基于智能软开关的三相不平衡配电网动态重构策略

针对单相分布式电源（DG）的接入会加剧配电网不平衡程度、增大网络损耗,且在严重不平衡时影响系统安全运行的问题,提出计及智能软开关（SOP）的三相不平衡配电网动态重构策略。首先,构建考虑SOP和DG电流不平衡度约束的三相不平衡配电网动态重构模型;然后,针对模型的非凸性将原模型转化为混合整数线性规划模型;最后,对改进的IEEE34节点配电网和某地78节点实际配电网进行算例分析,结果表明所提模型和策略可在保证配电网的安全运行的同时提升配电网的经济效益。     

Review of lithium-ion battery state of charge estimation

The technology deployed for lithium-ion battery state of charge (SOC) estimation is an important part of the design of electric vehicle battery management systems. Accurate SOC estimation can forestall excessive charging and discharging of lithium-ion batteries, thereby improving discharge efficiency and extending cycle life. In this study, the key lithium-ion battery SOC estimation technologies are summarized. First, the research status of lithium-ion battery modeling is introduced. Second, the main technologies and difficulties in model parameter identification for lithium-ion batteries are discussed. Third, the development status and advantages and disadvantages of SOC estimation methods are summarized. Finally, the current research problems and prospects for development trends are summarized.     

Statistical modeling of mains zero crossing variation in powerline communication

In this paper, authors investigate statistical modeling of measured mains Zero Crossing (ZC) non idealities in narrowband powerline communication systems (PLC) using time series approach based on autoregressive moving average model (ARMA). For this purpose, Box Jenkins analysis steps are deployed for detected ZC impulsive variations. Estimated models exhibit a good fit based on R-square metric reaching 90%. This modeling approach is extended to three measurement environment: in home, in lab and rural locations. Obtained models are useful for NB-PLC channel emulator implementation.     

An approach for the integration of renewable distributed generation in hybrid DC/AC microgrids

This paper presents an investigation of a hybrid DC/AC integration paradigm to establish microgrids (MGs) by using a conventional three-phase local power delivery system. This approach adds an additional DC power line to the local power distribution system in order to collect energy generated by distributed domestic renewable sources. The local renewable distributed generation (DG) works in conjunction with the conventional grid utility to reduce the power draw from the grid. Researchers designed an energy conversion station to mix energy from the local DGs with energy from the grid utility. This approach, therefore, uses a continuous energy mixing strategy for DC integration of local generation and grid energy to supply energy to MG consumers via the conventional three-phase power distribution system. Thus, local distributed renewable generators do not have to contend with AC integration problems, such as AC stability and line synchronization. This approach can facilitate the transformation of conventional local power distribution systems into reliable MGs in an affordable way for stakeholders and it is a step towards construction of future smart grids.     

Improved dielectric energy storage performance of Na0.5Bi0.5TiO3-based lead-free relaxation ferroelectric ceramics achieved by domain structural regulation and enhanced densification

There is still a problem of low energy storage density in dielectric capacitors which is a core component of power systems. For the improvement of the energy storage density, the linear dielectric material CaTiO₃ (CT) was introduced in Na_0.5Bi_0.5TiO₃ (NBT) ceramics in this paper. By modifying the A site, a new relaxor ferroelectric ceramic was successfully synthesized and attained a recoverable density (W_rec) of 2.34 J/cm³ at x = 0.18. Moreover, the preparation process was optimized in this paper. Through the viscous polymer process (VPP) route, the energy density (W_A) of 82NBT-18CT_VPP ceramic further reaches 6.45 J/cm³ at 340 kV/cm, with efficiency (η) up to 75% and a W_rec of 4.82 J/cm³. At the same time, the change of W_rec is small at temperature (30–150 °C) and frequency (1 Hz–300 Hz), which demonstrates its excellent stability. The discharge power density reaches about 180 MW/cm³ and the discharge time is 0.117 μs, which indicates its excellent pulse discharge performance. The results show that 82NBT-18CT lead-free relaxation ferroelectric material is expected to become ideal for high-energy storage applications.     

A focused review of the hydrogen storage tank embrittlement mechanism process

Hydrogen embrittlement is a widely known phenomenon in high-strength and storage materials. Hydrogen embrittlement is responsible for subcritical crack growth in material, fracture initiation, subsequent loss in mechanical properties, and catastrophic failure. Hydrogen is induced in the material during an electrochemical reaction between the hydrogen, storage materials, and high-pressure gaseous hydrogen environment. Various mechanisms which are responsible for crack development, growth, and fracture have been deliberated and reported. However, the fundamental mechanism of hydrogen embrittlement remains unclear. Several techniques such as linearly increasing stress test techniques (LIST), constant extension rate test (CERT) and slow strain rate testing (SSRT), thermal desorption spectroscopy (TDS), permeation testing (PT), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been utilized to determine the amount of hydrogen diffused and available in the hydrogen storage material. The review intends to categorize and provide a clear understanding of the degradation mechanism that occurs during hydrogen embrittlement. The improvement in mitigating the hydrogen embrittlement degradation as a function of modifying the structure and surfaces of the material is established. Prospects for addressing hydrogen embrittlement degradation through further experimental and numerical research are suggested. Lastly, this paper through recommendation endeavors to prevent hydrogen storage tank degradation and reduces high costs associated with the replacement of the component in renewable energy applications.     

Data-driven causal inference based on a modified transfer entropy

Causality inference and root cause analysis are important for fault diagnosis in the chemical industry. Due to the increasing scale and complexity of chemical processes, data-driven methods become indispensable in causality inference. This paper proposes an approach based on the concept of transfer entropy which was presented by Schreiber in 2000 to generate a causal map. To get a better performance in estimating the time delay of causal relations, a modified form of the transfer entropy is presented in this paper. Case studies on two simulated chemical processes, including the benchmark Tennessee Eastman process are performed to illustrate the effectiveness of this approach.     

A coupled power-voltage equilibrium strategy based on droop control for fuel cell/battery/supercapacitor hybrid tramway

In order to improve the robustness of the energy management system (EMS) and avoid the influence of demand power on the design of EMS, a coupled power-voltage equilibrium strategy based on droop control (CPVE-DC) is proposed in this paper. Making use of the principal that the DC bus can directly reflect the changes of load power, the proposed strategy couples DC bus voltage with output powers through droop control to achieve self-equilibrium. The proposed EMS is applied into a hybrid tramway model configured with multiple proton exchange membrane fuel cell (PEMFC) systems, batteries and super capacitors (SCs). FC systems and SC systems are responsible for satisfying most of the demand power, therefore the CPVE-DC strategy generates FCs and SCs reference power through power-voltage droop control on the primary control. Then batteries supplement the rest part of load power and generate DC bus voltage reference value of the next sampling time. With the gambling between output power and DC bus voltage, the hybrid system achieves self-equilibrium and steps into steady operation by selecting appropriate droop coefficients. Then the secondary control of the proposed strategy allocates power between every single unit. In addition, a penalty coefficient is introduced to balance SOC of SCs. The proposed strategy is tested under a real drive cycle LF-LRV on RT-LAB platform. The results demonstrate that the proposed strategy can achieve self-equilibrium and is effective to allocate demand power among these power sources,achieve active control for the range of DC bus voltage and SOC consensus of SCs as well. In addition, some faults are simulated to verify the robustness of the proposed strategy and it turns out that the CPVE-DC strategy possesses higher robustness. Finally, the CPVE-DC strategy is compared with equivalent consumption minimization strategy (ECMS) and the results shows that the proposed strategy is able to get higher average efficiency and lower equivalent fuel consumption.     

基于网架结构综合分析的开关布点优化规划

传统的配电网开关位置及数量的优化规划是将系统整体的可靠性指标及成本作为目标函数,对分段开关与联络开关的位置及数量进行优化,并没有通过寻找薄弱环节而达到快速有效提升系统可靠性的目的。将网架结构对可靠性的影响划分为“环节、联络和相互影响”3个方面,量化计算3个方面对不同负荷点可靠性的影响程度。将计算结果与分枝定界法相结合,得出基于网架结构综合分析的开关布点优化方法。针对供电可靠性的薄弱环节开展分析应用,结果表明,该方法使得开关的布点规划方案更贴近用户,更实用。     

Repulsive firefly algorithm-based optimal switching device placement in power distribution systems

To achieve optimal configuration of switching devices in a power distribution system, this paper proposes a repulsive firefly algorithm-based optimal switching device placement method. In this method, the influence of territorial repulsion during firefly courtship is considered. The algorithm is practically applied to optimize the position and quantity of switching devices, while avoiding its convergence to the local optimal solution. The experimental simulation results have showed that the proposed repulsive firefly algorithm is feasible and effective, with satisfying global search capability and convergence speed, holding potential applications in setting value calculation of relay protection and distribution network automation control.