17 or 29 301 or 305
Voltage 53 or 54 308, 309, 310 or
311, 312, 313
Current 60 314, 315, 316
MG.51.A9.02 - VLT is a registered Danfoss trademark
91
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