Home Information Types of Uninterruptible Power Supply (UPS)

Types of Uninterruptible Power Supply (UPS)

Passive Standby Uninterruptible Power Supply (Off-line) (VFD)

This type of UPS, also called Off-line UPS, is connected in parallel to the normal AC source. The current is filtered in order to attenuate the most frequent forms of disturbance. In the event of a power problem the UPS transfers the load to the batteries to supply stabilised power: the inverter only switches on when the mains fails or fluctuates outside the input voltage tolerances of the EMI filter or if it is fitted with Automatic Voltage Stabiliser (AVS).

Line Interactive Uninterruptible Power Supply (VI)

On this type of UPS the inverter is connected in parallel to the AC input and also charges the battery (interactive operation in reversible mode). When the AC input supply is not within strict amplitude and frequency tolerances, the load is powered by the inverter through the battery. The normal inverter output waveform is a stepwave or squarewave. This technique is rarely used for high power ratings as frequency regulation is not possible. Active Standby (or Line Interactive) technology is a recent
development made possible by the advent of microprocessors. The UPS is
fully controlled by a microprocessor which monitors the quality of the mains power supply and reacts to any variations. In the event of a power problem, the UPS transfers the load to the batteries to supply stabilised power. It is increasingly frequent to add a voltage compensation circuit, called a “booster”, that is enabled in the event of prolonged voltage drops.

On-Line Uninterruptible Power Supply (VFI)

On this type of UPS, also known as a double conversion UPS, the inverter draws its power continuously from the rectifier (converter). The current is completely regenerated by its transformation from AC to DC and back to AC, guaranteeing a constant level of quality, regardless of disturbance on the mains power source. By carrying out continuous double conversion, an On-Line UPS significantly attenuates electrical noise, which might otherwise damage a computer. When the AC input supply is not within the voltage and frequency tolerances, the battery is used to power the inverter. The inverter continually supplies the critical load with a true sinewave current. If a converter/inverter failure occurs, the continuity of the load power can be improved by activating the bypass source using a transfer switch.

 

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