Coupled inductor boost converter - Ripple current

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Discussion Overview

The discussion revolves around calculating the ripple current in a coupled inductor boost converter, specifically focusing on the variables ∆i1 and ∆i2. Participants are exploring the derivation of formulas for these ripple currents, considering the effects of voltage levels and time intervals in the converter's operation. The context includes design considerations for a boost converter as part of an assignment.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant seeks assistance in deriving formulas for ripple currents ∆i1 and ∆i2, expressing uncertainty about their correctness.
  • Another participant requests a schematic and time-domain waveforms to better understand the problem.
  • A participant mentions the need to derive expressions for ripple currents at specific time points (DT, T/2, DT+T/2, and T).
  • There is a discussion about the topology of the converter, with one participant clarifying that it is not a flyback converter.
  • One participant expresses curiosity about the use of coupled inductors and requests more information about the topology.
  • Another participant references a document that discusses a different topology involving coupled inductors, noting its potential for achieving a higher boost ratio.
  • There is uncertainty expressed regarding how the coupled inductor aspect contributes to ripple current management.
  • A participant offers to run a simulation to explore the topology further, indicating a willingness to assist despite time constraints.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the derivation of the ripple current formulas or the implications of using coupled inductors in this context. Multiple viewpoints and uncertainties remain regarding the topology and its effects.

Contextual Notes

Participants have not provided complete assumptions or definitions related to the ripple current calculations, and there are unresolved questions about the specific topology being discussed.

member 638480
I am trying to calculate the ripple current in boost converter for ∆i1 and ∆i2 between time intervals between DT and T, and also dependent on the voltage level (Vin or Vin-Vout). To find a formula for ∆i1 and ∆i2, two formulas have to be derived for them. This is done from the equation:
upload_2018-1-5_13-47-0.png

I derived equations for ∆i1 and ∆i2 as shown below, however I don't think this is right and I was wondering has anybody done this before that can provide some assistance, thanks!
upload_2018-1-5_13-48-14.png
 

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Tommy Drudy said:
I am trying to calculate the ripple current in boost converter for ∆i1 and ∆i2 between time intervals between DT and T, and also dependent on the voltage level (Vin or Vin-Vout). To find a formula for ∆i1 and ∆i2, two formulas have to be derived for them. This is done from the equation: View attachment 217893
I derived equations for ∆i1 and ∆i2 as shown below, however I don't think this is right and I was wondering has anybody done this before that can provide some assistance, thanks!
View attachment 217894
Welcome to the PF. :smile:

Can you post your schematic and time-domain waveforms with all of the times and such listed? Thanks, we should be able to help you on this.

BTW, is this for schoolwork?
 
Below is a screenshot of VL1 and VL2, it shows the voltage and ripple current when the switch is either on or off due to interleaving. The only unknown variables from the formula mentioned in my previous post is ∆i1 and ∆i2, which is replicated by the red line in this photo. That is why I am trying to derive an expression for the two ripple currents, in order to find their value at each point, ie DT, T/2, DT+T/2, and T.
upload_2018-1-5_17-21-55.png

This question is for a boost converter that I am trying to design as part of an assignment.
 

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juniorbvetran said:
Below is a screenshot of VL1 and VL2, it shows the voltage and ripple current when the switch is either on or off due to interleaving. The only unknown variables from the formula mentioned in my previous post is ∆i1 and ∆i2, which is replicated by the red line in this photo. That is why I am trying to derive an expression for the two ripple currents, in order to find their value at each point, ie DT, T/2, DT+T/2, and T.
View attachment 217902
This question is for a boost converter that I am trying to design as part of an assignment.
You didn't attach the schematic yet. Is this a flyback topology Boost converter?
 
berkeman said:
You didn't attach the schematic yet. Is this a flyback topology Boost converter?
Apologies, the topology is below, no its not a flyback.
upload_2018-1-5_17-32-10-png.png
 

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Interesting! I hadn't seen that topology before, but I work with Buck converters a lot more than Boost converters. Can you say more about it? Where did you find it? I can see the motivation for using 2 inductors, but why use coupled inductors? Thanks.
 
berkeman said:
I did a little Google searching on your thread title, but this topology is different than what you have posted so far...

http://www.onsemi.com/pub/Collateral/AN-5081.pdf.pdf
Ya I am not to sure, i just know the equations are used to derive the ripple current. I've had a good look around for a final derivation of the ripple current formula but there doesn't seem to be anything online.
 
I'm not intuitively seeing how the coupled inductor part would help the ripple current. Have you seen anything about the coupled inductor part of it?

If not, I'm sure others can chime in who have seen this topology before. Or worst case I can run a simulation on it this weekend at work (in all of my spare time... Ack). :smile:
 
  • #10
berkeman said:
I did a little Google searching on your thread title, but this topology is different than what you have posted so far...

http://www.onsemi.com/pub/Collateral/AN-5081.pdf.pdf
It looks like that (different) boost topology with coupled inductors is to get a higher boost ratio:
Conventional step up dc-dc converters or boost converters
are not suitable for high voltage conversion ratio since the
effective series resistor (ESR) of the boost inductor
prohibits the output voltage from increasing more than 10
times of the input voltage.In this article, a high step-up dc-dc converter
with tapped inductor or coupled inductor is introduced and its
operational principle and design procedure will be described
as well.

Where did you get your circuit from?
 
Last edited:

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