Appendix 2 Pi Regulation - Danfoss VLT 3500 Series Instruction Manual

PI Regulation
Appendix 2
The following instructions will enable quick and easy set-
up of the PI regulation and associated parameter
settings. Detailed information about each parameter can
be found in the parameter section of this manual.
Parameter 100:
Set the load type. There are several choices in each
group but variable torque medium or variable torque
medium with AEO will suit most pumps or fans.
Parameter 101:
Select closed loop operation.
Parameter 114:
Choose the type of feedback signal the transmitter is
using. The default value is current as it is the most
widely used signal type.
Parameter 115 & 116:
Are used to scale a display read-out which is proportional
to the feedback transmitter signal. The value is displayed
only if feedback has been selected in display mode. To
get to display mode from any other mode press MENU &
DATA keys simultaneously.
If a transmitter has a range of 0-5 bar, 0 can be set in
parameter 115 and 5 in parameter 116. In parameter 117
the unit bar can be programmed.
The default values are 0 & 100, to display 0-100%.
Parameter 117:
Choose the unit of measurement for scaling the
feedback signal of the transmitter set in parameter 115 &
116. The default value is %.
Parameter 119:
The feed forward factor allows a part of the set-point
signal to by-pass the PID regulator. This gives faster
response when starting up a system where the
integration time (parameter 122) is very long, and the
system error is small.
Set at 0%. Only add 5% at a time, and only if the system
takes a long time to start up. The drawing shows the
influence of the feed forward.
Feedforward
(P: 119)
Setpoint
or
+
Reference e
(Ramps
–
P: 215, 216)
Process
+
M
PID
Feedback signal
FB
factor
Parameter 120:
Controls the bandwidth of the output from PID controller.
Set at 100%.
Parameter 121:
Controls the gain of the system. For most fan and pump
systems it should not be higher than 0.9. If set to higher
values the system may become unstable.
• Centrifugal fans - between 0.1 - 0.6
• Centrifugal pumps - between 0.3 - 0.8
Parameter 122:
Improves the final accuracy by integrating out the error.
• Centrifugal fans - between 10-12 seconds
• Centrifugal pumps - between 3-8 seconds
Parameter 123:
Differential time is not used in pump and fan systems.
Set to Off.
Parameter 124:
If the feedback signal is fluctuating it can be dampened
with a time constant. This can occur on pump systems
where the pipe can be shut off quickly and cause a
standing wave of water.
Set initially to 0 seconds.
Parameter 125:
Leave at the default value of 100% unless the
following conditions occur.
• If the feedback signal does not match the standard
analog signal choices in parameter 412 & 413 a value
must be programmed which scales the feedback signal
to a standard analog value.
• When using min. speed, parameter 201, it must be
ensured that the min. speed % value is not greater than
the set-point % value, otherwise the min. speed will
over-ride the set-point.
(See example on page 112.)
111