Overview

This section covers the following topics:

• Plant Model

• Plant Inputs and Outputs

Plant Model

The plant is the system (process or device) you intend to control. The following figure shows a schematic example.

Plant with Input and Output Signals

A Model Predictive Control Toolbox design requires a plant model, which defines the mathematical relationship between the plant inputs and outputs. The controller uses it to predict plant behavior.

The toolbox software requires the model to be linear, time invariant (LTI). You can define such a model as follows:

• Create a transfer function, state space, or zero/pole/gain model using methods provided by the Control System Toolbox software

• Derive it from plant data using, e.g., methods provided by System Identification Toolbox software

• Derive it by linearizing a Simulink model

This chapter illustrates each of these approaches. Control System Toolbox, Simulink, and System Identification Toolbox documentation provides additional examples and details.

Back to Top

Plant Inputs and Outputs

Inputs

The plant inputs are the independent variables affecting the plant. As shown in Plant with Input and Output Signals, there are three types:

Measured disturbances.  The controller can't adjust them, but uses them for feedforward compensation.

Manipulated variables.  The controller adjusts these in order to achieve its goals.

Unmeasured disturbances.  These are independent inputs of which the controller has no direct knowledge, and for which it must compensate.

Outputs

The plant outputs are the dependent variables (outcomes) you wish to control or monitor. As shown in Plant with Input and Output Signals, there are two types:

Measured outputs.  The controller uses these to estimate unmeasured quantities and as feedback on the success of its adjustments.

Unmeasured outputs.  The controller estimates these based on available measurements and the plant model. The controller can also hold unmeasured outputs at setpoints or within constraint boundaries.

You must specify the input and output types when designing the controller. See Input and Output Types for more details.

Back to Top

Building Models

Linear, Time Invariant (LTI) Models

© 1984-2012- The MathWorks, Inc.    -   Site Help   -   Patents   -   Trademarks   -   Privacy Policy   -   Preventing Piracy   -   RSS