Push pull spwm inverter charger!!

[Adano]

Hi there my fellow erudite forum members...

I am embarking on a design of swpm dc-ac inverter with push pull configuration using Atmega8. I am using low frequency transformer. I have been able to generate the sine wave and was able to achieve decent pure sine wave at output after filtering. My problem however is the charging circuitry for the battery. I want to use the same transformer for charging the battery when mains is available, but i don't really get how to go about it.

From reading some post on the forum, I understand that i need to have a phase angle control at the secondary winding through a winding tap of say 140v. Also, during the charging phase, the switches(mosfet or igbt) must be kept off. My main problem is how to achieve the constant voltage current limited charging for SLA batteries using this scheme.

Chopping the input ac will regulated the voltage at the primary winding during charging, but how do i control current drawn?

Please, an explanation of to go about this will be highly appreciated. thanks in advance:smile:

 

[BradtheRad]

It will be a challenge to make your transformer do both jobs.

As an inverter...
You want your hi-V winding to be >low< impedance.
(The load is high impedance.)
You want a step up ratio of 30x.

Then as a battery charger it's the opposite...
You want your hi-V winding to be >>high<< impedance.
(The electric company is low impedance.)
You want a step-down ratio of 20x.

I assume your battery is 12V, and mains AC is 230 V.

 

[Adano]

@BradtheRad..........Thanks for the reply.

I think i quite understand your concerns, but this scheme is used in commercial dc-ac inverters too. There's a thread that addresses this partially which i am following keenly as well. See Here.

I have asked some questions there hoping to get some good response. Thanks all the same...

Adano.