Homebrewed Electricity > Wind

Appropriate generator characteristics for small wind turbine

(1/5) > >>

leheim:
Hello guys. I am working on a project that aims to implement an MPPT controller for a small wind turbine and evaluate the performance of the controller. I have built a wind turbine prototype using PVC pipes for rotor blades, a 3D-printed rotor hub and nacelle, and a metal pole tower. It is probably not the best wind turbine out there, but I think it will be sufficient for testing the controller. I have a PMSG that I want to use, but I am unsure if it fits the application. I am studying digital and embedded electronics, so I am a bit unfamiliar with electrical machines. Here is my thought process:

The prototype has a rotor radius R=0.6 m, and I will assume an efficiency Cp= 0.25 (while operating at the optimal tip speed ratio). For a wind speed Vw=10 m/s, the output power is P=Cp*(1/2)*ρ*π*R^2*Vw^3=173 W where ρ is the air density (1.225 kg/m^3). If the optimal tip speed ratio is TSR=7, it means that the rotor tip speed is Vr=70 m/s, which leads to an angular velocity of ω=116 rad/s and RPM=1114. The voltage constant of my PMSG is Ke=8.18 V/kRPM, which means that the output voltage is 9.11 V. Since the output power is 173 W, the output current will be 19 A.

It seems to me that it would be beneficial to operate at a higher voltage and RPM to avoid high currents so that the power electronics will be easier and cheaper. I'm thinking of using a three-phase uncontrolled rectifier, and maybe a boost converter to implement MPPT by controlling the load with the PWM signal. Ideally, I will be able to find modules for these so that I can focus on the control logic (sensors and MCU programming). Should I have a different generator? What should I look for? A PMSM with a higher Ke? Or are such current values normal/acceptable? Any help here is very welcomed :)

bigrockcandymountain:
Is 19a within the rated output of the generator? If it doesn't have a rated output, what is the output wire size?

I would probably just go for it.  Worst case just make some shorter blades that spin higher rpm and make less output. 

I'm interested to see how you do with the testing.  I don't know of any controllers that use true mppt for wind. 

Bruce S:
leheim;
Welcome to the forum.
I gotta say that is one fine printed covering.
Traditional ways of controlling the output are of course having the windmill held to a specific output that does not allow it to over spin that can cause blade or generator failure.
I too am curious about how your idea of MPPT will help with this. You could of course use a rotor spin sensor that starts turning the windmill out of the wind once max revs are met.

Do send a few more specs on the generator and wiring so we can assist further.

Cheers
Bruce S

Adriaan Kragten:
I have had bad wind tunnel experiencies with rotor blades made out of PVC because these blades are very sensible to flutter at high wind speeds if the the pipe thickness isn't very large. This is mainly because of the low torsion stiffness. Flutter is a combined bending and torsion oscillation. But if you use very thick pipe material, you should round the nose and sharpen the tailing edge otherwise the airfoil will have a too high drag/lift ratio for a rotor with a high design tip speed ratio. I have used 2 mm thick stainless steel for a rotor with cambered tapered blades as described in my public reports KD 616 and KD 617.

Matching in between rotor and generator is explained in chapter 8 of my public report KD 35. Any windmill rotor has a certain optimum cubic line. The optimum cubic line is given by formula 8.1 of KD 35. If the rotor is loaded such that the optimum cubic line is followed, it will run at the tip speed ratio for which the Cp is maximal. The generator winding and the generator load should be chosen such that the Pmech-n curve for the wanted load has two points of intersection with the optimum cubic line of the rotor which are lying not far apart. The Pmech-n curve for a certain winding depends on the voltage. The higher the voltage, the more the Pmech-n curve shifts to the right. Measured curves for different voltages are given in my public report KD 78 for a PM-generator made from an asynchronous motor using the standard 230/400 V, 3-phase winding.

Matching in between rotor and generator can only be checked if you have measured generator characteristics for the wanted load. So you need a test rig with which it is possible to measure the torque, the rotational speed and the generated electrical power. An example of such a test rig is given in my public report KD 595. All public KD-reports can be copied for free from my website: www.kdwindturbines.nl at the menu KD-reports.

In the photo's, I see no provision which turns the rotor out of the wind at high wind speeds. It is impossible to limit the maximum rotational speed only by the generator load because there is always a wind speed for which the rotor torque is higher than the peak torque of the generator. If this wind speed is reached, the rotor will speed up and the generator winding may burn. Wind turbines with no safety system are very dangerous. Five different safety systems which turn the rotor out of the wind at high wind speeds are described in my public report KD 485.

JW:
In the past that used "PVC blades" I remember a safety issue with those blades.

https://www.fieldlines.com/index.php?topic=140024.0

Navigation

[0] Message Index

[#] Next page