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d2d

Resample discrete-time model

Syntax

sys1 = d2d(sys, Ts)
sys1 = d2d(sys, Ts, 'method')
sys1 = d2d(sys, Ts, opts)

Description

sys1 = d2d(sys, Ts) resamples the discrete-time dynamic system model sys to produce an equivalent discrete-time model sys1 with the new sample time Ts (in seconds), using zero-order hold on the inputs.

sys1 = d2d(sys, Ts, 'method') uses the specified resampling method 'method':

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

  • 'tustin' — Bilinear (Tustin) approximation

sys1 = d2d(sys, Ts, opts) resamples sys using the option set with d2dOptions.

Examples

Example 1

Consider the zero-pole-gain model

with sample time 0.1 s. You can resample this model at 0.05 s 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

The inverse resampling operation, performed by typing d2d(H2,0.1), yields back the initial model H(z).

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

Example 2

Suppose you estimates a discrete-time model of a sample time commensurate with the estimation data (Ts = 0.1 seconds). However, your deployment application demands a faster sampling frequency (Ts = 0.01 seconds).

load iddata1
sys = oe(z1, [2 2 1]);
sysFast = d2d(sys, 0.01, 'zoh')

bode(sys, sysFast)

More About

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Tips

  • Use the syntax sys1 = d2d(sys, Ts, 'method') to resample sys using the default options for'method'. To specify tustin resampling with a frequency prewarp (formerly the 'prewarp' method), use the syntax sys1 = d2d(sys, Ts, opts). See the d2dOptions reference page.

  • When sys is an identified (IDLTI) model, sys1 does not include the estimated parameter covariance of sys. If you want to translate the covariance while converting the model, use translatecov.

See Also

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