Siemens PCS 7 4.3 Commissioning

Configuration of MPC with Slave Controller

18 MPC Level

V 1.0, Beitrags-ID: 42200753

4.3 Commissioning

The parameterization of the controller and the commissioning is done „from interior

to exterior” as in any cascade control. First the slave controller is tuned (see chap-

ter 3) and switched to automatic mode. Afterwards the slave controller is switched

to cascade mode and the master controller is parameterized. While tuning the mas-

ter controller please consider that the whole inner closed control loop of the slave

controller is the controlled process of the master controller. Therefore the adjust-

able parameters of the master controller are not independent of the tuning of the

slave controller. The step experiments for the identification of the MPC models can

only be executed after the linking of the stabilizing slave controller, as the addi-

tional proportional-only controller affects the sub transfer functions g22, g21 and

g12 (see Figure 4-2).

A dead band can be used in the slave controller, if the level is not to be exactly

controlled to its set point. The controller has no reason to interfere with the process

as long as the controlled variable is inside the dead band. The control deviation

seems to be zero for the controller. Therefore, the control signal can be smoothed

to avoid valve wear, and variations of the drain flow can be reduced to obtain a

smooth feed for the downstream process components. The dead band should be

adjusted before the measurement data for the MPC configurator is recorded, as the

dead band influences the behaviour of the slave control loop. A dead band of at

least the same size must also be specified for the corresponding control channel of

the master controller. Of course, the master controller is not able to reach the set

point more precisely as it is allowed by the dead band of the slave controller.