Improve Server Efficiency with Advanced Control Electronics
Improve Server Efficiency with Advanced Control Electronics
By Mark Gaboriault, Strategic Marketing Director,
Alexander Latham, Systems Engineer, and
Thomas Rowan, Strategic Marketing Manager,
Allegro™Microsystems，LLC
Power-management methods and three-phase BLDCs for cooling reduce data-center energy use. This note discusses emerging energy-conservation strategies and examines some of the Allegro™ products that support these technologies.
Introduction
The worldwide growth in computer server farms and Internet traffic has resulted in this infrastructure consuming global energy production at an accelerating rate. It is now estimated that the world’s 500,000 data centers and 32 million individual servers consume 1.5% of global electricity—about 300 TWh of electricity per year (reference 1).
With significant efficiency improvements already attained, attention is now turning to power and heat management at the server-component level, specifically the on-board cooling fans themselves, which consume 10% to 15% of the total power used by the server (reference 2).
Recent advances in integrated control electronics provide local closed-loop control of both supply to the server and demand within components. These advances also make it practical to migrate from traditional single-phase BLDC (brushless DC) motors to highly efficient three-phase BLDC motors for the fans, typically realizing up to 25% improvement in efficiency.
The electronic devices allow inexpensive management of server components with minimal contributions to thermal signature, power draw, or physical size. Some, such as theAllegro MicroSystems A4942 three-phase sensorless BLDC fan-motor driver chip, are small enough to fit onto the hub PCB of mini ducted fans. The hub PCB is a small ring-shaped board with as little as 5-mm effective width, to accommodate the rotor shaft (figure 1). Monitor ICs, such as theACS761., provide current and power monitoring and control, enabling hot-swap management at the individual server blade level.
图1标准机架式和刀片服务器中的风扇管理，电流传感，热插拔管理和POS调节应用。雷竞技最新网址
Energy reduction strategies
The latest generations of servers provide several new approaches to energy management, which allow rapid recovery of conversion costs—often within a year. For example, microprocessors have been designed for higher throughput in smaller packages, requiring less power and generating less heat.
Studies of the individual thermal sources, principally power supplies and microprocessors and their enclosures, have led to optimized heatsink geometries and component layouts, with channeled shrouds to direct laminar airflow across these key areas. This complements the more recent high-efficiency ducted miniature (less than 40-mm) tandem fan-motor assemblies, arranged in series or parallel arrays within these flow paths.
增加气流的效率和减少footprint, the integrated fans assemble in tandem pairs that share the same ducting. The two fans are, however, completely independent in terms of mounting shaft and drive electronics. While this could gain an advantage from modular control, in fact it can introduce problems effecting reliable sensorless motor startup: left to themselves, one of the motors will start first, causing airflow over the other fan and dragging the motor and interfering with the open-loop startup sequence.
类似的问题可能发生当一个球迷没有yet stopped turning when the motors restart. In the past, this phenomenon made it necessary to allow both fans to come to a complete stop before restarting. The new motor-driver ICs contain an adaptive startup algorithm that can interpret when the motor is being driven by airflow over the fan blades from the tandem fan or when the motor and fan are already in motion from a previous power cycle. The advanced IC can modify the power-on sequence to adjust for this and allow both fans to operate synchronously at maximum efficiency throughout the power cycles.
然而，固定气流的优化，并且PID控制系统的改进是在速度和空闲时间方面优化风扇使用。许多服务器只能使用少量的时间。低需求期间的能量可以通过带自动启动的低功耗模式甚至掉电模式来保存。
This can be accomplished by monitoring current consumption as the components operate, using current sensing ICs that can mount on the PCBs in the servers for lower-current onboard applications, or on supply lines for high-side current sensing. These compact ICs measure current magnetically, using the Hall effect, eliminating the need for sense resistors, which dissipate heat. For example, an integrated conductor, such as in the AllegroACS758., presents only 100 µΩ resistance, which is an order of magnitude lower than typical sense resistors, and results in significant power savings.
该技术还在紧凑的封装中提供隔离电流检测，为闭环反馈提供低电压输出信号。应用先进的PWM电机驱动器，这些器件可以控制电源电流浪涌，确保直接闭环风扇速度控制，以保持气流速度一致，与实际的冷却要求成比例。
This also results in material savings because motors do not have to be overdesigned to compensate for large motor-to-motor torque and speed variations. Individual motors often have electrical characteristics that vary more than 10% between units. In addition, the local environments in which the motors mount vary substantially and inconsistently in terms of electrical supply and load, as well as thermal loading from coolant flow and adjacent heat sources.
Advanced PWM motor drivers and hot-swapping current monitoring ICs can suppress current surges as the motors turn on. New device types apply soft-start PWM current-ramping techniques that allow the designer to optimize tradeoffs between surge current and power cycle times (figure 2).
图2.软启动在减少浪涌电流中的影响
Additional efficiency is gained by the test device—in this case, the A4942—which has advanced features that start to energize the motor phase windings in advance of the timing defined by the rotor position.
This phase advance technique ensures that the phase windings have reached the required current level at the point where the resulting forward torque on the rotor will be most effective, thereby improving motor efficiency. Note that the start and stop conditions are the same but with soft start, the maximum current is greatly reduced. The longer power-up may not be significant in start-stop fan applications, and can be programmed to tradeoff with power surge.
Integrating Hot-Swap Management
Existing server-blade technology seeks to minimize these variances by the modular approach, placing power supplies and cooling fans off-board from the memory storage and processor elements. However, this incurs significant risks in hot swapping. Current sensor ICs with integrated hot swapping controls manage power surges that occur due to the makes and breaks of electromechanical connections. The soft start of an external FET controls the hot-swap power surge and provides current limiting (figure 3). By controlling the FET turn-on time when power is connected, the hot-swap current-sensor IC, in this example the ACS761, reduces the inrush current from 32 A to 12 A.
图3.热插拔电流浪涌抑制模拟
热插拔管理会影响服务器中其他组件的设计。这减少了对高浪涌电流水平的额定组件的要求。另外，通过集成电流和功率限制，热插拔IC不仅最小化了必须从操作员隔离的板区域，以便符合UL 60950，而且还提供短路保护。
Three-phase motor advantages
Although single-phase BLDC motors cost less than three phase motors, increasing energy costs have made the higher efficiency of the three-phase motor an economic offset. Typical efficiency improvements from single-phase BLDC motors to three-phase BLDCs are approximately 25%.
Designs achieve further cost reductions using techniques such as motor soft start to reduce the current surges from the power supply at startup. This reduction in surge current also allows smaller FETs and reduces costs for power supplies.
Along with optimized motor drivers, power-regulation techniques can optimize the operation of various components and systems within the server. QFN-sized DC-to-DC regulators provide point-of-supply management integrated with advanced features, such as synchronous rectification for high efficiency, short minimum controllable on-times, and optimized high- and low-side FET RDS(on)五的比率IN/ VOUTratios commonly found in servers. These provide robust fault-tolerant power management to withstand variable operating conditions, and detect and report a wide variety of fault conditions.
具有先进集成电路控制和监控的三相BLDC电机现在提供了显着的效率，并提供了未来改进的路径。因为这些技术可以应用于子系统级别，所以它们可以扩展到DG（分布式发电）和CHP（组合热电和电源）系统。随着改进的电子评估技术，这些设备增强了与智能电网系统的服务器系统微电网集成。
参考：
1. Biello，David，Facebook可以展示如何减少互联网的不断增长的能源使用？，科学美国，2012年8月3日。
2. Neudorfer, Julius, How to Optimize the Energy Efficiency of Your Server, eWeek, March 5, 2009.
Originally published in Power Systems Design, December 2012. Reprinted with permission.
Copyright ©2012 Power Systems Design, all rights reserved
Portions not copyrighted by Power Systems Design copyright 2013, Allegro MicroSystems, LLC
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