Builiding of a complete 6kW PV inverter with MPPT chargers


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-dex-
Regular Member

Joined: 11/01/2024
Location: Poland
Posts: 86
Posted: 08:48am 06 May 2024      

Update regarding the MPPT system - I soldered new SiC B2D30065H1 diodes (52A continous current @ Tc=135°C), two pieces per module. Now MPPT works and survived tests    So far, the highest power from MPPT that I have seen is ~2kW - the pv panels did not allow more yet.


  nickskethisniks said  Now back to the blowing silicon, something we never did was actually calculating the minimum capacity/inductor. At least I didn't do that for the first version, I used as much as was practical.



As for the inductor, I personally checked it in several calculators, which suggested a certain minimum inductance value.

For the capacitance value of the capacitors, I was not able to calculate it. I did what was advised here - "any reasonable capacity value will do" or use what you have on hand. My capacitors are several-year-old storage units, measured parameters in the photo.

Can anyone calculate what capacity value will be safe?





  nickskethisniks said  
So I think I can say we all use to much capacitors, but this will give us a very long lifetime,although these are capable of providing a lot of current with low impedance. So if there is a sudden demand (inverter for instance) for current in the circuits it's possible its provided by the caps in the controller. The controller is to slow to change the duty cycle and lots of current will flow thru the MOSFET, and then thru the diode.



Is it possible to approach it from the other side and appropriately oversize the mosfet and diode for this event?


  nickskethisniks said  
Lesson learned and implemented a contactor between solar and regulators. I recently ruined one with rewiring so I want to build some MOSFET switches. Allthoug contactors are more robust but use more energy. There will be some back emk when disconnecting the panels, this will probably less when disconnecting the mppt outputs, but then you need to use output caps rated for the input voltage.


In my mpppts all PV side & output side capacitors are 300V rated.


So if one mppt has a shorted mosfet, it sends ~100V to the outputs of the other mppts. While other mpts runs, get 100V at ther outputs, they are safe or not?
I also saw in your built that you used diodes in series to connect the MPPTs, in this situation should block the high voltage from reaching the other MPPTs.




Back to protector & kilovac

I used this kilovac in my inverter. I will use the same model in OVP protect circuit on the MPPT bus. The G version is available in digikey, 48V coil with economizer.


AEV250_2.pdf