Xylem 19-001-350R2 PACE Integrated Pump Controller Human Machine Interface (HMI) for the Silent Storm VFD Pumping System – Technician Guide - Manual (Page 21)

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response to rapid changes in pressure, regardless
of the value of the pressure. This system uses this
to begin reducing VFD output speed when pressure
is rising quickly, helping to avoid overshoot. The
system can also detect fast pressure drops to begin
increasing VFD output speed before large errors
are detected, increasing the systems
responsiveness.
Good starting values are 25 for Kp and 12 for Kd.
Increase Kp when the system lags too long
changing the speed when pressure is away from
setpoint but relatively steady. Decrease Kp and
increase Kd to reduce overshoot. Decrease Kd
when the system becomes unsteady near setpoint
under steady demand. Generally speaking, only
use enough Kd to reduce overshoot.
Low and high flow settings:
The low flow and high flow settings are used
together to calculate the P and D terms at any given
time. The low flow settings are what the P and D
terms would be if flow were 0. The High Flow
settings are what the P and D terms would be if flow
were greater than or equal to “Max Flow for
Low/High Flow”. The value to use for each
parameter is calculated based on the flow at the
time.
Example: Low Flow Proportional is 10, and High
Flow Proportional is 20, “Max Flow for Low/High
Flow” is 2000. At 1000 gpm, the proportional value
will be calculated to be 15. At 1500 gpm, the
proportional value will be calculated to be 17.5.
Minimum Speed: This is the minimum speed that
the system will operate the VFD under PID control.
This speed should equal the minimum speed that
the pump will flow water at setpoint pressure.
Setting this value too high can cause
overpressurization at low demands, but having this
value too low can cause the PID to hunt since the
speeds below the “true” min speed are ineffective
and cause unnecessary delay in the PID when
operating in these speed ranges. Note that
allowances must be made for varying inlet pressure
and adjustable setpoints. Generally speaking, a low
Min speed is better than a too-high min speed, but
the closer to “true” min speed this is set, the better
the system will operate.
Control Deadband:
This value controls how far from setpoint the
pressure must be before the PID responds. The
units here are in 0.01 psi, so 25=0.25 psi (one
quarter-pound). This smooths the PID response
near setpoint and allows flow waves in the irrigation
to dissipate. However, to large a value here will
cause the system to delay response and could
cause the system to “get behind” in response to a
large change in demand.
Transition Control:
Starting Speed: Starting speed of the Main VFD
when the Main Pump first starts. Should be high
enough to “kick start” the pump since it is starting
under unsupplied demand, but care must be taken
not to force the system to overshoot under low
demand situations. Start the system with demand
just greater than the PM Pumps (or Jockey Pump,
as supplied) capacity and adjust for minimal
overshoot.
Combo Up (After XL Start): This setting controls
the speed the VFD running the main pump will be
forced to when a fixed speed lag pump starts. This
helps prevent overpressuring by reducing the
capacity of the VFD Pump, which is then being
provided by the fixed speed pump after it starts.
Generally set to 1/3 the value between min speed
and 32767. This speed will be held for “Hold Sec”,
which is generally set to 1 (may need to increase
for systems using soft-starters for fixed speed lag
pumps).
Combo Down (After XL Stop): This setting
controls the speed the VFD running the main pump
will be forced to when a fixed speed lag pump
stops. This helps replace the capacity provided by
the fixed speed pump and eliminate pressure dips
when these pumps are shut off. Generally set to
2/3 the value between min speed and 32767. This
speed will be held for “Hold Sec”, which is generally
set to 1.
Speed at 0 psi Startup: This setting controls the
speed the VFD of the Jockey OR main will start if
pressure is very low when the pump starts (see
deadband below). This setting should be adjusted
to be the point the pump just begins to flow water at
0 psi discharge. The actual starting speed will be
calculated between this speed and “Combo Down
(After XL Stop)” speed setting, depending on the
actual pressure at the time of start. A function is
used to calculate the speed between these points.
Threshold Deadband (psi): Determines the
pressure below setpoint to use the Threshold
function for determining starting speed. If set to
“20”, the threshold function is used to calculate
starting speed when pressure is equal to or less
than 20 psi below setpoint.
The VFD 1
st start factor corresponds to the starting
speed of the first main or Jockey pump starting on
VFD. A high value causes the VFD to start running
at a higher speed, creating more pressure. This