Homebrewed Electricity > Wind
Appropriate generator characteristics for small wind turbine
leheim:
Hello, again.
Thank you for the great response! And sorry for my late follow-up, it's been very busy at the university. An unnecessarily large number of meetings and emails with professors and academic departments to get access to test equipment and facilities, as well as thesis supervision. On top of it, attending career fairs, doing interviews etc. to land a job after the thesis, just the normal student life. I will try to answer your questions.
More specs for the generator (Alva X60-Kv120) can be found in the attached datasheet, or at the manufacturer's website (I can't link it, but it's on alvaindustries.com). It is designed to be used as a motor for large industrial drones. I can't find the rated current output listed in the datasheet, but I think it says 29.3 A (continuous) and 51.4 A (transient). The green/yellow output wires you see in the pictures are 2.5mm2 (best I could find at the workshop), and the small blue wires are from the thermistors in the generator.
I plan to acquire smaller rotor blades, and let the turbine rotate at a higher RPM which will generate more volts, like you suggest bigrockcandymountain. X60-Kv120 also has a higher efficiency at higher RPMs. I can maybe get my hands on the 28'' diameter "Alva & Mejzlik propellers", which you can see on the linked website. Then my turbine will be similar to the portable Shine Turbine (shineturbine.com), which by the way incorporates MPPT according the the user manual. I find it interesting that bigrockcandymountain says that you don't know of any wind controllers that use "true MPPT". If that is the case, my thesis may be more significant than I have thought. I have been trying to "angle" my thesis such that I don't just do something that many others have done already.
As I stated in the original post, the wind turbine design and functionality itself is not the main focus here, but rather the implementation and performance of the MPPT control strategy. However, I guess the wind turbine should be decent enough to be able to test the controller. My idea is that the controller should be able to optimize the power output for any given turbine. Considering safety features like overspeed protection, I think the solution will be to simply not set it up during strong winds (in addition to a stop switch which shorts the output wires). That is also the approach of the Shine Turbine.
I don't quite understand Bruce S's statement about "holding to a specific output that does not allow it to over spin". Are you referring to fixed-speed wind turbines? I have not chosen a specific MPPT implementation yet, but I have been looking at the simple "Perturb and Observe", where the duty cycle of the DC-DC converter is altered (perturbed), effectively changing the load, then observing the change of output power. If the output power is increasing, the controller will continue to alter the duty cycle in the same direction until the maximum power point is found.
My plan onwards is to do more research on different MPPT control strategies, and how to set up a good test scheme. I plan to to tests in the lab with a "back-to-back" setup with a motor that drives my generator. With the motor, I guess I can for example sweep RPM and wind speed/power with different constant loads, while measuring the output power. Then at a later stage, hopefully I will have time to to field tests (the most fun part).
Greetings,
Lars Erik
DamonHD:
My inner glass-half-empty wonders whether there are local maxima that "Perturb and Observe" would get stuck in. It seems sometimes to be a problem for solar PV for example.
Rgds
Damon
Mary B:
While we can help wit generic questions we CAN NOT do your work for you on a college thesis!
With 28" diameter rotor blades you will get very little output, capture area rules when it comes to amps!
MagnetJuice:
Hi leheim,
The motor that you have mounted on your turbine is too powerful and the RPM is too high. The specifications for that motor says that it will output 44 Volts at 5400 RPM. It will output 12 Volts at 1500 RPM.
Try to find a motor with maximum RPM of 500 to 1000.
I searched and the closest that I found that should work is this:
https://www.surpluscenter.com/Electrical/DC-Motors/DC-Motors-Face-Mount/12-Volt-DC-Salt-Spreader-Motor-Arrowhead-SAB0191-Arrowhead-SAB0191-10-3108.axd
That motor produces 12 Volts at 1050 RPM and should be good for about 200 Watts.
You should be able to find something similar to that in the EU.
That sounds like an interesting project.
EDIT:
I would not get those 28'' diameter Alva & Mejzlik propellers. They would spin faster, but they don’t have the torque to turn that big motor that you have now.
I looked at the little Shine Turbine and the specifications. It needs 10 m/s (22 MPH) to make 20 watts. IMHO that is a very expensive toy.
Ed
taylorp035:
I second MagnetJuice's comments. Radius of 0.6m = ~4 foot diameter. Your 121 RPM/volt spec on the data sheet is about 5x too high to hit a useful voltage. There are better BLDC motors out there with lower KV ratings, though getting down in the 15-30 kv range will be challenging without coging too much for start up and not being too expensive.
For example, 20 RPM/volt * 12 volts = 240 RPM cut in speed.
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