WHITEPAPER WHITEPAPER. GE s eboost Technology Reducing Data Center Power Consumption, Ensuring Power Quality. Silvio Colombi.

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1 GE s eboost Technology Reducing Data Center Power Consumption, Ensuring Power Quality Introduction: Playing the Percentages of Uninterruptible Power Supply Efficiency Paying the power bills for today s large-scale data centers is a major challenge, or strategic advantage, for information technology (IT) managers. Some estimates project that data centers alone consume two to two and a half percent of the electricity generated in the United States (1). A study by Frost and Sullivan found that the U.S. could reduce its yearly consumption of electricity by $3 billion by simply increasing the energy efficiency of uninterruptible power supply (UPS) systems in data centers from 90 to 98 percent (2). Other studies demonstrate the significant effects that efficient UPS systems have on the operating costs of individual data centers. One study projected that power lost as it passes through inefficient UPS systems can comprise as much as 10 percent of a data center s total power budget (2). Moreover, inefficient UPS systems dissipate more heat, which requires additional air conditioning and, again, increases energy costs. Another research project studied the energy consumption of a 50,000 square foot data center and found that by improving the energy efficiency of its UPS systems by just a few percentage points the center can save $3.1 million over 10 years (2). GE s eboost* UPS technology is inherently more power efficient than the double conversion UPS topology which is widely deployed in IT centers today. GE s eboost technology power efficiency is in the range of 98 to 99 percent as compared to 93 to 94 percent for modern double conversion UPSs. In addition, eboost takes advantage of patented high-speed control technologies to achieve power switching cycle times of two milliseconds (ms) or less, ensuring a reliable and continual supply of high quality power. WHITEPAPER Silvio Colombi Consulting Engineer, GE Critical Power Lorenzo Giuntini Lead Engineer, GE Critical Power This white paper explores the technologies that enable the power efficiency and reliability of GE s eboost-enabled UPS systems. eboost Architecture Breakthrough advancements in high-speed control technologies have changed the playing field for UPS systems in data centers by enabling new highly efficient multi-mode UPS architectures which are every bit as reliable as legacy UPS systems. In the past, most UPS systems provided power protection at the expense of power efficiency. Servers and other IT equipment can be very sensitive to fluctuations or inconsistencies in the quality of the electrical power provided by the utility. Even a brief power anomaly can force a server to shut down and begin a lengthy reboot cycle. Any equipment downtime caused by an anomaly in power quality can be quite costly for the IT center and the enterprise in terms of loss of data access, capacity, and service downtime. Downtime also affects the life of the server. To prevent these issues, most data center UPS systems, which protect the load 1

2 during a complete outage or other power anomalies, also call for all of the power provided by the utility to be routed through a UPS system where it can be closely monitored for power quality such as spikes and sags. This involves the utility power being converted twice: first from utility s alternating current (AC) to direct current (DC). From there it is converted back to AC to power the IT equipment in the data center. This so-called double conversion (Figure One) topology allows the UPS to closely analyze the quality of the power from the utility and head off any disturbances before it reaches the data center. In the case of a disturbance on the utility voltage, the inverter keeps providing safe and clean power to the load using either the main or battery power depending on the nature of the disturbance. A double conversion UPS filters out most of the utility disturbances automatically through a double conversion process. For a small disturbance, the rectifier keeps converting AC to DC and the inverter will provide clean power to the load without using the battery. For a bigger disturbance, the rectifier may switch off and the inverter will use the energy from the battery to provide clean and safe power to the load. Typical Data Center AC Critical Power System ( Four Power Conversions ) ( 1 ) ( 2 ) ( 3 ) ( 4 ) 15kVac 480Vac 480Vac 480Vac 208Vac Typical Critical Power System Efficiency 92-94% Utility MV/LV Transformers Switchgear Double Conversion UPS PDU 98-99% 92-94% 98% Figure One Unfortunately, power efficiency is the price paid for protection. Double conversion UPS systems have a typical power efficiency rating in the range of 92 to 94 percent. As a result, double conversion UPS systems place a steep toll on the yearly operating budgets of data centers. The relative cost of ownership over a typical 10-year product life cycle is considerably higher than that of UPS systems with power efficiency ratings in the range of 98 to 99 percent, such as GE s eboost-enabled UPS systems. GE s eboost technology pioneered a new generation of UPS systems which are more power efficient because they incorporate patented innovations in power monitoring and control technologies. Based on these breakthrough technologies, eboost meets the highest standards for reliability and high quality power. The eboost architecture (Figure Two) closely analyzes the power flowing from the utility. Power efficiency is maximized by allowing clean and consistent power to flow directly to a critical load such as a data center. GE s eboost technology reacts immediately typically in two milliseconds (ms) or less when an anomaly is detected on the main power source. Should a power outage, surge, sag, or some other type of disturbance be detected by a UPS running in eboost mode; it almost instantaneously provides good, high quality power from an alternative source, such as an inverter. It also simultaneously blocks the disturbance on the main power line from the load. And GE eboost technology does all of this in two ms or less. High quality power is provided so quickly that any IT equipment connected to the UPS is unaffected by the infinitesimal gap in power. 2

3 eboost Architecture Q2 Q1 K4 RECT IV Z LOAD TRASFORMER Figure Two For those power disturbances that are relatively minor, such as low-level voltage transients, filter circuits are integrated on the eboost architecture to condition the power coming from the utility. eboost Operations The innovative and, in some cases, patented technologies integrated into GE s eboost technology enhance how it performs two essential functions: 1) monitoring power quality at key points in the UPS architecture and 2) quickly turning on or off two critical switches that control the flow of power through the architecture. (Figure Three) UPS eboost Concepts UPS Brain Vin Vout Iout Ltr Medium voltage tranformer Outside world RECT IV Z LOAD TRASFORMER UPS Figure Three 3

4 Fast Switching When consistent high quality power is provided by the utility, it flows freely through the first of two switches in the eboost architecture. The first is a static switch module () located on the power input path from the utility, which is referred to as the bypass path because it bypasses the power conversion path through the UPS. The second switch is located at the inverter on the power conversion path. This switch remains closed when the UPS is operating in eboost mode. When GE s eboost technology s sensitive monitoring technologies detect any sort of deviation in the predefined power quality on the main or bypass power path, the inverter is immediately turned on to allow good, quality power to flow from the UPS inverter to the load. In the same instant, the switch on the bypass path from the utility is turned off to block the disturbance from reaching the load. Several patented innovations explained below allow eboost to accomplish these two switching processes in less than two milliseconds. The inverter can be activated in a fraction of a millisecond because the transformer is already magnetized. While GE s eboost technology allows power to flow directly from the utility along the bypass path, it also back-feeds power to the transformer to keep it magnetized. Once a power disturbance is detected, a control signal is sent to turn on the inverter. Since the transformer is already magnetized, inverter power can instantaneously flow to the load. Additionally, to block the power disturbance from reaching the load, the flow of power at the on the bypass path must be reversed. The typical is made up of thyristors, which are also referred to as silicon-controlled rectifiers (SCR). These block power from the utility when the current through the switch is reversed and crosses zero. To accelerate this process, the inverter produces a specific short voltage pattern. This forces the current to zero much faster. Once the current crosses zero, the effectively blocks the power flow from the utility and any disturbances along with it. The typical elapsed time for both of these switching processes averages two ms or less. Disturbance Detection, Analysis and Control In addition to fast power switching, the other critical aspect of the eboost technology s performance is advanced control technology which allow it to quickly detect any sort of disturbance on the main or bypass power path, and then analyze and identify the type of disturbance detected. It then instantaneously prescribes the actions appropriate to the characteristics of the disturbance. The two aspects of eboost that govern these control processes are the disturbance analyzer and transient inverter controller. Disturbance Analyzer The eboost architecture contains several real-time detectors which monitor the quality of power on the bypass path through the UPS. The disturbance analyzer rapidly determines the nature of the disturbance and reacts accordingly. It also communicates with the transient inverter controller so that the actions of both components are coordinated and synchronized. The following are the various power quality detectors which make up the disturbance analyzer. Instantaneous Adaptive Voltage Error Detector Disturbances on the bypass power path are monitored for amplitude and duration. When a disturbance is encountered, the instantaneous adaptive voltage error detector analyzes it and adapts the response to the nature of the anomaly. For example, a large disturbance will trigger a faster response as compared to a smaller disturbance which may or may not threaten power quality. 4

5 RMS Voltage Error Detector This component of the disturbance analyzer computes the root mean square (RMS) on all three of the UPS unit s output voltages. If one of the three RMS values exceeds the system s predetermined limits, eboost transitions to inverter power. Because the RMS value is determined over a complete power cycle, this detector identifies anomalies that are of longer duration than those detected by the instantaneous adaptive voltage error detector. Output Short Circuit Detector Should a short circuit occur on one of the output voltages of the UPS, this component will detect the presence of the short and follow the appropriate actions to reset any breakers or fuses on the circuit. Typically, current from the main utility supply line or bypass path will be used to temporarily increase the current and clear the breaker. Bypass Failure Detector In the event that the switch on the bypass path through the UPS fails, the low pass filters which make up this detector will identify the failure and engage inverter power. Missing Input Phase Detector If one of the three voltages or phases of the power on the bypass path falls below a certain limit, the missing input phase detector initiates an immediate transition to inverter power. eutral Current Detector In three-wire UPS systems where the neutral conductor is routed to ground, this detector monitors ground current for parasitic voltages. If the ground current exceeds a certain limit, indicating a critical disturbance on the main power supply line, the neutral current detector engages inverter power. Transient Inverter Controller The transient inverter controller employs several algorithms which oversee the operations of the inverter. Typically, the inverter is engaged when a power disturbance is detected on the bypass power path from the utility. When this happens, the inverter supplies high quality inverter power to the load. Conversely, the inverter is disengaged in favor of the bypass power supply path when the quality of the power from the utility has returned to an acceptable level. Several of the algorithms which comprise the transient inverter controller are worthy of note. Soft Transfer to Bypass An abrupt or instantaneous transition of the power source from the inverter back to the bypass path and main utility power can potentially cause oscillations or small momentary disturbances on the bypass power path. Instead, this transition is accomplished gradually inverter power decreases as the power on the bypass path increases to avoid these disturbances. Transient Stiffness Reduction To minimize small power disturbances during the transition from the bypass power path to the inverter power path, the transient stiffness reduction algorithm momentarily relaxes the control bandwidth on the inverter for a very short period of time (typically one ms). Parallel UPS Operations The flexibility inherent in the eboost architecture makes it very scalable so that parallel UPS systems can be deployed to accommodate IT data centers of any size. A key benefit of parallel UPS operations is the eboost technology s ability to apply all of the resources of multiple UPS systems as if they were one unified UPS. (Figure Four) 5

6 Of course, configuring multiple eboost UPS systems in parallel will allow the resulting system to serve a larger critical load, but it also eliminates the possibility that the failure of any one component can cause the data center s UPS to fail. The redundancy of a parallel eboost implementation eliminates the single-point-of-failure problem. GE s eboost technology s sophisticated control technologies allow multiple systems to automatically share responsibility for providing power to the load. In the event of a component failure or degraded performance in any eboost technology-enabled UPS, the power supplied by the other systems configured in parallel will increase to compensate for the decreased capabilities of the malfunctioning component. UPS Parallel Operation Concepts Q2 K4 RECT IV Z Q1 TRASFORMER Q2 LOAD K4 RECT IV Z Q1 TRASFORMER eboost Reliability Testing Figure Four The reliability of GE s eboost technology-enabled UPS can be defined by the ability of the UPS in eboost mode to safely supply power to the critical load. This reliability can be demonstrated through a series of tests involving the injection of power disturbances at the inputs to an eboost-enabled UPS. Measuring the power at the UPS system s outputs reveals the reliability of the UPS in eboost mode. These measurements can be plotted on a graph of acceptable power performance limits, such as the standards provided by the Information Technology Industry Council (ITIC). Figure five shows the results of such tests. The red dots indicate a power disturbance injected at the UPS inputs and the blue squares indicate actual power performance at the outputs. The ITIC standard for acceptable power quality for IT equipment is represented by the solid red line. The figure shows that all disturbances were reliably handled by the eboost UPS. That is, the power output by the tested UPS was consistently within the ITIC standards for power quality. 6

7 Plot Validation Test Results WHITEPAPER Percent of nominal 200 eboost Double Conversion Duration milliseconds Test results: Red dots event at UPS input; Blue square event at UPS output. Figure Five Conclusion The patented monitoring and control innovations incorporated in GE s eboost technology gives data center managers the ability to significantly reduce their operating costs by cutting energy consumption while, at the same time, ensuring a constant supply of good quality power to their IT equipment. These innovations place GE s eboost-enabled UPS systems among the most power efficient and reliable in the industry. The cost of ownership over the entire lifecycle of legacy low-efficiency UPS systems is exceedingly high, given the additional power consumption year after year. The eboost-enabled UPS systems deliver high quality power to IT centers and a reduced cost of ownership by lowering annual operating costs. For more information: info.criticalpower@ge.com References: ote: The figures cited in this article unless otherwise noted, are based on industry-standard information or data collected by GE in the deployment of critical power systems. The results cited in this article are not a guarantee of performance or specific results, and individual results may vary based on specifications and operating conditions. (1) U.S. Environmental Protection Agency (EPA), Report to Congress on Server and Data Center Energy Efficiency, Public Law , (2007) (2) Frost & Sullivan, Analysis of the Global Data Center Uninterruptible Power Supplies Market, Dec. 19, Shiloh Road, Plano, TX (toll-free in orth America) (direct number) info.criticalpower@ge.com GECriticalPower.com DEC-139, Rev. 03/14 *Trademark of General Electric Company. Copyright 2014 General Electric Company. All Rights Reserved. GE reserves the right to make changes to specifications of products described at any time without notice and without obligation to notify any person of such changes.