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Chapter 3 Building System Connections
© National Instruments Corporation 3-11 Xmath Control Design Module
feedback( )
Sys = feedback(Sys1,{Sys2})
The feedback( ) function connects two dynamic systems together in a
feedback loop as shown in Figure 3-4.
• By default, feedback is defined to be negative.
• Both systems must have the same sample rate.
• Improper dynamic systems (systems with more zeros than poles) are
not allowed.
• When only one system is specified, it must be square (it must have an
equal number of inputs and outputs).
Figure 3-4. Feedback System Configuration
For an example of how to implement unity gain feedback using the
feedback( ) function, refer to Example 3-4.
Example 3-4 Implementing Unity Gain Feedback Using feedback( )
tfsys2 = polynomial(-1)/polynomial([-2,-3]);
feedback(tfsys2) # Note that this implements
# negative unity gain feedback
ans (a state space system) =
A
-2 1
1 -4
B
0
1
C
e
1
u
1
y
1
Sys
1
Sys
+
–
Sys
2