| Generally there are three types of UPS on the market. The cheapest is VFD which is basically a battery parellel to the mains which in case of a power failure interrupts mains and inserts it's own voltage. Usually labelled as "offline" or "standby" UPS since they're not active most of the time. The output frequency and voltage is the mains output and voltage until switched over, something to keep in mind if devices are sensitive to that. These can simply switch back to mains when it's back since they usually use a simple transfer relay. VI (Line interactive, Delta Conversion) uses the mains frequency as orientation. They don't have a transfer and can basically just compensate whatever the mains is doing to output a 230V signal. Internally they have a inverter with AC input and AC ouput which means they measure if mains is coming back from there and adapt the signal on the internal inverter for the battery. If mains comes back on a VI they usually change frequency very abruptly which is not ideal from some devices. VDI is completely independent of both voltage and frequency as it first converts mains AC to internal DC, simply plugs in the battery into the DC and then converts DC to AC. They don't need to synchronize at all and are the more common for datacenters since they isolate the input fairly well from output and don't have to switch anything to go from mains to backup, DC voltage is fairly good for dealing with this. They are also most expensive. If mains comes back on a VDI they don#t do anything of notable interest other than switching the battery charger on. |