S4w's Wind Generator Notes

Well, Ive been very very busy with my electronics projects particularly with the sine wave inverter. I made many changes to it since I presented the schematics.

One important change that I made was the use of IGBTs instead of MOSFETS. IGBTs provide a much more robust inverter because we are dealing with high voltages. They are made to be tough and have much lower junction to case thermal resistance which helps a lot with the cooling.

First I made two separate driver boards, one for each IGBT module. One IGBT module contains both high side and low side switches in one package. You can see the picture below. The two IGBT modules are bolted on to a heatsink cluster and the driver boards bolt on directly to the IGBT modules.

After having that tested out and working fine I decided to make a single board for the inverter excluding the boost converter. I also made changes to the logic circuit. Instead of using all discrete components to generate the PWM signal I decided to use a microcontroller. For this task I chose the PIC16F877A which has plenty of power for pretty much anything we need to do. So, this board has the two drivers and the microcontroller generating the PWM all together. This approach was much more practical because of the ease of handling. Also, only a power cable need to be connected to it other than the two cables that bring the high voltage DC and the two output cables going to the filter.

The adition of the microcontroller also enables me to make this board do more stuff than before by only changing the software. For instance, you might have noticed that the board has a barrel power connector. This is used to input an AC signal from a wall transformer. With this data I can synchronize the output of my inverter with the grid and actually use this inverter as a grid tie inverter. Also notice 3 DIP switches in the board. I can select with those switches in what mode will the inverter operate. It can be used as a DC motor controller (controls the speed and direction with the two pots next to the switches), AC motor control, regular sine wave inverter and grid tie inverter.

Adding a microcontroller was a great deal not only because you can add more features with very little amount of hardware but also because it was actually much cheaper to build than using all discrete components.

It was truly a success, I got this beautiful sine wave at the output(top) and the unfiltered wave straight from the H Bridge (bottom):

Picture of the new inverter alone:

This is a picture of that board bolted on the the IGBTs and mounted into the case all wired up to the input filter capacitor:

I have a working boost converter for the sine wave inverter but I want to be able to extract more power out of it (so that it fit nicely in the box). Adding the new booster to the picture is the next step. Its almost finished. This one supports current limiter, its interleaved (2 converters per board). When no power is needed from them they will just shut down, then if a load is sensed only one of them will turn on. If only one booster can supply the demand the second one will not come on. In case its too much load then the second one will start. I do this like that mainly for efficiency's sake. There is no need to have more things running than necessary.

Right now I am also working on a set of tutorials on how to design a buck converter from scratch with great detail and illustrations. I will hopefully be able to finish that soon

I will also be putting up the schematics and source code for the new version of the inverter as soon as I am done with the buck converter. So, I will post them together.

Thanks for reading!