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Configuration of MPC with Slave Controller

Figure 4-2 Signal flow chart of MPC with subordinated stabilizing PID controller for the integral main transfer function g22

 

 

 

 

g11

CV1

 

 

 

g12

CV2

ModPreCon

MV1

 

 

 

 

 

 

 

 

.

MV2

 

 

 

 

 

 

 

 

 

 

g21

 

 

 

PI

CV2

 

 

 

 

 

 

CV2

LIC

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 windup 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.

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MPC Level

V 1.0, Beitrags-ID: 42200753

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Siemens PCS 7 manual MV1 MV2
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PCS 7 specifications

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