ABB ACS350 Series, User Manual

Page: 120 / 314

Program features
120
PID control
There are two built-in PID controllers in the drive:
• Process PID (PID1) and
• External/Trim PID (PID2).
The PID controller can be used when the motor speed needs to be controlled based
on process variables such as pressure, flow or temperature.
When the PID control is activated, a process reference (setpoint) is connected to the
drive instead of a speed reference. An actual value (process feedback) is also
brought back to the drive. The drive compares the reference and the actual values,
and automatically adjusts the drive speed in order to keep the measured process
quantity (actual value) at the desired level (reference).
The control operates on a 2 ms time level.
Process controller PID1
PID1 has two separate sets of parameters ( 40 PROCESS PID SET 1 , 41 PROCESS
PID SET 2 ). Selection between parameter sets 1 and 2 is defined by a parameter.
In most cases when there is only one transducer signal wired to the drive
,
only
parameter set 1 is needed. Two different parameter sets (1 and 2) are used e.g.
when the load of the motor changes considerably in time.
External/Trim controller PID2
PID2 ( 42 EXT / TRIM PID ) can be used in two different ways:
• External controller: Instead of using additional PID controller hardware, the user
can connect PID2 output via drive analog output or fieldbus controller to control
a field instrument like a damper or a valve.
• Trim controller: PID2 can be used to trim or fine tune the reference of the drive.
See section Reference trimming on page 101 .
Block diagrams
The figure below shows an application example: The controller adjusts the speed of
a pressure boost pump according to the measured pressure and the set pressure
reference.
A C T P A R F U N C D R I V E
E N T E R
L O C
R E M
R E S E T R E F
A C S 6 0 0
0 . . . 1 0 b a r
4 . . . 2 0 m A
3
3
2
PID
ref
k
ti
td
i
dFiltT
errVInv
oh1
ol1
%ref
4001
4002
4003
4004
4005
PIDmax
PIDmin
Switch
Speed
reference
Frequency
reference
9904 = 0
Example:
PID control block diagram
%ref = 4010
Pressure boost pump
ACS350
...
Actual values
4014
4021
AI1
AI2
IMOT
.
..