Why kind of help do you need?
When you say Sinewave UPS, I believe you mean AC.
H-bridge when pumped by AC input is like a bridge rectifier. The reason for this is to make it 'Transformerless', so the charger can be small, lightweight and cheaper to mass produce.
The boost converter part of the battery charger is still the same in principle of typical boost converter.
Sometimes, this kind of charger is more commonly called Transformerless adapter or battery charger.