User`s guide

d2c
11-48
11d2c
Purpose Convert discrete-time L TI models to continuous time
Syntax sysc = d2c(sysd)
sysc = d2c(sysd,method)
Description d2c converts LTI models from d iscrete to continuous time using one of the
following conversion methods:
The string
method specifies the conversion method. If method is omitted then
zero-order hold (
'zoh') is assumed. S ee “Continuous/Discrete Conversions of
LTI Models” in Chapter 3 of this manual and reference [1] for more details on
the conversion methods.
Example Consider the discrete-time model with transfer function
and sample time second. You can derive a continuous-time
zero-order-hold equivalent model by typing
Hc = d2c(H)
Discretizingthe resulting modelHc with the zero-order hold method (this isthe
default method) and sampling period gives back the original discrete
model . To see this, type
c2d(Hc,0.1)
To use the Tustin approximation instead of zero-order hold, type
Hc = d2c(H,'tustin')
'zoh'
Zero-order hold on the inputs. The control inputs a re
assumed piecewise constant over the sampling period.
'tustin'
Bilinear (Tustin) approximation to the derivative.
'prewarp'
Tustin approximation with frequency prewarping.
'matched'
Matched pole-zero method of [1] (for SISO systems only).
Hz()
z 1
–
z
2
z 0.3++
-----------------------------=
T
s
0.1
=
T
s
0.1
=
Hz
()