digital smps - adjustable buck output (B-G474E-DPOW1)

[hstetina]

Hello,

I have a digital buck converter with hrtim. I followed examples Buck_VoltageMode_HW etc. So far so good, output is stable, well regulated to fixed value.

But what if want adjustable output by the user? What is the strategy to do that? I can do a prescaler from feedback ADC to adjust the output, but i feel that it is not the right way to do that properly. 

I'm not well oriented in control theory, but when i set different output voltages in Biricha WDS, control B parameters are slightly different.

 

Unfortunately, I don't have access to bode plot.

What is the proper way to solve this?

1. Leave B parameters fixed and hope that smps will be stable with different output voltages
2. Make a lookup table with B parameters for lets say 0,5V steps in output
3. Calculate b parameters on MCU.
4. ???

Thank you for the suggestions.

 

Hynek

[ST_Sophia]

Hello Hynek, 

I do recommend using the WDS (https://www.biricha.com/st-wds.html) if you want to modify any parameter of the converter. The tool will take it into account, and compute the control coefficients, based on a methodology of converter modeling to generate a transfer function, that will be compensated with the control to reach stabilities criteria. You can check on the WDS the bode plot of the converter, the compensation and resulting plot of the closed loop. The tool proposes coefficients to be ported to the SW and confirms stability without manual placement of poles/zeros.

I hope it helps, 

 

Best regards.

[hstetina]

That is the way I'm doing it right now.

But the question is if i want variable output voltage 0-5V lets say for example adjustable by rottary encoder. I need to adjust control loop paremeters on the fly.

 

H.

 

 

[ST_Sophia]

During the start-up phase, the reference value is updated smoothly (using the systick routine) to reach the final reference value incrementally. I suggest that you generate the compensation coefficients based on the highest output voltage and use this ref to setup the output value you want. Please notice that changing the reference should be done (as for the start-up) incrementally.