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Forum Index : Electronics : Rafael MPPT Controller (for WG Powerboard)

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flyingfishfinger
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Joined: 12/09/2020
Location: United States
Posts: 100
Posted: 06:42pm 03 Jun 2021
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Hi,
I didn't want to derail Poida's thread about his MPPT so I'll put this here.

I've adapted his Brainboard for Wiseguy's Powerboard layout to fit right ONTO the 10-pin connector in a bid to reduce cables running around the place & keep things short. I've made a few changes:

- Added a hardware comparator & P-FET that could be used for a hard over-current shutoff. This is an adaptation of Poida's attempt at controlling this with a software interrupt, but I have no idea if it'll work yet.

- Added a few 0.1uF capacitors to decouple the 5V supply to the Nano and the LCD, I want to try to get the I2C display working properly. Should generally reduce noise.

- R, G & B LEDs - everyone needs Blinkenlights! For extra indicators.

- Optimized routing for the 10uF filters a bit, this should reduce the noise on the analog readings.

I don't have a 3D model of the Powerboard (wiseguy?) to check the fit with, but I'm 98% sure it'll fit.

I'm about to order some along with the Powerboard, and if it works I'll be happy to share the Gerbers for anyone who wants to try it.

In the meatime, here are schematic & screenshots if anyone's interested. I'll report back on how things go.








MPPT_NanoController.pdf

Cheers,
R
Edited 2021-06-04 04:58 by flyingfishfinger
 
wiseguy

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Joined: 21/06/2018
Location: Australia
Posts: 988
Posted: 12:55pm 04 Jun 2021
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  flyingfishfinger said  Hi,
I didn't want to derail Poida's thread about his MPPT so I'll put this here.

I've adapted his Brainboard for Wiseguy's Powerboard layout to fit right ONTO the 10-pin connector in a bid to reduce cables running around the place & keep things short. I've made a few changes:


I don't have a 3D model of the Powerboard (wiseguy?) to check the fit with, but I'm 98% sure it'll fit.



"I don't have a 3D model of the Powerboard"
Nor do I Rafael - sorry.  I need to create 3D models for all of my components - its on my to do list - I can just see it if I use binoculars......

I do need to get around to it though - takes out a bit of the guesswork and I will need my vernier & sample components a lot less when I design PCBs.  I have looked at how your pcb should fit and I dont think it will foul with anything. A component on my PCB could maybe be inserted on the underside if it helps.
If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike
 
flyingfishfinger
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Joined: 12/09/2020
Location: United States
Posts: 100
Posted: 04:48pm 04 Jun 2021
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No worries. What program do you use for the designs?

R
 
poida

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Joined: 02/02/2017
Location: Australia
Posts: 1387
Posted: 10:49pm 04 Jun 2021
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Rafael,
here are a couple of photos of the built board, to help you see what space there is
and is not.









wronger than a phone book full of wrong phone numbers
 
wiseguy

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Joined: 21/06/2018
Location: Australia
Posts: 988
Posted: 09:11am 05 Jun 2021
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  flyingfishfinger said  No worries. What program do you use for the designs?

R

I am using Altium Ver 17. What do you use - the 3d imaging looks very good.
If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike
 
flyingfishfinger
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Joined: 12/09/2020
Location: United States
Posts: 100
Posted: 03:28am 06 Jun 2021
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I use Diptrace. Easy to use generally and the first thing I learned, so I do my personal projects in it. Adding 3D models is really easy there if it's not part of the standard libraries - click to add a STEP file to the footprint, align it and done. The images I posted are just screenshots out of the previewer, but I can save off nice STEP models of the full assembly.

I'm surprised about Altium, it's known in the industry to have pretty good 3D output capability. I've never used it though so I'm uncertain how to set it up...

FYI, I ordered both the Powerboard and my Controller PCB and I'm waiting on FETs from Aliexpress. Not sure what to do about the choke and caps yet, I have a lead on a busted Fronius but that's kind of up in the air.

R
Edited 2021-06-06 13:29 by flyingfishfinger
 
flyingfishfinger
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Joined: 12/09/2020
Location: United States
Posts: 100
Posted: 10:37pm 22 Jun 2021
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I got PCBs, check them out! MOSFETS from Aliexpress arrived too.

Now I need order the rest of the parts... I haven't found anything to salvage a choke  and heatsink from yet, sadly.

Question: Did you guys end up putting a ferrite bead on each MOSFET gate pin? If yes, what size is it?

R
 
poida

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Joined: 02/02/2017
Location: Australia
Posts: 1387
Posted: 11:42pm 22 Jun 2021
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In my builds no ferrite beads were used.
If you can't find a choke then Digikey have them
a couple of these at $15 AU each,
probably $10 US will do.

If I recall, one pair of those cores with 9 turns and about a 1mm
gap in the inner core will be good for 2kW and about 20 Amps ripple
when taking 100V down to 45V.
maybe have a look at
http://www.thebackshed.com/forum/ViewTopic.php?TID=12027&P=17#147582
and the later post at
http://www.thebackshed.com/forum/ViewTopic.php?TID=12027&P=17#147632
Edited 2021-06-23 09:46 by poida
wronger than a phone book full of wrong phone numbers
 
flyingfishfinger
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Posts: 100
Posted: 10:17pm 23 Jun 2021
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Cool, I'll just grab those then.

Also, in your above pictures I see you're using a 1W 12V-12V regulator... but if this is used for the FET gate driver wouldn't we actually need more power?

R
 
poida

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Joined: 02/02/2017
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Posts: 1387
Posted: 01:16am 24 Jun 2021
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Driving the FET Gate is an operation that charges a capacitor.
So the only energy needed is to drive the 10K Gate to Source resistor
and to charge/discharge the FET's various capacitances, seen on the
Gate pin.

The time spent charging the Gate is about 600ns and average current is
about 0.5 Amp for that period of time.
See
https://www.thebackshed.com/forum/ViewTopic.php?PID=103706#103706#103706
for a typical Gate voltage during switching.
I show voltage across the Gate resistor
so we can determine the current.

(the Gate current really looks like it is charging a capacitor!
See the exponential decay?)

20KHz PWM means
20K switch events per second.
so that is a total of 20000 x 600 ns
or 0.012 seconds spent delivering this 0.5 Amp.
For the rest of the second, the Gate Drive bypass caps
will be charging from the supply.
It's about a 1% time driving the Gate and 99% of time
recharging the bypass cap.

Plus the 100% time spent powering the 10K Gate pulldowns.
There are two.
so that is 5K on 12V, 2.4mA

I reckon the gate drive current needed is
2.4mA for the two 5K and
1% of 0.5A x 2 for the two FETS = 10mA
so a total of 12.4mA @ 12V = 0.15W
wronger than a phone book full of wrong phone numbers
 
flyingfishfinger
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Joined: 12/09/2020
Location: United States
Posts: 100
Posted: 06:43pm 24 Jun 2021
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You're right, I didn't do the diligence for my part selection. Here it is:

The HY5110 has a total gate charge of 356 nC. We have a 10Ohm gate resistor in the design, so that means at 12V we can sink as much as 1.2A into EACH gate starting at t=0.

At 1.2A, we will charge 356 nC in 300 ns (ignoring the Miller plateau and the fact that charging current drops as we turn on for the moment, so this calculation will be an overestimate).

But if we have 2 (or even 3 FETs) and we want to switch them quickly, we will need 2.4 (or 3.6) amps if the driver can source this much.

The FOD3182 can source 3A of current, so let's assume we've built with 3 FETs and are maximizing this current.

That means we're delivering 36W for 0.006 seconds, for an average of 0.216W. If we populate 3 FETs and therefore also have 3.3k of pull-down, that's an additional 43mW for a grand total of 0.26W.

The 10uF output capacitor will discharge to 11.89V at every cycle.

For fun, I simulated a very similar MOSFET in LTSpice. The numbers roughly check out - the FET starts carrying the full drain current after about 300nsec, and the peak gate current is very nearly 1.2A:






Cool! Thanks for promting me to do the analysis as well.

On an unrelated note, what did you put between the FETs and the heatsink, some Sil-Pad esque material?

R
Edited 2021-06-25 05:37 by flyingfishfinger
 
poida

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Posts: 1387
Posted: 10:33pm 24 Jun 2021
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Sil-Pad. It's good enough.

The heat generation is mainly in the choke in my experience.
Typical high power testing has shown HS temps
of 40 C with a choke going to 50 C.
These temperatures are attained only after an hour or so at 2kW +

The mppt firmware will reduce output power linearly as the HS temp
exceeds a user defined temperature. I think I use 60C as the start point
and 70C as the end point. Power will be 100% converted at 60C and lower
and then it will be reduced to zero at 70C, following a linear rate of change.

This makes it nearly pointless to have a fan on the heatsink.

I found HS orientation to be "worth" a fan if you have the HS fins
vertically aligned to allow air movement up and out the top.

here is some data from my home system.
The output current and HS temperature for the mppt
connected to the 3kW North facing array.



I see no way the HS will exceed 60 C even if running at 40 Amps all day.
But this of course is highly dependent upon the HS size and
the HS used with this mppt is the same size as that shown in the
above photos.
wronger than a phone book full of wrong phone numbers
 
flyingfishfinger
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Joined: 12/09/2020
Location: United States
Posts: 100
Posted: 09:43pm 05 Aug 2021
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Sneak peek - still need to find wire to wind my choke and I don't really have a useable heatsink for the FETs :/


The LCD works from the controller board, but I haven't tested anything else yet...

R

EDIT: Shattered one of my new cores trying to gap it, guess testing is going to have to wait...  
Edited 2021-08-06 10:18 by flyingfishfinger
 
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