A Fast Non-Unit Protection Method Based on S-Transform for HVDC Line

To overcome the problems existing in the main protection of HVDC transmission lines, such as low reliability and poor ability of resisting high ground resistance fault, this paper proposes a novel non-unit protection method based on S transform. Analysis shows the high and low frequency components of the transient voltage signals suffer from different degrees of attenuation when they pass through the HVDC line boundary. Therefore, according to this characteristic, the voltage signals of specific frequency bands are extracted accurately using S transform, which be used to identify the internal from external faults. By comparing the high and low frequency components generated by the lightning disturbance with those generated by the faults, S transform based energy ratio criterion to identify lightning disturbance is constructed. In addition, for a bipolar HVDC transmission system, a method using the 0 Hz energy difference of S transform of the voltage transient signals is proposed to identify the faulted pole. Simulation results verify the feasibility and validity of the proposed protection method.     

A Geometric Mapping Cross Approximation method

The matrices of Boundary Element Method (BEM) are fully populated and require special compression techniques for the efficient treatment. In this article, the H-matrix representation is used to approximate the dense stiffness matrix in admissible blocks by low-rank matrices. This paper presents a Geometric Mapping Cross Approximation (GMCA) algorithm to compute the low-rank matrices. Compared with the Adaptive Cross Approximation (ACA), the GMCA determines the skeleton points from the two interacting groups of nodes by their spacing characteristics directly and, thus, has a remarkable non-iterative nature and requires some simple geometric transformations, only. Numerical examples show that the new algorithm is feasible.     

化学沉淀法表面修饰重钙及其在PVC中的应用

作为一种重要的无机填料,研磨重钙的尖锐的棱角和较大的晶体解理面影响了其应用效果,限制了其应用范围。本研究采用化学沉淀法对重钙进行表面修饰,改变了其微观结构和表面性能。温度为20?     

基于FPGA的国产MSA009加速度计测试系统设计

针对国产MEMS加速度计MSA009的工作原理和输出特性,设计了一种测试系统,以Spartan Ⅱ系列的XC2S30为主控芯片,并结合外围电路搭建了测试系统;基于ISE 8.1平台,采用VHDL硬件描述语言实现了对A/D转换芯片和Flash的控制,完成了加速度计输出信号的实时采集与存储;利用高精度三轴位置速率转台对测试系统进行试验验证,并对所采集的数据进行分析处理;经试验论证,该测试系统实现了对MSA009加速度计的测试,具有良好的实用性、稳定性.     

利用水平井技术提高欢西油田稠油储量动用潜力研究

欢西油田薄层稠油估算地质储量800×10~4 t,占稠油总储量的6.6%,由于油质稠、油层薄或受边底水的影响,利用直井开发无法实现经济有效开发。2007年以来,通过水平井开发技术研究,形成了一系列水平井开发薄层稠油的主要技术,可有效解决利用直井开发薄层稠油所遇到的各种难题,现场实施取得了较好的开发效果。     

锻件加热规范的制订

介绍了钢质锻件加热规范有关内容的理论计算公式，采用理论和实践相结合的方法，制订了具有实用性和可操作性及可达到优质、高效和低耗效果的锻件加热规范，以用于指导实际生产中锻件加热温度的控制。     

Towards Floor Identification and Pinpointing Position: A Multistory Localization Model with WiFi Fingerprint

International Journal of Control, Automation and Systems - The era of Internet of Things (IoT) has stimulated the diversification of wireless applications, and a pragmatic way is to adopt and...     

一种适用于高量程加速度计的标定方法研究

针对传统重力场标定方法的输入激励只能在±1g之间,无法满足高量程加速度计在满量程内标定需求的问题,提出了一种适用于高量程加速度计标定方法.首先,分析了标定原理与误差来源并建立了加速度计误差补偿模型,其次,设计了适用于高量程加速度计的十二位置标定方案并推导出标定参量计算方法,最后,通过精密离心机进行试验验证了标定方案的可...     

基于改进滑模观测器的永磁同步电机无位置传感器I／F起动方法

针对传统的永磁同步电机无位置传感器开环起动过程中存在启动电流大、功率因数小、抗负载扰动能力弱的问题,提出了一种基于改进滑模观测器的无位置传感器电流闭环I/F起动策略。起动加速阶段,在电枢绕组中产生幅值固定、频率逐渐增大的旋转电流矢量,使转子加速起动。当转速达到设定值时,检测指令位置角与用改进滑模观测器估算的转子位置角之间的偏差角,当该偏差角低于设定的阈值时,立刻切换至基于改进滑模观测器的无位置传感器电流解耦控制阶段。仿真和实验结果表明,采用所提起动策略后,起动电流可控,切换时刻的电流、转矩平稳无冲击。实验结果也验证了该起动策略能有效避免过流的产生,具有良好的动态性能和一定的抗负载扰动能力。     

叠层橡胶隔震支座的研制

叠层橡胶隔震支座是新型建筑隔震元件。研究了该支座的胶料配合,硫化工艺,结构设计及安装方法等。通过国家权威试验室测定,其胶料性能及产品力学性能均满足设计要求。