Intelligent (Active Inverter) Eco-Mode Approach can Provide UPS Efficiency without Availability Concerns
Data centers are currently undergoing a period of great change. Data center managers are struggling to keep pace with growing capacity needs while working under the constraints of tightened budgets and energy efficiency initiatives. New technologies such as virtualization and cloud computing are transforming data centers into dynamic environments, optimizing the space in ways not many could have predicted only a few short years ago.
Data centers are currently undergoing a period of great change. Data center managers are struggling to keep pace with growing capacity needs while working under the constraints of tightened budgets and energy efficiency initiatives. New technologies such as virtualization and cloud computing are transforming data centers into dynamic environments, optimizing the space in ways not many could have predicted only a few short years ago.
As the complexity of data center environments continues to grow, data center managers are increasingly concerned about maintaining or improving availability in increasingly dense computing environments while increasing efficiency and reducing costs. There are a number of technologies that are providing new options to help data centers meet these sometimes conflicting objectives.
One such option, an energy saving mode of operation (eco-mode) for UPS systems, while gaining a lot of attention in the industry, has been dismissed by many data center managers because of availability concerns. However, advances with technology show why not all energy savings modes of operation are created equal. In fact, a new “active inverter, intelligent eco-mode” approach, where the inverter and rectifier remain active, has quickly emerged as a viable option for data center managers looking for big UPS efficiency gains that do not compromise availability.
Recently, the use of eco-mode has been gaining support in the industry. The Green Grid, a global consortium of companies, government agencies and educational institutions dedicated to advancing resource efficiency in data centers and business computing ecosystems, included eco-mode in its Data Center Maturity Model. The Environmental Protection Agency (EPA) also mentions eco-mode in its ENERGY STAR for Uninterruptible Power Supplies specifications – which took effect in August 2012 – as one of the operating modes for efficiency improvements.
Eco-mode basically changes the way the UPS is employed to increase energy efficiency and reduce the operating expenses experienced in the data center. Eco-mode allows, for example, a double conversion UPS system to achieve the highest possible efficiencies by transferring the UPS to static bypass during normal operation. When power problems are detected, the UPS switches back to double conversion mode. The primary reason data center managers have not implemented eco-mode is because, for traditional eco-mode systems, the critical output voltage goes to zero volts during a utility loss event until the static bypass can be turned off and the inverter and rectifier turned back on.
In double conversion UPS systems, the rectifier and inverter are designed to run continuously with the rectifier directly powering the inverter and the inverter powering the critical output bus. With traditional eco-mode approaches, when the critical load is being powered through the bypass (i.e., eco-mode), the rectifier and the inverter are switched off; resulting in a delay and a notch in the output waveform when the critical load returned from eco-mode to double conversion mode. That notch allowed the downstream load to be exposed to certain AC bypass faults and disturbance conditions and, consequently, created a compromise to availability.
For traditional types of UPS systems, the inverter is not robust enough or controlled well enough to run in parallel with the static bypass utility source. This is where a change in technology was required, to a system that could run its inverter in parallel with the static bypass source. This technology is also used to provide superior output fault clearing capability (i.e., the ten times current fault rating of a continuous duty bypass static switch paralleled with the two times fault current rating of the UPS inverter), allowing a downstream fault to be quickly cleared in order to achieve high levels of critical bus availability over dynamic conditions. This technology also allows the UPS inverter to remain active when on bypass.
The active inverter intelligent eco-mode approach eliminates traditional eco-mode issues by keeping the inverter and rectifier in an active state. Because the inverter is kept in an active state, and is providing an output that matches the bypass, it is ready to accept the load immediately. As a result, the transfer to the inverter can be accomplished almost seamlessly. When the UPS senses bypass power quality falling outside accepted standards, the bypass opens and transfers power immediately back to the inverter until bypass anomalies are corrected. Once bypass power anomalies end, the critical load can be automatically returned to intelligent eco-mode.
Keeping the inverter in a constant state of preparedness does require additional control power; however, the power requirement is below 1 percent of the UPS rated power, creating potential savings of 4 to 4.5 percent compared with traditional double-conversion operating modes. The result is a more continuous output wave form, a more seamless transfer and possible UPS efficiency levels above 98 percent.
Also, keeping the rectifier in an active state ensures a constant float charge across the UPS battery, which is shown to have a significant impact on battery life. Constant float charging is the recommended method of operation from battery manufacturers. Research has shown that not maintaining a constant float across the UPS battery can accelerate grid corrosion, which can result in a reduction in battery life by a factor up to 4x. Also, with the rectifier available during the transfer back to dual conversion, cycling of the battery when changing modes is avoided.
So, for those data center managers who may have dismissed energy savings modes as a viable option because of availability concerns, I encourage you to consider the technology again. More specifically, take a look at an active inverter intelligent eco-mode. This advanced form of eco-mode can increase efficiency levels and eliminate much of the compromise to availability experienced by typical eco-mode approaches available in the past.
