多重化双向DC-DC变换器在DCM状态下电感电流纹波研究

本文首先分析了多重化双向DC-DC变换器的工作原理。在频域内分别对单个DC-DC变换器和多重化双向DC-DC变换器在电流断续状态下的电流用Fourier级数展开,导出了电流各次标准化谐波幅值及其比值与占空比的定量表达式。在时域内依据基于多重化结构的双向DC-DC变换器合成总电感电流波形特征导出了多重化双向DC-DC变换器与单个DC—DC变换器电感电流的脉动率比与占空比的定量表达式。定量表达式表明,多重化双向DC-DC变换器与单个DC—DC变换器相比,电感电流纹波及其谐波明显减小。这些定量表达式为大功率DC-DC变换器拓扑结构和工作点的选择提供依据。     

基于微控制器的脉宽调制编码器在轻轨车辆上的应用

脉宽调制编码器(PWM encoder)在铁路动车组和轻轨、地铁车辆上担负着牵引、制动指令传输的重要任务。文章主要阐述了基于微控制器的脉宽调制编码器的设计理念、硬件组成、软件实现及其内部控制逻辑关系。     

Critical assessment of five methods to correct for endogeneity in discrete-choice models

Endogeneity often arises in discrete-choice models, precluding the consistent estimation of the model parameters, but it is habitually neglected in practical applications. The purpose of this article is to contribute in closing that gap by assessing five methods to address endogeneity in this context: the use of Proxys (PR); the two steps Control-Function (CF) method; the simultaneous estimation of the CF method via Maximum-Likelihood (ML); the Multiple Indicator Solution (MIS); and the integration of Latent-Variables (LV). The assessment is first made qualitatively, in terms of the formulation, normalization and data needs of each method. Then, the evaluation is made quantitatively, by means of a Monte Carlo experiment to study the finite sample properties under a unified data generation process, and to analyze the impact of common flaws. The methods studied differ notably in the range of problems that they can address; their underlying assumptions; the difficulty of gathering proper auxiliary variables needed to apply them; and their practicality, both in terms of the need for coding and their computational burden. The analysis developed in this article shows that PR is formally inappropriate for many cases, but it is easy to apply, and often corrects in the right direction. CF is also easy to apply with canned software, but requires instrumental variables which may be hard to collect in various contexts. Since CF is estimated in two stages, it may also compromise efficiency and difficult the estimation of standard errors. ML guarantees efficiency and direct estimation of the standard errors, but at the cost of larger computational burden required for the estimation of a multifold integral, with potential difficulties in identification, and retaining the difficulty of gathering proper instrumental variables. The MIS method appears relatively easy to apply and requiring indicators that may be easier to obtain in various cases. Finally, the LV approach appears as the more versatile method, but at a high cost in computational burden, problems of identification and limitations in the capability of writing proper structural equations for the latent variable.     

Integrated sequencing and merging aircraft to parallel runways with automated conflict resolution and advanced avionics capabilities

Congestion in Terminal Maneuvering Area (TMA) in hub airports is the main problem in Chinese air transportation. In this paper we propose a new system to integrated sequence and merge aircraft to parallel runways at Beijing Capital International Airport (BCIA). This system is based on the advanced avionics capabilities. Our methodology integrates a Multi-Level Point Merge (ML-PM) system, an economical descent approaches procedure, and a tailored heuristic algorithm to find a good, systematic, operationally-acceptable solution. First, Receding Horizontal Control (RHC) technique is applied to divide the entire 24 h of traffic into several sub-problems. Then in each sub-problem, it is optimized on given objectives (conflict, deviation from Estimated Time of Arrival (ETA) on the runway and makespan of the arrival flow). Four decision variables are designed to control the trajectory: the entry time, the entry speed, the turning time on the sequencing leg, and the landing runway allocation. Based on these variables, the real time trajectories are generated by the simulation module. Simulated Annealing (SA) algorithm is used to search the best solution for aircraft to execute. Finally, the conflict-free, least-delay, and user-preferred trajectories from the entry point of TMA to the landing runway are defined. Numerical results show that our optimization system has very stable de-conflict performance to handle continuously dense arrivals in transition airspace. It can also provide the decision support to assist flow controllers to handle the asymmetric arrival flows on different runways with less fuel consumption, and to assist tactical controllers to easily re-sequence aircraft with more relaxed position shifting. Moreover, our system can provide the fuel consumption prediction, and runway assignment information to assist airport and airlines managers for optimal decision making. Theoretically, it realizes an automated, cooperative and green control of routine arrival flows. Although the methodology defined here is applied to the airport BCIA, it could also be applied to other airports in the world.     

CRH动车组列车牵引计算系统研究与设计

动车组列车牵引计算是高速铁路运营和设计过程中的一个基础性环节,研究和开发动车组列车牵引计算系统对于提高高速铁路运营和设计效率具有重要意义.本文依据业务需求,对动车组列车牵引计算系统进行了系统分析和系统设计,并重点探讨了动车组列车牵引计算的计算模型、动车组操纵策略、动车组过分相计算等问题,提出了单质点和多质点相结合的简化计算模型,最后开发了动车组列车牵引计算系统的原型系统.     

浅埋偏压连拱隧道中隔墙合理厚度的确定

以在建大跨、浅埋偏压高速公路连拱隧道具体项目为研究对象,采用基于地层结构的有限单元数值分析方法,对不同厚度的中隔墙进行受力状态分析,提出了该浅埋偏压连拱隧道中隔墙的合理厚度,研究思路可为类似工程提供借鉴。     

南京枢纽新建南京北动车所的必要性及整体布局方案研究

针对国内在新建高速铁路枢纽内,动车组配属及承担动车段(所)动车组检修工作量、检修设施规模的测算结果中表现出的不统一、不协调及不匹配等问题,本文以新建南京枢纽南京北动车所工程项目为依托,研究确定枢纽内动车组配属规模设计、承担动车段(所)动车组检修工作量及检修设施规模测算理论,提出了以全周转时间及日车公里法为指标的2种枢纽...     

Not bored yet - Revisiting respondent fatigue in stated choice experiments

Stated choice surveys are used extensively in the study of choice behaviour across many different areas of research, notably in transport. One of their main characteristics in comparison with most types of revealed preference (RP) surveys is the ability to capture behaviour by the same respondent under varying choice scenarios. While this ability to capture multiple choices is generally seen as an advantage, there is a certain amount of unease about survey length. The precise definition about what constitutes a large number of choice tasks however varies across disciplines, and it is not uncommon to see surveys with up to twenty tasks per respondent in some areas. The argument against this practice has always been one of reducing respondent engagement, which could be interpreted as a result of fatigue or boredom, with frequent reference to the findings of Bradley and Daly (1994) who showed a significant drop in utility scale, i.e. an increase in error, as a respondent moved from one choice experiment to the next, an effect they related to respondent fatigue. While the work by Bradley and Daly has become a standard reference in this context, it should be recognised that not only was the fatigue part of the work based on a single dataset, but the state-of-the-art and the state-of-practice in stated choice survey design and implementation has moved on significantly since their study. In this paper, we review other literature and present a more comprehensive study investigating evidence of respondent fatigue across a larger number of different surveys. Using a comprehensive testing framework employing both Logit and mixed Logit structures, we provide strong evidence that the concerns about fatigue in the literature are possibly overstated, with no clear decreasing trend in scale across choice tasks in any of our studies. For the data sets tested, we find that accommodating any scale heterogeneity has little or no impact on substantive model results, that the role of constants generally decreases as the survey progresses, and that there is evidence of significant attribute level (as opposed to scale) heterogeneity across choice tasks.     

Modelling contact mode and frequency of interactions with social network members using the multiple discrete–continuous extreme value model

Communication patterns are an integral component of activity patterns and the travel induced by these activities. The present study aims to understand the determinants of the communication patterns (by the modes face-to-face, phone, e-mail and SMS) between people and their social network members. The aim is for this to eventually provide further insights into travel behaviour for social and leisure purposes. A social network perspective brings value to the study and modelling of activity patterns since leisure activities are influenced not only by traditional trip measures such as time and cost but also motivated extensively by the people involved in the activity. By using a multiple discrete-continuous extreme value model (Bhat, 2005), we can investigate the means of communication chosen to interact with a given social network member (multiple discrete choices) and the frequency of interaction by each mode (treated as continuous) at the same time. The model also allows us to investigate satiation effects for different modes of communication. Our findings show that in spite of people having increasingly geographically widespread networks and more diverse communication technologies, a strong underlying preference for face-to-face contact remains. In contrast with some of the existing work, we show that travel-related variables at the ego level are less important than specific social determinants which can be considered while making use of social network data.     

船舶自动识别系统的信息传输

AIS的信息传输采用自组织时分多址技术。讨论基于这种技术的AIS信息传输格式、系统的同步、传播时延和保护时间等问题 ,分析了由保护时间限定的系统最大传播距离和岸台天线最大高度的计算方法。