Advanced UPS systems for cloud and hybrid IT

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The pace of change throughout the IT industry continues to accelerate, and data centres are no exception. Artur Faust, product manager 3-phase UPS, Data and IT Solutions at AEG Power Solutions, explains

Rapidly evolving business cases require IT to align with updated priorities in the short term – whether that is cloud computing, virtualization, social media or hybrid IT. Data centres must be flexible, and must be able to respond to change in only a few weeks rather than many months. System utilisation can vary significantly at a moment's notice, and systems must cope.

Not all data centres are able to meet these challenges. Instead, businesses are increasingly outsourcing to colocation facilities, creating hybrid IT environments. In turn, the colocation provider’s data centre must be flexible and responsive.

Whatever the data centre environment, it must be cost-effective – flexibility cannot come at the price of efficiency.

Changing demands for UPS
What do these demands for flexibility, responsiveness and cost-effectiveness mean for power in the datacentre?

Along with air conditioning, power management systems such as UPS are perhaps the most difficult parts of a data centre to change. It’s relatively easy to move servers around, but altering the infrastructure is more of a challenge.

UPS vendors have tried to respond to this need for flexibility, but with mostly mixed results.

Traditional monolithic UPS infrastructures are competitive on cost and have high mean time between failure (MTBF), but are inflexible: making changes involves waiting for installers, complicated planning, and the risks and downtime involved in switching the power off.

These rigid designs also suffer from low efficiency, because they cannot be re-configured to match the needs of the application and are therefore often running at far less than full utilisation. Once the utilisation of any UPS drops below about 30%, efficiency decreases rapidly.

Alternatively, some manufacturers have created modular designs that are more flexible. But these products have tended to suffer from high capital cost, as well as lower reliability as there are many separate modular blocks that can fail.

New UPS technologies
To overcome these problems, a third approach is a ‘block modular’ design for UPS, such as Protect Blue from AEG. Rather than modules with a capacity that can increase in small steps of say 30kVA, this approach uses blocks of typically 250kVA that can be added or removed as required to match demand.

The block modular design increases flexibility, and enables efficiency to be at least as high as pure modular alternatives. It also keeps the initial cost competitive, and delivers high reliability.

Increasing efficiency: 3 level IGBT
Whatever their configuration, all UPS strive for maximum efficiency. When AEG re-entered the data centre market, we realised we needed to take a step up in technology to achieve this. To boost the efficiency of our Protect Blue UPS to over 96%, we decided to use 3 level IGBT (insulated-gate bipolar transistor) technology with a bi-directional rectifier, rather than the more common 2 level IGBTs.

Figure 1 is a simplified view of how the UPS uses pulse width modulation (PWM) to create a sinusoidal output. The 3 level IGBT cuts the AC signal in 3 steps at typically 0V, 400V, 800V, as opposed to the two steps of the 2 level IGBT.

The PWM does not change instantaneously from one pulse to the next, as it takes some time for the current to start flowing once it’s switched on. This means there is an inefficiency where the PWM graph in Figure 1 deviates from the vertical, which results in energy losses via heat dissipation. The right hand side of Figure 1 shows this energy loss as a red area – you can see how the 3 level IGBT has lower losses, and hence higher efficiency, than the 2 level technology.

In fact, there is a limit of just over 94% in the efficiency that can be achieved with a 2 level topology. In contrast, with 3 level IGBTs AEG has already reached 96.4% efficiency in tests, and over 96% in the field with its Protect Blue UPS.

This high efficiency, and the power quality of the output, leads to typical 41% energy cost savings, which significantly reduce total cost of ownership (TCO). For a 1000kVA system with an average utilisation of 28%, this saving due to 3 level technology (compared to a 2 level based system) can be calculated to be around £9,000 per year in electricity costs – or around £12,000 per year once air conditioning effects are included.

While it is more efficient, 3 level IGBT technology can be more difficult to develop into reliable UPS systems. AEG’s Protect Blue includes customised components made by Infineon for AEG that help to optimize operational parameters, and ensure high MTBF in practice.

Flexible response
When computing loads in the data centre change, then the efficiency of the UPS drops as the load goes down. Protect Blue copes with this by higher efficiency linearity and switching blocks off in stand-by (idle mode), so the blocks that are still running are operating at a high percentage usage and are therefore more efficient. When required, blocks can re-start from idle mode and provide full power to the system within 2 to 5 milliseconds.

When you are considering which UPS to specify, a factor that is sometimes overlooked is how easy it is to reconfigure and move around. Firstly, does the UPS have sufficient physical robustness to be shifted to another location?

Then, in most UPS systems, the electrical panel is always fixed, and if you need to change anything you have to switch it off – which leads to inconvenient and costly downtime. With Protect Blue, AEG has made it simple to change your systems around with no downtime. LED indicators help make it easy for operators to know which switches can safely be altered. Changes such as adding or taking out a UPS block can be made ‘hot’ without having to cut the power.

Protect Blue also allows you to take out a module and use it as a single UPS somewhere else, increasing the flexibility of how the system can be re-used when requirements change.

Overall, the block modular concept means a UPS has the flexibility to meet customer demands in any scenario, from simple Tier I single bus arrangements, right up to a Tier IV fault tolerant system with multiple independent UPS.

Planning for the future
Customers today need a flexible UPS that is useful in the data centre a long time. Five or eight years is not a long enough life taking all initial planning and integration efforts into consideration – the UPS needs to provide enough efficiency and flexibility that will make it usable for at least 10 years, and ideally 15 or more. Of course, the UPS needs to be robust and innovative enough to last this long.

To achieve this kind of lifetime, a UPS needs to be able to adapt to change in different areas, including battery configurations, security levels, redundancy levels and different battery types. For example, with traditional systems, if you changed to Lithium Ion batteries, you would need a new UPS, whereas some newer designs such as Protect Blue will adapt effortlessly due to the geared concept of hardware and firmware with the capability for easy future upgrades.

When specifying a UPS, you should also consider how it will adapt to multiple different architectures in the future. Is it capable of working with solar power, for example, or connecting to a smart grid or micro grid?

Figure 2 shows different modes of operation that are possible with Protect Blue. The diagram also shows how each UPS works as its own bypass, which provides multi-level redundancy with no single point of failure, and hence increases reliability.

Conclusions
The fast pace of change in today’s data centres means that UPS need to be flexible and easy to reconfigure, but cost pressures mean that efficiency and total cost of ownership are just as important as they have always been.

AEG has responded to this demand with new block modular designs of UPS, which provide efficiency of above 96%, as well as the highest level of reliability. With these UPS, it is simple to build highly customized solutions for data centres.





Figure 3: product photo of Protect Blue from AEG Power Solutions

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