峰值电流控制的PFC变换器快时标分岔控制

峰值电流控制方式是PFC开关变换器的一种常用方式,由于输入电压的时变性造成在输入交流电压过零点处出现输入交流电流的快时标分岔现象,该现象会严重影响PFC变换器的性能,因此采用一种合理有效的分岔控制手段是非常重要的。文中深入分析了峰值电流控制PFC变换器工作原理,从理论上分析了PFC变换器出现快时标分岔现象的根源。在谐振分岔控制理论的基础上提出了一种比较有效的控制器参数选择方法,可以较好地实现PFC变换器的快时标分岔控制,因此改善了PFC变换器的性能。理论结果得到了数值仿真分析和实验的验证。     

Regional-scale electric power system planning under uncertainty—A multistage interval-stochastic integer linear programming approach

In this study, a multistage interval-stochastic regional-scale energy model (MIS-REM) is developed for supporting electric power system (EPS) planning under uncertainty that is based on a multistage interval-stochastic integer linear programming method. The developed MIS-REM can deal with uncertainties expressed as both probability distributions and interval values existing in energy system planning problems. Moreover, it can reflect dynamic decisions for electricity generation schemes and capacity expansions through transactions at discrete points of a multiple representative scenario set over a multistage context. It can also analyze various energy-policy scenarios that are associated with economic penalties when the regulated targets are violated. A case study is provided for demonstrating the applicability of the developed model, where renewable and non-renewable energy resources, economic concerns, and environmental requirements are integrated into a systematic optimization process. The results obtained are helpful for supporting (a) adjustment or justification of allocation patterns of regional energy resources and services, (b) formulation of local policies regarding energy consumption, economic development, and energy structure, and (c) analysis of interactions among economic cost, environmental requirement, and energy-supply security.     

超高压裂缝型气藏分层压裂技术及应用

塔里木油田A气藏埋藏深、压力高、应力大、天然裂缝发育\,储层厚度大,是典型的超高压裂缝型气藏。储层笼统压裂效果差,采用分层压裂改造技术,取得较好的效果。针对超高压深井裂缝型气藏分层压裂难度大的特点,优选完井封隔器+压裂封隔器+滑套作为分层压裂工具;采用测井地应力解释和优化射孔模拟方法,进行分层优化;密度为1.32g/cm³的加重压裂液体系能降低井口施工压力;使用高压施工设备,能满足地面高施工压力的要求。针对超高压深井裂缝型气藏分层改造技术的研究和认识,对类似气藏改造有借鉴和推广作用。     

基于改进三线性流模型的多级压裂页岩气井产能影响因素分析

页岩气多级压裂形成的复杂裂缝网络会改变其原有的气体渗流模式,形成多个独有的流动阶段。因此,常规的产能模型不能有效模拟其压力、流量变化规律。为了增加页岩气产能模拟精度和对压裂施工优化做出指导,在耦合三线性渗流和球形双重介质渗流模型的基础上,考虑解吸和滑脱等机理,建立了改进的三线性流产能预测模型,并进行了解析求解和数值反演。计算结果表明,页岩气的解吸对提高单井产能,延长稳产期具有重要意义;储层中的微裂缝能够通过控制气体在基质与人工裂缝之间的窜流最终影响页岩气井产能;人工裂缝导流能力对页岩气井产能的影响覆盖了整个生产周期的中前段,然而随着人工裂缝导流能力的增加,产能的增长幅度变缓,证明了页岩气藏不需追求高导流能力裂缝的理论,缝间距主要影响线性流时间的长短;汇聚效应在投产初期对产能具有不可忽视的影响。研究结果对于深化页岩气井生产动态认识和提高页岩气藏开发效率具有重要意义。     

Quantitative assessment of retained austenite in quenching and partitioning treated multiphase steel

For multiphase steel, an efficient and accurate quantitative analysis of constituent phases is critical in understanding the mechanical mechanism and optimising its properties. A method based on image digitisation and the concept of categorised linear interception has been proposed to study the amount of retained austenite (RA) residing in different phases in quenching and partitioning treated multiphase steel. It was found that RA at different locations transformed in different strain stages due to considerable influence from the surrounding phases, and the stability of each type of RA was estimated according to the above mentioned method. The proposed multistage transformation was proved to be more accurate than a single stage stability model.     

Modeling of switching frequency instabilities in buck‐based DC–AC H‐bridge inverters

In this paper, the dynamical behavior of a full bridge DC–AC buck inverter controlled by fixed frequency and PWM is studied. After showing that the system can undergo both period‐doubling and Neimark–Sacker bifurcation at the fast scale (switching period) by using the exact switching model, an exact solution discrete‐time model able to predict both instability phenomena is derived. The model is obtained without making the quasi‐static approximation and it can be used to obtain the useful operation region in the multi‐dimensional design parameter space from time domain simulations in a very fast and accurate manner. Based on the study of the system, some design guidelines are provided. Copyright © 2010 John Wiley & Sons, Ltd.     

DG integrated multistage distribution system expansion planning

In this paper, a framework is presented to solve the problem of multistage distribution system expansion planning in which installation and/or reinforcement of substations, feeders and distributed generation units are taken into consideration as possible solutions for system capacity expansion. The proposed formulation considers investment, operation, and outage costs of the system. The expansion methodology is based on pseudo-dynamic procedure. A combined genetic algorithm (GA) and optimal power flow (OPF) is developed as an optimization tool to solve the problem. The performance of the proposed approach is assessed and illustrated by numerical studies on a typical distribution system.     

Transversal thermal patterns in packed‐bed reactors with simple kinetics: Bifurcation criterion and simulations

We derive a new criterion for transversal instability of planar fronts based on the bifurcation condition dV_f/dK|_K=0 = 0, where V_f and K are the front velocity and its curvature, respectively. This refines our previously obtained condition, which was formulated as α = (ΔT_adPe_T)/(ΔT_mPe_C) > 1 to α > 1 + |δ|, where ΔT_ad and ΔT_m are the adiabatic and maximal temperature rise, respectively, Pe_C and Pe_T are the axial mass and the heat Pe numbers, respectively, and δ is a small parameter. The criterion is based on approximate relations for ΔT_m and V_f, which account for the local curvature of a propagating front in a packed bed reactor with a first‐order activated kinetics. The obtained relations are verified by linear stability analysis of planar fronts. Simulations of a simplified 2D model in the form of a thin cylindrical shell are in good agreement with the critical parameters predicted by dispersion relations. Three types of patterns were detected in simulations: “frozen” multiwave patterns, spinning waves, and complex rotating–oscillating patterns. We map bifurcation diagrams showing domains of different modes using the shell radius as the bifurcation parameter. The possible translation of the 2D cylindrical shell model results to the 3D case is discussed. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

A combined approach to determine workpiece-tool-press deflections and tool loads in multistage cold-forging

Press and tool deflections have significant influence on the accuracy of products and tool service life in cold-forging processes. This paper presents a combined experimental-numerical approach to determine the deflections of the workpiece-tool-press (WTP) system and tool loads to improve product accuracy in a multistage cold-forging process. The measurements of deflections of the vertical mechanical press for the determination of the press flexibility matrix were performed in dynamic operating conditions. Numerical modelling of the vertical mechanical press and a multistage forging system was performed in order to evaluate the tool loads, the displacements and the rotations of the entire WTP system. The press flexibility matrix in combination with finite element (FE) model of the press and multistage process enable predictions of the elastic displacements and rotations of the tool and the press ram as well as determination of the evolution of the resultant force in order to design a reliable multistage cold-forging process. By redesigning the time sequences and evolution of the multistage forming operations during the press stroke, the evolution of the resultant force and the torque are optimized. This approach has been successfully applied to improve the prediction of tool loads, WTP deflections and rotations for the production of the automotive starter side plate.     

一种考虑相关需求的多级库存控制优化模型

在技术驱动的全球化市场,供应链管理已经成为企业和学者共同面对的重要课题。库存控制问题则是企业供应链管理中一个很重要的环节。该文研究了在供应链管理的环境下,由K个配送中心,每个配送中心由Nk个零售商组成的配送网络的库存控制问题。凭着对实际配送系统的观察和分析,在综合考虑了同一产品在不同零售点需求的相关性,以及同一产品在不同周期需求相关性的情况下,以最小化库存成本和运输成本之和为目标,一定的服务水平为约束,建立了多级库存控制优化模型。