Difference between revisions of "Using tfest to find a system model"
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(Created page with "Category:Electronics {{Template:20.309}} Here is some example code that demonstrates how to use <tt>tfest</tt> to fit a linear model to frequency response data: <tt> %Ge...") |
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Here is some example code that demonstrates how to use <tt>tfest</tt> to fit a linear model to frequency response data: | Here is some example code that demonstrates how to use <tt>tfest</tt> to fit a linear model to frequency response data: | ||
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%Generate some synthetic frequency response measurement data | %Generate some synthetic frequency response measurement data | ||
s = tf( [ 1 0 ], 1 ); | s = tf( [ 1 0 ], 1 ); | ||
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EstimatedTransferFunction = tfest( frequencyResponseData, initalModel ); | EstimatedTransferFunction = tfest( frequencyResponseData, initalModel ); | ||
end | end | ||
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{{Template:20.309}} | {{Template:20.309}} | ||
Revision as of 14:52, 9 April 2019
Here is some example code that demonstrates how to use tfest to fit a linear model to frequency response data:
%Generate some synthetic frequency response measurement data
s = tf( [ 1 0 ], 1 );
highPass = s / ( s + 1 )
[ magnitude, phase, frequency ] = bode( highPass );
% add some random noise
noiseStandardDeviation = 0.05;
magnitude = magnitude + noiseStandardDeviation * randn( size( magnitude ) );
phase = phase + noiseStandardDeviation * randn( size( phase ) );
numeratorForm = [ 1 0 ]; % decreasing powers of s -- numerator for HPF has no constant term, so set it to zero (otherwise tfest will fit a constant value)
denominatorForm = [ 1 0 ]; % decreasing powers of s -- numerator for HPF has no constant term, so set it to zero (otherwise tfest will fit a constant value)
estimatedTransferFunction = FitTransferFunction( magnitude, phase, frequency, numeratorForm, denominatorForm )
function EstimatedTransferFunction = FitTransferFunction( MagnitudeRatio, PhaseDifferenceDegrees, FrequencyHertz, NumeratorForm, DenominatorForm )
% convert magnitude and phase to single complex vector
complexResponseData = MagnitudeRatio .* exp( 1i .* PhaseDifferenceDegrees .* pi ./ 180 );
% create optional initial model for tfest so that known zero
% coefficients can be constrained
initalModel = idtf( NumeratorForm, DenominatorForm );
zeroCoefficients = find( NumeratorForm == 0 );
for ii = 1:numel( zeroCoefficients )
initalModel.Structure.Numerator.Free(ii) = false;
end
zeroCoefficients = find( DenominatorForm == 0 );
for ii = 1:numel( zeroCoefficients )
initalModel.Structure.Denominator.Free(ii) = false;
end
frequencyResponseData = frd( complexResponseData, FrequencyHertz, 'FrequencyUnit', 'Hz');
EstimatedTransferFunction = tfest( frequencyResponseData, initalModel );
end
