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Explore the Working Principle and Benefits of Different Types of UPS System Configurations

2023/05/24 04:00 PM By 許育榮

Source: Power Electronic News

An uninterruptible power supply (UPS), also referred as battery backup, is used for providing emergency power to a load. It is a device that allows a computer to function for at least a few more minutes when the primary power source is lost or the voltage level drops. 


UPS systems contain batteries that kick in and provide battery backup while also offering protection from damages caused by power surges. In commercial and industrial areas, including hospitals, small offices, electric point of sales terminals, manufacturing facilities, and telecommunication centers all over the world, UPS systems are widely used when the usual generator system fails. 

Depending upon the model of UPS, the output waveforms are either sine-wave or simulated sine-wave. Sine-wave output is the best waveform with high-quality output. It has the shape of an AC power signal from the utility, which has a smooth and repetitive oscillation. UPS systems generate sine-wave power to control sensitive electronic appliances. Simulated sine-wave output, on the other hand, produces a stepped, approximated sine wave by using a pulse-wave–modulation technique and thus can supply more cost-effective battery backup power for equipment that does not require sine-wave output. 

The following are three major types of UPS system configurations. 

1. Offline/standby UPS: the entry-level power protection

Offline/standby UPS is the most basic UPS system and a cost-effective choice. This UPS topology is designed for consumer electronics, POS systems, entry-level computers, security systems, and other basic electronic equipment. Offline UPS is a good option for devices under 1,500 VAC and those that require low power capacity and cost. It is widely used in small offices, personal home computers, and more.


Here, the load is directly powered by the input power, and the backup power is invoked during the failure of the utility power. The battery, battery charger, and inverter are kept off but still remain connected to the mains power to ensure the battery is always fully charged. When the mains power voltage is lost or exceeds the limits, the switch automatically connects the inverter output to the critical load.

2. Line-interactive UPS: the intermediate level power protection

This UPS topology is best for usage in areas where outages are rare but power fluctuations are common. Thus, it is widely used for consumer electronics, gaming systems, PCs, network equipment, home-theater electronics, and more. It can deliver both power conditioning and battery backup. It has an autotransformer that incorporates a wide array of input power fluctuations, for both undervoltage and overvoltage, before switching to battery backup. In addition, as the inverter is always kept on and connected to the output, it provides filtering switching transients.

3. Online/double-conversion UPS: the ultimate-level power protection

Double-conversion UPS modules can offer uninterrupted power to heavy loads. With the help of a rectifier, the online/double-conversion UPS does filtration and conversion of input power to DC power, and then DC power to AC output. In this smart design, when a power loss happens, the rectifier simply drops out of the circuit and the batteries keep the power steady and unchanged. When power is restored, the rectifier resumes carrying most of the load and begins to charge the batteries.


As safeguarding heavy IT loads and protection against all power problems is very important, enterprises mostly prefer to use double-conversion UPS. These systems also provide frequency regulation, which is required for use in backup generator systems to safeguard from variations common at generator startup. The inverter in an online/double-conversion UPS is always kept on.

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