03-07-2012, 04:53 PM
INTERNAL MODEL CONTROL (IMC)
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IMC Background
In process control, model based control systems are mainly used to get the desired set points and reject small external disturbances. The internal model control (IMC) design is based on the fact that control system contains some representation of the process to be controlled then a perfect control can be achieved. So, if the control architecture has been developed based on the exact model of the process then perfect control is mathematically possible.
IMC basic structure
The exceptional characteristic of IMC structure is including the process model which is in parallel with the actual process or the plant. Here, „*‟ has been used to represent signals associated with the model.
Introduction
The IMC design procedure is exactly the same as the open loop control design procedure. Unlike open loop control, the IMC structure compensates for disturbances and model uncertainties. The IMC filter tuning parameter “lem” is used to avoid the effect of model uncertainty. The normal IMC design procedure focuses on set point responses but with good set point responses good disturbance rejection is not assured, especially those occurring at the process inputs. A modification in the design procedure is proposed to enhance input disturbance rejection and to make the controller internally stable.
IMC design procedure
Consider a process model Gp*(s) for an actual process or plant Gp(s). The controller Qc(s) is used to control the process in which the disturbances d(s) enter into the system. The various steps in the Internal Model Control (IMC) system design procedure are:
APPLICATIONS
At steady state, the controller response has no offset i.e. perfect control is obtained.
The controller is used to get input tracking as well as disturbance rejection responses.
Provides time delay compensation.
[attachment=26581]
IMC Background
In process control, model based control systems are mainly used to get the desired set points and reject small external disturbances. The internal model control (IMC) design is based on the fact that control system contains some representation of the process to be controlled then a perfect control can be achieved. So, if the control architecture has been developed based on the exact model of the process then perfect control is mathematically possible.
IMC basic structure
The exceptional characteristic of IMC structure is including the process model which is in parallel with the actual process or the plant. Here, „*‟ has been used to represent signals associated with the model.
Introduction
The IMC design procedure is exactly the same as the open loop control design procedure. Unlike open loop control, the IMC structure compensates for disturbances and model uncertainties. The IMC filter tuning parameter “lem” is used to avoid the effect of model uncertainty. The normal IMC design procedure focuses on set point responses but with good set point responses good disturbance rejection is not assured, especially those occurring at the process inputs. A modification in the design procedure is proposed to enhance input disturbance rejection and to make the controller internally stable.
IMC design procedure
Consider a process model Gp*(s) for an actual process or plant Gp(s). The controller Qc(s) is used to control the process in which the disturbances d(s) enter into the system. The various steps in the Internal Model Control (IMC) system design procedure are:
APPLICATIONS
At steady state, the controller response has no offset i.e. perfect control is obtained.
The controller is used to get input tracking as well as disturbance rejection responses.
Provides time delay compensation.