Which can be activated very rapidly, being semiconductor based, and within a fraction of cycle time.
Of course it can. But should not. Imagine, mains power disappear at the bottom of AC sine. You had -110 V on the hot wire at that moment. Then, you start DC-AC converter that starts from top of AC sine at +110 V on the hot wire.
Guess, would be your devices glad if they suddenly get a surge from -110V to +110V "within a fraction of cycle time.". What if you have some inductive or capacitive load on the UPS output?
That is why there is a delay in switching from mains to battery or vice versa in cheap UPS.
Just take oscilloscope and check how that works if you are in doubt.
Of course it can. But should not. Imagine, mains power disappear at the bottom of AC sine. You had -110 V on the hot wire at that moment. Then, you start DC-AC converter that starts from top of AC sine at +110 V on the hot wire.
Guess, would be your devices glad if they suddenly get a surge from -110V to +110V "within a fraction of cycle time.". What if you have some inductive or capacitive load on the UPS output?
That is why there is a delay in switching from mains to battery or vice versa in cheap UPS.
Just take oscilloscope and check how that works if you are in doubt.