ABB ACS550 Series, User Manual

Page: 175 / 310

ACS550 User’s Manual 175
Parameters
Group 81: PFC CONTROL
This group defines a Pump-Fan Control (PFC) mode of operation. The major
features of PFC control are:
• The ACS550 controls the motor of pump no. 1, varying the motor speed to control
the pump capacity. This motor is the speed regulated motor.
• Direct line connections power the motor of pump no. 2 and pump no.3, etc. The
ACS550 switches pump no. 2 (and then pump no. 3, etc.) on and off as needed.
These motors are auxiliary motors.
• The ACS550 PID control uses two signals: a process reference and an actual
value feedback. The PID controller adjusts the speed (frequency) of the first
pump such that the actual value follows the process reference.
• When demand (defined by the process reference) exceeds the first motor’s
capacity (user defined as a frequency limit), the PFC control automatically starts
an auxiliary pump. The PFC also reduces the speed of the first pump to account
for the auxiliary pump’s addition to total output. Then, as before, the PID controller
adjusts the speed (frequency) of the first pump such that the actual value follows
the process reference. If demand continues to increase, PFC adds additional
auxiliary pumps, using the same process.
• When demand drops, such that the first pump speed falls below a minimum limit
(user defined by a frequency limit), the PFC control automatically stops an
auxiliary pump. The PFC also increases the speed of the first pump to account for
the auxiliary pump’s missing output.
• An Interlock function (when enabled) identifies off-line (out of service) motors, and
the PFC control skips to the next available motor in the sequence.
• An Autochange function (when enabled and with the appropriate switchgear)
equalizes duty time between the pump motors. Autochange periodically
increments the position of each motor in the rotation – the speed regulated motor
becomes the last auxiliary motor, the first auxiliary motor becomes the speed
regulated motor, etc.
Code Description
8103 REFERENCE STEP 1
Sets a percentage value that is added to the process reference.
• Applies only when at least one auxiliary (constant speed) motor is running.
• Default value is 0%.
Example: An ACS550 operates three parallel pumps that maintain water pressure in a pipe.
• 4011
INTERNAL SETPNT
sets a constant pressure reference that controls the pressure in the pipe.
• The speed regulated pump operates alone at low water consumption levels.
• As water consumption increases, first one constant speed pump operates, then, the second.
• As flow increases, the pressure at the output end of the pipe drops relative to the pressure measured at the input
end. As auxiliary motors step in to increase the flow, the adjustments below correct the reference to more closely
match the output pressure.
• When the first auxiliary pump operates, increase the reference with parameter 8103
REFERENCE STEP
1.
• When two auxiliary pumps operate, increase the reference with parameter 8103
REFERENCE STEP
1 + parameter
8104
REFERENCE STEP
2.
• When three auxiliary pumps operate, increase the reference with parameter 8103
REFERENCE STEP
1 + parameter
8104
REFERENCE STEP
2 + parameter 8105
REFERENCE STEP
3.