Design Methodology for a Medium Voltage Single Stage LLC Resonant Solar PV Inverter

An inverter is generally employed with MV LFT to connect to the grid in a grid-tied PV system. However, in some single-stage topologies, the LFTs are replaced by HFT combined with an unfolder inverter. Generally, these topologies have limited use at high-power MV grids due to high switching losses on the primary side. This study proposes an LLC resonant converter-based single-stage inverter design procedure. Resonant converters make use of ZVS to reduce switching losses. The design includes both the resonant tank as well as output filter components. The design is verified by simulations in MATLAB/Simulink for various loads and input voltages at 13.8kV grid output voltage. THD simulations validate the filter design

A Comprehensive Review on Constant Power Loads Compensation Techniques

Microgrid, because of its advantages over conventional utility grids, is a prudent approach to implement renewable resource-based electricity generation. Despite its advantages, microgrid has to operate with a significant proportion of constant power loads that exhibit negative incremental impedance and thus cause serious instability in the system. In this paper, a comprehensive review is presented on accomplished research work on stabilization of dc and ac microgrid. After reviewing these, microgrid system stabilization techniques are classified with required discussions. As found out in this paper, the stabilization techniques can basically be classified as compensation done: 1) at feeder side; 2) by adding intermediate circuitry; and 3) at load side. Finally, after analyzing the merits and drawbacks of each generalized technique, several infographics are presented to highlight the key findings of this paper

The diagnostic value of the field assessment stroke triage for emergency destination tool in identifying the obstruction of large cerebral vessels; a systematic review and meta-analysis

Objective: In this study, we investigate the diagnostic value of the Field Assessment Stroke Triage for Emergency Destination (FAST-ED) tool in the diagnosis of large vessels occlusion (LVO) in a systematic review and meta-analysis. Methods: We conducted a search in Medline (PubMed), Embase, Scopus and Web of Science databases until the 21st of September 2022, as well as a manual search in Google and Google scholar to find related articles. Studies of diagnostic value in adult population were included. Screening, data collection and quality control of articles were done by two independent researchers. The data were entered and analyzed in STATA 17.0 statistical program. Results: The data from 30 articles were entered. The best cut-off points for FAST-ED were 3 or 4. The sensitivity and specificity of FAST-ED at cut-off points 3 were 0.77 (95% CI: 0.73-0.80) and 0.76 (95% CI: 0.72-0.80), respectively. These values ​​for cut-off point 4 were 0.72 (95% CI: 0.65-0.78) and 0.79 (95% CI: 0.75-0.82), respectively. Meta-regression showed that the sensitivity and specificity of FAST-ED performed by a neurologist was more accurate compared to emergency physician (p for sensitivity=0.01; p for specificity<0.001) and emergency medical technicians (p for sensitivity=0.03; p for specificity<0.001). Finally, it was found that the sensitivity of FAST-ED performed by the emergency physician and the emergency medical technician has no statistically significant difference (p=0.76). However, the specificity of FAST-ED reported by the emergency physician is significantly higher (p<0.001). The false negative rate of this tool at cut-off points 3 and 4 is 22.5% and 28.8%, respectively. Conclusion: Although FAST-ED has an acceptable sensitivity in identifying LVO, its false negative rate varies between 22.5% and 28.8%. A percentage this high is unacceptable for a screening tool to aide in the diagnosis of strokes considering it has a high rate or morbidity and mortality. Therefore, it is recommended to use another diagnostic tool for the stroke screening

Chance-Constrained Optimization of Energy Storage Capacity for Microgrids

The optimal storage capacity is a crucial parameter for stable and reliable operation of microgrids in an islanded mode. In this context, an analytical method is developed to robustly formulate and analyze energy storage capacity deploying chance constrained stochastic optimization. More specifically, the goal is to determine an appropriate size for an energy storage to reach a specific loss of load probability (LOLP) in a microgrid with large penetration of renewables considering generation and load forecast error. The total cost is minimized over optimal storage capacity as well as over generators power, while accounting for generation and storage power and energy constraints. It is postulated that the shortage/surplus power will be derived from/injected to the storage system. However, due to stochastic nature of load and renewables and an inevitable forecast error, the renewable generation output or the load power may not be accurately acquired. Thus, the total storage power and energy constraints are posed as chance constraints, for which conservative convex approximations are employed for tractability. In particular, to overcome the difficulty brought about by the large size of the optimization problem, a separable (distributed) structure is pursued, and the dual decomposition method is adopted to obtain optimal solutions. Numerical tests verify the effect of prior knowledge in modeling the uncertainty in optimal choice of storage capacity

Age Estimation of a Hybrid Energy Storage System for Vehicular Start–Stop

Ultracapacitors are energy storage devices that have shown outstanding capability in a vast spectrum of applications, mainly in energy storage systems required to deliver short bursts of electrical energy. Ultracapacitors possess high power density while batteries possess high energy density. In this paper, a hybrid energy storage device comprising a lithium-ion ultracapacitor module and a lead acid battery was modeled, built, and tested for vehicular start–stop application, which requires a much larger number of engine cranking events than conventional vehicles. The combination of a lead acid battery with Li-ion ultracapacitors was chosen due to the fact that the vast majority of vehicles utilize lead acid batteries to crank the internal combustion engine. This allows retrofitting this hybrid setup in conventional vehicles along with the start–stop feature without inflicting damage to the already installed lead acid battery. The start–stop feature puts high stress on the lead acid battery, contributing to its faster aging. This feature is commonly found in hybrid vehicles to save the unnecessarily burned fuel during idling. This paper discusses aging of the lead acid battery as a result of being used in hybrid vehicles equipped with start–stop when used alone versus when used in the hybrid setup. The paper shows cranking tests performed on a number of cars to obtain voltage, current, power, and energy requirements for combustion engine cranking. Mathematical derivation, analysis, and an energy storage age estimation method are also presented. A set of cranking events followed by capacity checks performed on two automobile energy storage systems, one being a lead acid battery alone and the other being the proposed hybrid module, show the advantage of integrating the ultracapacitor module with the lead acid battery to extend its life span almost fivefold in a hybrid automobile

Study on dormancy breakage and germination in three species of Hawthorn (Crataegus aminii,C. persica and C. babakhanloui)

Crataegus from Rosaceae family is a tree that has medical and ornamental applications. Seeds of this genus have germination problem and may not germinate for 2 to 3 years. There are limited information about germination of different species. Therefore, study on germination of three native species of Iran, Crataegus aminii,C. persica and C. babakhanloui is conducted and the most effective treatment was determined. To evaluate the germination and breaking seed dormancy of three species, an experiment was carried out as a completely randomized design with four treatments and three replications. Seeds were imposed under physical stimulator treatment, including, scarification and warmth followed by cold stratification. Results indicated that in all treatments, scarification is effective for permeability to water of seed coat and breakage of seed dormancy. Germination rate in treatment 4 (impose to running water for 24h, then 3 month warmth, followed by 4.5 month cold stratification) had the highest rate. The highest percentage of germination and vigor were in treatment 3 (sowing the seeds outdoors at the beginning of summer). The number of the seeds that have embryo in each fruit is determined. More than 80% of fruits have only one embryo

Overall Efficiency Improvement of a Dual Active Bridge Converter Based on Triple Phase-Shift Control

This paper proposes a control scheme based on an optimal triple phase-shift (TPS) control for dual active bridge (DAB) DC–DC converters to achieve maximum efficiency. This is performed by analyzing, quantifying, and minimizing the total power losses, including the high-frequency transformer (HFT) and primary and secondary power modules of the DAB converter. To analyze the converter, three operating zones were defined according to low, medium, and rated power. To obtain the optimal TPS variables, two optimization techniques were utilized. In local optimization (LO), the offline particle swarm optimization (PSO) method was used, resulting in numerical optimums. This method was used for the low and medium power regions. The Lagrange multiplier (LM) was used for global optimization (GO), resulting in closed-form expressions for rated power. Detailed analyses and experimental results are given to verify the effectiveness of the proposed method. Additionally, obtained results are compared with the traditional single phase-shift (SPS) method, the optimized dual phase-shift (DPS) method, and TPS method with RMS current minimization to better highlight the performance of the proposed approach

Development of a Medium Voltage, High Power, High Frequency Four-Port Solid State Transformer

The power and voltage levels of renewable energy resources is growing with the evolution of the power electronics and switching module technologies. For that, the need for the development of a compact and highly efficient solid-state transformer is becoming a critical task in-order to integrate the current AC grid with the new renewable energy systems. The objective of this paper is to present the design, implementation, and testing of a compact multi-port solid-state transformer for microgrid integration applications. The proposed system has a four-port transformer and four converters connected to the ports. The transformer has four windings integrated on a single common core. Thus, it can integrate different renewable energy resources and energy storage systems. Each port has a rated power of 25kW, and the switching frequency is pushed to 50kHz. The ports are chosen to represent a realistic industrial microgrid model consisting of grid, energy storage system, photovoltaic system, and load. The grid port is designed to operate at 4.16kVAC corresponding to 7.2kV DC bus voltage, while the other three ports operate at 500VDC. Moreover, the grid, energy storage and photovoltaic ports are active ports with dual active bridge topologies, while the load port is a passive port with full bridge rectifier one. The proposed design is first validated with simulation results, and then the proposed transformer is implemented and tested. Experimental results show that the designed system is suitable for 4.16kVAC medium voltage grid integration