Obtaining the small signal transfer function of resonant LLC converters by PSIM - revised

[@ruixiong5237]

Thanks a lot. I tried the simulation in PSIM. It works as you showed. Really beautiful.

[@sambenyaakov]

Great to hear!

[@deemaarabiat6624]

can you send the simulation file for me if you still have it please

[@gokhansen1980]

Thank you very much for this valuable presentation.

[@sambenyaakov]

Thanks for comment.

[@ssackirann]

Thank you for the video. It gives an understanding of control in llc Can you please do video about small signal analysis of llc converter without simulation. The methodology also the background knowledge needed to derive the small signal equivalent off llc when it is frequecy controlled or fixed frequecy duty controlled..The main idea beyond extended describing function.

[@sambenyaakov]

Thanks for comment.

[@andreschneider3147]

Great video! Thank you for sharing your knowledge!

[@sambenyaakov]

Thanks for comment

[@LarsHagemann]

Thanks for the video! It made me understand what happens when we do a small signal analysis of a converter. Now that the transfer function is determined how would we do the control? On the internet they say the closed loop bode plot should have -20db/Dec at the crossover frequency and a lot of papers I found just did a control that delivered a bode plot with -20db/Dec for the whole small signal frequency range It's pretty hard to find a reasonable explanation how to implement the control

[@sambenyaakov]

Look up the videos on control in my KZbin channel

[@simasnaderi3997]

Professor thank you very much for your great explanation. Is there any chance to design a controller based on the obtained graph for the LLC converters. How the output of controller must be connected to the suggested modulator?

[@sambenyaakov]

Not sure I follow the question.

[@matanlevy]

Thanks for the informative video! I'm trying to simulate myself but encountered some issues: 1. I have noticed you are obtaining the transfer function for a converter with 100kHz resonant frequency around the DC operating point of 80kHz. Is this method applicable for all operating conditions of the converter (even in very low output power where the current to the output is not continuous). 2.As you have pointed out, prior to running the AC sweep i performed a few simulations to make sure the excitation results in a "clean" sinusoid at the output - which for some reason i could not get as you have at slide 15. I have a feeling it have something to do with the time-step (1nsec) which has a pretty strong effect on the results. Can you please comment on this? 3. The values of the simulation do not add up to me, Q=0.085 , R=50 , can you please confirm Thank you!

[@sambenyaakov]

The method should be OK for all operating points but there might be a problem of simulation errors due to unclean waveforms/

[@robertovolpini9359]

Dear Sam, thanks a lot for this valuable video, I appreciated a lot. I work in designing of LLC converter since many years, but I focus on resonant tank and I'm not used to design the loop controll, that for LLC seem stronger than others converters topologies. I have a question that coming out from your sentence at 5:22 (video time) where you say that the small signal changes the frequency, this is true in closed loop conpensation, correct? if so, from the picture I see that the small input noise makes noise on the output voltage, and in same time this menas that the loop is open... can you help to understand me in what I'm wrong? Thanks a lot in advance for your reply BR/Roberto

[@sambenyaakov]

All that is explained is open loop transfer function as clearly said, NEEDED for designing the compensator.

[@nicolarosano]

This video gives an intuive explanation about major aspects. Congrats. The thing I'm missing is the "-1" in the Voltage Vontrolled Current Generator. Is there a specific meaning for that? Thanks and regards prof.

[@sambenyaakov]

To which slide or minute are you referring?

[@omarel4874]

Hi Sir, first of all thank for your videos with high educative content. I still don't get the difference between the 'static' transfer function and the 'dynamic' one. Why can't we say that linearizing the circuit (diodes and mosfets) by doing the ac analysis using PSIM is equivalent to injecting a small signal at a specific bias point and then measuring the output with respect to the input? Thank you again!

[@sambenyaakov]

ac analysis is done by amplitude perturbation. In the case of resonant converters you need frequency perturbation.

[@vickybidawat1956]

Static here mere large signal TF (Like the way we have Vout=DVin in Buck). Dynamic TF here means small signal TF (The analytical expression has complex math in it, but one can use this approach to see the load model bode plot and design an appropriate compensator for CL system design). Hope that helps. :)

[@shreelokhande]

Gr8 video, thank you sir.

[@sambenyaakov]

Thanks for comment

[@uzbek40]

I believe there is a misstype in the expression for FM modulation on slide 14. I think there is a cosine function missing in the expression.

[@sambenyaakov]

Hi Alex, Thank you for pointing out the typo. You are absolutely right. However since this error does not change much the content of video, I will leave it like that for eternity

[@ananthahegde8476]

Sir, how does one get the static transfer function using psim ?

[@sambenyaakov]

One wayis to run time domain simulation in which the frequency is swept at low rate.

[@levnemets2148]

As a comment, I would like to add , that Simetrix/SIMPLIS can do this much faster. For example, for LLC circuit it take only 4 second to obtain Bode Plot for a range of 10Hz to 100kHz with 20points per decade. And it even can be done by free student version of Simetrix/SIMPLIS.

[@sambenyaakov]

Hi Lev, Thank you for the comment. The objective of the video is to explain by an example the time domain extraction of transfer functions of resonant converters. The reason I have picked up PSIM is because it is an intuitive, easy to use, simulator.

[@sambenyaakov]

Thanks for comment

[@ramanamanohar3688]

Dear sir, I am looking for the Simetrix/SIMPLIS based small-signal analysis, If you have an LLC model for the small-signal can you share @ my email ID : [e-mail] Thanks Manohar

[@vickybidawat1956]

@lev: SIMetrix can't do it, as it does linearization step in the ac analysis. So one need to do this bode measurement the same way Prof. Sam BY has explained here. Yes, if you use Simplis then you can run AC analysis on your time domain model and can get faster run time to plot bode of the TF.