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c2dOptions

Create option set for continuous- to discrete-time conversions

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Syntax

opts= c2dOptions
opts= c2dOptions('OptionName',OptionValue)

Description

opts= c2dOptionsreturns the default options forc2d.

opts= c2dOptions('OptionName',OptionValue)accepts one or more comma-separated name/value pairs that specify options for thec2dcommand. SpecifyOptionNameinside single quotes.

Input Arguments

Name-Value Arguments

Method

Discretization method, specified as one of the following values:

'zoh'

Zero-order hold, wherec2dassumes the control inputs are piecewise constant over the sample timeTs.
“呸”

Triangle approximation (modified first-order hold), wherec2dassumes the control inputs are piecewise linear over the sample timeTs. (See[1], p. 228.)
'impulse' Impulse-invariant discretization.
'tustin'

Bilinear (Tustin) approximation. By default,c2ddiscretizes with no prewarp and rounds any fractional time delays to the nearest multiple of the sample time. To include prewarp, use thePrewarpFrequencyoption. To approximate fractional time delays, use theFractDelayApproxOrderoption.
'matched'

Zero-pole matching method. (See[1], p. 224.) By default,c2drounds any fractional time delays to the nearest multiple of the sample time. To approximate fractional time delays, use theFractDelayApproxOrderoption.
最小二乘的 Least-squares method. Minimize the error between the frequency responses of the continuous-time and discrete-time systems up to the Nyquist frequency.

For information about the algorithms for each conversion method, seeContinuous-Discrete Conversion Methods.

Default:'zoh'

PrewarpFrequency

Prewarp frequency for'tustin'method, specified inrad/TimeUnit, whereTimeUnitis the time units, specified in theTimeUnit的性质,鉴别器etized system. Takes positive scalar values. A value of 0 corresponds to the standard'tustin'method without prewarp.

Default:0

FitOrder

Fit order for最小二乘的method, specified as an integer. Specifies the order of the discrete-time model to be fitted to the continuous-time frequency response. Leave the default option 'auto' to use the order of the continuous-time model, and change it to an integerNto use anNth-order fit. Reducing the order helps with unstable poles or pole/zero cancellations atz = -1.

Default:'auto'

FractDelayApproxOrder

Maximum order of the Thiran filter used to approximate fractional delays in the'tustin'and'matched'methods. Takes integer values. A value of 0 means thatc2drounds fractional delays to the nearest integer multiple of the sample time.

Default:0

Examples

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This example uses:

Open Live Script

Generate two random continuous-time state-space models.

sys1 = rss(3,2,2); sys2 = rss(4,4,1);

Create an option set forc2dto use the Tustin discretization method and 3.4 rad/s prewarp frequency.

opt = c2dOptions('Method','tustin','PrewarpFrequency',3.4);

Discretize the models,sys1andsys2, using the same option set, but different sample times.

dsys1 = c2d(sys1,0.1,opt); dsys2 = c2d(sys2,0.2,opt);

References

[1] Franklin, G.F., Powell, D.J., and Workman, M.L.,Digital Control of Dynamic Systems(第3版),Prentice Hall,1997.

Version History

Introduced in R2012a

See Also