100W Solar Flyback Grid-Tie Inverter (Part1)

It has been an ambition of mine to design and build a practical grid tie inverter using a microcontroller. After many attempts using various topologies, I have finally achieved a decent level of success and would like to share it here.

This project will detail how to design a single stage grid tie inverter capable of delivering up to 100Watts of output power to the grid. It operates with a power factor of 0.99 @ 100W and an efficiency up to 84%. An actual working protype will be presented. It should be noted that I used parts that I had lying around from other projects so any equivalent type parts could easily be substituted and should work just fine.

To understand how I phase lock the output of the grid tie inverter to the utility grid mains, please see my first instructable. I use the same approach here.

STM32 Duino Grid-Tie PLL : 8 Steps - Instructables

These are the parts I had laying around which I used to make the prototype.

Microcontroller - STM32F103C8 "Maple Mini Clone"

Flyback Transformer - ETD44 with .030 gapped core 328nH Primary = 7T(5 x AWG#21) Secondary 24T(2 x AWG#23)

Flyback Mosfets - FDP24N40 (x2 in parallel) N-CH 400V, 24A, 175mΩ Rdss-on

20mH Inductor - I used an ETD39 E-I core .015 gapped using several layers of polyester tape and apprx 100T AWG#23

Full Bridge Mosfets - (x4) MDF11N60 600V, 11A, 0.5Ω Rdss-on

Half Bridge Mosfet Driver - IR2104 (x2) 600V dependant High/Low side outputs with 520ns deadtime

Precision Isolation Amplifiers - ACPL-790A-000E (x2)

Isolated DC to DC converters - 1Watt (12-13.5Vin / 12Vout 85mA) and 1Watt (12-13.5Vin / 5Vout 200mA)

DC to DC Buck Converter Module - 8-40Vin / 1.25-32Vout adjustable (4A)

Relay - SPST 12Vdc / 250VAC 7A contacts (salvaged from an old UPS)

Stepdown Transformer - 230VAC to 18VAC - used for grid signal. I could have used another ACPL-790A-000E instead

350W Switching power supply - 24-30V adjustable used for testing

Oscilloscope - OWON SDS1102 - 2 Channel 100MHz

Multimeter

DC energy meter

AC energy meter

This demo showcases the inverter into a resistive load as well as in grid-tie mode.

In this tutorial I will go over the theory of operation using a simplifed schematic.

For the mathmatical analysis and design formulas I relied heavily on the following white paper;

(PDF) Optimum Design of the Current-Source Flyback Inverter ...

I use Tina TI for this simulation tutorial

TINA-TI Simulation tool | TI.com - Texas Instruments

Here we go over the simulated waveforms versus the actual Oscilloscope data.

In the comming weeks I hope to replace the bench power supply with a solar panel. The unit will grid tie and perform MPPT (Maximum Power Point Tracking) in a fully autonomous mode.

Here is the link to my google drive where you can find some of the files for this project.

https://drive.google.com/drive/folders/1HWgin2wWfDlhCqH6FCOZARka4PANMugO?usp=sharing