Coupled inductor boost converter - Ripple current

[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:

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!

 

[berkeman]

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.

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?

 

[member 638480]

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.

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

 

[berkeman]

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?

 

[member 638480]

You didn't attach the schematic yet. Is this a flyback topology Boost converter?

Apologies, the topology is below, no its not a flyback.

 

[berkeman]

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]

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

 

[member 638480]

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.

 

[berkeman]

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).

 

[berkeman]

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?