Uninterruptible Power Supply Topologies

 

Uninterruptible Power Supply - on-line

This type of uninterruptible power supply (UPS) is also known as a double-conversion UPS - schematic. In a double-conversion uninterruptible power supply, the inverter draws its power continuously from the rectifier (converter) when the mains supply is within its input voltage window. Outside this the battery is used to power the inverter.

An automatic bypass provides safe failure to mains if the UPS is overloaded or develops a fault condition. Where EMI filters are used to help neutralises spikes and electrical noise, the load may be routed through these on bypass to provide further protection.

An external bypass allows the UPS to be isolated for maintenance without disruption. This is the most sophisticated form of power protection for critical loads with a wide range of options including extended runtimes and at larger kVA sizes parallel and N+1 configuration - schematic.

OPTIMUM level Power Protection - from 700VA to 800KVA (single and three phase) - Voltage and Frequency Independent (VFI) according to BS EN 62040-3:2001.

A continuous source of uninterruptible power with conditioning (stabilisation and regulation) and safe failure to mains where the Uninterruptible Power Supply output is independent of mains voltage and frequency variations. Most on-line uninterruptible power supplies can also be used as frequency converters.

How The On-line Uninterruptible Power Supply Tackles Power Problems

Output Waveform

The uninterruptible power supply inverter continually supplies the critical load with a true sinewave; this output sinewave is generally cleaner and more stable than the actual local mains supply. This ensures that the connected equipment operates flawlessly.

Sags and surges

The critical load is continuously supplied with a clean and stable sinewave from the inverter. When the mains supply input is within a specified window (voltage or frequency) the UPS rectifier converts the supply mains AC into DC to charge the batteries and to supply the inverter. When this window is exceeded, the supply to the inverter is taken from the batteries; therefore no disruption to the output occurs. To prevent unnecessary battery usage, if the sag or surge is less 40mS in duration, some UPS will ride through without any use of the battery which preserves battery charge and life.

Transients, spikes and electrical noise

The critical load is continuously supplied with a clean and stable sinewave from the UPS inverter. Transients, spikes and electrical noise present on the supply mains are filtered by Electro Magnetic Interference (EMI) and noise filters and/or a transformer (on-line UPS dependent) before they can reach the rectifier and the load.

Brownouts

The critical load is continuously supplied with a clean and stable sinewave from the UPS inverter. When the mains supply input is within a specified window (voltage or frequency) the rectifier converts the supply mains AC into DC to charge the batteries and to supply the inverter. When this window is exceeded during a brownout, the supply to the inverter is taken from the batteries; therefore no disruption to the output sinewave occurs.

Short duration mains failures

Some on-line uninterruptible power supplies can ride through short duration mains failures of up to 40mS duration without taking any power from the battery, which preserves the battery charge and life.

Long duration mains failure - blackouts

During blackouts the UPS inverter is supplied by the battery. The battery autonomy (battery operation time) can be extended using battery extension packs and/or generators.

Recharge

The battery charger will generally recharge the battery to 80% within 8-12 hours to provide sufficient battery autonomy for the next supply failure. Where the battery is extended, additional battery chargers can be added to maintain a reasonable recharge time. Sometimes the battery charger within the UPS is sufficient to recharge any additional battery. An uninterruptible power supply battery charger should also incorporate advanced battery management features such a temperature compensation, deep discharge and over voltage protection.

Other advantages

An on-line uninterruptible power supply is the most sophisticated type and is generally capable of being paralleled to achieve higher output ratings and/or N+1 configurations from 10kVA and above - schematic. The products in this range also cater for single or three phase inputs, and single or three phase outputs. The other advantage over a line interactive UPS is that an on-line UPS has a built in automatic bypass. This will transfer the connected loads to the mains supply should the UPS develop a fault condition i.e. its inverter fail or be overloaded. Larger on-line uninterruptible power supplies also include built-in maintenance bypasses.

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