Inverters that convert DC into AC are pretty commonplace, some cars even have standard AC receptacles in them for you to plug in your favorite appliance. However, there’s a particular type of inverter called a grid tie inverter that allows you not only to make AC, but also inject it back through an AC outlet to power other devices in conjunction with the normal AC service. Why? Maybe you want to use your own generator or solar power. In some cases, the power company will pay you if you produce more power than you consume. Maybe you just want to know you can do it. That seems to be the motivation behind [fotherby’s] build, which is quite substantial.
The setup only handles about 60 watts, but it does all the functions you need: DC to AC conversion as well as phase and voltage matching. Actually, just converting DC to AC is almost trivial if you don’t care about the waveform. But in this case, you do care that you can create an AC signal to match the one already on the line.
The project is simplified by the use of a STM32F407 board which has some nice high-speed A/D as well as a TI H-bridge board. Another simplification was the use of a transformer, so the inverter only has to create 40V. This is a non-trivial and somewhat dangerous project. However, [fotherby] provides a lot of detail and theory, so even if you don’t want to build it, you might enjoy looking over the work.
Speaking of safety, the system detects if the utility voltage looks bad and if it is, the system shuts down the inverter. This helps prevent islanding — where a utility or electrician thinks a circuit is not live, but voltage is coming from another source.
Overall, this was a very interesting project, especially if you aren’t usually dealing with the power line. Obviously, if you wanted to do this in North America, you’d need some modifications. No matter where you are if you attempt this we suggest you review some safety guidelines.