National Instruments Xmath Interactive Control Design Module ICDM - Manual (Page 21)

Chapter 2 Introduction to SISO Design
Xmath Interactive Control Design Module 2-6 ni.com
The plant and the alternate plant have very different uses in ICDM, and
therefore different data flow characteristics.
The plant transfer function is read from Xmath into the ICDM Main
window, and is then exported to the synthesis windows that need it—Pole
Place, LQG, and H
∞. In other words, the controllers designed using the
Pole Place, LQG, or H
∞ Synthesis windows are based on the plant transfer
function. You cannot change the plant transfer function in ICDM except by
reading in a new plant from Xmath.
The alternate plant transfer function can be read into ICDM from Xmath,
or set equal to the plant transfer function. Its properties are very different
from the plant transfer function, however:
• Using the Alternate Plant window, the user can graphically manipulate
the alternate plant transfer function.
• The alternate plant transfer function is never exported to—that is, used
by—the synthesis windows that need to know the plant: Pole Place,
LQG, H
∞.
The alternate plant transfer function is used to verify a controller design
that was based on the plant transfer function. The alternate plant transfer
function is used only to show the alternate plant plots in the ICDM Main
window. Refer to the What the ICDM Main Window Plots Show section.
Summary
The plant transfer function is used for design; the alternate plant transfer
function is used for (robustness) analysis or validation.
The distinction is not so important for PID and root locus design, because
the controller does not depend on the plant.
Origin of the Controller
The controller can originate from—that is, be designed by—several
possible sources:
• An Open Synthesis window—For example, if the Pole Place Synthesis
window is open, then the current controller is determined by the Pole
Place Synthesis window. When you interact with the Pole Place
window by dragging a closed-loop pole to a new location, you will
be changing the current controller transfer function C.
• The History window—If the History window is open, the controller
comes from the list of controllers that have been saved on the history