Two phase interleaved buck converter with no coupled inductor

Thread Starter

Yin Min

Joined Jun 24, 2019
27
Hello,

I bought the TIDA-010042 board for MPPT battery charging with solar panel. It uses two phase interleave buck converter with no coupled inductors. I don't understand so much about two phase interleaved buck converter. Especially, how to calculate the output voltage. In this TI board, when input solar panel voltage is 36V, the output voltage after inductors is 22V. But I like to get 24V output voltage. How can I change to get 24V output voltage?

Please help me explain if anyone knows about that. Thank you.

For your reference,
https://www.ti.com/tool/TIDA-010042
 

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Ian0

Joined Aug 7, 2020
2,220
Nothing tricky about interleaved buck converters. Just two buck converters supplying the same load.
All the calculations about duty cycle etc. are the same as for a single converter. Each one of the pair is designed to supply half the current.

In a buck converter the source only supplies power when the pass transistor is switched on. If the duty cycle is low, and the step-down ratio is high, then brief high current pulses are taken from the supply, which creates a lot of ripple. The clever bit about interleaving is to switch the second converter on whilst the first one is off, which reduces the ripple.
obviously both have to have the same duty cycle, so, unless the duty cycle happens to be 50% and the output half the input there will still be some ripple.
 

Thread Starter

Yin Min

Joined Jun 24, 2019
27
Hi
Thanks for your reply.

That means if I want to increase the output voltage, i need to increase the duty cycle. For interleaved buck converter, both sides duty cycle have to increase so that the ripple will cancel each other. Please correct me if I am wrong.

Best regards,
Yin Min
 

Ian0

Joined Aug 7, 2020
2,220
Hi
Thanks for your reply.

That means if I want to increase the output voltage, i need to increase the duty cycle. For interleaved buck converter, both sides duty cycle have to increase so that the ripple will cancel each other. Please correct me if I am wrong.

Best regards,
Yin Min
You got it!
 

andrewmm

Joined Feb 25, 2011
1,470
What voltage cell do you have connected to the output ?
I must admit to only quick skim of the data sheet,

but it seems the eval board will output a voltage to charge you battery,
The battery is part of the feedback loop
It strikes me, that if you have no battery on its output, and hence no load,
the feedback is going to go to a default, which could well be 22 v and zero current,
 

eem2am

Joined Jul 22, 2012
13
Battery chargers need to be output current regulated, and need output voltage limitation in the case that no battery is connected to the output.
A battery charger cannot regulate its output voltage...the battery does that
 

Thread Starter

Yin Min

Joined Jun 24, 2019
27
What voltage cell do you have connected to the output ?
I must admit to only quick skim of the data sheet,

but it seems the eval board will output a voltage to charge you battery,
The battery is part of the feedback loop
It strikes me, that if you have no battery on its output, and hence no load,
the feedback is going to go to a default, which could well be 22 v and zero current,
Hi,

The output is actually to connect with 24V battery pack. But I don't have actual battery pack now and I dare not to test first with actual battery pack also. So, I am using electronics load(E load) setting CV mode as a battery simulator connecting to the battery output J5 and use the power supply as solar panel input J6.
In the design guide, for 24V system, the solar panel voltage is set 36V and showing some waveforms for 24V battery. But in my board, when I set the panel voltage 36V, the battery output (J5) got only 22V. So, I cannot set the E load CV mode more than 22V. If more than 22V, E-load cannot draw the current from the power supply, means the board cannot charge the battery. Of course, it mentioned the input panel voltage range from 30V to 44V for 24V system.
I am not sure if it is because of the E-load or not. If with actual battery pack, maybe it will response different way. But chance is less. I think it will behave the same way.
Anyway, I like to get 24V at battery output when panel voltage is 36V.
 

Thread Starter

Yin Min

Joined Jun 24, 2019
27
Battery chargers need to be output current regulated, and need output voltage limitation in the case that no battery is connected to the output.
A battery charger cannot regulate its output voltage...the battery does that
Yes. When I set the solar panel 36V, the output voltage limitation is 22V only. What I need is 24V battery output. Now, in my case, I cannot charge the battery more than 22V. So, I like to increase output voltage limitation by changing something that I don't know.
 

andrewmm

Joined Feb 25, 2011
1,470
Question, does not a CV load draw current to get the volts it is set for ?
what current is the load taking ?

I think this is also a MPPT charger,
they vary the output voltage / current dependent upon the power available ,

How much power are you putting into the panels ?
 

Thread Starter

Yin Min

Joined Jun 24, 2019
27
Question, does not a CV load draw current to get the volts it is set for ?
what current is the load taking ?

I think this is also a MPPT charger,
they vary the output voltage / current dependent upon the power available ,

How much power are you putting into the panels ?
CV load draws the current to get the volts which I set but have to be lower than 22V battery output.
the load is taking all power from the panel.
In MPPT charger, output voltage is varying based on the panel voltage changes. So, I want to make the output voltage 24 at panel voltage 36V.
 

andrewmm

Joined Feb 25, 2011
1,470
CV load draws the current to get the volts which I set but have to be lower than 22V battery output.
the load is taking all power from the panel.
In MPPT charger, output voltage is varying based on the panel voltage changes. So, I want to make the output voltage 24 at panel voltage 36V.
what is your current taken from the 36v panel ?
 

andrewmm

Joined Feb 25, 2011
1,470
How are you simulating the cells ?
the MPPT is varying the current drawn form the cells to maximise there power output ,
Cells are not constant voltage , variable current,
 
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