National Instruments 370757C-01 用户手册

marg = smargin(SysH, delb {scaling, graph})

The 

smargin( )

 function plots an approximation to the stability margin 

of the system as a function of frequency. For a full discussion of 

smargin( )

 syntax, refer to the MATRIXx Help. The approximation is 

exact if the number of uncertain transfer functions is less than four and 

scaling="OPT"

 (optimum scaling). 

In other cases, the approximation is generally considered to be extremely 
good. Refer to the 

approximation is always conservative. 

smargin( )

 always will report a 

margin that is less than or equal to the actual margin. 

The 

smargin( )

 function counts the columns in 

delb

 to calculate the 

number of uncertainties k. It then assumes that the last k inputs of 

SysH

 are 

signal r in Figure 2-2, and the last k outputs are signal q. To create a Nominal 
System, refer to the Creating a Nominal System section.

Figure 2-2.  Nominal Closed-Loop System

To better understand how to create H(s) in Figure 2-3, you will examine 
a SISO tracking system with three uncertainties. 

δ

1

 is a multiplicative 

actuator uncertainty, while 

δ

2

 and 

δ

3

 are multiplicative sensor uncertainties. 

Known Closed-Loop System

w

r

z

q

H(s)

size 

k

size 

k