Online Pure Sine Wave UPS

[boss.electron]

Dear Members,
I am new in electronics. I planned to design an online UPS 1200VA.
I have read the microchip PICREF-1 circuit.
I have attached the minimum parts of the circuit. I have few questions:
1) What is the purpose of Free Running circuit, with details clarification. Purpose of the circuit, If I don't use it then which function will be removed.
2) The author of documents claims its 70% efficiency. From this circuit, would anyone please tell which portion of the circuits kills the efficiency? I know 99% efficient inverter also possible.
3) And Can anyone please tell the standard core number like ETD49 for 8 transformers.

Thanks for helping.

 

[BradtheRad]

Efficiency is greatest when you can switch components full on or full off. This is possible with square wave inverters. Then the inefficiency is chiefly in the transformer(s).

However when you want sine waves...

then you must devise ways to operate components at in-between states of conduction, which dissipates power as heat, dropping efficiency...

Or store and release energy in capacitors/inductors...

Or switch multiple components on/off in PWM, and filter the pulses to create the sine curve.

As a rule, the more efficiency you want, the more time and effort the topology will require.

 

[boss.electron]

Dear BradtheRad,
Thanks for your quick reply.
I uploaded the circuits in earlier post.
1) Would you please tell the purpose of free running chopper circuit in brief. If I don't use it then which function will be removed.
2) And from the above circuit, which section I need to improve on priority basis, to increase the efficiency.
3) And can you please refer any guide for ferric transformer building guide, so that I can easily understand the core, copper turns and copper wire gauge.

 

[pradhan.rachit]

For transformer building construction, 'Power Supply Cookbook' by Marty Brown is a useful resource...SMPS is very well explained in that book...

 

[FvM]

I uploaded the circuits in earlier post.

Unfortunately incomplete. Some schematics are doubled, others missing.

1) Would you please tell the purpose of free running chopper circuit in brief. If I don't use it then which function will be removed.

Can't be clearly determined from the shown documents. The triple converter topology is unusual in my view. I guess there are text descriptions along with the figures.

2) And from the above circuit, which section I need to improve on priority basis, to increase the efficiency.

Counter question, if I say it's section x, do you know how to improve it? You either understand about posible efficiency lacks and how to get rid of it, or none of both. In any case it's mostly guessing without empirical measurements.