The purpose of a UPS system must be to protect critical loads with the highest level of efficiency and availability.  

In any industry, there is always innovation and advancement.  In the UPS world, there have been changes in topology from single standalone units to multiple redundant configurations, the establishment of the transformerless based design and the Modular concept. These changes have been driven primarily by the increasing cost of energy hence seeking higher and higher efficiency was the goal, but also by eliminating so-called single points of failure and therefore, attaining the highest availability, i.e no downtime.  

High efficiency is more or less a given nowadays so how to achieve the highest availability?

One innovation is Distributed Active Redundant Architecture (DARA), taking downtime from seconds to the milliseconds level.

This technology and the true modular hot-swap capability provides industry-leading availability of 9 nines (99.999999999).  DARA is a concept introduced by CENTIEL into its 4th generation UPS CumulsPowerTM True Modular UPS design.

So what exactly is DARA?

D is for Distributed

Distributed means that a decentralised architecture is utilised so that there is no single active component which can be a potential single point of failure.  No single control board, no single system static switch, no single parallel bus etc, etc.  Each module within the frame is a UPS in its own right. Each module is actually a fully independent and self-isolating intelligent module with all the building blocks of a standalone UPS unit – rectifier, inverter, static switch, battery charger, intelligence (CPU and communication logic), mimic panel.

Take the modules out of the frame, put them beside each other on the floor, cable them up and you have a traditional looking multi-UPS parallel redundant system.

For most modular UPS units, however, the commonly used single system, separate static switch is of most concern, it becomes a potential single point of failure. 

A is for Active

A is the automated democratic decision making process which is the real differentiator in DARA. It means the sum of the decision determines the total system action or reaction to any issues.   

In a standard modular UPS where modules share the load, if one has a problem it could signal all the modules go to static bypass.  However, a true modular UPS with DARA makes democratic decisions, when a fault is recognised in one module but the others do not, then they will remain online while the problematic module is switched off automatically and isolated.  The automated process removes some of the human element which has led to datacentre power failures in recent years.   

R is for Redundant

From a technological point of view, building redundancy into the UPS system increases availability.  Redundancy simply means adding extra modules which will support the load in the event of failure.  By utilising a true N+1 configuration, a failure in one module results in that module being isolated, leaving the remaining modules supporting the load.  This results in high availability and low downtime and the rapid hot swap modular concept offers the lowest mean time to repair, it takes minutes to replace a module.

However, duplication and redundancy of UPS components must also apply to communication between modules too.  The most simple communications bus is a single cable, a break could potentially compromise the entire system. A ring circuit eliminates this as the signals can simply communicate the other way around the ring. 

Want even more assurance, how about a Triple Mode communications bus?  As its name suggests, there are three paths of communication with three separate ring circuits, and three brains in each module communicating with the three brains in all the other modules – it’s the belt, braces, and buttons DARA approach.

A is for Architecture

The overall architecture in CENTIEL’S CumulusPowerTM Modular design is a completely decentralised one, where no common component can act as a potential single point of failure.  Instead of one brain, there are multiple brains which work together to make the best decision for the whole.


What does a UPS do?…easy, it protects your critical load against mains’ failures.  There are many different solutions to the same problem, therefore, it is important to check the configuration and the definition of a modular system carefully and seek expert advice before making that expensive purchase.

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