3-Phase Generator

Thread Starter

abuhafss

Joined Aug 17, 2010
200
Hi

First of all, this is not a project. I was just designing a set-up in my mind. I have very little experience of 3-phase generators. I need some help to understand the concept. Please see the attached diagram below:3-Phase Gen.png

For example:
A 3-phase generator, producing say 15-30VAC 10A.
A full-wave rectifier (15A) is used to convert into DC and then supply to load.

My Question:
During operation, if there is rapid switching in each phase line using some control circuit, will there be any sort of high voltage spikes?
If yes, deploying protection diodes as shown will provide the protection? If this protection set-up is not workable, can anybody suggest some better alternate?
 

Lestraveled

Joined May 19, 2014
1,946
Your schematic is of the standard 3 phase transformer and rectifier. I don't see what protection your "protection diodes" give you. Could you be more specific about the purpose of this circuit and about the protection diodes.
 

Thread Starter

abuhafss

Joined Aug 17, 2010
200
Your schematic is of the standard 3 phase transformer and rectifier. I don't see what protection your "protection diodes" give you. Could you be more specific about the purpose of this circuit and about the protection diodes.
Thanks for your response.

First of all, it is not 3-phase transformer.....it's a 3-phase generator.

I am driving a 3-phase generator with a powerful stream of water. To regulate the output I am currently using a motorcycle's regulator/rectifier, which is a shunt type regulator. It is working fine except that it gets quite hot. I am planning to design my own regulator. I was considering to regulate by rapidly switching off/on each phase at a preset threshold voltage.

What my actual concern is that I am not sure, if switching off a phase will cause a high voltage spike (which I expect within the winding of the generator). If there will be spikes, will the diodes provide protection against them
 

Lestraveled

Joined May 19, 2014
1,946
the "protection diodes" are shorting part of the three phase bridge.
How can the diodes short the bridge?? They are identical to the diodes in the bottom of the bridge.

................ I was considering to regulate by rapidly switching off/on each phase at a preset threshold voltage.............
You will certainly generate some very BIG spikes using this method. I suggest that you consider a different way to regulate. How about a switching regulator at the output?
 

Thread Starter

abuhafss

Joined Aug 17, 2010
200
You will certainly generate some very BIG spikes using this method.
So, the protection diodes would not do the job? Any other suggestions for protection?

How about a switching regulator at the output?
Yes, that could be done. But, I was thinking before rectification with an idea that rectifiers and the generator winding would have some relaxation when switched off.
 

Lestraveled

Joined May 19, 2014
1,946
......... I was thinking before rectification with an idea that rectifiers and the generator winding would have some relaxation when switched off.
To switch 3 phase power to achieve voltage regulation is very complex. What specifically are you thinking about?

On the other hand, the voltage and current you are talking about is well within the capabilities of a switching converter and would be very economical.

What is your target voltage?
 

tcmtech

Joined Nov 4, 2013
2,868
Personally I wouldn't worry about it. SCR based AC to variable DC power converters don't have a problem with switching on and off all through each phases cycle.

If you want to regulate your output voltage I would recomend doing something other than just turning the entire AC part of the system on and off to do it and do as others have said and use a dedicated buck converter on the DC end control things from there.

Either that or keep your load dump type regulation systems in place but use a larger heatsink on it if heat is a concern to you.
 

Thread Starter

abuhafss

Joined Aug 17, 2010
200
What specifically are you thinking about?
I am thinking to design the regulator in such a way that generator winding and the rectifiers should get some relaxation. Continuous load on the winding and rectifiers make them hot, particularly the rectifiers.

My idea is to sense voltage from the output, compare it with preset threshold and then use some suitable switching devices to switch the 3-phase power.

What is your target voltage?
Target is 15V.
 
Last edited:

Lestraveled

Joined May 19, 2014
1,946
I suggest that you look at PWM charge controllers used in solar power systems. They are cheap, readily available, and are programmed with good battery charge profiles. The voltage range of your generator/rectifier system is perfect for these controllers.

Google "Xantrex C35". It would be perfect for your application.
 

crutschow

Joined Mar 14, 2008
24,130
The only practical way to control the voltage of a permanent magnetic generator is to short the output as a motorcycle shunt regulator does, since open circuiting the generator will generate large and possibly damaging voltages.
Using protection diodes with the generator open-circuited will dissipate as much (or more) power than shorting the output.
Here's an article I wrote on a low power motorcycle regulator design which may be of interest to you.
 

Thread Starter

abuhafss

Joined Aug 17, 2010
200
crutschow

Referring to your article, would you please specify how the Triple Diode CMXD2004TO should be mounted in the ambient air stream.
Should it be placed away from the body of the regulator, particularly the fins of heatsink?
Can 3 x 1N4148 be used instead of the triple diode?
 
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