AC power is stable and clean upon generation. But during transmission and distribution, it is subject to voltage sags, spikes and complete failure that may interrupt computer operations, cause data loss and damage equipment. When it comes to safeguarding critical IT loads, only online double conversion technology protects fully against all these power problems, providing the highest levels of security for networks.
An online UPS system is usually called double conversion as well because incoming power is converted to direct current (DC) and then converted back to AC. This AC-DC/DC- AC design ensures an increased degree of isolation of the load from the irregularities on the main supply.
The online UPS takes the incoming AC power supply and converts it to DC using a a rectifier to feed the battery and the connected load via the inverter so that no power transfer switches are necessary. If the main AC input fails, the rectifier drops out of the circuit and the batteries keep the power flowing to the device connected to the UPS. When AC input power is restored, the rectifier resumes carrying most of the load and begins charging the batteries.
Because power runs through an online UPS continually, output is a perfect sine wave. This type of UPS protects the critical load from virtually all power disturbances, including subtle harmonics and waveform distortion.
This means the quality of power from online UPS is significantly better than that of other technologies. Offline and line-interactive technologies reduce the impact of spikes, surges and sags by either clipping the peaks and valleys, boosting power or switching to battery backup. Within the normal track of an electrical sine wave, however, most power fluctuations are left alone. Online UPS regenerates the sine wave, not just conditioning of the raw utility supply.
An online UPS delivers continuous, high-quality AC power to equipment with no break when transferring to battery, protecting equipment from virtually all power disturbances due to blackouts, brownouts, sags, surges or noise interference. A true online, double-conversion UPS provides 100% power conditioning, zero transfer time to battery, no change in output voltage and better transient suppression than line-interactive units.
Online double conversion is the most common UPS mode of operation used for protecting large data centers by providing the highest level of power quality to the load always. Online systems also provide frequency regulation, essential for use with backup generator systems to protect from variations common at generator start up.