In your system there is no any support from the NATURE.
Power from wind, water, sunlight etc……
UPS uses batteries to store power and an inverter to supply AC power from the batteries when main power is not available. When main power is restored, a rectifier is used to supply DC power to recharge the batteries.
So these two conditions inverting DC to AC to supply 110V or 230V & DC to charge the batteries done in separately.
in high frequency inverters the battery voltage is converted to high frequency and then step up using transformer.
Again it is converted to dc using rectifire and then it is converted to the desire frequency.
HOW this high dc voltage is converted to desired frequency of ac voltage.
in many ups systems two transformers are used one for step up and another is used for battery charging. is it possible to use one transformer for both purposes.