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I have 900W (150W*6Panels) solar panels and 12V inverter (1000VA) which have inbuilt PWM solar charge controller. The distance between pannels and inverter is around >10m and the wires are 6 sq mm only. At this distance inverter shows upto 40A max current from solar pannels at and the wire gets quite hot and waste a lot of power. (Around 150w I assume) (Panels' voltage ~18V, Voltage at input to inverter ~13-14V Depending on usage)

I tried to reduce the distance to around 4-5m and the inbuilt charge controller has been burned twice(Not surprised since inbuilt controller has to dissipate more power in this case). Luckily warranty covered me. So the Inbuilt charge controller is very inefficient.

So i am getting only max 450-500w and 350-400w average usable power.

I want to design a Buck-Boost converter for Solar Panels so that i can connect panels in series and step down the voltage (15V or so) at inverter's input. (Please dont tell me that the inbuilt controller might burn once again, In future i will upgrade to 24v system and maybe design my own charge controller for lead acid batteries, So i definitely need a buck-boost converter)

Now you might ask why buck-boost and why not just buck converter. I will happily make a buck converter if you give me a design which uses n channel mosfets at low side switching.

So i tried to design one with the schematic from GreatScott and burned my arduino nano accidently as i didnt have a gate driver and applied 12V to pin D6 of arduino accidently. Link to his instructible page: https://www.instructables.com/id/DIY-BuckBoost-Converter-Flyback/

Schematic:BuckBoost Schematic Arduino

I didn't use feedback as i was just testing. The circuit worked good in buck mode for a while without heating too much. I burned my arduino because i didn't have a gate driver.

So the question is:

Should i use arduino nano( max frequency 63khz) or STM32 microcontroller(>63khz possible, cheaper) to generate pwm signal? I will be using IRFZ44N or IRF3205 mosfets.(Later one is good) (Please suggest pwm frequency for keeping switch losses low so that i can get away with using less mosfets in parallel, if 63khz is enough with reasonable inductor cost, i will go for the Nano blindly)

Please also suggest inductor value and its current capability. (Is 6uH correct at 63khz)

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For your Buck Converter How much load regulation and line regulation you want?

For example, For 12V Output if you take 1% Regulation then you are allowing your output voltage to vary 1% from 12V during no load to full load.

Speaking about PWM Freuency usually, Buck Converter will range from 100KHz to even 4MHz.

However, using Digital Control it is not possible to go above 63kHz or 100kHz without High Resolution PWM. Hence, you should consider STM32F334R8 otherwise you may face stability issue in closed loop control.

Your switching loss is definately depends upon switching frequency but not only switching frequency, MOSFET parasitics are also plays important role. Based upon your mosfet you should choose 100kHz. to avoid high switching loss.

For calculation of inductance, you can use Power Stage Designer from Texas Instrument

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I know I am bit late on this, but I think my answer may help.somebody.

Why not give the task of smps to the chip which is designed for it?

Use SG3525 in push pull configuration. Short it's pins 1 and 9. Then supply voltage from 0 to approx 3.6 to its pin 2 to control the duty. You can use the PWM output of uC and have low pass filter ahead to convert the PWM to fixed voltage. Then apply this voltage to pin 2 of SG3525 to control duty cycle. This control voltage can be varied by changing the duty cycle of the uC's pwm.

You can use any uC for this and because the task of smps and drive is offloaded, the uC can focus on other things.

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