This example shows how to create a MIMO frequency-response model
using frd.
Frequency response data for a MIMO system includes a vector of complex response data for each of the input/output (I/O) pair of the system. Thus, if you measure the frequency response of each I/O pair of your system at a set of test frequencies, you can use the data to create a frequency response model:
Load frequency response data in AnalyzerDataMIMO.mat.
load AnalyzerDataMIMO H11 H12 H21 H22 freq
This command loads the data into the MATLAB® workspace as
five column vectors H11, H12, H21, H22,
and freq. The vector freq contains
100 test frequencies. The other four vectors contain the corresponding
complex-valued frequency response of each I/O pair of a two-input,
two-output system.
Tip
To inspect these variables, enter:
whos H11 H12 H21 H22 freq
Organize the data into a three-dimensional array.
Hresp = zeros(2,2,length(freq)); Hresp(1,1,:) = H11; Hresp(1,2,:) = H12; Hresp(2,1,:) = H21; Hresp(2,2,:) = H22;
The dimensions of Hresp are the number of
outputs, number of inputs, and the number of frequencies for which
there is response data. Hresp(i,j,:) contains the
frequency response from input j to output i.
Create a frequency-response model.
H = frd(Hresp,freq);
H is an frd model
object, which is a data container for representing frequency response
data.
You can use frd models with many frequency-domain
analysis commands. For example, visualize the response of this two-input,
two-output system using bode.
Tip
By default, the frd command assumes that
the frequencies are in radians/second. To specify different frequency
units, use the TimeUnit and FrequencyUnit properties
of the frd model object. For example:
H = frd(Hresp,freq,'TimeUnit','min','FrequencyUnit','rad/TimeUnit')
sets the frequency units to in radians/minute.