基于改进型二阶广义积分器的同步信号检测

为了满足三相电压在不对称、直流分量及谐波畸变等情况下并网变换器的控制需求,需要准确地检测出电压信号的正序分量、幅值和基波频率。基于双二阶广义积分器锁频环的方法可实现电压在不对称和畸变下同步信号的提取。但当电压信号含有直流分量和多次谐波时,基本的SOGI结构滤波效果不理想,追踪的波形波动比较大,并降低了追踪速度。文中介绍一种改进的SOGI结构,该结构在SOGI的基础上增加求差节点和自适应滤波器,并保留SOGI-FLL的优势。电压的幅值和基波频率能准确快速被检测出来,很好的减小频率跳变后的波动、滤除谐波和消除直流分量。MATLAB仿真结果表明,其改进方法在电压信号不对称、直流分量及多次谐波存在条件下准确地检测出正序分量和基波频率。     

基于支护预应力场的松软围岩锚杆支护护表构件优选

针对石窟煤业松软围岩锚杆支护效果差的问题,采用实验室仿真试验对钢筋托梁、W钢护板2种护表构件的支护预应力场进行监测,得出各护表构件在支护围岩各区域的应力分布差异。试验结果显示,锚杆支护预应力场沿杆体由上至下形成“拉—压—压”的应力集中区分布格局,因表面接触方式不同,2种构件支护预应力场主要在围岩浅部压应力作用区域产生差异;在100 kN预紧力下,钢筋托梁、W钢护板的支护预应力在围岩表面峰值分别为0.8、0.6 MPa,W钢护板产生的0.15、0.05 MPa压应力区域面积较钢筋托梁分别增加41.67%、21.69%。W钢护板支护预应力在围岩表面分布更为平均,预应力整体扩散范围更高,可有效适应于松软围岩。将试验结论在现场进行了工业性试验,获得了较好的支护效果。     

风电机组变流器电流谐波水平案例分析

直驱机组全功率变流器的使用,一定程度上影响了机组馈入电网的电能质量。针对两类1.5MW直驱并网风力发电机组,从整机角度上描述了机组配置,比较了I型变流器、II型变流器的拓扑结构与控制原理。依据IEC标准检测方法,通过现场实测,对比研究了这两类机组电流谐波、间谐波、高频分量的释放水平及特征。结果表明,变流I型、变流II型机组电流谐波释放水平均符合并网要求,变流I型机组电流谐波水平2.52%低于变流II型机组3.44%。     

三相有源滤波器直流侧电容与电压波动关系分析及设计

有源滤波器的直流侧通常配置很大的电解电容,电解电容器的电压纹波额定值较低,损耗较大,应对电容值做出合理选择以避免内部发热。面对大容量的谐波补偿要求,并联有源滤波器(Shunt Active Power Filter,SAPF)需要进一步降低系统体积和成本。针对电容值与直流电压纹波关系这一问题,分析了三相SAPF补偿系统的瞬时功率流动,得到对直流电压波动有影响的功率分量,并在特定的负载条件下求取了振荡功率的积分值,得到电容能量波动的精确值,提出了一种考虑电容纹波电压关系的电容容量优化设计方法。利用MATLAB仿真模型并与其他文献比较,验证了所提思路及结果的正确性及有效性。     

基于EEMD-AR模型的丹江口水库年径流随机模拟与预报

基于水库历史年入库径流序列组分分析和识别,采用线性趋势回归检验法、有序聚类法、方差线谱法等方法,推求出序列趋势项、跳跃项及周期项等确定性成分,提出基于集合经验模态分解法(EEMD方法)的水库年径流自回归随机模拟模型(EEMD-AR),并应用于丹江口水库的年径流随机模拟和预报中。通过EEMD分解,解决了当丹江口水库历史年径流序列为非平稳序列时不能直接应用自回归模型(AR)进行随机模拟和预报的问题。模拟结果表明,EEMD-AR模型能较好地模拟丹江口水库年径流序列并保持原历史序列的统计特性,且模型预报精度符合要求。     

表面工程技术在海洋工程装备中的应用

随着我国对海洋资源开发和利用的快速发展,对先进海洋工程装备的需求日益强烈,尤其是对某些关键部件的表面性能要求越来越高。然而,单从提高材料自身性能的角度来满足对高性能的要求几乎是不可能的。表面工程技术是提高材料表面性能的重要方法,它能够在不破坏材料自身性能的前提下,对材料表面性能进行强化或再生,使材料或部件表面具备耐磨、耐蚀、抗氧化、耐热、绝缘、密封和隔热等性能中的一种或几种。因此,表面工程技术已成为实现海洋工程装备材料最终性能的重要手段。对海洋工程装备中涉及到的材料表面改性技术、应用和发展进行了综述。最后,指出了一些重要问题,展望了将来的研究方向。     

飞机刹车组件液压试验台设计

飞机刹车组件是飞机制动系统中的一个重要部件。针对其性能测试要求,设计了测试飞机刹车组件性能的液压试验台。该试验台可以对飞机刹车组件进行排气功能、高压保压功能、往复试验功能、低压保压功能、测间隙功能、微压保压功能等性能进行测试。为了满足被测试压力范围极为宽泛和液压阀切换的可靠性要求,采取了3套独立的供油系统。针对具体的测试环境和性能要求,在设计上重点解决了几个关键问题。结果表明,该试验台能够满足测试要求。     

龙门加工中心功能部件时序分布优化研究

为了优化龙门加工中心功能部件动作时序以提高生产效率,按照功能－运动－动作对龙门加工中心进行结构化分解,根据结构化分解和符号有向图提出了龙门加工中心功能部件动作模型。在模型分析过程中引入甘特图技术,辅助龙门加工中心换头换刀动作的设计工作。采用PMC控制结合宏程序的方法,实现新动作的立卧刀库换刀电气控制,提高了功能部件动作效率。     

Neutron computed tomography of plasma facing components for fusion experiments

In nuclear fusion experiments, divertor plates are used to remove energy and particles from the plasma. These divertor plates can be made of water-cooled copper heat sinks covered by carbon fiber composite (CFC) protection tiles. During operation, surface temperatures in excess of 1000 °C are reached for typical heat loads of 10 MW/m². The large mismatch in the coefficients of thermal expansion for CFC and Cu causes high stresses and possibly bonding defects. Growing joint defects, which lead to unacceptable overheating of the protection tiles, are critical for the lifetime of the components.A prototype component was subjected to 10,000 cycles at 10 MW/m² to study the crack growth mechanism. Neutron computed tomography offers the possibility to analyze such structures on centimeter-sized samples non-destructively with a high spatial resolution. At the ANTARES neutron imaging facility of the FRM II reactor, the samples were loaded with a contrast agent and examined with neutron computed tomography.     

Concept selection of car bumper beam with developed hybrid bio-composite material

Application of natural fibre composites is going to increase in different areas caused by environmental, technical and economic advantages. However, their low mechanical properties have limited their particular application in automotive structural components. Hybridizations with other reinforcements or matrices can improve mechanical properties of natural fibre composite. Moreover, geometric optimizations have a significant role in structural strength improvement. This study focused on selecting the best geometrical bumper beam concept to fulfill the safety parameters of the defined product design specification (PDS). The mechanical properties of developed hybrid composite material were considered in different bumper beam concepts with the same frontal curvature, thickness, and overall dimensions. The low-speed impact test was simulated under the same conditions in Abaqus V16R9 software. Six weighted criteria, which were deflection, strain energy, mass, cost, easy manufacturing, and the rib possibility were analyzed to form an evaluation matrix. Topsis method was employed to select the best concept. It is concluded that double hat profile (DHP) with defined material model can be used for bumper beam of a small car. In addition, selected concept can be strengthened by adding reinforced ribs or increasing the thickness of the bumper beam to comply with the defined PDS.