UPS topology drives increase in uptime


Advances in UPS design are increasing efficiency and resilience, writes Centiel UK managing director Mike Elms…

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 the nirvana of eliminating single points of failure, attaining the highest availability – ie no downtime. 

Most major manufacturer’s UPS equipment have very high online operating efficiencies and there are now more modular type systems on the market. High efficiency is more or less a given, nowadays, so how do you achieve the highest availability? 

One innovation is Distributed Active Redundant Architecture (DARA), taking downtime from seconds to the milliseconds level. This technology and modular hot-swap capability provides availability of 9 nines (99.999999999). DARA is a concept introduced by Centiel into its 4th generation UPS CumulsPower 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. 

There is no single control board, no single system static switch and no single parallel bus. 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 – including rectifier, inverter, static switch, battery charger, intelligence (CPU and communication logic) and 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, as it can become 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 not the others, 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 data centre 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 that 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, while 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. 

For increased assurance, a triple mode communications bus is provided. As the 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.

A is for Architecture

The overall architecture in Centiel’s CumulusPower 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 that work together to make the best decision for the whole.


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


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