Actually, theres quite a few types of UPS
The Standby UPS
The Standby UPS is the most common type used for Personal Computers. Switches to the battery / inverter as the backup source should the primary source fail. When that happens, the transfer switch must operate to switch the load over to the battery / inverter backup power The inverter only starts when the power fails, hence the name "Standby." High efficiency, small size, and low cost are the main benefits of this design. With proper filter and surge circuitry, these systems can also provide adequate noise filtration and surge suppression.
The Line Interactive UPS
The Line Interactive UPS, is the most common design used for small business, Web,and departmental servers. In this design, the battery-to-AC power converter (inverter) is always connected to the output of the UPS. Operating the inverter in reverse during times when the input AC power is normal provides battery charging. When the input power fails, the transfer switch opens and the power flows from the battery to the UPS output. With the inverter always on and connected to the output, this design provides additional filtering and yields reduced switching transients when compared with the Standby UPS topology. In addition, the Line Interactive design usually incorporates a tap-changing transformer. This adds voltage regulation by adjusting transformer taps as the input voltage varies. Voltage regulation is an important
feature when low voltage conditions exist, otherwise the UPS would transfer to battery and then eventually down the load. This more frequent battery usage can cause premature battery failure. However, the inverter can also be designed such that its failure will still permit power flow from the AC input to the output, which eliminates the potential of single point failure and effectively provides for two independent power paths. High efficiency, small size, low cost and high reliability coupled with the ability to correct low or high line voltage conditions make this the dominant type of UPS in the 0.5-5kVA power range.
The Standby-Ferro UPS
The Standby-Ferro UPS was once the dominant form of UPS in the 3-15kVA range. This design depends on a special saturating transformer that has three windings (power connections). The primary power path is from AC input, through a transfer switch, through the transformer, and to the output. In the case of a power failure, the transfer switch is opened, and the inverter picks up the output load. In the Standby-Ferro design, the inverter is in the standby mode, and is energized when the input power fails and the transfer switch is opened. The transformer has a special "Ferro-resonant" capability, which provides limited voltage regulation and output waveform "shaping". The isolation from AC power transients provided Standby-Ferro UPS systems are frequently represented as On-Line units, even though they have a transfer switch, the inverter operates in the standby mode, and they exhibit a transfer characteristic during an AC
power failure.
The Double Conversion On-Line UPS
This is the most common type of UPS above 10kVA. The block diagram of the Double Conversion On-Line UPS, is the same as the Standby, except that the primary power path is the inverter instead of the AC main. In the Double Conversion On-Line design, failure of the input AC does not cause activation of the transfer switch, because the input AC is charging the backup battery source which provides power to the output
inverter. Therefore, during an input AC power failure, on-line operation results in no transfer time. Both the battery charger and the inverter convert the entire load power flow in this design, resulting in reduced efficiency with its associated increased heat generation. This UPS provides nearly ideal electrical output performance. But the constant wear on the power components reduces reliability over other designs and the energy consumed by the electrical power inefficiency is a significant part of the life-cycle cost of the UPS. Also, the input power drawn by the large battery charger is often non-linear and can interfere with building power wiring or cause problems with
standby generators.
The Delta Conversion On-Line UPS
This UPS design, illustrated in Figure 5, is a newer, 10 year old technology introduced to eliminate the drawbacks of the Double Conversion On-Line design and is available in sizes ranging from 5kVA to 1.6MW. Similar to the Double Conversion On-Line design, the Delta Conversion On-Line UPS always has the inverter supplying the load voltage. However, the additional Delta Converter also contributes power to the inverter output. Under conditions of AC failure or disturbances, this design exhibits behavior identical to the Double Conversion On-Line. A simple way to understand the energy efficiency of the delta conversion topology is to consider the energy required to deliver a package from the 4th floor to the 5th floor of a building. Delta Conversion technology saves energy by carrying the package only the difference (delta) between the starting and ending points. The Double Conversion On-Line UPS converts the power to the battery and back again where as the Delta Converter moves components of the power from input to the output.
My UPS is the "The Line Interactive UPS"
http://www.belkin.com/IWCatProductPage.process?Product_Id=153757
