Miniature Wind Turbine, obtaining a constant voltage using PWM

[AndyMc12]

Hello everyone,

I'm currently designing a miniature wind turbine as a project for my final year in University. To run through the basic concept, I have a DC motor - AC generator configuration. I power the DC motor using a power supply which in turn gives me a three phase AC voltage out; rectifying this was no issue. However, the next stage is driving me mad as I'm struggling to incorporate PWM in order to obtain a constant DC voltage for the following charging circuit.
The initial idea I have is to use a 555 timer in order to generate PWM to power a semiconductor switch which will turn it on and off giving me a constant voltage according to the components that follow.
Say I have a range of voltages, from 5V-15V powering the PWM generator (555 timer) and want anywhere between 6-10V as the output, what I'm struggling to get my head around is how I take the square wave output off the 555 timer which powers the semiconductor switch (transistor or FET) and ensure the duty cycle of the timer is always going to give me the desired output. Feedback is the obvious answer but again I'm not exactly sure how to set that feedback up.
I really hope this makes sense and appreciate any advice given!

 

[Pommie]

What I'm trying to "get my head around" is how a DC motor produces three phase! Maybe you need to explain it better.

Mike.

 

[AndyMc12]

The DC motor powers an AC generator in the configuration.

Andy.

 

[Pommie]

Maybe you need to explain it better. Is the DC motor pretending to be a wind turbine? Is the three phase coming from a brushless DC motor. Again, maybe you need to explain it better.

Mike.

 

[AndyMc12]

Apologies for the clarity of my description. So the varying supply into the DC motor does replicate the wind strength a turbine would experience. In terms of the motor it is brushless. My main concern which is what I'm trying to get an answer to is the PWM part of the circuit. I have a voltage to the input of this circuit and I need to generate a desired voltage range for the output of the PWM circuit.
Andy

 

[kubeek]

What are you trying to do with the output voltage? Charge a battery?
Normally no one uses straight PWM to do anything as it will not be very efficient or easy to use. You would use a switch mode dc-dc converter to get the desired output. If your output voltage is allways lower than what the generator produces, then you need a step down (buck) topology. If it is possible that generator voltage is lower than what the load needs, then you need a buck-boost topology.

 

[AndyMc12]

Precisely that charge a battery. The input for the charging circuit has to be between 6-10V. The problem I'm having is the input is never constant (5-15V) and I'm aware of the basics for boost, buck and buck-boost, but implementing this into a circuit with the 555 along with the necessary feedback is eluding me.

 

[Pommie]

If you are taking three phase and rectifying it into a capacitor then you will experience heating in your generator. You need to investigate three phase power factor correction to get the most power out of your generator.

Mike.

 

[kubeek]

Does it really have to be a 555? That is a poor choice for implementing a smps controller.
You will need to implement some form of feedback, where your output voltage influences the PWM until the output is what is set.

 

[AndyMc12]

It doesn't have to be a 555 timer no, I just want something that isn't a chip that does all of the work (i.e DC-DC converter), because its not much of a project then. The PWM is a necessity for the project however.

 

[kubeek]

I think you could use for example mc34063 buck coupled with something along the lines of this to get current limiting https://e2e.ti.com/blogs_/b/powerho...tant-current-constant-voltage-buck-converter#

 

[rjenkinsgb]

What's the winding configuration and rectifier setup you are using?
If that can be rearranged to get a slightly higher voltage at your minimum speed, the overall regulation system would be much simpler.


For basic PWM regulation, you can have the 555 free running and use a comparator between the sawtooth voltage on the timing cap and an "error signal" obtained by comparing the output voltage to a reference.

As the error signal varies, the comparator switches at a different level of the sawtooth, giving a varying duty cycle PWM square wave.