Can we get accurate frequency sweep results for converters with a variable switching frequency using Analysis tools?

Question

Hi there,

I am trying to obtain the frequency response of a closed-loop buck converter. I am using a boundary control method to regulate output voltage of the buck converter.In this case, switching frequency is varying slightly in steady state operation( sometimes 6.944 kHz and sometimes 7.352 kHz for given operating conditions). I tried Ac sweep,impulse response analysis method as well as Mutitone analysis to obtain the frequency response from Vref to Vc.I used a value close to the switching period as the system period where ever it needed but i was unsuccessful in getting the results that i expected and mostly solutions did not even converge.

Could you please advice on how to use analysis tools for a converter with variable switching frequency to obtain the frequency response? Is there any demo model that i can follow and understand. Really appreciate your help on this.  

Thanks

Dilan

Comments

Hi Dilan,

As always, if you are able to post a model here it is more helpful for the community to assist you. But generally, for circuits without a fixed (periodic) operating point or switching frequency, the Multitone Analysis is the only one well suited to finding a stable frequency response. This is because both the AC Sweep and Impulse Response Analyses have a periodicity requirement. There is a built-in demo model "Half-Bridge LLC Converter with Analysis Tools" that shows exactly what you are trying to do, and uses the Multitone Analysis tool. Please check this out and come back with any additional questions.

Regards,
Kris