single phase to three phase inverter

[dr.power]

Hi guys,

Can somebody tells me how an AC single phase to three phase inverter converts ONE phase of the mains to three? What componenets are able to do that in such a circuit and produce 129 degrees out of phase?
I just took one of then a part but did not notice how it does that? It has a black box in a huge heat sink having more more than 15 pins...

Thanks.

 

[carbonzit]

Hi guys,

Can somebody tells me how an AC single phase to three phase inverter converts ONE phase of the mains to three? What componenets are able to do that in such a circuit and produce 129 degrees out of phase?

You do mean 120°, dontcha? (I ASS-U-ME that that was a typographic error on your part)

 

[dr.power]

You do mean 120°, dontcha? (I ASS-U-ME that that was a typographic error on your part)

Sorry my typo. Surly I meant 120 degrees out pf phase for the outputs...

 

[carbonzit]

There must be come capacitive or inductive elements in the converter that create the phase lags for the two legs that are synthesized. Notice any capacitors or inductors in your converter?

 

[Sceadwian]

Sorry carbonzit, but that is only true if you would be attempting this using only analog circuitry and has nothing to do with inverters, inverters convert DC to AC. Analog single to three phase conversion using a phase shift network is only practical in limited applications and efficiency is pretty bad compared to an inverter.

An inverter would handle it by rectifying mains to DC and then using three seperate inverters (in the same package possibly) synchronized to provide the phase shift required.

If you just need a quick and dirty single to three phase solution for testing purposes (IE not tightly controlled voltages) all you have to do is couple the output shafts of a single phase motor to a three phase motor, all you need to do is bolt them together on a common frame. Single phase in, three phase out, make sure you provide for a ground on the three phase side, floating three phase could be nasty.

 

[shortbus=]

@dr.power - if your calling a VFD an inverter, it takes the single phase AC and rectifies it to DC then inverts it back to three phase AC.

 

[Sceadwian]

shortbus, VFD's can be single phase.

 

[jpanhalt]

If you just need a quick and dirty single to three phase solution for testing purposes (IE not tightly controlled voltages) all you have to do is couple the output shafts of a single phase motor to a three phase motor, all you need to do is bolt them together on a common frame. Single phase in, three phase out, make sure you provide for a ground on the three phase side, floating three phase could be nasty.

An even simpler way is to wire one winding of a 3 phase motor to single phase, put a pulley/sheave on it, and give it a kick with your foot to get it rotating. Then apply power. You get 3 phase from the three windings. A little more sophisticated version uses a capacitor. Look up three-phase converter. I have been using a one-capacitor, auto-start version for over 25 years. No problem when it runs small (1 to 3 HP) three-phase motors.

John

 

[Grossel]

There must be come capacitive or inductive elements in the converter that create the phase lags for the two legs that are synthesized. Notice any capacitors or inductors in your converter?

I would assume that inverters is digitally controlled so the output voltage and frequensy easilly can be changed.
The input must of course be rectified into DC.

 

[jpanhalt]

The input must of course be rectified into DC.

Only if you are talking about a VFD. The OP's question was not about a VFD, so far as I could tell. Simple single-phase to 3-phase rotary converters have been used for many decades as I described. The most important rule is that the coasting/generating 3-phase motor be larger than the first motor that needs to be started. After that, each 3-phase motor that is added adds to the power capacity of the system.

John

 

[Sceadwian]

jpanhalt....

single phase to three phase inverter

Please note the key word here.... is inverter. Inverters require DC to start with..

 

[jpanhalt]

Hi guys,

Can somebody tells me how an AC single phase to three phase inverter converts ONE phase of the mains to three?

It seems obvious to me the poster is interested in converting single phase to three-phase, not a VFD. My comment was directly specifically at your solution, which used a motor-generator. It was neither an inverter per se nor the simplest solution.

John

 

[tcmtech]

I take it you guys never visit the RE sections.

There is some guy who wrote a DIY how to on rotary phase conversion and how its done in an efficient and reliable manor!

https://www.electro-tech-online.com/threads/3-phase-converter-schematic-miller-system.100563/

Its not inverter based but its still a rather basic but highly reliable, efficient, and well proven design.

 

[carbonzit]

This is starting to sound like a demented game of "telephone". Sheesh!

1. Jpanhalt: where do you get rotary phase converter out of something the O.P. clearly described as being a solid-state unit with no moving parts? Sure, we know that rotary converters exist and are still used. This clearly is not a rotary converter. (To quote the O.P., "It has a black box in a huge heat sink having more more than 15 pins.")

2. Sceadwian, you're apparently ASS-U-Ming that since the O.P. called it an "inverter" that it must, in fact, be such a thing (i.e., a DC to AC converter). I'd bet money that what they have is simply a single-phase AC to 3-phase AC converter.

Of course, we won't know any of this for sure until the O.P. pays another visit here to confirm or deny, so why don't we tame down the speculation just a wee bit until they do?

 

[jpanhalt]

@tcmtech,

What you describe is very similar to my design from 1984, including the use of a voltage relay to control start-up; except, I saw no need for three capacitors, if all I was running was machine tools with 2HP motors and was using a "heavy-iron" Lincoln 3-phase for my generator. I only need one converter.

John

 

[tcmtech]

I am going to go with sceadwain on this one. As the OP stated its a barge black thing attach to a heat sink with 15 pins on it which is most likely a typical 6 pack IGBT or power transistor switching device package similar to this one.
View attachment 50A 1200V IGBT 6-PACK.pdf

That device in itself gets its switching logic driven from a circuit board usually with a micro controller to minimize parts along with a basic AC to DC rectifier and capacitor bank system to produce the necessary high powered DC it needs for its power inputs.

Relating to the AC in AC out concept solid state inverters do in fact first convert the input AC, which can be single or three phase, into a stable DC buss voltage and then reconvert it back into the variable frequency and voltage three phase AC output by a combination of PWM and frequency control.

Basically its really just a big three phase stepper motor driver circuit when reduced to its simplest small scale equivalent.

And no its not something most people could build and have a reliable design in the end that could ever come close to what a common off the shelf VFD unit sells for new or used.

 

[Grossel]

tcmtech: The pdf files two first pages seems to be empty. It could be a bug in Nitro pdf reader, but still.

 

[carbonzit]

tcmtech: The pdf files two first pages seems to be empty. It could be a bug in Nitro pdf reader, but still.

Works fine here; must be a bug in your PDF reader. Why don't you just use Adobe Reader?

 

[Sceadwian]

This is starting to sound like a demented game of "telephone". Sheesh!

There have been far worse many times. Threads tend to derail about this point, it's the nature of an open post forum with a decent user base and posting base.