The Power Experts

UPS topologies: How do the choices stack up in today’s world?

When it comes time to replace a UPS it can be hard to choose the best system for your facility. There are best-practice trends and variables that need to be considered before replacement.

Your power needs may have changed since you purchased that old UPS, and they may change further still as your company grows. The size and location of your data center may have grown or you may be about to expand. Taking a fresh look at your current and future power needs should be your first step.

Have you considered the impact of newer trends in data centers such as edge computing? For example, double conversion online has historically been used for applications over 10kVA.  However, with the growth of remote servers and cloud computing, network connectivity has become more critical and customers are starting to use double conversion online UPS topologies for their critical networking gear even in the lower power ranges starting at 1500VA. Now that the on-site load you need to protect has been pared down to mission critical information only, your choice of UPS to ensure uptime is even more important.

Another trend to consider is that the sizing of UPS systems has changed and company’s no longer routinely purchase oversized UPS. Now that pressure is on to be more efficient, UPS systems are smart-sized to provide just what is needed so that companies are not paying for more product, or cooling of that product, than they need.

Despite the growth of double conversion online UPSs in lower power single phase applications, as more value-priced options, standby and line interactive UPSs still have their place in your organization.  With these changes to the industry in mind, let’s take a fresh look at the most popular UPS topologies, the differentiating features of each, and their common applications.

Standby UPS

The Standby UPS is the most common type of UPS found in offices and it is best for non-critical servers.

  • Applications: Commonly used for Small Office and Home Office (SOHO) applications for personal workstations, home entertainment equipment, gaming consoles etc.  These are generally low-powered UPSs for non-critical equipment.
  • Topology: Features a transfer switch set to choose the filtered AC input as the primary power source, and it switches to the battery/inverter as the backup source if the primary source fails. When that happens, the transfer switch must operate to switch the load over to the battery/inverter backup power source. The inverter only starts when the power fails.
  • Benefits: The standby features high efficiency in a small footprint and low initial cost.
  • Limitations: It is impractical for use over 2kVA. It uses the backup battery during brownouts leading to wear and tear on the battery. It does not have an internal bypass switch to go to street power if the UPS fails.

Line Interactive UPS

The Line Interactive UPS is best for basic office equipment such as local workstations.

  • Applications: Line Interactive – small office applications such as non-critical servers, non-critical medical equipment, etc.
  • Topography: In this topology, the battery-to-AC power converter (inverter) is always connected to the output of the UPS. Operating the inverter in reverse during times when the input AC power is normal provides battery charging. When the input power fails, the transfer switch opens and the power flows from the battery to the UPS output. With the inverter always on and connected to the output, this design provides additional filtering and yields reduced switching transients when compared with the standby UPS topology.
  • Benefits: The line interactive offers high efficiency, small size, low cost and reliability along with the ability to correct low or high line voltage conditions.
  • Disadvantages: It is impractical for use over 5kVA. It does not have an internal bypass switch to go to street power if the UPS fails.

Double Conversion Online UPS

The Double Conversion On-Line UPS is the most common type above 10 kVA.

  • Applications include networking closets, critical applications, data centers, facilities, and networking switches, and networking gear.
  • Topography: In this topography, failure of the input AC does not cause activation of the transfer switch, because the input AC is charging the backup battery source which provides power to the output inverter. Therefore, during an input AC power failure, on-line operation results in no transfer time. The online, double conversion UPS has an internal static bypass, ensuring that if your UPS requires maintenance or experiences a catastrophic failure, you may be able to keep your critical loads online during repair or replacement.
  • Benefits: Provides the highest level of protection by isolating the equipment from raw utility power. It offers excellent voltage and frequency regulation and ease of paralleling. It is the only UPS that provides power with zero transfer time to the battery, making it ideal for sensitive equipment. Ideal for mission-critical edge computing which is usually in the 1–100 kVA range. UPS systems used in edge computing are more likely to have a higher average redundancy to ensure the greatest availability and reliability because will be primarily responsible for handling network switching, routing, load balancing, security, and audit trail while also doubling up for running data processing pipelines.Has an internal bypass switch to go to street power if the UPS fails.
  • Disadvantages: The double conversion on-line can have low efficiency with greater heat dispensation and it is expensive for use under 5kVA.

For more information about UPS topologies and choosing the right one for you, call 800-876-9373 or email