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What is a UPS and how does it work?

The UPS, or Uninterruptible Power Supply, functions as a critical element to guarantee numerous services in our daily lives

We live in a hyper-connected world that demands the immediate and uninterrupted availability of countless services. In our day-to-day lives, thousands of elements, whose existence and function many of us are unaware of, are involved in ensuring that every cog in our society always functions perfectly. There is no denying the discomfort we feel every time communication networks or electricity goes down. For this reason, and despite the fact that technological investment in telecommunications infrastructures and electricity grids is making significant progress in guaranteeing service in all geographies, it is essential to have support or emergency devices to prevent damage in the event of an unexpected interruption. One of these elements, which we are going to talk about today, are UPS or Uninterruptible Power Supply Systems, also widely known by their acronym UPS (Uninterruptible Power Supply).

These devices are present in places as diverse as data centres, hospitals, office buildings, industries, transport infrastructures such as ships, or any other point that requires a reliable, quality power supply that is available at all times. They are responsible for guaranteeing the continuity of the electrical service when the grid experiences a failure or interruption of any kind.

In effect, the UPS is a backup so that, in the event of a power cut, the services of our systems do not fall, as they are devices capable of providing electrical energy to other equipment through their batteries without the need to depend on a grid. The autonomy time of the UPS is determined by the type and number of batteries in the system. The more batteries, the more power outage time we will be able to withstand.

Thus, a UPS ensures that, for example, the energy needed by an operating theatre for a critical operation remains stable at all times; that the data centres that allow the internet connection to reach our homes do not cease their activity if there is a power surge due to an electrical storm; or that the communication systems of a ship do not suffer a fall, endangering maritime traffic, due to a critical power supply error. Perhaps now you are a little more aware of the importance of these unknown devices.

UPS, or Uninterruptible Power Supply
UPS, or Uninterruptible Power Supply

In addition, a UPS works as a filter for those electrical systems or devices connected to the grid. That is to say, if we connect one of these Uninterruptible Power Supply Systems to a boat, for example, we would protect all the computer equipment from possible surges or voltage peaks, interferences, frequency variations or micro interruptions; the performance of the UPS would filter all of this, achieving a perfect cleaning of the output sine wave. Thus guaranteeing not only the proper functioning of the equipment connected to the grid, but also its longevity.

How does an Uninterruptible Power Supply (UPS) work?

To understand how these elements work, it is first necessary to know what components make up a UPS. Let’s see:

  • Rectifier/Charger: It is in charge of converting the Alternating Current electricity, which arrives through the grid, into Direct Current, either to charge the batteries or to feed the inverter.
  • Batteries: They provide the electrical energy necessary to power the system in the event of a power outage.
  • Inverter: This is an element that converts the electricity—coming either from the rectifier or from batteries—from Direct Current into Alternating Current, to be distributed to the systems connected to the UPS.
  • Static and maintenance bypass: This is the type of electrical circuit that the UPS contains and allows the electric charge to be connected directly to the main grid (or a separate one) when the UPS is at fault.
  • Control unit: This is the smart element with which the Uninterruptible Power Supply System is equipped. Depending on the type of device and its functions, it will allow a series of functionalities via software or others.

What would be its normal functioning?

When the UPS is operating normally, i.e. with an available and good quality power supply, the electricity enters through the UPS connection to the grid and passes, in the first instance, through the rectifier, which converts the electricity from alternating current to direct current.

This transformation is necessary because part of the electricity must be stored in the battery—where the current must be direct current—and the rest of the electricity continues on its way to the inverter, which returns it to alternating current to power the systems connected to the UPS.

What happens when there is a power failure?

Imagine that the grid is no longer available or that the voltage is not within permissible quality limits; changing the current flow. In this case, the inverter would be powered by the DC voltage provided by the batteries. The inverter output would remain unaltered and therefore the electric charge connected to the system would continue to operate without interruption.

The autonomy time, or the time during which the batteries can be supplying the system, will depend on the consumption required by the charge supplied by the equipment and the capacity of the battery. When the main supply voltage is restored, i.e. reaches a value within the permitted tolerances, the rectifier resumes operation and normal operation is restored.

The batteries recover from the discharge suffered in the absence of power by recharging through the DC voltage supplied by the rectifier/charger.

What if there is a failure in the UPS or we need to carry out maintenance work?

If there is a fault in the UPS, the static bypass is automatically activated, instantly transferring the electric charge to the main power supply grid (or the bypass) when there is an overload or a short-circuit. Thus, whatever the operation, the UPS ensures that there is no interruption in the power supply. Hence its name.

There are different UPS circuits or types that contain more or less elements, either protection or filter elements, to guarantee “clean” electricity; but all of them contain at least these elements that we have mentioned. For the correct operation of the UPS, the most advanced UPSs have control units and software that provide real-time information for the user, as well as personalised functionalities.

Supsonik, 35 years providing power electronics