Appropriate generator characteristics for small wind turbine

Thread Starter

leheim

Joined Jan 24, 2024
1
Hello guys. I am working on a project that aims to implement an MPPT controller for a small wind turbine and evaluate the performance gain compared to having no MPPT. I have built a wind turbine prototype using pvc pipes for rotor blades, 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 \(R\) of 0.6 m, and I will assume an efficiency \(C_p\) of 0.25 (while operating at the optimal tip speed ratio). For a wind speed \(v_w\) of 10 m/s, the output power is \[ P=C_p\frac{1}{2}\rho\pi R^2v_w^3=173 \text{W} \] where \(\rho\) is the air density (1.225 kg/m^3). If the optimal tip speed ratio \(\text{TSR}\) is 7, it means that the tip speed \(v_r\) is 70 m/s, which leads to an angular velocity \( \omega \) of 116 rad/s and \(\text{RPM}\) of 1114. The voltage constant \(Kv\) of my PMSG is 8.18 V/kRPM, which means that the output voltage \(V_o\) 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/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 find modules for these so that I can focus on the control logic (sensors and MCU programming). Gears don't make sense for a wind turbine of this size. Should I have a different generator? What should I look for? A PMSM with a higher \(Kv\)?
 

schmitt trigger

Joined Jul 12, 2010
901
Indeed, a permanent magnet, three phase BLDC would be the easiest for this application.
But because you are dealing with such a wide range of speeds, perhaps a device with a separately excited field, like a car’s alternator, might be a better solution.
 

Claudio Hase

Joined Jan 20, 2023
1
I imagine that an automotive alternator really is the best solution. As it is for an experiment, you can buy it used, very cheap.
Another advantage is the external excitation, easy to control, and maintain a safe limit at high speeds, and at low speeds you have the advantage of having a large number of poles.
Your MPPT can even act on excitation !
 

MisterBill2

Joined Jan 23, 2018
18,535
Certainly an electromagnet produced field is simpler to control the output than a permanent magnet field. But that electromagnet consumes power that is then not available for a load. So there is a tradeoff.
As far as operating at the maximum power point, a consideration of what the load needs to have supplied also needs consideration. If the load is batteries then the load is more predictable and the requirements fairly well defined.
 
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