Here is the Description of the issue: We have a 3-phase generator that in its standard working conditions, turning speed is around 3000 to 8500 rpm (which means that the output frequency is around 50 Hz to about 140 Hz). The manufacturer states that the output voltage (phase to phase) is between 35 and 95 V AC depending on speed and 300 W output power is guaranteed even in 3000 rpm without decreasing in voltage level. I want to build a regulator for this generator that be able to give me 30 V DC - 10 A (300 W). The simple solution is using a 3-phase rectifier and a buck regulator. But this solution is two main drawbacks:

• The first is for 10 A I would have a 10 A * 1.4 V = 14 W loss just in rectifying circuit and for 90% efficiency I can have total of 30 W in losses. So 14 W its just a lot.
• The second is in the case of 95 V AC I would have almost 127 V DC after rectifing! And no ready to use ICs like LM2596 and common buck controllers can handle such voltages.

My primary solution is using 6 MOSFETs (instead of a 3-phase-diode-bridge) like inverters used to control speed of induction motors. And get 30 V DC right after them.

 

How will you cope with intrinsic drain-source diode in the MOSFETS?

 

Use Germanium diodes. They only have a .3 - .5 volt drop.

That or buy a lower amperage 24 volt alternator being they typically put out around 28 - 29 volts and their voltage feedback sensing line can be used to cheat their voltae up a bit with a few diodes.

You can find them online for less than $70 if you are willing spend a bit of time looking around.

 

How will you cope with intrinsic drain-source diode in the MOSFETS?

Easy, Connect the MOSFET in reverse so the body diode conducts in the direction you want. Make it work for you instead of against you.

See the last paragraph here.
https://www.electronicsweekly.com/m...-technologys-active-bridge-rectifier-2013-06/

 

Easy, Connect the MOSFET in reverse so the body diode conducts in the direction you want. Make it work for you instead of against you.

The idea was to control the output voltage using the MOSFETs but the diode will conduct whether you want it to or not.

 

The idea was to control the output voltage using the MOSFETs but the diode will conduct whether you want it to or not.

The OP said the idea is to have (1) an efficient regulator, and (2) a voltage regulator.

His idea of doing them both in one step will not work.

The simple solution is using a 3-phase rectifier and a buck regulator.

My suggestion was to address (1).

And, a very efficient bridge allows him to use a step down transformer so he still has an efficient bridge even though he is at lower voltage. Then he can use his buck regulator (with reasonable input voltage.

 

To block in both directions you could use two MOSFETs back-to-back.
That would require 12 MOSFETs for a 3-phase bridge.

 

Another option would be to use a SCR based combination rectifier and phase angle controlled voltage regulator unit like many smaller engines use that have permanent magnet alternators behind the flywheel.

As far as efficiency goes, loosing ~ 14 watts out of 300 is not that bad. ~95% efficiency, and if the load demand Vs power source capacity are so close to its limits to where 14 watt is a critical loss the whole power supply system is under sized.

Also without knowing what the load is and to what degree of voltage regulation and ripple is it tolerant to, all of anything anyone posts is just speculation anyway.

 

To block in both directions you could use two MOSFETs back-to-back.
That would require 12 MOSFETs for a 3-phase bridge.

How use two MOSFETs back-to-back?

 

How use two MOSFETs back-to-back?

You connect them source-to-source.
The two substrate diodes are than back-to-back, and since MOSFETs conduct equally well in both directions when ON, the pair will block in both directions when OFF and conduct in both directions when ON.

 

Here is the Description of the issue: We have a 3-phase generator that in its standard working conditions, turning speed is around 3000 to 8500 rpm (which means that the output frequency is around 50 Hz to about 140 Hz). The manufacturer states that the output voltage (phase to phase) is between 35 and 95 V AC depending on speed and 300 W output power is guaranteed even in 3000 rpm without decreasing in voltage level. I want to build a regulator for this generator that be able to give me 30 V DC - 10 A (300 W). The simple solution is using a 3-phase rectifier and a buck regulator. But this solution is two main drawbacks:

• The first is for 10 A I would have a 10 A * 1.4 V = 14 W loss just in rectifying circuit and for 90% efficiency I can have total of 30 W in losses. So 14 W its just a lot.
• The second is in the case of 95 V AC I would have almost 127 V DC after rectifing! And no ready to use ICs like LM2596 and common buck controllers can handle such voltages.

My primary solution is using 6 MOSFETs (instead of a 3-phase-diode-bridge) like inverters used to control speed of induction motors. And get 30 V DC right after them.

But the problem is "ready to made controllers" like LTC3722 have just a lot of functions and protections that i should use dosens of circuits to manually create them. such a big work! and Of course the Propability to failure in such circuits would be much more than Single-Chip-Solutions like "LM2596" .So if you know any IC(buck regulators...Buck controllers... 3phase bridge controllers and...)or have any discreet circuit solution in mind, I'll be grateful if share it with me here.

 

Hi everyone and thanks for considering my problem.

Maybe tcmtech is right and I shoud explain more.

First I thought about using schottky diodes that have less forward voltages, but as the forward voltage drops, the allowable reverse bias voltage also drops! As an example “STPS3045C” is power schottky with 0.5v forward drop and 45v allowable reverse bias. The best diode I found was “MBR 20200” with 200v reverse bias capability and 0.9v forward drop which means 18W loss in 10A “just in rectification circuit”.

Second I thought about buying ready made AC-DC Modules. The best I found was “EA15A3H” that is Generator Automatic Voltage Regulator. “I think” it exactly did what I told you about(using inverter bridge). I can’t use that module cause it designed for 380v line voltage and my generator produse 35-95VAC…

Third, I thought about fly backs that uses isolated transes. for 300W the trans became big and I don’t have space for it. Also I think I can solve the problem without trans(I also don’t need isolation…).

Fourth, I posted my problem in All About Circuits)

I also shoud stress that the size and efficiency are important for me and the Price not!(don’t think that I’m rich)

If you have any other suggestions Let me know. Thanks all…

 

[You have to use Low Vf Or Ultra Low Vf Power Shottkey diodes of proper current rating. You can use diodes in parallel to distribute the current through the diodes.