.ThermoPower.Functions.OffsetController

Information

This model is useful to compute the steady state value of a control variable corresponding to some specified setpoint of an output variable, and to reuse it later to perform simulations starting from this steady state condition.

The block has two different behaviours, depending on the value of the steadyState parameter.

When steadyState = 1, the deltaCO input is ignored, and the block acts as a standard PI controller with transfer function Kp*(1+1/sTi) to bring the process variable connected to the PV input at the setpoint value, by acting on the control variable connected to the CO output. The setpoint value is SP0 at time zero, and may change by deltaSP from Tstart to Tend; this can be useful to bring the process far away from the tentative start values of the transient without any inconvenience. The control variable can be biased by biasCO to start near the expected steady state value of CO.

When steadyState = 0, the PV input is ignored, and the CO output is simply the sum of the deltaCO input and of the freezed steady-state output of the controller.

To perform a steady state computation:

1. Set steadyState = 1 and suitably tune Kp, Ti and biasCO
2. Simulate a transient until the desired steady state is achieved.
3. Set steadyState = 0 and continue the simulation for 0 s
4. Save the final state of the simulation, which contains the initial steady-state values of all the variables for subsequent transient simulations

To perform experiments starting from a steady state:

1. Load a previously saved steady state, to be used as initial state
2. Perform the simulation of the desired transient. The offsetCO input value will be automatically added to the previously computed steady state value.

Revision history:

• 15 Feb 2004 by Francesco Casella:
  First release.