ABB COMMANDER C355 - Cascade Control with Feedforward Operations

27
350.0
351.5
70
Master
Deviation
M.PV –
M.SPt
OP1
•1
207.0
207.0
OP1
MST
SLV
Slave
Deviation
S.PV –
S.SPt
2 OPERATOR LEVEL…
2.8 Cascade Control with Feedforward (Template 13)
For cascade control, two internally-linked PID controllers are used, with the first (master) PID
controller providing the set point for the second (slave) controller. The feedforward disturbance
variable signal is added to the master output (slave set point). The disturbance signal is weighted by
the feedforward gain (FFGn) and the feedforward bias (FFbs) values.
Master Process Variable (M.PV)
Master Control Set Point (M.SPt)
['SPLO' to 'SPHI' – see Section 5.5]
Adjustable in Local control only
Slave Control Output
[0 to 100% (–10 to 110% for analog outputs)]
Adjustable in Manual mode only.
Slave Process Variable (S.PV)
Slave Set Point (S.SPt)
['SPLO' to 'SPHI' – see Section 5.5]
Adjustable in Manual mode only
Note. The
L
L
R
key can be used in this frame to
change between cascade ( R symbol is lit) and
local slave set points.
Continued…
•1 With the Ramping Set Point function enabled (see Section 4.3, Set Points/ Ramp Rate), the
bargraph shows the actual deviation (PV/Ramping Set Point value). The digital display shows
the target set point value.
M.SPt
I/P1
I/P2
OP1
Local
Set
Point
Master PV Input
Slave PV Input
Local Slave
Set Point
Slave
PID
Control Loop
M.PV
LSPt
S.SPt
I/P3
Feedforward Disturbance Variable
M.OP x
CrtO + CbiA
Master
PID
Control Loop
∑
DV x FFGn + FFbS
Manual
Output
S.SPt
L
L
R
Profile Set Point
Fig. 2.7 Cascade Controller with Feedforward