Author Topic: [MPPT Charge controller] Increase current capacity  (Read 362 times)

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Offline Pineapple Dan

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[MPPT Charge controller] Increase current capacity
« on: April 14, 2021, 02:52:10 pm »
I made a charge controller using a pair of IPP040N06 mosfets. Works fine with a single 100w panel, but a 300w (~33v MPP @ 9A) panel is too much for it without a fan. The heatsink I have on it isn't great (13C/W)

If I want to switch 20A @ 125KHz what would be the best solution? Parallel mosfets? Multi-phase? It's just the high-side mosfet that's warming up a bit too much.
Should I go back to using a 33uH inductor and reduce the switching speed? Don't think my drive signal is too bad - have attached some waveforms

Anything I might have overlooked that could be heating up the mosfet?

I had a look at the TI reference design https://www.ti.com/tool/TIDA-010042 and they have gone multi-phase for handling similar current.
 

Offline penfold

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Re: [MPPT Charge controller] Increase current capacity
« Reply #1 on: April 14, 2021, 03:16:20 pm »
How are you presently using the "pair" of MOSFETS? Synchronous buck converter or are they in parallel?

If it's designed around 100W, I wouldn't be surprised if it starts to get hot at 300W but would be useful to see a schematic if you want a more precise critique, the waveforms don't look too bad.

For the circa 30V @ 20A mark, I would start to consider an interleaved design. It would be possible to just design a single buck stage at that power rating, but you can probably optimise an interleaved pair better. It is also preferable with PV inputs to keep the input ripple current low, another thing that an interleaved solution would allow, (considering the discontinuous input current of a buck (I'm assuming it's a buck you've built, please correct if wrong)). If it were a normal stiff voltage source, I would suggest 2 interleaved is probably enough, but my gut instinct would be for 3 with a PV source at those ratings.
 
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Offline Pineapple Dan

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Re: [MPPT Charge controller] Increase current capacity
« Reply #2 on: April 16, 2021, 11:32:19 pm »
Thx for getting back. Yes it is a synchronous buck. Have attached a schematic (I'm not bothering with the RF snubber, although it is included on the schematic. It was not doing a whole lot for me as far as I could tell).

I suppose I'll start to re-work it into an interleaved one, knew I would have to bite the bullet at some point. Panels getting very big now, I was intending this version of it to be sufficient for ""one panel"" but those are going up to 450W these days. Will have to turf out the 16F1509 for a dsPIC but all good fun  :-+

 

Offline David Hess

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Re: [MPPT Charge controller] Increase current capacity
« Reply #3 on: April 17, 2021, 02:17:19 am »
Conduction losses are skewed by the duty cycle so if the duty cycle is far from 50%, it is common to use a larger MOSFET with a lower on-resistance for the switch which is conducting for a longer time.  Using two identical MOSFETs when the duty cycle is skewed is not optimal.

 

Offline Pineapple Dan

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Re: [MPPT Charge controller] Increase current capacity
« Reply #4 on: April 17, 2021, 08:00:37 pm »
This should be alright since I'm going down to about 14v at the most. I must try 24v charging though and see how it gets on. Think it's switching losses that are causing my bother - Q3 would be conducting all the time and it's only getting lukewarm
 


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