Estimate Online Frequency Response of Non-Isolated DC-DC Converter

R2026b

In this step of the Non-Isolated DC-DC Converter Controller Design Workflow example, you estimate the online frequency response of the non-isolated DC-DC converter plant to obtain a data-driven model for controller tuning. To get started, open the project and click the Sim FRE Workflow shortcut on the project toolstrip.

This workflow extracts the plant frequency response of a DC-DC converter under open-loop control, enabling advanced control-gain estimation and stability analysis. The plant frequency response is defined as Vout/Duty and is obtained by modulating the open-loop control output (duty cycle) with sinestream perturbations. A well-conditioned frequency response estimation (FRE) result gives you a data-driven plant model that captures effects the analytical transfer function misses, including component nonlinearities, quantization, and sampling dynamics.

The model references the Buck plant subsystem equivalent to the Buck circuit in BOOSTXL-BUCKCONV. The model parameters are loaded from BuckVoltageControlF28379dData.m.

Configure FRE Injection Parameters

Configure the frequency-response injection parameters. Define a series of frequencies and amplitudes to inject over the open-loop control input.

% Load specific hardware parameters
BuckVoltageControlF28379dData;
freq        = [200 500 700 1000 2000 3000 5000 10000 20000 30000];%Hz Frequencies to be injected
Amplitudes  = 0.1; % duty cycles [0,1] % Amplitude of sine signals to be injected
NumSetPeriod = 4; % Number of settling periods for the frequency injection
NumEstPeriod = 2;% Number of estimation periods for the frequency injection

Generate FRE injection signals

Option 1: using Sinestream block

modelName1 = 'createSineStream';
load_system(modelName1);
TestTime = 0;
for index = 1:length(freq)
    TestTime = TestTime + (NumSetPeriod+NumEstPeriod) / freq(index);    
end
TestTime = TestTime*1.01;
SimTime1 = TestTime;
out = sim(modelName1);
sineLUT = out.FreInj;
IdxLUT  = out.Idx;
disp(['Look up table length = ' num2str(length(sineLUT))]);
Look up table length = 12903

Option 2: using API

Open the model and update sinestream signal generator block

[sineLUT, IdxLUT] = generatePerturbSignal('sine', Tsc, ...
    'Frequency', freq, ...
    'Amplitude', Amplitudes, ...
    'NumSetPeriod', NumSetPeriod, ...
    'NumEstPeriod', NumEstPeriod);
Look up table length = 12780

Simulate FRE Model

modelName2 = 'BuckFrequencyInjectionSim';
open_system(modelName2);
simTime3 = length(sineLUT) * Tsc + 0.02;
sim(modelName2);
close_system(modelName2);

Plot the Frequency Response 

opts=bodeoptions;
opts.FreqUnits='Hz';
opts.Grid='On';
opts.MagVisible ='On';
opts.PhaseVisible ='On';
Buck_FREResponse_sim = frd(FRD.Data, freq * 2 * pi);
figure('Name','FRE plot')
bodeplot(Buck_FREResponse_sim,'r*-',opts);
title('DC-DC Buck');

See Also

Topics