User's Manual

Configuration of MPC with Slave Controller

MPC Level

V 1.0, Beitrags-ID: 42200753

Figure 4-2 Signal flow chart of MPC with subordinated stabilizing PID controller for the

integral main transfer function g22

The slave controller stabilizes the control variable CV1 in general. The integral ef-

fect of the main transfer function g22 is compensates as well as the integral effect

of the coupling transfer function g21. The influence of MV2 on CV1 is also modified

by the slave controller due to g12.

All general notes on the configuration and commissioning of cascade controls are

relevant for this case (see Figure 5-1):



To get a correct anti windu

p calculation of the master controller, the range of

the manipulated variables of the master controller (respectively the corre-

sponding MPC channel) must be equal to the range of the external set point of

the slave controller (PID.SP_ExtHiLim… SP_ExtLoLim). Typically the MV limits

for automatic mode MViHiLim…MViLoLim are set tighter than the ones for

manual mode MViManHiLim…MViManLoLim in an MPC. Hence, the limits for

manual mode are set equal to the limits of the set point of the slave controller

and the ones for automatic mode are set even tighter only if necessary.

 The master controller must be set to “tracking mode”, if the slave controller is

not in cascade mode (automatic mode with external set point) but in any other

mode (e.g. manual or automatic mode with internal set point) with no reaction

to instructions by the master controller (announced by PID.CascaCut= true).

The “tracking mode” must also be activated if a bad status of measurement

data at the master controller is detected. An OR-combination of both conditions

is passed to the binary input MPC.MV2TrkOn. To ensure a bumpless switching

back to cascade mode, the manipulated variable of the master controller

MPC.MV2Trk is linked to the current set point PID.SP of the slave controller.

 The cycle time of the slave controllers in cascades must be at least as fast as

the cycle time of the master controller. In the present case this is ensured

automatically: the slave P(ID) controller runs in a standard fast cycle of the

automation system (typically 1s), while the MPC is moved to a slow cycle spe-

cific to the application after the model identification.

g22

g21

g12

g11

LIC

ModPreCon

MV1

MV2

CV1

CV2