I have a varsity project that requires me to build an inverter that will facilitate grid tying. I have basic knowledge of electronics but not enough seemingly to indulge in such an extensive project. A wind turbine will produce a 12 VDC output that will be connected to a charge controller to regulate the input voltage flowing into a battery bank.

The inverter I need to build should then convert the 12 VDC into 230VAC, 50Hz as that is the frequency of operation in South Africa. I need to be able to tie the inverter into the main's grid as the payback period of the system is part of the project. The grid tied system should also enable the system to run during situations whereby no power is generated from turbine. A load of between 500-700 W is expected at the output.

Could anyone please suggest the best possible approaches or reads that could enable one to design the inverter part to have a minimum and maximum input shutdown voltage of 10-15 V and produce a rather pure sine wave at the output with minimum harmonic distortions of around 220-230 VAC.

Much thanx

 

That's quite a sophisticated project, even for a pro.

 

And unsafe and possibly illegal to actually complete.

 

If your homemade grid-tie project has a design flaw, you may feed power back into the line during a power outage or when the lines are disconnected for maintenance. This may result in the electrocution or death of an electrical lineman that was expecting the disconnected lines to be "safe".

Grid-tie systems are required to pass stringent and expensive safety testing and certification to make sure they fail in a safe manner and don't make the power lines more dangerous for the linemen.

Before you even consider connecting an uncertified home-made power backfeed project to the power grid, I would suggest you contact the local power company so you can get an earful from them, and so they know who to come find when one of their employees accidentally gets killed fixing a downed line.

 

Are you sure it was intended for you to design the grid tie inverter itself or just put the overall system together? There are grid tie inverters already for sale which are as simple as just connecting it and turning it on. These ready made inverters have already gone through the extensive (and very expensive) testing and certification that's required. I have trouble believing that a competent instructor would have you design something like this for a varsity project. I get a feeling it's just a proof of concept thing you might be taking too literally.

 

Are you sure it was intended for you to design the grid tie inverter itself or just put the overall system together? There are grid tie inverters already for sale which are as simple as just connecting it and turning it on. These ready made inverters have already gone through the extensive (and very expensive) testing and certification that's required. I have trouble believing that a competent instructor would have you design something like this for a varsity project. I get a feeling it's just a proof of concept thing you might be taking too literally.

Thank you very much for the feedback guys and i'll look into the safety and legal aspects with the local electricity company.

Projects span over a year's duration and the first semester is usually an introductory and research phase where one is expected to familiarise with the chosen research or design topic of interest. My project is a design project and I fully acknowledge that there will be flaws with my final product in comparison to an off the shelf ready made inverter but part of the key requirements to obtain my degree is to show a critical idea mindset in a relatively new area of expertise.

Any suggestions on the best inverter topology or design approaches will be greatly appreciated as this will be the main focus of the project, with other necessary hardware being bought.

 

Wow, you ARE serious.

You must not put a research device on a live power grid where it can literally injure or kill people. It would be completely irresponsible for both you to do so, or for your school to allow or even recommend you do it.

Who are these people anyway? School name, location, professor?

I have a hard time believing this is really a serious request from a school, and you're not just trying to come up with a cheap hack on your own, to spin your power meter backwards and heck with all the safety precautions.



The only legal and responsible way to proceed, as an educational project that will NEVER be used on the actual power grid without further testing and actual official certifications, is to use it on a test AC power source unconnected to the main grid.

This can be done with a standard engine-powered generator driving a dummy load. If you can successfully grid-tie against the generator, you will cause the generator to back off on its fuel consumption until it is basically just idling to keep spinning, as your experimental device powers the dummy load instead.

No actual real grid-tied power production or cost savings can be expected from doing this, but your university professors should already know that.



Going all the way to building an actual device for sale to others will cost tens of thousands to hundreds of thousands of US dollars to complete, through whatever is your government's local certification agency. Here it is Underwriters Laboratories, but you may fall under CE labeling.

http://crownaudio.com/amp_htm/certifmarks/certifmarks.htm

 

Thanks DMahalko

And I guess the standard engine-powered generator driving a dummy load is a very good practical replacement instead of tying it to the grid for reasons you have clearly highlighted, lol.

The wind turbines' working conditions will be simulated in the laboratories and there'll be a constant wind supply, with the cut-in speed and maximum power output at a specific speeds being noted.

 

Designing all this for safety first ought to score points with a professor. I actually see more room for creativity in designing all the fail-safe behaviors than for "just" the power transfer hardware. Making an in-phase, regulated sine wave isn't the easiest thing in the world but it's been done. Where's the fun in that?

 

You need to design this around an INDUCTION GENERATOR.

The wind is used to "push" an induction motor serving as a wind generator. The motor will be connected directly to the mains and serves in this capacity by running as a motor whenever it is connected to the grid. When this motor is driven by the wind and tries to go faster it becomes a generator and will put power back on the grid. No need to control phase or frequency. The motor does all that. This method does consume grid power when wind speeds drop below the needed minimum value. A method to disconnect automatically when not generating, and reconnect again will be the most difficult to achieve.

Google the capitalized words above and research/read all about it.