# How to maintain a stable voltage on a Wind Turbine for Inverter

I'm doing some experiments on a wind turbine in my spare time. At the moment, my system runs well and I can measure good output values from my generator. For example:

• 38V @18Hz at 30 RPM
• 97V @37Hz at 60 RPM
• 220V @72Hz at 120 RPM
• 343V @108Hz at 180 RPM
• 466V @144Hz at 240 RPM

The maximum measured current output is 18A.

Now, I would like to use an inverter in order to obtain a three phase output. The problem is that I tried to search on the net and I only found inverters for solar panels which require a stable voltage input (my rectified voltage output keeps changing depending on the RPMs). My system has a variable voltage output depending on the RPMs (obviously) and the frequency changes when the RPMs increase, too.

What is the most suitable solution to obtain a stable voltage output regardless the input RPMs? Is there a commercial inverter which accepts variable inputs?

Thank you!

You first have to rectify your variable frequency AC to DC, then use an inverter which turns DC into the AC of the grid. There are inverters in the market which include the rectifier.

There is an alternative solution which involves a rotor-fed asynchronous machine. The idea is to feed the difference AC frequency to the rotor so the stator frequency keeps being in phase with the grid. That way, the inverter doesn't have to pass all the power the turbine delivers. It was somewhat popular 20 years ago, when big inverters had been incredibly expensive.

• Yes, I already rectify the output of my generator, but the problem is that I can't find a 8-10kW inverter which is able to accept variable voltage as input. Even if I rectify the voltage, it keep changing depending on the RPMs. Can you suggest me a good inverter for my case? Commented Dec 5, 2018 at 9:40
• The voltage spread of commercial wind turbine inverters seems to be around 2.5. So, a 500V inverter accepts down to 200V on its input. You have to specifically look for wind turbine inverter, they are meant to deal with both problems. Commented Dec 5, 2018 at 9:49
• I already tried to look for "wind turbine inverter" but I only found scientific papers or small companies which never reply to my messages (may be they are not running anymore). I am really not able to find a commercial wind turbine inverter. Commented Dec 5, 2018 at 10:14
• I was also considering to use a constant speed drive (or gearbox) like the ones used for the airplanes but I'm not able to find any of these devices for commercial use. Commented Dec 5, 2018 at 11:04
• You are in the 10kVA range. That's a medium-sized windmill with about 100m² cross section to wind. Sure about that? ABB has some offerings for such generators. Commented Dec 5, 2018 at 12:54

For example the ACS 355 would work for you. You can select the right power and it is very easy to install. In serveral industries such products are called "drives" and not "inverter" as in academic literature.

• VFDs are generally not suitable to act as inverters. They don't give a sinusoidal output and will probably fault out if they don't detect a motor load - hence the "D" in VFD.. Commented Dec 30, 2018 at 7:25
• The documentation says "... includes easy to use libraries for applications in wind, water, solar, drives, motion, robotics and safety". Inverter voltage is sinusoidal and it can work without motor detected. But maybe not the best choice I have to admit. We employed the ACS800 for grid interfacing, but this is in a higher power range than what is discussed here.
– UweD
Commented Dec 30, 2018 at 10:34
• I still can't see how you intend the OP use that to run from a DC supply with the 38 - 466 V DC supply range listed in the question. A VSD will be designed to run with the internal DC bus at 450 to 550 V on a 400 V AC supply. If the DC bus voltage is low the drive will shut down. If it is high it will dump into the brake resistor (if fitted) but that will have limited time use before it burns out. Had you some other plan? Commented Dec 30, 2018 at 13:46
• Unfortunately, ABB doesn't provide any product for wind application anymore. Commented Dec 30, 2018 at 16:47