Franklin Electric CERUS X-DRIVE CXD-003A-4V, Installation And Operation Manual

Page: 103 / 252

ADVANCED APPLICATION OPTIONS
Dual PID Loop Control
103
Dual PID Loop Control
Balancing Pressure in Large Systems Using Multiple Pumps
Booster pumps connected in series in long pipe systems and controlled by VFDs can be set for automatic
pressure balancing without the need for communication.
Each pump has its own VFD with suction (ST) and discharge (PT) pressure transducers. When there is a long
distance between pumps, the discharge pressure at any one pump will typically be greater than the suction
pressure at the next pump.
•
The discharge side is programmed as a standard constant pressure PID loop (PID 1). Refer to “Standard
Operation with PID Feedback Control” on page 69 .
• The suction side transducer is installed and programmed as an Auxiliary input in inverse mode (PID 2).
When suction pressure of PID 2 is at or above its setpoint
[ADV2–38]
, normal VFD operation will be main -
tained using the PID 1 loop.
When pump 1 suction pressure drops below PID 2 setpoint because of inadequate water supply, PID 1 High
Freq Limit will be decreased to reduce flow, prevent cavitation, and prolong pumping time. The pump 1 dis
-
charge pressure will drop and VFD2 will decrease its High Freq Limit and VFD3, etc. will follow. In this way,
all pumps will act the same without any communication between them.
To enable this feature, set the following parameters:
AUX AI Select [ADV2–58]: Select the terminal (
AVI1, AVI2, ACI
) with the PID 2 transducer connection. Set unit
type and scaling in [ADV2-59] to [ADV2-61] .
PID2 Output [ADV2–36]:
This parameter should be set to 1_Limit 1
P
st
P
PID .
PID2 Type [ADV2–37]: This parameter should be set to
1_PID Inverse
for this application.
PID2 Setpoint [ADV2–38]:
Desired suction pressure.
PID2 P-Gain [ADV2–39]: Set the proportional gain value for PID2 operation. Default = 30%
PID2 I-Gain [ADV2–40]:
Set the integral gain value for PID2 operation. Default = 1 second.
PID2 Low Limit [ADV2–41]: Set the minimum frequency for PID2 output. Range =
[SET–22]
to
[ADV2–42].
PID2 High Limit [ADV2–42]:
Set the maximum frequency for PID2 output. Range = [ADV2–41] to [SET–23].
Pump 1 Pump 2 Pump 3
PT1-PT3 are Discharge Pressure Transducers (PID 1)
ST1-ST3 are Suction Pressure Transducers (PID 2)
ST1 PT1 ST2 PT2 ST3
PT3
70 PSI
70 PSI 40 PSI
70 PSI 40 PSI
40 PSI
VFD-1 VFD-2 VFD-3
X-Drive X-Drive X-Drive