ACS550 User’s Manual 121
Start-Up
PID Controller – Advanced
ACS550 has 2 separate PID Controllers:
• Process PID (PID1) and
• External PID (PID2)
Process PID (PID1) has 2 separate sets of parameters:
• Process PID (PID1) SET1, defined in Group 40 and
• Process PID (PID1) SET2, defined in Group 41
You can select between the 2 different sets by using parameter 4027.
Typically two different PID-Controller sets are used when the load of the motor
changes considerably from one situation to another.
You can use External PID (PID2), defined in Group 42, in 2 different ways:
• Instead of using additional PID-controller hardware, you can set outputs of the
ACS550 to control a field instrument like a damper or a valve. In this case, set
Parameter 4230 to value 0. (0 is the default value.)
• You can use External PID (PID2) as an additional PID-controller to Process PID
(PID1) to trim or fine-tune the speed of the ACS550.
Code Description
4001 GAIN
Defines the PID Controller’s gain.
• The setting range is 0.1… 100.
• At 0.1, the PID Controller output changes one-tenth as much as the error value.
• At 100, the PID Controller output changes one hundred times as much as the error value.
Use the proportional gain and integration time values to adjust the responsiveness of the system.
• A low value for proportional gain and a high value for integral time ensures stable operation, but provides sluggish
response.
If the proportional gain value is too large or the integral time too short, the system can become unstable.
Procedure:
• Initially, set:
• 4001 GAIN = 0.1.
• 4002 INTEGRATION TIME = 20 seconds.
• Start the system and see if it reaches the set point quickly while maintaining stable operation. If not, increase GAIN
(4001) until the actual signal (or drive speed) oscillates constantly. It may be necessary to start and stop the drive to
induce this oscillation.
• Reduce GAIN (4001) until the oscillation stops.
•Set GAIN (4001) to 0.4 to 0.6 times the above value.
• Decrease the INTEGRATION TIME (4002) until the feedback signal (or drive speed) oscillates constantly. It may be
necessary to start and stop the drive to induce this oscillation.
• Increase INTEGRATION TIME (4002) until the oscillation stops.
•Set INTEGRATION TIME (4002) to 1.15 to 1.5 times the above value.
• If the feedback signal contains high frequency noise, increase the value of Parameter 1303 FILTER AI1 or 1306
FILTER AI2 until the noise is filtered from the signal.
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