直流电网阻抗建模与振荡机理及稳定控制方法

维持直流母线电压稳定是直流电网高效、安全、稳定运行的前提。多个电压源变换器(Voltage Source Converter,VSC)经下垂控制接入直流电网,下垂控制等效于在VSC直流端口增加虚拟电阻,实现多VSC之间的功率分配的同时增加了系统阻尼。但研究发现,采用直流电压下垂控制的VSC,其输出阻抗会在电压控制带宽外呈现负阻性,该负阻抗会与线路阻抗、负载输入电容及恒功率负载(Constant Power Load, CPL)相互作用,引起直流系统振荡。针对此问题,建立了典型的单母线直流电网系统小信号模型,分析了直流系统的稳定性。提出一种虚拟阻容性阻抗的稳定控制方法,使得VSC输出阻抗在电压控制带宽外保持较大的正阻性,抑制直流系统的振荡。同时所提方法能够增大VSC直流端口的容性阻抗,增强直流系统的惯性,提升母线电压抗负载波动的能力。最后,仿真验证了所提控制方法的正确性和有效性。     

Multi-Objective Approach for Reconfiguration of Distribution Systems with Distributed Generations

This paper presents a fuzzy multi-objective based heuristic algorithm for network reconfiguration of distribution systems considering distributed generations (DGs). The objectives of reduction of real power loss, branch current carrying capacity limit, maximum and minimum voltage constraints, and feeder load balancing are considered for performance enhancement of the distribution system. Since these objectives are non-commensurable and difficult to solve simultaneously using conventional approaches, they are converted into fuzzy domain and a fuzzy multi-objective function is formulated. A sensitivity analysis based on voltage profile improvement and real power loss reduction is used for obtaining optimal locations of DGs and genetic algorithm is used for optimal sizing of DGs. The proposed reconfiguration algorithm is implemented in two stages, initially in the first stage without incorporating DGs and in the second stage incorporating DGs for obtaining an optimal distribution system network reconfiguration. The advantage of the proposed method is demonstrated through a seventy node four feeders and a sixteen node three feeders distribution systems.     

Agglomeration,Differentiation and Creative Milieux: A Socioeconomic Analysis of Location Behaviour of Creative Enterprises in Shanghai

This paper presents an empirical study on the location choice of creative enterprises in Shanghai. It is suggested that categorical differences between different subsectors of creative industries are significant, especially with regard to a division between technology-intensive sectors and culture-related agencies. Creative enterprises from technology-intensive sectors such as architecture design and IT enterprises appear to differ greatly from cultural and fashion related agencies in location choice due to the disaggregated knowledge inputs involved in the production processes, as well as the divergences in market operation. Meanwhile, this study suggests that some location variables for creative industries (e.g. human capital and face-to-face contact) highlighted by West-based studies on the “creative class” are relevant in the case of Shanghai while other factors like sexual tolerance bear minor importance.     

Systems,habitats or places: evaluating the potential role of landscape character assessment in operationalising the ecosystem approach

A key challenge for research and practice is to understand how the ecosystem approach can be rolled out in spatial planning, management and decision-making. Any framework used to apply the ecosystem approach needs to not only be environmentally coherent but also socially meaningful. Drawing on semi-structured interviews and case studies, this paper examines the potential role of one place-based approach, landscape character assessment, as a medium to ensure socio-ecological relevance in operationalising the ecosystem approach. Our findings show that although place-based approaches have value as frameworks for distilling the ecosystem approach into a manageable form, their ecological relevance is a subject of debate. However, the potential relationship between landscape character, function and ecosystem services presented a powerful pathway for operationalising the ecosystem approach. The ecosystem approach may, in turn, complement landscape character assessment by providing a framework for exploring the functional dimension of landscape condition.     

On pre-filling probability of flood control detention facilities

Flood control detention facilities are widely used for stormwater control in urban areas. Standard design procedures are in most cases based on the design storm approach: a single flood event at a time is considered, at the beginning of which the facility is assumed completely empty. The possibility of pre-filling from previous events is then neglected and underestimation of storage volume may occur. In this paper an analytical probabilistic approach to estimate the probability of pre-filling is presented and its effects, due to outflow rate and storage volume, are investigated. Two different strategies for the outlet control are analysed. Results are validated on a case study.     

Multi-scale damage analysis for a steel box girder of a long-span cable-stayed bridge

Accurate evaluation of the effect of possible damage in critical components on the dynamic characteristics of a structure is of critical importance in developing a robust structural damage identification scheme for a long-span cable-stayed bridge. The strategies of finite element (FE) modelling of a long-span cable-stayed bridge for multi-scale numerical analysis are first investigated. A multi-scale model of the Runyang cable-stayed bridge is then developed, which is essentially a multi-scale combination of a FE model for modal analysis of the entire bridge structure and FE sub-models for local stress analysis of the selected locations with respect to the substructuring method. The developed three-dimensional global-scale and local-scale FE models of Runyang cable-stayed bridge achieve a good correlation with the measured dynamic properties identified from field ambient vibration tests and stress distributions of a steel box girder measured from vehicle loading tests, on the basis of which the effectiveness of some damage location identification methods, including a modal curvature index, a modal strain energy index and a modal flexibility index, are evaluated. The analysis results show that the effect of the simulated damage in various components of the steel box girder on the dynamic characteristics of a long-span cable-stayed bridge should be properly considered in structural damage analyses using multi-scale numerical computation.     

沈阳市城区老年人春季出行活动特征研究

在老龄人口急剧增加的今天,在城市规划及建筑设计领域,依据老年人生活行为特征进行适老化设计的研究日益成为被关注的焦点。本研究运用活动日志调查法对沈阳市城区老年人春季24h行为活动进行调查,并运用活动分析法对调查到的老年人出行相关信息进行分析,进而指出在时空约束下,沈阳市城区老年人春季出行活动特征及移动一活动行为模式。     

绿色施工在工程项目中的应用

结合工程实践介绍绿色施工主要途径、方法和措施,探索建立绿色施工的发展模式,发挥绿色施工的引领和示范作用,实现"四节一环保"。     

Extending and operationalizing construction productivity measurement on building projects

Measuring construction productivity in an accurate, repeatable and reliable way represents a significant problem at a building project level of enquiry. The research develops a measurement framework that balances simplified data gathering against explanatory ability. It aims to assist analytically driven process improvement. Debate and discourse are used to draw upon the extant literature in creating a logic-based flow of ideas to develop the framework. Targeted use of empirical cost and site process data from case studies are presented to punctuate the discourse. The derived approach advocates multifactor measurement inclusive of labour and temporary production infrastructure inputs, set against Gross Floor Area outputs. Emphasis is placed on separately measuring homogenous and heterogeneous parts of work processes. A reductionist approach is used to operationalize measurement where projects are categorized according to fitness-for-purpose criteria and links made between systems, activities and tasks. Emphasizing measurement of homogenous parts of the work is new to the literature. It enables delineated measurement between work involving mass economies of scale (homogenous work), versus customized work (heterogeneous work). The approach enables improved benchmarking, diagnostic and predicative options. A course of ongoing research is provided to assist ongoing development and implementation.