Control System Toolbox™

d2d - Resample discrete-time LTI model or add input delay

Syntax

sys1 = d2d(sys,Ts,method)

Description

sys1 = d2d(sys,Ts,method) resamples the discrete-time LTI model sys to produce an equivalent discrete-time model sys1 with the new sample time Ts (in seconds). The string method specifies the resampling method among the following:

• 'zoh' — Zero-order hold on the inputs

• 'tustin' — Bilinear (Tustin) approximation

• 'prewarp' — Tustin approximation with frequency warping. Specify the critical frequency Wc (in rad/s) as a fourth input by

 sys = d2d(sys,Ts,'prewarp',Wc)

The default is 'zoh' when method is omitted.

Example

Consider the zero-pole-gain model

with sample time 0.1 second. You can resample this model at 0.05 second by typing

H = zpk(0.7,0.5,1,0.1)
H2 = d2d(H,0.05)
Zero/pole/gain:
(z-0.8243)
----------
(z-0.7071)
 
Sampling time: 0.05

Note that the inverse resampling operation, performed by typing d2d(H2,0.1), yields back the initial model .

Zero/pole/gain:
(z-0.7)
-------
(z-0.5)
 
Sampling time: 0.1

See Also

c2d, d2c, ltiexamples

d2c

damp