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What are the types of uninterrupted power supplies?

Uninterrupted Power Supplies – Which Technology is Ideal for You?

There are six types of uninterrupted power supplies (UPS) commonly encountered, namely double-conversion online UPS, line-interactive UPS, standby UPS, standby-ferro UPS, and

delta-conversion online UPS technologies. All of these are based on the need for an alternating current (AC) power backup source for critical loads.

Of these six, three uninterrupted power supplies dominate in areas such as the protection of critical distributed IT infrastructure. The three major types of UPS technologies are online double-conversion, line-interactive and standby (also called offline and battery-backup). Uninterrupted power supplies are defined by how power flows through them to keep critical loads energised.

Each of these technologies has advantages and may be required to provide cost-effective and comprehensive power supply protection at more complex sites. Choosing an uninterrupted power supply for a specific application involves considering several factors. Examples include the load size, the duration for which the load must be carried, the site location and how crucial it is for the protected equipment to have continuous, clean power. Budgetary considerations are also a factor when specifying uninterrupted power supplies for grid power backup.

Double-conversion Online Uninterrupted Power Supplies

A double-conversion online UPS converts incoming grid (AC) power into direct current (DC) and then back to AC. The power runs through the double-conversion online UPS continually and the output is a perfect sine wave. This AC-DC/DC-AC design provides increased isolation of the load from the irregularities on the grid supply including even subtle harmonics and waveform distortions. A true online, double-conversion UPS provides total power conditioning, no transfer time, and no change in output voltage These units essentially double as power conditioning units as well as uninterrupted power supplies. They even provide frequency regulation. So, when they are fed AC from backup generator systems, they protect the load from the frequency variations experienced at generator start-up.

For sites where more than 10kVA of power is required, double-conversion online uninterrupted

power supplies are usually the units of choice. AC grid power feeds a rectifier (AC-to-DC converter) and then this DC is fed to an inverter that creates AC power once again. A backup battery is wired into the DC line providing a store of DC power. The battery is charged by the rectifier. No power transfer switches are necessary resulting in a design that has no transfer time. When grid power input fails, the batteries keep the power flowing. When grid power is restored, the rectifier picks up the load and starts recharging the batteries. This feature is essential for sensitive electronic equipment that cannot handle even momentary dips in power.

Grid power is subject to voltage sags, spikes and outages that may interrupt operations, cause data loss and damage sensitive electronic equipment. For the protection of critical IT loads, online double-conversion technology is the only system that protects fully against poor grid power supply. They provide the highest degree of security for communication and data networks.

The only downside of this design is the fact that the inverter and rectifier contained in it are continuously active. Consequently, double-conversion online uninterrupted power supplies do not have the inherent reliability of some of the other designs, but in terms of clean and continuous power output, this type of UPS delivers ideal power.

Line-interactive Uninterrupted Power Supplies

Line-interactive uninterrupted power supplies are the most-used UPS design. With this design, grid power, or whatever the primary source of AC power is, is fed through a transfer switch to an inverter and then to the load. The inverter is always active and, when grid power is available, it converts incoming AC power to DC which is used to keep the backup battery charged. If the grid power fails, the transfer switch opens, and the inverter takes DC power from the battery and converts it to AC to energise the load.

Keeping the inverter active provides improved power filtering and reduces potential switching transients. The major benefits of line-interactive UPS systems are their low cost, reliability, and excellent efficiency. They can also support low- or high-voltage applications. Line-interactive UPS systems provide both power conditioning and battery backup, but power conditioning is usually subject to a four- to six-millisecond interruption in power when transferring to battery which may affect sensitive equipment negatively.

Line-Interactive uninterrupted power supplies are particularly effective in regions where grid failures are rare, but the power quality is poor with frequent fluctuations. These systems can cope with a wide range of input voltage variations before engaging battery backup. They are far better at controlling fluctuations than offline systems. The voltage boost circuitry that most line-interactive UPS systems employ and the range of input voltages that they accept deliver a high degree of protection against most common grid power issues. They also provide a good balance between power conditioning and cost.

The fact that line-interactive UPS systems rely on energy stored in the battery to achieve power conditioning is a downside. They tend to cycle their batteries more frequently than online UPS systems that use the double-conversion process to condition power. This can lead to shortened battery life or premature battery failure.

Standby or Battery-backup Uninterrupted Power Supplies

A standby UPS charges the backup battery using line voltage. DC from the battery is fed through an inverter to a transfer switch. When the grid supply is lost, the transfer switch switches on the standby power path. The inverter is typically inactive until the power fails, which explains the name ‘standby’ or ‘backup’ UPS. The active switching to battery results in a brief interruption in power while the transfer occurs. The primary advantage of this type of UPS is its low cost. The quality of a standby UPS is determined by its capability to handle a wide range of power fluctuations before switching to and draining the battery. Another indication of quality is the speed of the switch to battery power. The faster this is, the less likely power anomalies will be. Typically, a six- to eight-millisecond break in power when transferring to battery backup can be expected. Most standby UPS systems will also provide basic surge protection.

A standby UPS is best suited for loads less than 1500 VA and less sensitive or critical applications. It is ideal for lower power loads and where cost is a concern. During power outages, they provide sufficient time to save work in progress and execute the orderly shutdown of equipment.

Less Common UPS System

Delta-conversion online UPS technology is relatively new and was introduced to address some of the drawbacks of the double-conversion online UPS. The main benefit of the design is greater compatibility with generator sets eliminating the need for oversized wiring or generators.

Connect with the Power System Experts

PacB Power Solutions is an industry leader in the provision of diesel generators but also offers renewable energy solutions and uninterrupted power supplies. If you need an integrated power system or a standalone UPS, then talk to PacB. We have a range of reliable systems available and are the proud suppliers of the MAKELSAN UPS product range. We can assist with units from as small as 1 kVA through to and including 800 kVA. The MAKELSAN UPS range is neutral and short-circuit-protected which is essential to ensure that your equipment is properly protected. Our competent technical team is always available to provide support. Contact PacB today for anything related to power systems and uninterrupted power supplies.