Thermal effects of bioimplants.

Implantable devices are well on the way to becoming small, dedicated, and highly complex embedded systems. As such, they are plagued by the same thermal management problems that afflict the computer industry: increased functionality causes increased heat generation. Herein, the effects of various parameters on the temperature increase in the human body tissue are considered, with a focus on a specific proposed implant: a dual-unit retinal prosthesis to restore partial vision to the blind . This particular example is educative since it includes most of the potential causes of thermal dissipation: a microchip that could dissipate relatively large power, a telemetry system, and a potentially large number of stimulating electrodes. The power dissipation characteristics of implanted electronic systems will have increasing importance for the design of future implantable devices. It was shown in this article that in some cases, this power dissipation can lead to temperature increases in the human tissue that are not negligible. In particular, the design of implantable stimulating devices with a large number of stimulating channels must be performed with a clear idea of the potential thermal implications of the device. Fortunately, reliable numerical and experimental methods are available to characterize the temperature increase caused by the implantable device. These methods should be used during the design phase of these devices.     

A miniaturized neuroprosthesis suitable for implantation into the brain

This paper presents current research on a miniaturized neuroprosthesis suitable for implantation into the brain. The prosthesis is a heterogeneous integration of a 100-element microelectromechanical system (MEMS) electrode array, front-end complementary metal-oxide-semiconductor (CMOS) integrated circuit for neural signal preamplification, filtering, multiplexing and analog-to-digital conversion, and a second CMOS integrated circuit for wireless transmission of neural data and conditioning of wireless power. The prosthesis is intended for applications where neural signals are processed and decoded to permit the control of artificial or paralyzed limbs. This research, if successful, will allow implantation of the electronics into the brain, or subcutaneously on the skull, and eliminate all external signal and power wiring. The neuroprosthetic system design has strict size and power constraints with each of the front-end preamplifier channels fitting within the 400 /spl times/ 400-/spl mu/m pitch of the 100-element MEMS electrode array and power dissipation resulting in less than a 1/spl deg/C temperature rise for the surrounding brain tissue. We describe the measured performance of initial micropower low-noise CMOS preamplifiers for the neuroprosthetic.     

Experimental Validation of a State Model for PEMFC Auxiliary Control

This work aims to validate experimentally a state model for a Proton Exchange Membrane Fuel Cell (PEMFC) system control. In this model, the air-supply dynamic is analyzed. The air is assumed to be compressible, and the model takes into account the compressor, the humidification device, the inlet and outlet manifolds, the fuel-cell stack, and the proportional solenoid valve at the outlet. This model is described by the following variables: the total mass flow, the pressure, the temperature, and the relative humidity. The effect of the air-supply device on the system's behavior (stack voltage$ldots$) is analyzed and validated on a 600-W power PEMFC fuel experimental data. The model results fit well with the experiment and it will help to optimize the stack net power.      

功率器件散热特性的非稳态测量方法

采用集总参数法对功率器件的散热体系进行了分析,推导了功率器件非稳态导热过程中温度变化的规律,给出了一种通过测量非稳态导热过程中的温度变化曲线确定散热体系特性参数的方法。以模块电源为例,实际测量了在不同状态下电源模块升温及降温过程中的温度变化特性。测试结果与理论预测基本相符,表明这种方法可有效用于工程实际中。该方法不仅可以避免冗繁的计算,且通过实验可方便地测试出功率器件的散热特性,并能够预测其使用过程中的最大温升,尤其适用于散热结构复杂、散热边界条件不易确定的应用场合。     

起重机驱动装置冷却结构设计及温升运行特性分析

起重机用新型驱动装置采用外转子结构,且相对于传统起升机构的一体化程度更高,易造成定子绕组散热困难。有别于传统电机设备的断续工作制,对温升计算提出了新的问题。根据设备特点,设计空心轴风冷的冷却结构。基于流体力学和传热学基本原理,建立流固耦合数学模型。以一台额定功率为90 kW的驱动装置为例,通过计算流体力学软件及其嵌入的自定义函数,依据传统起重机械设计要求的机构工作级别和极限操作工况,进行编程及模拟仿真。将温升计算结果与同等条件下试验数据进行对比,验证计算方法的科学性,并分析冷却机构的合理性,最终结果为后续起重机驱动装置的散热研究提供参考依据。     

大功率电力电子器件相变冷却技术的实验研究*

大功率电力电子器件的冷却散热问题,已成为集成化大电容发展的瓶颈,受到越来越广泛的关注。文中采用相变冷却技术,设计两种冷板:带有强化换热结构和非强化换热结构,用于绝缘栅双极型晶体管模块(Insulated Gate Bipolar Transistor IGBT)散热,对两种冷板温度分布进行数值模拟,并利用自建的实验平台对两种冷板的性能进行模拟试验。结果表明:两种结构的冷板均能满足功率器件的结温要求,同功率条件下,带有强化换热结构的冷板温度更低,具有更好的均温性,在3 000 W和4 000 W功率下,冷板温度分别为56.6℃和59.5℃,为系统结构设计提供指导。     

基于MATLAB\Simulink的快速FCS-MPC级联H桥STATCOM耗散功率计算及分析

针对一种应用于级联H桥STATCOM的快速FCS-MPC策略,基于MATLAB/Simulink建立的通用器件耗散功率计算模型,结合器件特性及工作状态参数,仿真计算耗散功率,得到各种极端工作条件下,器件稳态耗散功率值及结点温度的波动范围。通过实验平台测试,验证了此方法的有效性和准确性。定量分析了电网电压、控制时间和开关损耗权重系数等参数改变对器件耗散功率的影响,为设备产品化热设计提供了参考范围及典型值,有利于分配合理的通路热阻,评估变流器热管理的合理性和可靠性。     

基于两段式水煤浆气化的IGCC系统变工况特性

整体煤气化联合循环(integrated gasification combinedcycle,IGCC)机组在一定情况下处于非设计工况运行。为了研究IGCC系统变工况特性,采用ThermoFlex软件建立基于两段式水煤浆气化技术的200 MW级整体煤气化联合循环系统模型,主要考查燃气轮机负荷、整体空分系数Xas、大气温度、大气压力对系统性能的影响。研究结果表明,降低燃气轮机负荷或者提高大气温度系统效率均呈先升高而后降低的趋势。整体空分系数Xas增加,机组发电效率降低。大气压力对系统效率影响较小。上述条件下采用两段水煤浆气化技术,系统性能可以得到有效改善。研究结果可为采用两段式水煤浆气化技术的IGCC系统的设计、运行提供参考。     

基于电热模型的IGBT结温预测与失效分析

针对绝缘栅双极型晶体管(IGBT)工作过程中结温难以测量的问题,提出一种基于IGBT电热模型的结温预测方法,并对由结温过高引起的失效进行实验分析.根据IGBT结构特点建立通态压降模型,考虑到器件内部参数和半导体物理常数与温度的关系,建立IGBT导通功耗与结温关系的电热模型.通过联立IGBT结-壳传热方程和电热模型进行热平衡分析,从而得到稳态时的结温.实验结果表明,通过仿真得到的结温基本与实际测量得到的结温值相吻合,结温过大会导致电极根部焊料熔化和表面连接键丝断裂.所提方法通过监测壳温可实时预测IGBT结温,具有方便快捷的优点.     

张北柔性直流电网交流耗能装置运行特性仿真

为验证利用可控硅将大功率电阻快速投入交流系统的耗能装置能否在投运后安全可靠运行,从而解决张北柔直工程双极性接线故障状况下过负荷造成的线路和设备损毁问题,该工作通过PSCAD电磁暂态仿真软件建立了张北换流站交流耗能装置的电路模型;然后对耗能装置的运行特性进行了分析,并模拟了过剩风能与耗能装置分组投切时系统的电压电流;最后...     

固体继电器受热载荷作用的数值模拟分析

针对固体继电器受热问题,基于热弹性力学理论建立了三维有限元数值模拟分析模型。研究了固体继电器在功率耗散情况下,受热载荷作用时的温度分布和热应力分布,并通过对不同参数下温度和热应力的模拟,初步分析了影响固体继电器热性能的各设计因素。所得的计算结果可为产品的改进提供依据。     

Spray cooling thermal management for increased device reliability

A study has been conducted to quantify the ability of spray cooling to handle transient die power dissipation, as well as to quantify its effect on device reliability. The transient study was conducted with a bare die thermal test vehicle, while the device reliability studies were conducted with a dual Opteron Compact PCI single board computer. For the transient response studies, the high heat transfer coefficients associated with the spray cooling enabled the die to transition from one steady-state point to another in under 2 seconds, when cycling the power delivered to the die between 0 and 94 W. For the device reliability studies, an air-cooled version of the server board was compared to a spray cooled version, for the same clock frequency and supply voltages. For identical conditions, the spray cooled microprocessor processor diode temperature was 33.3/spl deg/C lower, and the die dissipated 35% less power. The paper will present an analysis that explains the manner in which modern microprocessors operate, and will explain the reason for the higher power dissipation associated with the hotter microprocessor.     

含电转热氢装置的综合能源系统经济运行

为解决富余电力对电网的冲击问题,需要为分布式电源配置储能装置,以提高综合能源系统运行经济性。将富余电力转化为氢气已经被证明是有效的处理方法,然而传统的电氢转换效率通常低于70%,且忽略了转换过程中的热损失问题。基于此,首先,介绍了一种考虑热回收的电转氢技术,即电转热氢技术。其次,将电转热氢技术应用于电解槽中,提出了一种含电转热氢装置的综合能源系统模型。同时,以购电成本、购气成本以及富余电力惩罚成本最小为目标,协同考虑电转热氢装置的温度特性,设计了三种不同的工作场景。最后,使用改进粒子群优化算法求解可知,引入电转热氢装置后,系统交易成本降低了1.48万元。算例结果表明,电转热氢装置的加入能够有效提高综合能源系统的经济性,验证了所提模型的有效性。     

基于半导体温差发电模块的锂电池充电装置

研究了半导体温差发电模块输出电压/输出功率与冷热面温度差的关系,并搭建了利用半导体温差发电模块产生的电能作为能量的一种锂离子蓄电池充电装置。首先在实验的基础上,讨论温度差和半导体温差发电模块输出电压及输出功率的关系;然后设计了利用3片温差发电模块工作在温差150K下输出14￣20V不稳定的电源。根据温差发电模块输出电压不稳定的特点,设计了一个稳压电路。最后,用MAX1679芯片实现4.2V锂离子蓄电池的充电电路,该电路具有预充功能,并且完成快充后进入脉冲充电阶段,既能实现完全充电又能减小持续大电流充电造成的损耗。     

基于热管散热的LED器件封装热分析

大功率发光二极管(Light Emitting Diode,简称LED)结点温度的高低汽接影响到LED的寿命和可靠性,故保持LED结温在允许的范围内,是大功率LED封装和应用必须解决的核心问题.提出将扁平热管应用在大功率LED的散热上;比较了扁平热管和铜板两种散热方式下 LED的结点温度和热阻的热特性.研究结果表明,在输入功率为3 W时,热管冷却LED的结点温度为52℃,而铜板冷却LED的结点温度为83℃,对应的系统总热阻分别为8.8 K/W和19K/W.由此证明,在大功率条件下,热管的散热能力明显优于传统的铜板散热.     

大功率LED热管散热器研究

大功率LED的结点温度过高会降低其发光效率和可靠性,并缩短使用寿命,这也是限制LED光源大规模应用的主要瓶颈。为了解决大功率LED芯片的散热问题,本文提出了一种热管与空气强制对流相结合,并采用蜂窝板作为蓄热结构的热管散热装置,建立了三维模型,采用CFD软件对其进行了数值计算,主要研究了热功率、散热片间距和风压对散热器性能的影响。模拟结果表明该散热器能有效地降低大功率LED结点温度,结点温度随输入功率成线性变化,得出了散热片合理的间距,通过综合考虑散热、风机功耗、稳定性等因素,确定风压的值。     

Finite element power diode model optimized through experiment‐based parameter extraction

This paper presents a finite element physics‐based power diode model with parameters established through an extraction procedure validated experimentally. The model core is a numerical module that solves the ambipolar diffusion equation through a variational formulation followed by an approximate solution with the finite element method. Other zones of the device are modeled with classical methods in an analytical module. This hybrid approach enables accurate modeling and simulation of power bipolar semiconductor devices, using standard SPICE circuit simulators, with low execution times. As physics‐based models need a significant number of parameters, an automatic parameter extraction method has been developed. The procedure, based on an optimization algorithm (simulated annealing), enables an efficient extraction of parameters using some simple device waveform measurements. Implementation details of power diode model, in IsSpice simulator, are presented. Experimental validation is performed. Results prove the usefulness of the proposed methodology for efficient design of power circuits through simulation. Copyright © 2008 John Wiley & Sons, Ltd.     

Negative gate-overlap in nanoscaled DG-MOSFETs with asymmetric gate bias

The transfer characteristics of double-gate (DG) MOSFETs are numerically simulated with 2D quantum drift-diffusion (QDD) model. Negative gate-overlap is introduced in devices to optimize the dynamic capacitance characteristics to get the best speed performance. Separate controlling of the back-gate to vary the threshold voltage is investigated, which makes the device convenient to adaptive for more versatile applications, in both high speed and low power dissipation.     

基于IAP WS-IF97的管内阻力件能量损失计算模型与分析

热电厂蒸汽管网普遍存在管道阻力件引起的能量损失。为了准确计算蒸汽流经阻力件产生的可用能损耗,提出了蒸汽管网系统能量计量的新观点,即通过IAPWSIF97的蒸汽状态方程,推导出阻力发生过程的熵方程,得到可用能损失计算模型。校验分析结果表明,用该模型计算蒸汽流经阻力件的能量损失,较传统方法方便、准确。     

Temperature‐dependent modeling and performance analysis of coupled MLGNR interconnects

The temperature‐dependent circuit modeling and performance in terms of propagation delay, power dissipation, and crosstalk‐induced voltage waveform at the far end of victim line of multilayer graphene nanoribbon (MLGNR) interconnects have been analyzed at 22 nm technology node. A comparative performance analysis between MLGNR interconnects with resistance estimated using temperature‐dependent model and temperature‐independent model is examined. The results obtained are also compared with capacitively coupled interconnects of copper (Cu). The results show that as the temperature is varied from 300 K to 500 K, MLGNR has lower propagation delay and power dissipation as compared to Cu for 1 mm long interconnects. It is also observed that because of the dominance of both low resistance and ground capacitance compared to Cu, MLGNR has better crosstalk‐induced delay and voltage waveforms with rise in temperature at the far end of aggressor and victim line, respectively. Further, simulated results show an average relative improvement in propagation delay of 37.24% and corresponding improvement in power dissipation of approximately 19.59% by using a temperature‐dependent model in comparison to a temperature‐independent model of MLGNR resistance with interconnect lengths varying from 200 to 1000 μm. The reduction in the time duration of victim output pulse over these interconnect lengths also shows a significant improvement of approximately 35% by using temperature‐dependent model as against temperature‐independent model of MLGNR resistance.