DPA – the smart modular UPS design

Many organisations today depend entirely on their ICT equipment’s uninterrupted availability to stay in business.

However, while demanding better protection than ever from their UPSs, users face unprecedented constraints on their budgets as well as pressure to ‘go green’. Modular UPS topology is the answer for ICT operators facing these pressures and is currently the fastest growing segment of the 3-phase UPS market.

However, customers must take great care when selecting a modular UPS because not all modular UPS systems are the same. Parallel architecture limited only to modular design does not guarantee the highest power protection. The success of a parallel modular system depends largely on the design of the parallel architecture and on the level of intelligence of the individual UPS modules.

The majority of modular 3-phase UPS systems currently available use the traditional technology. Traditional technology means that some of the components are shared by the individual UPS within the system. As an example such system may have a system logic that is common for all UPS modules – creating a severe single point of failure. If an increase in the power rating, or “capacity”, of the UPS system is the sole reason for paralleling then such a traditional UPS system might be a valid solution due to a lower price. Such “centralised” systems compromise the UPS system’s availability. The system is only as reliable as its weakest single point of failure component is.

UPS systems based on DPA (Decentralised Parallel Architecture) in contrast do not share any common components. DPA means that each UPS module contains all the hardware and software required for full system operation. The major benefit of a DPA system is very high power availability. Each UPS module has its own independent static switch, rectifier, inverter, logic control, control panel and battery charger. Even the batteries can be configured separately for each module if required. With all of the critical components duplicated and distributed between individual units, potential single points of failure are eliminated. System uptime is further maximised by the true safe-swap modularity of the modules.

Increased flexibility is another benefit. Each UPS unit’s availability can be defined as a ratio between its Mean Time Between Failures (MTBF) and Mean Time To Repair (MTTR). Modular systems based on DPA are free of single points of failure and maximise the system‘s mean time between failure (MTBF). Quick and simple repair by safe-swapping modules while the UPS is online minimises the system‘s mean time to repair (MTTR). This benefit is key to users, but cost savings accrue as well. Inventory cost for specialist parts is reduced, and the need for highly skilled on site technicians is eliminated.

Modular topology provides secure power with high availability and efficiency – and it does it cost-effectively too. Although the initial capital cost of a true modular system is typically slightly above the ones based centralised parallel architecture, the picture changes when Total Cost of Ownership (TCO) is taken into account. Improved energy efficiency as well as other savings mean that the modular system’s extra cost will be recovered within its first year of operation. Longer term costs will also favour the modular system. The first is the extremely high availability arising from the significantly reduced repair time, which is a fundamental consideration for any UPS purchaser. The reduced floor space requirement and the flexibility to adapt quickly to changing critical load demands, will also be attractive propositions to many ICT equipment operators.

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