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I'm pretending to make a system that charge batteries (or a single battery) and then produces 3 independent AC outputs (all having the same common, in a star connection).

But I want to have independent control of the frequency, (relative) phase angle and voltage of each output, as the intention isn't necessarily to feed a 3-phase motor. For instance, I wish to be able to completely turn off one of the outputs and produce just 2 phases in 90 º if I want.

Or put all the outputs in phase and parallel them to have a higher current single-phase output.

I guess that the outputs will be driven by 3 independent PWM circuits which I'll control with a micro-controller, but that isn't my question right now.

My question is what is the best scheme for the conversions needed, from the AC network to the AC outputs.

I guess that the cheapest and most practical solution for the battery side is using a 24 V 20 A power source with a current regulation circuit to charge a car battery.

The problem is what I do after that. Should I use an inverter to step up those 12 V to 300 V (for example), rectify and filter that to 300 V DC and then use the PWM circuits with those 300 V (with their output directly feeding the loads)?

Is there another better scheme for all of that?

Thanks!

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  • \$\begingroup\$ Does "intention isn't necessarily to feed a 3-phase motor" mean you might want to feed a 3-phase motor, but want to also supply other loads that you don't want to describe? If you want to feed any kind of load with a combination of two or three outputs, the the outputs will need to be very carefully coordinated to provide a specific performance. I don't believe that you can design something with three independent outputs that you can adjust every which way and connect a load with two or more connection points between any combination of three outputs and a common point. \$\endgroup\$ – Charles Cowie Oct 3 '20 at 22:51
  • \$\begingroup\$ It might help if you could describe the purpose of this system and the expected performance. \$\endgroup\$ – Charles Cowie Oct 3 '20 at 22:57
  • \$\begingroup\$ What I meant is that feeding a 3 phase motor is also between the plans, but not only. For most things that aren't induction motors, the outputs will just behave as regular outlets, to feed chargers, computers etc (they'll just be connected in 2 points, not 3). The point is that I want the same micro-controller to coordinate the 3 outputs, all of them having a common. But right now my worry is of the high number of conversions I have, from AC to 12V, then from 12 V to higher voltage DC, then from DC into AC again. I'm trying to figure the most efficient way to do that. \$\endgroup\$ – user2934303 Oct 4 '20 at 0:20
  • \$\begingroup\$ If you need variable frequency just for one three-phase motor, it will likely be best just to design an inverter dedicated to that. Design another for fixed-frequency, fixed-voltage, sized for the maximum current you will need. I can not imagine why you would need 2-phase, but if you do, design a 3rd inverter or consider a Scott-T transformer. \$\endgroup\$ – Charles Cowie Oct 4 '20 at 12:20

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