Three Phase Generation from a Wave Energy PM Generator

[powertrainee]

I am doing some research into wave energy.

As such, I am trying to understand the stator construction for a linear permanent magnet generator that allows for three phase generation.

So for example:

http://www.earthtechling.com/wp-content/uploads/2010/02/seabased-wave-energy-converter.jpg

If the rotor (translator) is a set of powerful permanent magnets, how can the stator be designed to intercept the changing flux which results in a three-phase induced emf. I've gone through some papers, however I am not getting a clear picture.

Thanks for your help!

 

[powertrainee]

Also - I found the following presentation:

http://www.cst.com/Content/Document...n of 3 Phase Tubular PM Linear Generators.pdf

On slide 5, I don't particular method by which three-phase voltage is induced in the stator - even more so with linear as opposed to rotational motion.

Again, any help is appreciated!

 

[MikeHalloran]

Since you clearly can't just tie it to the grid,
you might be better off to make a single phase generator and feed its output to a converter with three phases out.




Mike Halloran
Pembroke Pines, FL, USA

 

[powertrainee]

Oh I do understand that. I am not actually not looking to make anything, just trying to understand the principle of the stator design. I can't figure it out though.

 

[Compositepro]

Sine waveforms,(single or three phase) are a result of rotating machinery or harmonic oscillation. There is no way you could mechanically synchronize wave motion to the power grid. It would be done electronically.

 

[MikeHalloran]

I see how it works.
Because the magnet pitch is not equal to the winding pitch, you can get three phase power, sort of, from the oscillatory wave motion.

What you DON'T get is three phases whose summed magnitude is a relatively constant sum.

Instead, you get three phases whose magnitude sums to a time-varying function, probably roughly sinusoidal, that's in phase, not with the power grid, but with the waves.

You could rectify that to DC, filter it heavily, and use an inverter to push power into the grid and sell it.


Mike Halloran
Pembroke Pines, FL, USA

 

[jpts]

You can make it as three-phase PM synchronous generator (linear instead of rotational in this case), but you definitely need a converter to synchronize with the grid. This is because generator output (and voltage) frequency will vary with the waves, and on the grid side you need constant 50 Hz (in europe).

Location of the converter can be on the shore for example due to prcatical reasons.

 

[waross]

Look at linear motors. A synchronous linear motor should work as a generator.
en.wikipedia.org/wiki/Linear_motor


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[cswilson]

Looking at Slide 5 of your second link that you are struggling with, note that there are 2 slider "features" per 3 stator "features". The slider features are alternating north and south poles from the permanent magnets. The stator features are the phase windings.

Take one of the slider magnetic poles. As it is pushed past each stator winding, it will create a voltage in that phase. The next slider pole, of opposite polarity, is 1-1/2 phases away, creating phase. voltages of the opposite sign. Considering the constant speed case first for easy understanding, we are creating 3 (approximately) sinusoidal waveforms, each 1/3 of a cycle apart.

At non-constant speeds, these are no longer sinusoidal functions of time, but they are of position (with the magnitude proportional to the speed).

As others have said, these work on the same principle as linear permanent magnet motors, which are now very common in certain industries. Virtually every explanation I have seen for these says to think of it as a "rolled out" rotary motor of the same type.

Curt Wilson
Delta Tau Data Systems