Optimal Operating Points Research Articles

Performance assessment and optimization of concentrated solar power plants with paired metal hydride-based thermochemical energy storage

The main objective of this study is to evaluate the innovative future concept of a concentrated solar power (CSP) plant, specifically focusing on a CSP-driven Rankine cycle. Additionally, a suggested energy storage solution for the analyzed CSP plant is the thermochemical energy storage (TCES) approach. The TCES system used paired metal hydrides integrated with phase change material (PCM). A comprehensive mathematical model has been developed to enable performance predictions for the entire CSP plant as well as each of its components. This model considers the thermal coupling between the solar field, the thermochemical storage system, and the power block in order to assess the overall performance of the CSP plant. Utilizing this successfully verified model with reference data, a parametric study is conducted on various operating parameters to identify optimal operating points for the storage system in relation to the overall efficiency of the CSP plant. Furthermore, the critical issue of appropriate and novel concepts for MHs-based TCES integration in CSP plants is discussed in detail. The CSP plant's performance was examined as a function of storage cycle duration, charging and discharging temperatures, melting PCM temperature, and thermal efficiency. Based on the findings, it has been observed that higher charging temperature and integration of PCM into the thermochemical energy storage (TCES) system can lead to a significant reduction of 13-fold in the required solar collector area and a notable increase of 77 % in the efficiency of the CSP plant. Thus, the proposed TCES system appears to be the most promising future heat storage system for CSP plants.

BPG-based compression analysis of Poisson-noisy medical images

The subject matter is lossy compression using the BPG encoder for medical images with varying levels of visual complexity, which are corrupted by Poisson noise. The goal of this study is to determine the optimal parameters for image compression and select the most suitable metric for identifying the optimal operational point. The tasks addressed include: selecting test images sized 512x512 in grayscale with varying degrees of visual complexity, encompassing visually intricate images rich in edges and textures, moderately complex images with edges and textures adjacent to homogeneous regions, and visually simple images primarily composed of homogeneous regions; establishing image quality evaluation metrics and assessing their performance across different encoder compression parameters; choosing one or multiple metrics that distinctly identify the position of the optimal operational point; and providing recommendations based on the attained results regarding the compression of medical images corrupted by Poisson noise using a BPG encoder, with the aim of maximizing the restored image’s quality resemblance to the original. The employed methods encompass image quality assessment techniques employing MSE, PSNR, MSSIM, and PSNR-HVS-M metrics, as well as software modeling in Python without using the built-in Poisson noise generator. The ensuing results indicate that optimal operational points (OOP) can be discerned for all these metrics when the compressed image quality surpasses that of the corresponding original image, accompanied by a sufficiently high compression ratio. Moreover, striking a suitable balance between the compression ratio and image quality leads to partial noise reduction without introducing notable distortions in the compressed image. This study underscores the significance of employing appropriate metrics for evaluating the quality of compressed medical images and provides insights into determining the compression parameter Q to attain the BPG encoder’s optimal operational point for specific images. Conclusions. The scientific novelty of the findings encompasses the following: 1) the capability of all metrics to determine the OOP for images of moderate visual complexity or those dominated by homogeneous areas; MSE and PSNR metrics demonstrating superior results for images rich in textures and edges; 2) the research highlights the dependency of Q in the OOP on the average image intensity, which can be reasonably established for a given image earmarked for compression based on our outcomes. The compression ratios for images compressed at the OOP are sufficiently high, further substantiating the rationale for compressing images in close proximity to the OOP.

A Proton exchange membrane water electrolysis cell model for analyzing the effects of liquid water supply characteristics on cell performance

Proton exchange membrane water electrolyzers (PEMWE) have significant potential for green, high-purity hydrogen production. This study proposes a pseudo-two-dimensional cell-level model that considers all the physical characteristics involved in water electrolysis (WE), such as electron transport in the electrodes, proton transport in the membrane electrode assembly (MEA), water transport between the anode and cathode, gas diffusion in the porous electrodes, two-phase transport in the porous electrodes, and flow channel (FC), including the channel pressure drop and heat conduction across the cell. Liquid water dispersion at the electrode/channel interface is proposed based on a geometrical analysis of the bubble patterns inside the anode channel. The model was validated against the experimental data. The simulation results showed the effects of the liquid water supply characteristics on the cell operation, demonstrating that uniform water, temperature, and pressure distributions on the cell are required for higher performance. Furthermore, efficiency maps with operating constraints under different conditions provide basic guidelines for determining the optimum point of PEMWE operation. The proposed model is appropriate for extensive analysis of physical phenomena inside the PEMWE and rapid simulation for cell optimization.

Modeling and Experimental Investigation of the Interaction between Pressure-Dependent Aging and Pressure Development Due to the Aging of Lithium-Ion Cells

In order to meet the increasing demands of the battery in terms of range, safety and performance, it is necessary to ensure optimal operation conditions of a lithium-ion cell. In this thesis, the influence of mechanical boundary conditions on the cell is investigated theoretically and experimentally. First, fundamental equations are derived that lead to coupled models that can be parameterized based on specific cell measurements and predict the pressure evolution due to capacity aging and vice versa. The model is used to derive optimal operating points of the cell, which can be considered in the module design.

Numerical investigation of nozzle shape effect on the flash boiling phenomenon

Small nozzles may be used as an element of novel steam traps in steam heating systems or shell-coil (JAD) heat exchangers. Phenomena occurring in these nozzles should be analyzed to find their optimal operating points and avoid steam losses. Therefore, the paper presents a numerical investigation of the effect of the nozzle shape on the flash boiling phenomena. Particularly, the study aimed to check the relation between the shape of the decompression part of the nozzle and the mass flow rate of the mixture of water and vapor flowing through it for different pressures and undercooling of water at the nozzle inlet. Two geometries of the divergent part of the nozzle, i.e. the stepped and conical, were considered. In the analysis, two-phase flow in the decompression part of the nozzle was accounted for by applying the mixture model. The dynamics of the phase change process during the flash boiling were described with the Zwart-Gerber-Belamri model, additionally supplied with the polynomial relationship linking the saturation pressure and temperature of the water. In the first step, a credibility analysis of the model was conducted. The simulated results were compared to the literature’s reference results, and a good agreement was achieved. Moreover, the independence of results on the grid size and turbulence modeling in the bulk flow and near-wall region was shown. In the second step, a series of simulations were carried out for both nozzle geometries (stepped and conical), three nozzle neck diameters, three pressures, and eleven undercooling of water at the inlet to the nozzle. The shape of the divergent part of the nozzle was found to influence the characteristics of flash boiling flow significantly. However, it did not affect the mass flow rate of water flashing through the nozzle. For both geometries, the predicted mass flow rates were the same.

Single and multi-objective optimization of PVT performance using response surface methodology with CuO nanofluid application

The nanofluid application in photovoltaic thermal (PVT) systems is widely known as an effective solution for improving output performance. However, studies exploring the optimum operation point of PVT systems with nanofluid application are scant in the current literature. The novelty of the study lies in exploring the optimum operating conditions of each PVT output using single-objective optimization and the overall performance optimization using multi-objective study. The conditions were explored with the application of copper oxide nanofluid as a coolant in PVT systems. The investigation was conducted using a numerical equation-based model developed in TRNSYS simulation environment. An experimental test was conducted to validate the outputs of numerical model. After validating the numerical model, TRNSYS model was investigated for 0.10%-0.50% volume concentration and 60–120 kg/h mass flow. The output data was then imported into Design-Expert software for performance optimization. Central composite design was selected as it is the most suitable fractional factorial design option in response surface methodology. In single-objective investigation, the optimization conditions for PVT outputs are identified as follows, the optimum electrical efficiency output was 14.64% at 90 kg/h fluid flow and 0.10% concentration, the thermal efficiency output was 34.94% at 120 kg/h fluid flow and 0.50% concentration, the overall energy efficiency output was 49.28% at 88 kg/h fluid flow and 0.10% concentration, the overall exergy efficiency output was 16.45% at 60 kg/h fluid flow and 0.50% concentration. The multi-objective study indicated that the collective performance of PVT outputs is optimum at 91 kg/h fluid flow and 0.10% concentration.

Thermodynamic analysis and comprehensive system optimization of the near zero emission hybrid power based on SOFC-ICE integrated system fueled with ammonia

The highly efficient heat and mass integrations fueled with ammonia of solid oxide fuel cell and reciprocating piston internal combustion engine are conducted from the viewpoints of characters of restrained / unrestrained chemical reaction and principle of energy cascade utilization. According to previous studies, we classified such integrations into serial and parallel topologies. Based on the detailed and verified models, the power matching limits of serial and parallel integrations are proposed first, showing a narrow scale of power matching of fuel cell and engines, due to the finite engine displacement. Furthermore, based on the design concepts of serial and parallel integrations, the improvement and optimization of combined systems were conducted, which showed that the possibly highest efficiency of serial and parallel systems can reach 70.53% and 68.40%, respectively. Additionally, the exergy analysis of systems could prove that such heat and mass integrations can effectively use remaining heats and fuels, leading to less exergy destructions and optimal designs and operation points achievement, while the maximum exergy destruction occurs at engine. Finally, the environmental analysis results showed that the corrected NO, NO2, N2O and NH3 emissions can reach 0.01 mg/kWh, 5.00 μg/kWh, 29.50 mg/kWh and <5 ppm, achieving near zero emissions.

Electrochemical Cells for Novel Routes to Ammonia

Ammonia is an extremely important chemical compound. Annual production exceeds 180 million tons of which ~80% is used for fertilizer production. The conventional production route is CO2 intensive and almost 2% of global anthropogenic CO2 emissions stems from ammonia synthesis. This will have to change over the coming decades to ensure the politically targeted emission reductions.The synthesis gas a mixture of N2 and H2 will have to be produced in a green and sustainable manner eventually only relying on green power and sustainable synthesis routes as discussed in [1]. High temperature electrochemical cells can play a role in this, not only for providing a green stream of hydrogen, but also in realizing the required N2 as discussed in [2]. Here, a special mode of operating an SOEC was proposed including feeding some air together with the steam to the SOEC cathode to produce directly a N2/H2 mixture suitable for down-stream ammonia synthesis. This can be done with excellent efficiency [2].Here, we shall present a different and in several aspects advantageous route for providing N2 for green ammonia synthesis. It is suggested to produce the N2 by electrochemical pumping the oxygen out of an air stream. The overall energy efficiency of the concept will be discussed in detail. However, the motivation to pursue this route relies on that it would be applicable on “small” scale. Considering the scale of renewable electricity sources it would be advantageous if also ammonia synthesis could be scaled down to match the small scale and distributed nature of renewable electricity generation. Here, a technology that scales just like the electrochemical routes to be applied for the Hydrogen production would be advantageous. Whereas cryogenic distillation is an energy efficient route to provide N2 it is a technology, that would not scale down well.A solid oxide cell for electrochemical production of N2 by oxygen extraction from air was developed. 5*5 cm pieces were prepared and characterized both with respect to electrochemical performance and long term durability as tracked over 2000 hr. The cells are based on a ~10 micron CGO (Ce0.9Gd0.1O2) electrolyte sandwiched between composite supports (electrodes) made in either LSCF/CGO, or LSF/CGO. (LSCF=La0.6Sr0.4Co0.2Fe0.8O3- δ , LSF= La0.6Sr0.4FeO3- δ). To boost performance at low temperature the electrodes were infiltrated with Pr-oxide [3]. The performance with the different supports is compared at a range of temperatures and current densities with and without infiltration. Both materials were found to perform well and enable current densities ~0.8 A/cm2 at ~ 150 mV polarization, when tested at 700 oC. A 90% pure N2 stream can be produced with at a cell voltage below 150mV at temperatures from 700-800 ºC. As illustrated in Fig. 1, a purer N2 stream with 96% N2 could be produced at a cell voltage below 200 mV. Also a 98% pure N2 stream was demonstrated. Moreover, the cells were demonstrated to operate without degradation over a 2000 hr. period.The results are quite promising in terms of the excellent durability demonstrated and in terms of absolute energy consumption. For comparison with literature, the energy consumption is related to the removed oxygen rather than the produced N2. At 150 mV the energy consumption is ca. 0.7 kWh/m3 of oxygen extracted. This compares well with performance reported by Wang et al. [4] describing a similar concept. The energy consumption is ca. twice what it takes to produce the oxygen via cryogenic distillation. Here, it should be noted, however, that all the produced heat (0.7 kWh/m3) can be directly utilized in synthesizing the H2 needed for the ammonia due to the endothermic nature of steam splitting. Hence, the energy invested in producing the N2 is not really wasted in this case, as also discussed in [2].The results of detailed electrochemical testing will be presented and the factors limiting cell performance will be discussed. Finally, an analysis of what dictates the optimal point of operation in terms of energy consumption and component volume and reliability is presented. Acknowledgment The work was supported by the EU commission via project; ARENHA, H2020 GRANT AGREEMENT: 862482. References Campion, N., Nami, H., Swisher, P. R., Hendriksen, P. V., & Münster, M. (2023). Renewable and Sustainable Energy Reviews, 173, 113057. 2022.John Bøgild Hansen and Peter Vang Hendriksen 2019 ECS Trans. 91 2455.Hendriksen, P. V., Khoshkalam, M., Tong, X., Tripkovic, D., Faghihi-Sani, M. A., & Chen, M. 2019 ECS Transactions, 91, 1413-1424.Mei Wang, Kamil Maciej Nowicki, and John Thomas Sirr Irvine, Journal of The Electrochemical Society, 2022, 169, 064509 Figure 1

An investigation of the aeration proportion effect at the supply and recycle chambers on the optimal operation point of the U-type loop seal and the maximum solid circulation rate in a fluidized bed reactor

A loop seal is used to control a solid circulation rate and loop seal aeration ratios at the supply and recycle chambers are another factor that affects its efficiency and circulating behaviors of solid particles in a fluidized bed reactor. This research aimed to find the proper aeration proportion and operation point of the loop seal that affected the highest solid circulation rate. A riser used in the experiment had a cross-sectional area of 100 × 100 mm2 and 4500 mm height above a distributor plate. A U-type loop seal was constructed by a supply chamber and a recycle chamber with the same cross-sectional area. A horizontal passage of 50 mm length was connected with both chambers. The sand was a bed particle with an average diameter of 320 μm. The loop seal aerations were fed at the bottom of the supply and recycle chambers. It was found that the loop seal could not operate with supply-aeration flow rate percentages (PQS) of 0% and 100%. The PQS of about 73% gave the maximum solid circulation rate and was an optimal operation point at which air supplied at the supply chamber started bypassing into the recycle chamber.

Research on Solid Oxide Fuel Cell System Model Building and 3D Testing Based on the Nodal Idea

The Solid Oxide Fuel Cell (SOFC) system is a highly intricate system characterized by multiple variables and couplings. Developing an accurate model for the SOFC independent power generation system is of paramount importance. Conducting experimental studies on the SOFC system is costly, and it carries certain risks due to the requirements for pure hydrogen, high-temperature environments, and other factors. To address these challenges, a high-performing model that precisely reflects the inherent characteristics of the SOFC is essential for dynamic static analysis and the identification of optimal operating points. This paper presents a SOFC system model based on current controls, which was implemented in the MATLAB/Simulink environment, and it utilized a nodal approach for modeling. The model incorporated a cold air bypass, which enabled the more precise control of the SOFC reactor’s inlet and outlet temperatures. Furthermore, a 3D test and verification method are proposed in order to focus on the influence of input parameters on the four electrical characteristics, and four thermal characteristics, of output parameters. By conducting one-dimensional, two-dimensional, and three-dimensional studies of these output parameters, a more intuitive understanding of the system’s response to changes in input parameters was obtained. Under conditions wherein all other variables were kept constant, the entire system attained its maximum efficiency at approximately FU = 0.8, BP = 0, and AR = 6. The outcomes of this study have significant implications for exploring the optimal operating point in the SOFC independent power generation system in an in-depth manner. It provides valuable insights for enhancing the system’s efficiency and performance.

Multidimensional Ripple Correlation Technique for Optimal Operation of Triple-Active-Bridge Converters

The paper presents a multidimensional ripple correlation search technique of optimal operating points of triple active bridge (TAB) converters. Such converters present multiple modulation parameters that should be exploited to achieve high operation efficiency. On the other hand, the several degrees of freedom available make the identification of optimal parameters a challenging task, not easily tackled analytically or in closed form. A model-free on-line search method based on the ripple correlation technique is then proposed in this paper. The proposed method finds the optimum modulation parameters of TAB converters utilizing a three-dimensional ripple correlation control. The key property of the proposed solution is the adoption of orthogonal perturbation signals, where the orthogonality is simply obtained using different injection frequencies. The multidimensional correlation technique originally shown herein can be applied to other generic optimization problems. The proposed search is verified through a hardware-in-the-loop validation setup and an experimental prototype rated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$5kW$</tex-math></inline-formula> .

A Non-Equilibrium Thermodynamic Approach for Analysis of Power Conversion Efficiency in the Wind Energy System

This article proposes an approach and develops an appropriate method of applying linear non-equilibrium thermodynamics to analyze energy processes, in particular using the example of the wind energy conversion system (WECS) with a directly connected vertical axis wind turbine (VAWT) and vector-controlled permanent magnet synchronous generator (PMSG). The main steps of the proposed approach are the description of the component subsystems as universal linear or linearized energy converters (ECs), which are characterized by several dimensionless parameters, the main one of which is the degree of coupling between their input and output. According to their value, as well as justified efficiency criteria, the optimal operating points of each ECs can be easily found. Such an approach makes it possible to abstract from physical laws of a different nature and equally assess the work of each of the subsystems. The next step is a connection of the received ECs. As shown in the paper, for the most common cascade connection of ECs, there are the best conditions for their connection, under which the newly formed equivalent EC can have maximum efficiency. This opens up an opportunity to analyze the influence of already real parameters of cascaded interconnected subsystems on the quality of their connection and justify specific solutions that would not have been seen without this approach. For example, in this study, from all parameters of the PMSG, only the selection of the optimal rated inductance of the armature winding made it possible to improve the quality of the connection of the PMSG with a specific VAWT and approximate the efficiency of the entire WECS to the maximum possible, especially in medium and high winds.

Optimizing Multidimensional Perceptual Quality in Online Interactive Multimedia

Network latencies in online interactive multimedia applications may lead to a degraded perception of quality, such as lower interactivity or sluggish responses. We can measure their degradations in perceptual quality by the just-noticeable difference, awareness, or probability of noticeability ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">note</sub> ); the latter measures the likelihood that subjects can notice a change from a reference to a modified reference. In our previous work, we developed an efficient method for finding the perceptual quality for one metric under simplex control. However, integrating the perceptual qualities of several metrics is a heuristic. In this paper, we present a formal approach to optimally combine the perceptual quality of multiple metrics into a joint measure that shows their tradeoffs. Our result shows that the optimal balance occurs when the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">note</sub> of all the component metrics are equal. Furthermore, our approach leads to an algorithm with a linear (instead of combinatorial) complexity of the number of metrics. Finally, we present the application of our method in two case studies, one on VoIP for finding the optimal operating points and the second on fast-action games to hide network delays while maintaining the consistency of action orders.

Optimal Service Provisioning in Mobile 5G and Beyond Systems

One of the fundamental challenges that needs to be addressed in 5G and beyond systems relates with delivery of demanding uninterrupted services to mobile users. In this context, this paper provides an overview of relevant architectural options taking into consideration user mobility requirements and proposes suitable resource allocation schemes to enable optimal service provisioning under mobility considerations. The proposed schemes are evaluated through a purposely developed multistage optimization framework. This evaluation framework facilitates optimal placement of network and compute resources minimizing the associated infrastructure operational costs. Our results have been produced using real user mobility statistics as well as lab based profiling measurements of the 5G infrastructure and provide a detailed trade-off analysis between latency and infrastructure related costs indicating optimal operational points for different scenarios.

Supercapacitors Fast Ageing Control in Residential Microgrid Based Photovoltaic/Fuel Cell/Electric Vehicle Charging Station

The demand for microgrids and their applications in buildings, industries and for very specific applications is increasing over time. Most of these microgrids are dependent on renewable energy sources, which brings along problems of intermittent energy production. To maintain the balance of the grid, normally storage devices are used. Supercapacitors (SCs) are emerging as one of the potential solutions to solve the issue of intermittent energy production by renewable sources because of their high-power densities and rapid charge/discharge capability. In other terms, SCs can charge, and discharge rather quickly as compared to traditional lithium-batteries. This usage makes it interesting for optimizing decentralized energy generation-based PV systems operations. In this paper, the authors propose the supercapacitors fast ageing control in residential microgrid, including electric vehicle charging station based Photovoltaic-Fuel Cell system. Supercapacitors fast ageing control concept focuses on keeping the electrical parameters of the SCs around the optimal operation points by smoothing the power fluctuations in the system. The used SCs model is essentially based on the intermittent current waveforms along with variable temperature conditions. It enables us to describe the degradation of the supercapacitor’s parameters based on the effects of the temperature and the DC-current undulation. To maintain the electrical parameters of SCs around the optimal operation points, the authors propose a new control based on maintaining the SCs resistance at a minimal level and its capacitance at a maximal level by adjusting the SCs current control according to the optimal operating points tracking. The results validate the effectiveness of the approach, this is important because controlling the fast degradation of capacitance optimizes the lifetime of SCs system. Future research may explore scalability to large microgrids and integration with diverse renewable energy systems.

Role of permeability coefficients in salinity gradient energy generation by PRO systems with spiral wound membrane modules

Processes that can transform a salinity gradient into electrical energy have gained attention in recent years. One such process, which uses semipermeable membranes to generate electrical energy through a turbine, is pressure retarded osmosis (PRO). As a potential renewable energy technology, this process could also be integrated in desalination plants to reduce the energy consumption. However, principally because of certain drawbacks concerning membrane and module characteristics, PRO technology has not yet been fully exploited at commercial scale. This study aims to assess the impact of membrane permeability coefficients on the energy generated by full-scale single-stage PRO systems. This allow an evaluation of the performance of PRO modules in series considering variation of the permeability coefficients that may be due to the impact of fouling. An evaluation was made of the HTI OsMem™ 2521 spiral wound membrane module considering a diameter of 8 inches (high up-scaled active area) and different permeability coefficient ranges. The results showed that a 50% water permeability coefficient decrease would produce an approximately 25% decrease in the amount of energy that could be generated, while a 50% increase in the solute permeability coefficient would have virtually no effect when considering optimal operating points. Variation of the water permeability coefficient had more impact on the potential amount of generated energy than variation of the solute permeability coefficient.

A Decentralized Blockchain-Based Energy Market for Citizen Energy Communities

Despite the fact that power grids have been planned and utilized using centralized networks for many years, there are now significant changes occurring as a result of the growing number of distributed energy resources, the development of energy storage systems and devices, and the increased use of electric vehicles. In light of this development, it is pertinent to ask what an efficient approach would be to the operation and management of future distribution grids consisting of millions of distributed and even mobile energy elements. Parallel to this evolution in power grids, there has been rapid growth in decentralized management technology due to the development of relevant technologies such as blockchain networks. Blockchain is an advanced technology that enables us to answer the question raised above. This paper introduces a decentralized blockchain network based on the Hyperledger Fabric framework. The proposed framework enables the formation of local energy markets of future citizen energy communities (CECs) through peer-to-peer transactions. In addition, it is designed to ensure adequate load supply and observe the network’s constraints while running an optimal operation point by consensus among all of the players in a CEC. An open-source tool in Python is used to verify the performance of the proposed framework and compare the results. Through its distributed and layered management structure, the proposed blockchain-based framework proves its superior flexibility and proper functioning. Moreover, the results show that the proposed model increases system performance, reduces costs, and reaches an operating point based on consensus among the microgrid elements.

Enhancing electric vehicle penetration and grid operation performance in old residential communities through hybrid AC/DC microgrid reconstruction

The widespread popularity of electric vehicles (EVs) imposes great challenges for distribution grids, such as feeder congestion, voltage deviation, and so forth. Although building new electrical facilities is feasible to release more capacity for EV integration, this is not a wise scheme to be applied in old residential communities owing to huge costs and limited spaces. In light of this, the paper proposes an easy-to-implement and cost-effective hybrid AC/DC microgrid reconstruction scheme for low-voltage distribution grids of old residential communities. The advanced power electronic device called smart interlinking unit (SIU) is incorporated in prior power distribution rooms of residential communities, featuring integrated structure, dedicated interfaces, and flexible control capability. The SIU-based architecture reuses existing redundant transformers and power lines to form AC/DC subgrids. An outstanding transfer capacity improvement and power loss reduction via the DC renovation are quantified. Considering the varied efficiency characteristics of multiple power converters and transformers, a hierarchical coordinated operation strategy is proposed for this architecture to realize the overall energy-saving operation. The optimal operation point tracking and AC/DC voltage regulation are included in the strategy design. Regarding the target scenario in the case study, the adopted reconstruction scheme would achieve a significant 297% of the maximum EV penetration. The real-time voltage regulation for AC and DC feeders is also realized to avoid possible voltage violations. Additionally, the proposed architecture and operation strategy could obtain about 10% of load ratio improvement and 1.5% of average efficiency promotion compared to the traditional AC architecture.

SCOPF considering voltage and power fluctuation under renewable energy integration

Security-Constrained Optimal Power Flow (SCOPF) method could generate system optimal operation point, which guarantee system security by avoiding any overload whenever expected N-1 contingencies occurred. However, renewable power integration increases uncertainty of system security, which is not well treated in conventional SCOPF model. Then this study proposes an improved SCOPF model, which aims at optimizing outputs of generators to increasing security of system facing challenges by N-1 contingencies accompanied by renewable power fluctuations. Semi-invariant is employed to express the stochastic behavior of wind and photovoltaic power generation. Considering the influence of transformer transformation ratio on admittance matrix, the uncertainty of injected renewable power is combined with the adjustable characteristics of network parameters to obtain the fluctuation model of branch power and bus voltage. Therefore, the constraints for SCOPF are restated to treat the problem that expected value based traditional model makes errors to confirm overload. The probability analysis for branch overload allows this study to present a potential reduced contingency set, in which small-probability events are rationally excluded. Thus, the constraint quantities as well as the complexity of the optimization problem are effectively reduced to decrease the computation burden. A Benders decomposition method based interior point approach is used to solve the improved SCOPF optimization model. Case studies based on IEEE39 bus system demonstrate the efficiency of proposed method.

Adaptive design for the connection of multicell HHO generator with solar photovoltaic panels

Hydrogen is considered a new source of energy and one of the sources of clean energy. One of the most widely used methods of hydrogen production is water electrolysis. Water electrolysis causes water molecules to break down into hydrogen and oxygen by passing an electric current through water molecules and using an intercellular membrane. If the intercellular membrane is removed, hydrogen gas and oxygen are mixed to produce hydroxy gas. This gas, which contains hydrogen and oxygen molecules, has been considered an auxiliary fuel and combustion enhancer. In this research, the design and construction of a multi-cell electrolyzer producing hydroxy gas without a membrane was carried out using 316 stainless steel sheets. Potassium hydroxide (KOH) solution was used as an electrolyte to increase water conductivity, and solar panels were used to supply the energy required for the electrolyzer. Adjusting the number of electrolyzer plates with the voltage of the solar panels is one of the most critical points in the optimal design of this combined system. The effect of parameters on the amount of hydroxy gas production, energy intensity, and production per electrolyzer surface has been evaluated. The experimental results show that due to the internal resistance of each electrolyzer cell, the voltage of each cell varies between 2 and 3 V in different currents. The number of series cells in the electrolyzer determines its total voltage, which should be matched to the solar system to stay at the optimum point of operation. In the studied electrolyzer, optimized design of electrolizer have 18, 17 and, 15 plates, when one, two, and three 325W solar panels is used, respectively. In the next step, the daily test is performed for optimized electrolyzers. Daily production per surface of the solar panel for the three states was 530, 600 and 533L/m2, respectively. This indicates that daily production increases with increasing the number of panels but specific production per solar panel area may not increase and will have an optimal value. So, in the combination of an HHO generator with a solar system, the number of electrolyzer plates and also the surface area of solar panels should be optimally selected to achieve the optimum operation. This issue can be completed with accurate modeling in future studies.