RealInfo said:
Hi all
How exactly synus output voltage is generated in UPS systems ?
I understand how rectangular or PCM voltage is generated but in case when pure synus voltage is needed , how this is done ?
Thanks
Elico
Cheap designs use a transformer. The output side (appliance side) will
have the line voltage on it, passing through the output side as it goes
to the receptacles. As this is taking place, the other side of the
transformer (low side) is generating a low voltage, a voltage that
matches your battery. THe battery is connected to the center tap of the
low side (+) and will be a push pull type of inverter.
When commercial power is present on the high side of the transformer
it will also be present on the low side. This voltage should match the
battery voltage or actually be a little higher. Because when it is a
little higher it is also used to charge the battery! Of course there is
some more intelligence behind it to control the charge rate. This also
may explain why some UPS systems will not charge a battery that is to
low, because the active circuit is not operating due to insufficient
battery voltage.
When line voltage goes away or even dips in the middle of a wave the
low side will see an absence of voltage or I should say the unloaded
inverter will now detect a load present to it's inverter transistors and
thus create current in the primary at that moment.
Just think of an inverter operating at all times into a push pull
primary (low side) but the secondary has voltage is back feeding it. The
primary side will not generate any current because it is being
canceled out however, when the back feed takes a lunch break at any time
on the sine wave, there will be no canceling of currents and thus at
that point, the inverter will contribute current to the needed high side
voltage.
That is the best I can explain it.
You can do this with high frequency toroidal transformers too, the
difference being you need to monitor the line voltage directly
from your low side inverter circuit to know when and at what phase
angle to come in on.
Jamie
