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关键词： Microchannel heat sink   Flow boiling heat transfer   R245fa   Liquid cooling technology  

摘要： Two-phase microchannel heat sink has received extensive attention due to its small size, high heat transfer efficiency, good temperature uniformity, and low working fluid charge. Heat flux and mass flow rate are important parameters that affect the heat transfer performance of two-phase microchannel heat sink. For different heat fluxes, if the mass flow rate is not reasonable, dry-out may occur, which will significantly reduce the heat transfer performance. In order to further explore the influence of mass flow rate and heat flux on heat transfer characteristics, the flow boiling heat transfer performance and flow regimes under different mass flow rates and heat fluxes were studied for a two-phase microchannel heat sink using R245fa as the working fluid. The results showed that when the mass flow rate was 100 kg/(m(2)center dot s), the boiling heat transfer coefficient of R245fa showed a trend of increasing firstly and then decreasing with the increase of the heat flux. At a higher heat flux, the local dry-out in the microchannels began to appear, and the heat transfer performance decreased significantly. And the higher the heat flux was, the more serious the dry-out was. There was no obvious dry-out phenomenon when the mass flow rate was 150-300 kg/(m(2)center dot s) and the heat flux was below 500 kW/m(2). The research provided a valuable reference for exploring the influence of the mass flow rate and the heat flux on the flow boiling heat transfer characteristics of the microchannel heat sink. (c) 2023 Elsevier Ltd. All rights reserved.

关键词： IGBT solder layer   packaging reliability   interconnection technology   thermal conductivity characteristics   thermal-mechanical coupling  

摘要： The insulated-gate bipolar transistor (IGBT) represents a crucial component within the domain of power semiconductor devices, which finds ubiquitous employment across a range of critical domains, including new energy vehicles, smart grid systems, rail transit, aerospace, etc. The main characteristics of its operating environment are high voltage, large current, and high power density, which can easily cause issues, such as thermal stress, thermal fatigue, and mechanical stress. Therefore, the reliability of IGBT module packaging has become a critical research topic. This study focuses on the damage of power device solder layers and applies heat transfer theory. Three typical solders for welding IGBTs (92.5Pb5Sn2.5Ag, Sn3.0Ag0.5Cu (SAC305), and nano-silver solder paste) are analyzed using JMatPro software to simulate their characteristics. First, a finite element analysis method is used to simulate the entire IGBT module with ANSYS Workbench platform. The study compares the impact of three types of solders on the overall heat transfer of the IGBT module under normal operation and welding layer damage conditions. The characteristics are analyzed based on changes in the junction temperature, heat flow path, and the law of thermal stress and deformation. The findings indicated that under steady-state working conditions, adjacent chips in a multi-chip IGBT module had significant thermal coupling, with a maximum temperature difference between chip junctions reaching up to 13 degrees C, and a phenomenon of heat concentration emerged. The three types of solders could change the thermal conductivity and heat transfer direction of the IGBT module to varying degrees, resulting in a temperature change of 3-6 degrees C. Under conditions of solder layer damage, the junction temperature increased linearly with the severity of the damage. In the 92.5Pb5Sn2.5Ag and Sn3.0Ag0.5Cu (SAC305) solders, the presence of intermetallic compounds (IMCs) led to more stress concentration points i

关键词： 绝缘栅双极型晶体管并联   串联电感   对偶原理   均流   缓冲电路  

摘要： 多个绝缘栅双极型晶体管(insulategatebipolar transistor,IGBT)并联是大功率电力电子应用领域提高设备电流等级的一条重要途径,而实现IGBT之间的并联均流则是保证其安全稳定运行的关键。文章在对IGBT串联均压缓冲机理研究的基础上,从在IGBT两端并联电容可降低电压变化率的原理出发,推断出可通过串联电感来抑制IGBT电流的变化,进而应用对偶原理构建出一类基于串联电感的并联均流缓冲电路及其改进型拓扑。结合模态图从理论上分析新型缓冲电路工作原理,发现所提出IGBT并联均流缓冲电路具备结构简单、易于实现的优点,还兼具静态和动态均流效果。仿真和实验表明所提出方法可以有效抑制过电流,降低电流不均衡度。

关键词： 无刷直流电机   矢量控制   粒子群算法   PID控制器   闭环控制  

摘要： 无刷直流电机具有运行效率高、调速性能好、结构简单、维护方便、运行可靠的优点,是电动汽车驱动系统的理想动力来源;然而,目前电机控制器响应速度慢、控制精度低、稳定性误差大、抗干扰力弱;为了解决这些难题,通过建立无刷直流电机的数学模型,研究电机的矢量控制算法基本原理以及实现方式,设计出了电流、转速双闭环的调速控制系统,通过引入先进的控制策略来提高控制器性能;最后,在电机的阶跃响应测试中,采用传统PID控制器作为转速控制外环的矢量控制策略,在稳定时间以及超调量两个方面,都不如SPSO-PID控制器;不管是从0转速时刻启动,还是转速突变的情况,传统PID控制器的超调量基本都在10%以上,SPSO-PID控制器的超调量基本控制在5%以内;实验结果表明,与传统PID控制相比,在相同的调整频率下;本次设计的控制器具有调节时间小,调速范围广,转速波动小的优点,验证了设计的可行性。

关键词： 变频器与伺服驱动   模块化   层次化   教学改革  

摘要： 随着职业教育改革深入,越来越多的高职院校开展现代学徒制人才培养模式改革,针对百色职业学院电梯工程技术专业《变频器与伺服驱动》课程存在问题,以培养职业能力为目标,坚持德技并修,采取基于“分层递进,模块设计、技能强化、创新引领”的理念,对教学内容、评价指标进行重构设计,根据学生的认知规律,把内容设计为四个模块化、四个层次,采用过程性评价的方法评价学生学习效果。从人文素养、社会技能、自主学习、意志品质、钻研精神等方面思政元素,充分挖掘课程的思政元素,进行全方位育人,达到培养电梯工程技术专业具有爱国情怀、职业素养及高技能人才的目标。

关键词： 半桥型激光器   异常功率数据   数据采集   K-Means算法   特征提取  

摘要： 为提高异常功率采集稳定性及准确性,增强工业企业加工工艺水平,研究半桥型IGBT连续激光器异常功率数据采集技术。采集半桥型IGBT连续激光器功率数据;应用K-Means算法聚类采集到的激光器功率数据,并提取聚类后激光器功率数据的偏度、峭度、功率谱比值特征;以提取到的激光器功率特征为输入,构建卷积神经网络异常功率识别模型,通过执行参数初始化、向前传播输入、向后传播误差以及反复迭代操作后,结合置信区间,判断输出连续激光器异常功率数据异常与否,完成半桥型IGBT连续激光器异常功率采集。实验结果表明:该方法可以实现半桥型IGBT连续激光器功率数据特征提取以及异常功率采集,异常功率采集的稳定性、准确性以及效率均较高。

关键词： 异步电动机   永磁同步电动机   矢量控制   教学设计  

摘要： 交流电机的矢量控制技术为当今电气传动领域的支撑技术之一,对机电一体化技术、自动化技术的发展有着重要影响。由于该理论与技术的重要性,相关知识的传播与推广很早就引起了人们的重视。在高等院校里,交流电机矢量控制技术几十年来经历了从研究生教育到普及化教育的过程。针对当前交流电机矢量控制理论在教学中存在的一些弊端以及教学中的重点、难点问题,提出了一些应对措施与教学方法的建议。

关键词： 变频器   电力系统   干扰  

摘要： 变频器是电力系统中最为重要的控制设备之一。如变频器在使用中会受到多种因素干扰,导致对电力系统的控制能力出现下降。部分因素对变频器的干扰最终会使电力系统无法正常运转,严重的导致多种安全隐患问题出现,甚至造成电力系统的安全事故出现。因此工作人员需要积极的寻找解决各种问题的方法,探究对变频器造成影响因素的消除,制定全新的解决方案,考虑解决方案的合理性与科学性,防止再次引发故障问题。

关键词： 变频器   焦化   干熄焦   提升机  

摘要： 为探讨变频器在焦化干熄焦提升机上应用时的故障,采用理论结合实践的方法,立足变频器在焦化干熄焦提升机上应用时常见的故障,来分析变频器的结构组成和运行原理,并提出常见故障的解决方法。分析结果表明,在焦化干熄焦提升机上应用变频器,可实现对提升机的自动化、智能化控制,精确调整提升机的运行速度,降低能耗。但变频器长期在恶劣的环境下运行,难免会出现一些故障,影响焦化干熄焦提升机运行的可靠性,需要结合故障的成因,选择有针对性的解决方法,才能发挥出变频器的作用和功能,提升生产效率,获得更大的经济效益。