Practical application analysis of various types of UPS systems

　　As time goes by, the number of UPS products in the industry has gradually increased. Different types of UPS are suitable for different purposes, and no one type of UPS is suitable for all applications.

　　Now, APC white papers give clear definitions of each UPS type, in-depth analysis of the practical applications of each system, and list the advantages and disadvantages of each system. With this information, you can make an informed decision and choose the UPS topology that suits your needs.

　　UPS Type

　　Backup

　　Online interactive

　　Backup-Ferromagnetic Resonance

　　Double conversion online

　　Delta conversion online

　　Backup UPS

　　The backup UPS is the most common type used for personal computers. In the block diagram shown in Figure 1, the transfer switch is set to select the filtered AC input as the main power source (solid line path), and once the main power fails, it will switch to the battery/inverter as the backup power source. Once this happens, the transfer switch must be operated to switch the load to the battery/inverter backup power source (dashed line path). The inverter only starts when the power fails, so it is called "backup". The main advantages of this design are high efficiency, small size and low cost. If appropriate filtering circuits and surge protection circuits are used, these systems can also provide appropriate noise filtering and surge suppression functions.

　　Line-interactive UPS

　　The line-interactive UPS is the most common design used for small businesses, websites, and departmental servers. In this design, the battery-to-AC power converter (inverter) is always connected to the output of the UPS. If the inverter is operated in reverse when the input AC power is normal, the battery will be charged.

　　Once the input power fails, the transfer switch opens and supplies power to the UPS output from the battery. Compared to the backup UPS topology, this design further enhances filtering and reduces switching transient overvoltages because the inverter is always on and connected to the output.

　　Backup-Ferro-Resonance UPS

　　The Standby-Ferro UPS was once the most widely used UPS type in the power range 3-15kVA. This design relies on a special saturated transformer with three coils (power connections). The main power path passes through the AC input power, the transfer switch and the transformer, and finally connects to the output terminal. When the power fails, the transfer switch will open and the inverter will supply power to the output load.

　　In a standby-ferro-resonant design, the inverter is in standby mode and is activated when the input power fails and the transfer switch is open. This transformer has a special "ferro-resonant" function that can provide limited voltage regulation and output waveform "shaping". The protection provided by the ferro-resonant transformer against transient overvoltages of the AC power supply is as good as or even better than any filter. However, the ferro-resonant transformer itself will produce severe output voltage distortion and transient overvoltages, which may cause more serious consequences than improper AC power connection. Even if this UPS is designed as a standby UPS, the ferro-resonant transformer will generate a lot of heat due to its own low efficiency.

　　In addition, these transformers are larger than conventional isolation transformers, so backup-ferroresonant UPS are usually very large and heavy 　　.

　　This is the most commonly used UPS type for power supplies in the 10kVA and above range and is the same as the standby design except that the primary power path is an inverter (rather than AC mains).

　　In a double conversion online design, a failure in the input AC power does not activate the transfer switch because the input AC power is always charging the backup battery, which then supplies power to the output inverter. Therefore, there is no time required to transfer to the online operating state when the input AC power fails.

　　In this design, the battery charger and inverter will convert all the load power and will be less efficient due to the increased heat generated.

　　This UPS provides very ideal power output performance. The reliability of this design is higher than other designs, but the continuous wear and tear of power components reduces this reliability, and the power consumption due to power inefficiency accounts for a large part of the UPS's life cycle cost. In addition, the input power obtained by large battery chargers is often non-linear, which may interfere with the building power system or cause the backup generator to fail.

　　Delta conversion online UPS

　　This technology was introduced 10 years ago to overcome the shortcomings of the double conversion online design and is suitable for applications ranging from 5kVA to 1.6MW. Similar to the double conversion online design, the Delta conversion online UPS always provides the load voltage from the inverter. However, the additional Delta converter also supplies power to the inverter output. In the event of an AC power failure or disturbance, this design behaves exactly the same as the double conversion online design.

　　Summary of UPS Types

　　The following table describes the characteristics of different UPS types. UPS characteristics (such as efficiency) are determined by the UPS type you choose. Because technology application and production quality have a greater impact on characteristics (such as reliability), in addition to considering design characteristics, the following factors must also be evaluated.

　　Industrial applications of various types of UPS

　　Over time, the UPS products currently available in the industry have gradually included the various types of designs mentioned above.

　　Different UPS types have different characteristics, which makes them suitable for different applications. The APC product range reflects this diversity, as shown in the following table:

　　Different types of UPS are suitable for different purposes, and no one type of UPS is suitable for all applications. The purpose of this article is to compare the advantages and disadvantages of different UPS topologies currently on the market.