通过先进的控制电子设备提高服务器效率
通过先进的控制电子设备提高服务器效率
由Mark Gaboriault，战略营销总监，
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).
具有显着的效率改进，现在关注服务器组件级别的电源和热量管理，特别是在车载冷却粉丝本身，这消耗了服务器所使用的总功率的10％至15％（参考2）。
集成控制电子设备的最新进展为服务器提供了本地闭环控制，并在组件内部需求。这些进步还可以从传统的单相BLDC（无刷DC）电机中迁移到高效的三相BLDC电机，用于风扇，通常实现效率高达25％。
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，提供电流和电源监控和控制，在各个服务器刀片级别启用热插拔管理。
Figure 1 Fan-management, current-sensing, hot-swap-management, and PoS-regulation applications in standard rack-mount and blade servers.
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.
对各个热源的研究，主要是电力供应和微处理器及其外壳，导致优化的散热片几何形状和部件布局，具有通道的护罩，以直接穿过这些关键区域的层流气流。这补充了最近近期的高效导管微型（小于40毫米）串联风扇电机组件，在这些流动路径中串联或平行阵列排列。
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.
当电机重启时，当一个风扇尚未停止转动时，可能会出现类似的问题。过去，这种现象使得在重新启动之前允许两个粉丝来完成完整的停止。新的电动机驱动器IC包含一个自适应启动算法，当电动机通过串联风扇或电机和风扇从先前的电源循环开始时，可以解释电动机时通过气流驱动。高级IC可以修改上电序列以调整此功能，并允许两个风扇在整个电源周期中以最大效率同步运行。
Optimization of airflow is fixed, however, and improvements in PID control systems are required to optimize fan usage in terms of speed and idle time. Many servers are utilized only a small percentage of the time. Energy during the low demand periods can be saved by low-power modes or even power-down modes with automatic startup.
这可以通过监控电流消耗作为组件操作的电流检测IC来完成，该电流检测IC在用于低电流车载应用程序的服务器中的PCB上，或用于高侧电流检测的电源线。雷竞技最新网址这些紧凑的IC测量电流磁力，使用霍尔效应，消除了对感测电阻的需求，耗尽热量。例如，诸如Allegro中的集成导体ACS758，仅具有100μΩ的电阻，这是比典型感测电阻低的数量级，并导致显着的功率节省。
This technology also provides isolated current sensing in a compact package, providing a low voltage output signal for closed-loop feedback. Applied with advanced PWM motor drivers, these devices can control supply current surges and ensure direct closed loop fan speed control to hold the airflow rate consistent and in proportion to the actual cooling requirement.
这也导致材料节省，因为电动机不必过度指定以补偿大的电动机到电动机扭矩和速度变化。各个电机通常具有在单元之间变化超过10％的电气特性。另外，在电源和负载方面，电动机安装在电源和负载方面的局部环境以及来自冷却剂流动和相邻热源的热负荷。
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).
Figure 2. Effect of soft start in reducing surge current
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.
集成热插拔管理
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.
Figure 3. Hot-swapping current-surge suppression simulation
Hot-swap management affects the design of the other components in the server. This reduces the requirement for components to be rated for high inrush current levels. Additionally, by integrating current and power limiting, the hot-swap IC not only minimizes the board area that must be isolated from the operator for compliance with UL 60950, but also provides short-circuit protection.
Three-phase motor advantages
虽然单相BLDC电动机成本低于三相电动机，但增长的能源成本使三相电机的效率提高了经济偏移。单相BLDC电机到三相BLDC的典型效率提高约为25％。
设计使用电机软启动等技术实现进一步的成本降低，以减少启动电源的电流电源。这种浪涌电流的降低还允许较小的FET并降低电源的成本。
除了优化的电机驱动器外，功率调节技术可以优化服务器内各种组件和系统的操作。QFN大小的DC-TO-DC调节器提供集成的供应点管理，具有先进的功能，例如高效率的同步整流，最小可控的次数，以及优化的高和低侧FET rDS(on)ratios for V在/ V出在服务器中常见的比率。这些提供强大的容错电源管理，可承受可变操作条件，并检测并检测各种故障条件。
三相刷马达使用先进的integrated circuit control and monitoring are providing significant efficiency gains now, and provide a path to future improvements. Because these technologies can apply at the subsystem level, they can scale to both DG (distributed generation) and CHP (combined heat and power) systems. With the improved electronic evaluation techniques, these devices enhance server-system microgrid integration with Smart Grid systems.
References:
1. Biello, David, Can Facebook Show How to Reduce the Growing Energy Use of the Internet?, Scientific American, August 3, 2012.
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.
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