Modeling and operation optimization of RE integrated microgrids considering economic,energy, and environmental aspects

Microgrids provide promising solution for integration of renewable energy sources in the electrical grid. To exploit the key benefits, achieving the economical operation of renewable aided microgrids has become necessary and is a challenging task. This paper presents an efficient optimization model to minimize the operational cost of a solar integrated microgrid. We formulate a joint optimization mixed integer problem for appropriate modeling of the system under various practical constraints. An efficient solution is obtained with a distributed approach such that the original problem is solved in two stages. Dual decomposition approach is adopted for cost, emissions, and solar share optimization. Lagrange relaxation, Lambda iteration method, and binary integer programming are employed to obtain the joint optimization solution. Finally, the performance of the proposed model is validated through simulations that show that an overall cost reduction of 4.2070e+04 $ and emission reduction of 7.2001e+03 kg are achieved with the proposed model.     

增强现实场景下移动边缘计算资源分配优化方法

针对高速数据传输及计算所带来时延和终端设备能耗问题，提出了一种在上行链路采用等功率分配的传输方案。首先，依据增强现实（AR）业务的协作属性建立了针对AR特性的系统模型；其次，详细分析了系统帧结构，建立以最小化系统消耗总能量为优化目标的约束条件；最后，在保障延迟和功耗满足约束的条件下，建立了基于凸优化的移动边缘计算（MEC）资源优化求解数学模型，从而获得最优的通信和计算资源分配方案。与独立传输相比，该方案在最大延迟时间分别为0.1 s和0.15 s时的总能耗降幅均为14.6%。仿真结果表明，在相同条件下，与基于用户独立传输的优化方案相比，考虑用户间协作传输的等功率MEC优化方案能显著减少系统消耗的总能量。     

Electronic and structural properties of low-index L12–Al3Zr surfaces by first-principle calculations

The atomic relaxations, electronic properties and surface energies of low index L1₂-Al₃Zr surfaces were studied by using the first-principles method based on the density functional theory. Five low index surfaces with different terminations are studied systematically. The study shows that atomic relaxations occur mainly within the outermost two layers. The stoichiometric (111), non-stoichiometric (110) and (001) surfaces with different terminations are investigated. The (111) surface which has the lowest surface energy and is independent on the chemical potential of Al atom is found to be the most thermodynamically stable surface. For the non-stoichiometric surfaces, the AlZr terminated (001) surface and Al terminated (110) surface are metastable under an Zr-rich and Al-rich condition respectively. These results are in consistant with the results of density of states. The lattice misfit between α-Al and L1₂-Al₃Zr is not more than 1.65% by our calculation, indicating L1₂-Al₃Zr is a potent effective heterogeneous nucleating agent for α-Al.     

Control synthesis for polynomial discrete-time systems under input constraints via delayed-state Lyapunov functions

This paper presents a discrete-time control design methodology for input-saturating systems using a Lyapunov function with dependence on present and past states. The approach is used to bypass the usual difficulty with full polynomial Lyapunov functions of expressing the problem in a convex way. Also polynomial controllers are allowed to depend on both present and past states. Furthermore, by considering saturation limits on the control action, the information about the relationship between the present and past states is introduced via Positivstellensatz multipliers. Sum-of-squares techniques and available semi-definite programming (SDP) software are used in order to find the controller.     

烃链功能改性剂对三元乙丙橡胶/凹凸棒土复合材料性能的影响

采用机械共混法制备三元乙丙橡胶(EPDM)/凹凸棒土(AT)复合材料,考察了不同结构的烃链功能改性剂对复合材料硫化性能、力学性能和应力松弛行为及相结构的影响,探究3种烃链功能改性剂对凹凸棒土在复合材料中分散作用的机理。结果表明,改性剂锚固在AT表面并与EPDM有良好相容性,使AT在EPDM中有更好分散性。改性剂添加量为AT的1%时,对EPDM/AT复合材料的力学性能改善效果最明显,其中,以胺基为端基,相对分子质量为2000左右的改性剂使EPDM和AT两相的界面结合性最好,复合材料的拉伸强度提高了304.34%,综合性能提高最为显著。     

Electrocatalytic activity of perovskite-based cathodes for solid oxide fuel cells

A very active cathode material for intermediate temperature - solid oxide fuel cells (IT-SOFCs) is obtained by mixing La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) powders. Three different volume ratios are considered: BSCF-LSCF 50-50 v/v% (BL50), BSCF-LSCF 70-30 v/v% (BL70) and 30–70 v/v% (BL30).The electrodes are slurry coated on Ce_0.8Sm_0.2O_2-δ electrolyte and sintered at 1100 °C. After the sintering step XRD-analyses highlight relevant cation inter-diffusion within the mixed powders. As a result, an enhanced activity of BL30-BL70 electrodes towards oxygen reduction reaction is detected in comparison to LSCF or BSCF pure powders. A polarization resistance of 0.021 Ω cm2 at 650 °C for BL70 is obtained, one of the lowest value reported in literature for SOFC cathodes. Furthermore, all the electrodes show lower activation energy than the two reference materials in the considered temperature range (500–650 °C) and two different kinetic regimes are identified at the extremes of this range. Effect of the applied overpotential (0–0.3 V) on the electrode kinetic is also investigated.After a preliminary ageing, performed at 650 °C for 200 h by applying a current density of 200 mA cm-2, the electrodes preserve a remarkable performance as IT-SOFC cathodes, despite an initial degradation. A stable value of 0.048 Ω cm2 of polarization resistance for the sample richer in BSCF is recorded.     

Nonlinear analysis of cable structures using the dynamic relaxation method

The analysis of cable structures is one of the most challenging problems for civil and mechanical engineers. Because they have highly nonlinear behavior, it is difficult to find solutions to these problems. Thus far, different assumptions and methods have been proposed to solve such structures. The dynamic relaxation method (DRM) is an explicit procedure for analyzing these types of structures. To utilize this scheme, investigators have suggested various stiffness matrices for a cable element. In this study, the efficiency and suitability of six well-known proposed matrices are assessed using the DRM. To achieve this goal, 16 numerical examples and two criteria, namely, the number of iterations and the analysis time, are employed. Based on a comprehensive comparison, the methods are ranked according to the two criteria. The numerical findings clearly reveal the best techniques. Moreover, a variety of benchmark problems are suggested by the authors for future studies of cable structures.     

Understanding CO2 electrochemical reduction kinetics of mixed-conducting cathodes by the electrical conductivity relaxation method

Electrochemical reduction reaction is an important approach to utilize CO₂ and convert it into valuable products. Exceptional reaction kinetics at a high temperature of solid oxide electrolysis cells (SOECs) attracts particular attention. In this work, we propose to investigate CO₂-RR kinetics using a new theoretical method based on the electrical conductivity relaxation (ECR) technique on a typical mixed-conducting Sr₂Fe_1.5Mo_0.5O_6-δ (SFM) electrode. Three kinetic parameters that are commonly adopted in the typical electrochemical test experiments consisting of overpotential, current density and area-specific resistance (ASR) are derived. The overpotential resulted from the difference in the oxygen partial pressure is caused by the change of CO₂ partial pressure, while current density from the surface reaction rate constant. Accordingly, area-specific resistance, as well as overpotential-current density relationship, can be derived. We believe that this work brings a new method to study the kinetic process of CO₂ electrolysis and to evaluate the electrocatalyst activity of developed new electrode materials as well as to benefit the designing of novel electrode electrocatalysts for highly efficient solid oxide electrolysis cells.     

Proximal extrapolated gradient methods for variational inequalities

The paper concerns with novel first-order methods for monotone variational inequalities. They use a very simple linesearch procedure that takes into account a local information of the operator. Also, the methods do not require Lipschitz continuity of the operator and the linesearch procedure uses only values of the operator. Moreover, when the operator is affine our linesearch becomes very simple, namely, it needs only simple vector–vector operations. For all our methods, we establish the ergodic convergence rate. In addition, we modify one of the proposed methods for the case of a composite minimization. Preliminary results from numerical experiments are quite promising.     

Lagrangean relaxation approach to joint optimization for production planning and scheduling of synchronous assembly lines

This paper focuses on simultaneous optimisation of production planning and scheduling problem over a time period for synchronous assembly lines. Differing from traditional top-down approaches, a mixed integer programming model which jointly considers production planning and detailed scheduling constraints is formulated, and a Lagrangian relaxation method is developed for the proposed model, whereby the integrated problem is decomposed into planning, batch sequencing, tardiness and earliness sub-problems. The scheduling sub-problem is modelled as a time-dependent travelling salesman problem, which is solved using a dynasearch algorithm. A proposition of Lagrangian multipliers is established to accelerate the convergence speed of the proposed algorithm. The average direction strategy is employed to solve the Lagrangian dual problem. Test results demonstrate that the proposed model and algorithm are effective and efficient.