Datacenter are physical facilities that are hosting massive numbers of servers and the associated support infrastructure, also can be seen as an information technology (IT) system and supporting infrastructures combined together. The information technology system equipment includes servers, telecommunication and storage systems, to provide services to the end load. And supporting infrastructures include power delivery and cooling technology systems. The power includes backup power generators, uninterruptible power supplies system (UPSs), and power distribution unit’s system . And the Cooling Technology systems include server, fans, computer room air conditioners, chillers, and cooling towers. The main function of the data center is to provide reliable power, security, cooling, and network connectivity to computer equipment

Uninterruptible power supplies design and topology 

- The UPS provides backup power when utility power fails, either long enough for critical equipment to shut down gracefully so that no data is lost, or long enough to keep required loads operational until a generator comes online. 
The UPS system is a backup source of power, installed between the mains power supply and the critical end loads, to provide two functions. 
           -A, it provides a secure power source when the main AC power supply fails, then supported the load while the power source shifts from utility to a standby generator. 

           -B, it provides a clean, stable and regulated supply when the mains supply is present. An ideal UPS should be able to deliver uninterrupted power, at the same time providing the necessary power conditioning for critical loads. 

For these reasons, electric utility companies considered UPS to be the primary source of standby power protection. UPS systems can provide power for up to several minutes. However, a standby power system is needed for longer outages Even a momentarily loss of power can cause IT systems and sensitive equipment to crash and lose data in a data center.

 A UPS maintains power by switching instantaneously to batteries in the event of utility power failure; they also condition the power supply to reduce unwanted spikes and harmonics Different types of UPS have been designed to correct a variety of power problems, such as: 

•  Sags: transient under voltage. 
•  Brownouts: under-voltage for a period of time (milliseconds to days). 
•  Spikes: very brief, but high energy bursts (lasting only a few milliseconds), Spikes are typically caused by lightning or malfunctions in the power supply and can damage sensitive solid-state components and destroy data in digital equipment. 
•  Surges: relatively short duration (from milliseconds to seconds) of high voltage power surges. Line noise: distortions superimposed on the power waveform which are caused by electromagnetic interference.
• Frequency variation: deviation from the nominal frequency, which causes motors to increase or decrease speed. 
•  Switching transient: instantaneous under voltage, which may cause erratic behavior in some equipment resulting in memory loss, data error and loss, and component stress.
•  Harmonic distortion: multiples of power frequency superimposed on the power waveform, which causes excess heating in wiring and fuses.

Uninterruptible power supply operating modes in double conversion 

 The inverter is connected in series between the AC input and the application. 


         

Normal mode

-During normal operation, all the power supplied to the load passes through the rectifier which converts input AC power to DC power. The inverter converts DC power to AC power for the critical load. The conversion from AC to DC and back is the reason why the system is known as double conversion. It is the only UPS system that provides the load with continuously processed and backed-up power Stored or battery backup mode When the AC input main fails, the rectifier will shut down, at which stage the battery, without interruption using a static switch, provides an alternative DC power source for the inverter via the DC converter. The UPS continues to operate on battery power until the end of battery backup time or utility power returns to normal mode.

Bypass mode

In this bypass mode, the critical load is supported directly by utility power through the UPS bypass, sometimes referred to as a static switch, in the event of the following UPS failure (A fault within a critical section of the UPS) The load exceeds the maximum rating of the system, at which stage the static switch automatically transfers the load to the bypass supply to protect the inverter. When the UPS is manually transferred to bypass in order to undertake maintenance safely without disrupting power to the load However, the output of the bypass mode is not protected from voltage or power outages from the main source. Also, the UPS must be synchronized with the bypass power to ensure load supply continuity. The figure above shows the operating modes of the double-conversion static UPS system. 


  TO SUM UP
-Power sags, surges, and outages are not only unavoidable but more than capable of damaging valuable IT equipment and bringing productivity to a halt. That’s why planning and deploying a robust power protection solution is absolutely vital. An uninterruptible power system (UPS) is the central component of any well-designed power protection architecture.