APC uninterruptible power supply systems below 5000VA adopt two basic design schemes: online interactive and dual conversion online. The vast majority of factors used to determine which type of UPS to purchase are intuitive and easy to understand, such as battery backup time, cost, size, manufacturer, number of output sockets, manageability, and so on. However, there are still some less intuitive factors that are not easy to understand. The most difficult to understand and currently the most discussed factor is topology. The topology structure (internal design) of APC UPS power supply affects the working mode of APC UPS power supply in various environments.
Due to some statements claiming that certain topology structures have outstanding performance and are absolutely essential for mission critical applications, it can mislead the selection of the correct topology structure. Because these statements usually come from manufacturers in order to promote their claimed “high-performance” topology, it is difficult to make wise decisions based solely on such statements. The purpose of publishing this white paper is to objectively illustrate the advantages and disadvantages of the two most common topology structures: online interactive and dual conversion online.
There is little debate about the advantages and disadvantages of these two topologies in the high and low power ranges. When it exceeds 5000VA, online interactive mode is impractical based on experience due to its large scale and high cost. At the low end (below 750VA), dual conversion online is rarely considered due to the practicality of other topologies (including online interactive) for smaller loads.
The debate about dual conversion online and online interactive topology structures usually focuses on the power range of 750VA to 5000VA. Within this range, each topology structure does not have outstanding advantages in terms of functionality and economy compared to another topology structure, and should be analyzed based on specific installation situations. Although online interactive has become the most widely produced and deployed topology within this power range, with the development of semiconductor technology and manufacturing technology, the price of dual conversion online UPS has significantly decreased. The price disadvantage compared to online interactive UPS is no longer obvious, making it much more difficult to choose between the two than in the past. To choose the best topology structure in this “overlapping” situation, it is necessary to comprehensively evaluate each topology structure.
It is crucial to understand the requirements of the protected equipment and the environment in which APC UPS will be installed before making any decisions regarding the UPS topology. Understanding these basic requirements is essential before drawing a wise conclusion on which UPS topology structure can better meet application requirements.
IT equipment and AC power supply: switch mode power supply (SMPS)
Electricity is usually transmitted in the form of alternating current (AC), whether it is mains or backup generators. The AC voltage changes between positive and negative (ideally a perfect sine wave), passing through two zero voltages per cycle. Although it may not be noticeable to the naked eye, when the voltage crosses zero and changes polarity, the light bulb connected to the mains will actually blink 100 or 120 times per second (for 50 or 60 cycles of AC power, respectively).