Why scope in "Closed Loop Control of a DC-DC Buck Converter" can not show current output ?

Question

Chakrit Phongoen 2023-9-24

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https://ww2.mathworks.cn/matlabcentral/answers/2025102-why-scope-in-closed-loop-control-of-a-dc-dc-buck-converter-can-not-show-current-output

编辑： Sayan 2023-10-25

Hello, everyone. I have a problem with my experiment, which is related to a buck converter circuit I built using the "BOOSTXL-BUCKCONV BoosterPack" as a reference. Initially, I changed the input voltage from 9 volts to 15 volts and modified the load resistor to 1 ohm. Then, I aimed for an output voltage of 5 volts and an output current of 5 amps. I completed the circuit and used it with the F28379D Launchpad board, using the "f28379D_DCDC_Buck.slx" program and the host model "c2000_DCDC_Buck_host_model.slx". Everything in the experiment seems to be working fine, except for one abnormality: the graph displaying the output current on the scope in the program is not reaching the desired value of 5 amps; it only goes up to 4 amps, as shown in the attached image.Even though I use an oscilloscope to measure the output current, it shows a normal output current of 5 amps. However, on the host model's scope screen in Simulink, it displays less than 5 amps. When I try to increase the output current to more than 4 amps, the graph on the scope decreases gradually, eventually reaching 0. I'm not sure what I did wrong or where I should make corrections. If anyone could help me, I would greatly appreciate it. I've been stuck with this issue for a month now. Thank you very much for your assistance.

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Answer 1

Sayan 2023-10-23

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https://ww2.mathworks.cn/matlabcentral/answers/2025102-why-scope-in-closed-loop-control-of-a-dc-dc-buck-converter-can-not-show-current-output#answer_1339036

编辑：Sayan 2023-10-25

Hi Chakrit Phongoen,

I understand from your issue that the current reading in the scope of Simulink reads zero when the input voltage is varied to get the output voltage of 5 volts, while the oscilloscope reading of the current of the load is non-zero.

The possible reasons and fixes for the same are mentioned below:

The input voltage set is not sufficient to make the inductor current continuous. You can set the required input voltage to remove the discontinuity.
The values set for proportional and integral gain may not be properly tuned. You can find the tuned values by making another Simulink model emulating the behavior and your requirements and tuning the parameters.
The current measured through the "ADC" block in the Simulink model is the measurement of current through the inductor, whereas you may be measuring the average value of load current.

Further information can be found in the video and the model files at the following link on File Exchange:

https://www.mathworks.com/matlabcentral/fileexchange/61420-dc-dc-buck-converter-example

Hope this helps in resolving the issue.