电磁搅拌对大圆坯结晶器冶金行为影响的探讨

 为了探究结晶器电磁搅拌(M EMS)对大圆坯结晶器内综合冶金行为的影响。以大断面圆坯连铸结晶器冶金行为为研究对象，基于电磁热流体与凝固传输理论建立三维耦合数值模型。揭示大圆坯连铸常用五孔水口浇注条件下结晶器内电磁场、流场、传热与凝固等综合冶金行为，提出电磁搅拌对结晶器冶金性能影响的多参量评价方法。以中碳铬钼齿轮钢650 mm大圆坯连铸为例，指出结晶器电磁搅拌存在最佳搅拌电流，可获得相对较好的综合冶金效果。具体表现为弯月面保持一定的切向速度和过热度，有利于保护渣的熔化和夹杂物的上浮去除；液面波动幅度在控制范围内，可避免卷渣、改善表面质量；结晶器内钢液过热得到有效耗散，有利于等轴晶形核改善铸坯内部质量；侧孔出流钢液速度得到有效控制，可抑制注流对初凝坯壳的冲刷，提高了初生坯壳生长的均匀性。此外，电磁搅拌产生的水平旋流强度也可得到有效控制，有利于避免常见的皮下白亮带现象。     

Design and analysis of an aging‐aware energy management system for islanded grids using mixed‐integer quadratic programming

The rapid increase of renewable energy sources made coordinated control of the distributed and intermittent generation units a more demanded task. Matching demand and supply is particularly challenging in islanded microgrids. In this study, we have demonstrated a mixed‐integer quadratic programming (MIQP) method to achieve efficient use of sources within an islanded microgrid. A unique objective function involving fuel consumption of diesel generator, degradation in a lithium‐ion battery energy storage system, carbon emissions, load shifting, and curtailment of the renewable sources is constructed, and an optimal operating point is pursued using the MIQP approach. A systematic and extensive methodology for building the objective function is given in a sequential and explicit manner with an emphasis on a novel model‐based battery aging formulation. Performance of the designed system and a sensitivity analysis of resulting battery dispatch, diesel generator usage, and storage aging against a range of optimization parameters are presented by considering real‐world specifications of the Semakau Island, an island in the vicinity of Singapore.     

Development of new energy management strategy for a household fuel cell/battery hybrid system

This work aims to construct an efficient and robust fuel cell/battery hybrid operating system for a household application. The ability to dispatch the power demands, sustain the state of charge (SOC) of battery, optimize the power consumption, and more importantly, ensure the durability as well as extend the lifetime of a fuel cell system is the basic requirements of the hybrid operating system. New power management strategy based on fuzzy logical combined state machine control is developed, and its effectiveness is compared with various strategies such as dynamic programming (DP), state machine control, and fuzzy logical control with simulation. Experimental results are also presented, except for DP because of difficulties in achieving real‐time implementation and much faster response to load variation. The given current from the energy management system (EMS) as a reference of the fuel cell output current is determined by filtering out various harmful signals. The new power management strategy is applied to a 1‐kW stationary fuel cell/battery hybrid system. Results show that the fuel cell hybrid system can run much smoothly with prolonged lifetime.     

Energy management system for smart grid: An overview and key issues

Energy crisis and the global impetus to “go green” have encouraged the integration of renewable energy resources, plug-in electric vehicles, and energy storage systems to the grid. The presence of more than one energy source in the grid necessitates the need for an efficient energy management system to guide the flow of energy. Moreover, the variability and volatile nature of renewable energy sources, uncertainties associated with plug-in electric vehicles, the electricity price, and the time-varying load bring new challenges to the power engineers to achieve demand-supply balance for stable operation of the power system. The energy management system can effectively coordinate the energy sharing/trading among all available energy resources, and supply loads economically in all the conditions for the reliable, secure, and efficient operation of the power system. This paper reviews the framework, objectives, architecture, benefits, and challenges of the energy management system with a comprehensive analysis of different stakeholders and participants involved in it. The review paper gives a critical analysis of the distributed energy resources behavior and different programs such as demand response, demand-side management, and power quality management implemented in the energy management system. Different uncertainty quantification methods are also summarized. This review paper also presents a comparative and critical analysis of the main optimization techniques used to achieve different energy management system objectives while satisfying multiple constraints. Thus, the review offers numerous recommendations for research and development of the cutting-edge optimized energy management system applicable for homes, buildings, industries, electric vehicles, and the whole community.     

Short‐Term Wind Power Prediction for Wind Turbine via Kalman Filter Based on JIT Modeling

This paper addresses wind power prediction, which is known to be a key technology in energy management systems. In this paper, a 24‐h‐ahead power prediction method using a filter theory is proposed for wind power generation. The prediction method is a simple algorithm. The procedure of prediction consists of two steps: the data processing and the calculation of the predicted values. In data processing, in order to obtain the correlative data from the database, we employ just‐in‐time modeling. In the calculation of the predicted values, we propose a regression model for wind speed and wind power, and the unknown parameters are estimated using a constrained Kalman filter. Moreover, in the procedure used to estimate the unknown parameters, reduction and convergence of the variables are also guaranteed. Finally, the advantages of the proposed method over the conventional method are shown through actual prediction evaluations.     

Biomechanical risk assessment during field loading of hydraulic stretchers into ambulances

The process of loading a stretcher into an ambulance is known to cause a high incidence of back injuries among paramedics. This study aimed to assess the forces at L5/S1 during real-life stretcher loading activities and to determine the variables that contribute significantly to these forces. Analyses involved 58 paramedics (111 shifts) and 175 stretcher loading activities. Estimates of compression and shear forces at L5/S1 were calculated using the 3DSSPP program. Seventy-one percent of loading activities exceeded the safe loading level of 3.4 kN compression force at L5/S1 (mean: 3.9 kN, min–max: 2.1–7.0 kN). About 92% of the variance can be predicted from a combination of several variables, notably hand load (mean: 0.72 kN/number of paramedics) and back sagittal flexion (mean: 32°). Recommendations to reduce the risk of back injuries are proposed with regard to stretcher and ambulance loading design as well as training in stretcher lifting for paramedics.Relevance to the industryThe results of this study suggest that ambulance stretcher manufacturers should make ergonomic design changes to reduce the physical strain on paramedics’ backs during the process of loading a stretcher into an ambulance. Other preventive measures (e.g., training) must be formulated and applied to reduce the risk of back musculoskeletal disorders during the loading of stretcher patients. For instance, training should focus on back posture, teamwork and equipment/patient positioning on stretchers.     

Comparative study of direct and indirect forging processes for rheological material of A356 aluminium alloy

Abstract

Using a vacuum electromagnetic stirring system, a high quality rheological material is developed in order to fabricate the engineering components without defects like internal porosities, which are caused by the entrapment of external air into the melt and impurities arising from the penetration of surface oxides by vacuum electromagnetic stirring. For practical application in vehicle industry, forming of the knuckle component that is used in automobiles was demonstrated by both direct and indirect type rheoforging processes. Here, insufficient filling behaviour occurred during direct forging processes, whereas indirect rheoforging of material with a solid fraction of 30–40% produced a completely formed knuckle component; thus, an indirect forging process may be suitable for forming the knuckle part. Through microstructural investigations and tensile tests before and after T6 heat treatment of the material, mechanical properties were characterised. By obtaining data about the rheoforging process and material properties of the rheoforged product associated with microstructural features, feasibility for future practical application was investigated. Moreover, the die structure for direct and indirect rheological forging processes was comparatively studied.     

基于能量管理系统的广域备用电源自动投入装置控制策略研究

针对110 kV电网站端的备用电源自动投入(以下简称备自投)装置在实际运行中存在的问题,在基于能量管理系统(energy management system,EMS)的广域备自投控制策略中提出了10 kV单母线分段、双分段四母线备自投,110 kV线路、站间备自投的启动判据和动作逻辑.对备自投装置之间、站端备自投与广域...     

华中电网分布式网络建模与实时信息共享方案

分析了当前调度控制中心网络建模的现状和存在的问题,根据华中电网的运行特点和实际情况,设计了一套分布式网络建模与实时信息共享方案.该方案提出按调度范围实现分布式建模与数据采集的原则,在进行设备命名规范化的基础上,进行网调与省(直辖市)调模型的拼接,形成全网模型.该方案还对模型拼接流程、公共信息模型(CIM)优化方法、实时信息共享等进行了详细说明.     

三电平悬浮斩波器性能研究

采用两电平控制技术的磁浮列车悬浮斩波器由于较大的输出纹波电流引起的悬浮力波动,影响了悬浮控制的精度和稳定性.提出了一种采用三电平控制的悬浮斩波器,分析了其主电路和工作原理,针对输出电流纹波、响应速度、输入电源电压对输出电流的影响等3方面进行了对比仿真分析,并给出了试验验证结果.