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The increasing demands for reducing greenhouse emissions and improving fuel efficiency of marine transportation have presented opportunities for electric ships. Due to the complexity of multiple power resources coordination, varied propulsion loads, changeable economical, and environmental requirements, power/energy management system (PMS/EMS) becomes essential in both designing and operational processes. The existing literature on PMS/EMS can be categorized into rule-based and optimization-based approaches. Compared to the rule-based PMS/EMS, which relies heavily on human expertise, as well as predefined strategies and priorities, the optimization-based approaches can offer more efficient solutions and are more widely used nowadays. This article provides a comprehensive review of the marine optimization-based power/energy management system and discusses the future trends of PMS/EMS in ship power systems.

Feature selection (FS) is an essential technique widely applied in data mining. Recent studies have shown that evolutionary computing (EC) is very promising for FS due to its powerful search capability. However, most existing EC-based FS methods use a length-fixed encoding to represent feature subsets. This inflexible encoding turns ineffective when high-dimension data are handled, because it results in a huge search space, as well as a large amount of training time and memory overhead. In this article, we propose a length-adaptive genetic algorithm with Markov blanket (LAGAM), which adopts a length-variable individual encoding and enables individuals to evolve in their own search space. In LAGAM, features are rearranged decreasingly based on their relevance, and an adaptive length changing operator is introduced, which extends or shortens an individual to guide it to explore in a better search space. Local search based on Markov blanket (MB) is embedded to further improve individuals. Experiments are conducted on 12 high-dimensional datasets and results reveal that LAGAM performs better than existing methods. Specifically, it achieves a higher classification accuracy by using fewer features.

This paper investigated the techno-economic viability assessment of solar PV/wind/diesel generator (DG)/battery hybrid energy systems (HES) for powering an isolated rural health clinic in northern Nigeria. HOMER–software tool developed by the US National Renewable Energy Laboratory (NREL) has been utilized for the techno-economic assessment of the proposed HES. The results of the simulation reveal that PV/DG/battery HES with 5.43 kW PV, 2 kW DG, 3.06 kW power converter, and 10 units of batteries emerged as the optimum system and most preferable with the minimum Net Present Cost (NPC) of $16,457 and Cost of Energy (COE) of $0.259/kWh compared to other system cases. The outcome also shows that the optimized solution is environmentally friendly as it presented an acceptable carbon dioxide emission of 1304 kg/year, which was about 80% and 82.5% less than that of system case 3 (DG/battery) and system case 5 (DG-Only). To have a good understanding of the operation of various system configurations considered, details of the system’s battery storage status and power flow are discussed via the energy balance of the various system configurations. This analysis shows operating cost, fuel cost, COE, fuel consumption, and renewable fraction are sensitive to the variation in all the considered sensitivity parameters.

In this study, soybean straw (SS) as a promising source of glycolaldehyde-rich bio-oil production and extraction was investigated. Proximate and ultimate analysis of SS was performed to examine the feasibility and suitability of SS for thermochemical conversion design. The effect of the co-catalyst (CaCl2 + ash) on glycolaldehyde concentration (%) was examined. Thermogravimetric-Fourier-transform infrared (TG-FTIR) analysis was applied to optimize the pyrolysis temperature and biomass-to-catalyst ratio for glycolaldehyde-rich bio-oil production. By TG-FTIR analysis, the highest glycolaldehyde concentration of 8.57% was obtained at 500 °C without the catalyst, while 12.76 and 13.56% were obtained with the catalyst at 500 °C for a 1:6 ratio of SS-to-CaCl2 and a 1:4 ratio of SS-to-ash, respectively. Meanwhile, the highest glycolaldehyde concentrations (%) determined by gas chromatography–mass spectrometry (GC–MS) analysis for bio-oils produced at 500 °C (without the catalyst), a 1:6 ratio of SS-to-CaCl2, and a 1:4 ratio of SS-to-ash were found to be 11.3, 17.1, and 16.8%, respectively. These outcomes were fully consistent with the TG-FTIR results. Moreover, the effect of temperature on product distribution was investigated, and the highest bio-oil yield was achieved at 500 °C as 56.1%. This research work aims to develop an environment-friendly extraction technique involving aqueous-based imitation for glycolaldehyde extraction with 23.6% yield. Meanwhile, proton nuclear magnetic resonance (1H NMR) analysis was used to confirm the purity of the extracted glycolaldehyde, which was found as 91%.

Power grid pattern is expected to evolve from generator-based power systems towards converter-based systems in the forthcoming decades. Therefore, grid-forming converters will be pertinent to interconnected power grids in pursuance of enhancement their resilience against disturbances. This paper introduces a new efficient damping control method for grid-forming converters that provides a smooth power modulation and an efficient damping response against frequency and voltage deviations. First, an averaged state-space representation for a grid forming application in dq synchronization frame is derived. Based on this model, a new hybrid damping controller, including the concept of state feedback control and PI control, is proposed to address the main issues in existing controllers. The state feedback controller is optimally designed using a linear-quadratic regulator (LQR) approach to optimize the system performance. Moreover, the PI controller is optimally designed using the pattern search algorithm. The proposed damping control method integrates optimally between the control loops through a mapping matrix to rapidly synchronize with the grid and efficiently damp the oscillations. Simulations are carried out to prove the proposed method robustness. Finally, a comparative study using controller hardware-in-the-loop (CHiL) is employed against conventional system to validate the proposed damping method.

Biomass is one of the key components for bioenergy generation in recent epoch as traditional resources and depleting swiftly. Going through this fact, the present study aims to appraise the feasibility of Holy Thistle (HT) to produce energy and valuable organic chemicals through pyrolysis. The HT was pyrolyzed at four heating rates including, 10, 20, 30, and 40 °C min−1 to perform thermo kinetic modeling and estimate thermodynamics parameters to establish the pyrolysis reaction process. The pyrolysis process of HT illustrated about 85–88 % of thermal degradation achieved through three different stages from 30 to 800 °C. The major degradation stage was observed from 170 to 450 °C with 55% to 60 % product formation from mainly cellulose and hemicelluloses components. Moreover, the average activation energy and pre-exponential factors demonstrated to be 183–184 kJ mol−1 and 1010 min−1 to 1025 min−1, respectively. The pyrolytic products exhibited agreement to the cleaner production of bio-gas, char and bio-oil which is evident for the potential and productivity of the feed combination.

Microgrid is one of the promising green transition technologies that will provide enormous benefit to the seaport, as a solution to the major concerns in this sector, namely energy crisis, economical and environmental pollution. However, finest design of the microgrid is a challenging task considering different objectives, constraints and uncertainties involved. To ensure the optimal operation of the system, determining the right configuration framework and size for each component in the seaport microgrid at the minimum cost is a vital decision at the design stage. This paper aims to design a hybrid system of seaport microgrid with optimally sized component .The selected case study is the Port of Aalborg, Denmark. The proposed grid-connected structure consists of renewable energy sources (photovoltaic system and wind turbines), an energy storage system and cold ironing as seaport’ loads. The architecture is then optimized by utilizing HOMER to meet the maximum load demand by considering a few parameters such as solar global horizontal irradiance, temperature and wind resources. Then, the best configuration framework is analyzed in terms of economic feasibility, energy reliability and environmental impact.

This paper presents a comprehensive study that aims to establish the meaningful range for the ratios of full-bridge cells to the total number of cells per arm, in which the performance of the mixed cells modular multilevel converter (MC-MMC) can be customized by trading the number of FB cells for high value features such as: resiliency to DC faults, reduced capital costs of DC circuit breakers (DCCBs) and running costs of the semiconductor, and continued operation. The MC-MMC design for particular ratio of FB cells to total number of cells per arm to achieve tailored features at system level is termed as an customized modular multilevel converter (CMMC). The primary motivation for the CMMC is to facilitate the use of low-cost and relative slow mechanical DC circuit breakers, with fault isolation times in the order of 8 ms to 12.5 ms. With these objectives to be achieved, interruption of power flows across the DC grid and surrounding AC grids must be minimized. It has been found that after certain ratios of FB cells to total cells per arm, the CMMC starts to exhibit current limiting mode, which helps to reduce DCCBs current breaking capacities and extend critical fault clearance times for remote converters from the fault point. Results of the pole-to-ground and pole-to-pole DC faults, semiconductor loss studies, and extended control range indicate that the presented CMMC is promising for future realization of DC grids.

The introduction of a decentralized energy system in remote rural areas with limited or no access to power supply can improve the quality of life of people living in these areas. Renewable energy technology can play a key role in electricity generation, as grid expansion is not a cost-effective option. In this study, we focused on the techno-economic feasibility and optimal design of a hybrid micro-hydro-photovoltaic-diesel-battery-wind power system designed to electrify a typical remote village located in the southern part of Nigeria. We aimed at achieving the electrification at minimal cost while taking into cognizance the constraints of environmental pollutant emission. In this study, the technical details, as well as the economic feasibility of setting up such a power system, were determined using the hybrid optimization of multiple energy resources (HOMER) simulation tool. Different combinations of energy resources including solar, wind, hydro, and diesel were compared and analyzed. The system performance and economics using some determinant factors such as the cost of energy, operation, and maintenance cost, net present cost, excess electricity, capacity shortage, generator fuel consumption rates, and cost, load fulfillment, and CO2 and other pollutant gas emission savings were determined. The experimental results and the comparative analysis revealed that a hybrid hydro/PV/wind/diesel/battery system was the most ideal and preferred option for off-grid rural electrification. The simulation results also indicated that the optimal system had a net present cost (NPC) and cost of energy (COE) of $1.01 m and $0.106/kWh, respectively, with a renewable fraction of 77.4% and environmental pollutant emission of 228,945 kg/year. This system was found to be environmentally friendly as it emitted the least pollutant gas among all the considered configurations. Bearing in mind the recent advocacy towards the actualization of Sustainable Development Goal (SDG) number 7, this work was found to be in alignment with the tenet of “Affordable and Clean Energy”.

In concert with the transformation of conventional passive power distribution system, distributed energy resources (DERs) have progressively become participants in the provision of electricity services in active distribution networks (ADNs). In this paper, we propose a systematic valuation process to quantify the value of DERs in the ADN context. The paper first provides comprehensive insights into the impacts of DERs on ADN and the society as a whole. Given the technological, locational, and temporal diversity of DERs, a two-part scheme is developed to value and compensate DER portfolios proposed by customers and independent third parties. In particular, DERs are valued for their benefits and costs in both short and long terms. An integrated resource planning model is formulated to quantify the value of a given DER portfolio to be installed, where bi-level optimization techniques are applied to coordinate decisions on ADN planning and operations. In order to determine the short-term operation benefits of the DER portfolio on a continuous basis, a retail market operation model is developed based on peer-to-peer energy transactions among prosumers, when the impacts of DERs on ADN operations are monetized by distribution locational marginal prices. It is finally concluded in the paper that the proposed valuation scheme will not only contribute to the proactive investment of DERs in ADN but also help enhance the role of DERs in offering affordable, reliable, resilient and sustainable electricity services to customers.

In three-phase systems, using the delayed signal cancelation (DSC) operators is one of the most popular approaches for designing advanced phase-locked loops (PLLs), particularly for applications where a high disturbance rejection ability is demanded. In single-phase systems, however, they have not received a considerable attention. The aim of this paper is to develop advanced DSC-based PLLs for single-phase applications. To this end, three PLLs are designed and presented. The first is based on adaptive DSC operators, and the other two are based on nonadaptive operators. The design aspects of these PLLs are discussed in detail, and their performances are evaluated using experimental results.

Most photovoltaic (PV) plants conduct operation and maintenance (O&amp, M) by periodical inspection and cleaning. Such O&amp, M is costly and inefficient. It fails to detect system faults in time, thus causing heavy loss. To ensure their operations are at an ideal state, this work proposes an unsupervised method for intelligent performance evaluation and data-driven fault detection, which enables engineers to check PV panels in time and implement timely maintenance. It classifies monitoring data into three subsets: ideal period A, transition period S, and downturn period B. Based on A and B datasets, we build two non-continuous regression prediction models, which are based on a tree ensemble algorithm and then modified to fit the non-continuous characteristic of PV data. We compare real-time measured power with both upper and lower reference baselines derived from two predictive models. By calculating their threshold ranges, the proposed method achieves the instantaneous performance monitoring of PV power generation and provides failure identification and O&amp, M suggestions to engineers. It has been assessed on a 6.95 MW PV plant. Its evaluation results indicate that it is able to accurately determine different functioning states and detect both direct and indirect faults in a PV system, thereby achieving intelligent data-driven maintenance.

The dc component, which may be caused by different factors in the grid voltage, is one of the disturbances that may severely affect the performance of grid synchronization systems and, therefore, grid-tied power converters. In the phase-locked loop (PLL) and frequency-locked loop (FLL)-based grid synchronization systems, which this article focuses on, some solutions to deal with this challenge have been proposed in the literature. One of the best available solutions is adding dc rejection/estimation loop(s) to a standard PLL and FLL structure. This approach provides an estimation of the dc component and, at the same time, makes the PLL and FLL immune to disturbance effects of the dc component. Despite their implementation simplicity, no linear model for the grid synchronization systems with the dc rejection/estimation capability has yet been presented. The main aim of this article is to fill this research gap. It will be shown that developing such models facilitates the examination and the performance enhancement of the grid synchronization systems under study.

In practice, because of different factors, the supply voltage (especially in the distribution level) almost always has some degrees of imbalance and harmonic pollution. With increasing the level of these power quality issues in recent years, their monitoring and compensation using custom power devices have received much attention. In addition, modern power converter based renewable energy sources are expected to provide some ancillary services to mitigate these power quality issues. These tasks and requirements often involve using a signal processing tool for the online detection of the fundamental sequence components and harmonics of the voltage and/or current signals. The typical choice for this purpose is the discrete Fourier transform as it offers a fast computational speed. It, however, may not be a very attractive solution for applications where the selective extraction of a few frequency components is required as it demands a high computational effort. In such scenarios, using time-domain signal decomposition algorithms is more desirable. Generally speaking, these algorithms are nonlinear feedback control systems, which include two or more dynamically interactive frequency-Adaptive filters tuned to concerned frequency components. The complex structure of these algorithms, however, makes them complicated to analyze, especially for those who are not experienced in this field. This article aims to address this difficulty by developing harmonic models for these algorithms and investigating them. To this end, three case studies are considered. Through a harmonic linearization procedure, developing harmonic models for them is shown. The accuracy of these models is then investigated, and performing the harmonic stability analysis using them is demonstrated.

In recent years, single-phase frequency-locked loops (FLLs) are gaining more popularity as a signal processing and synchronization tool in a wide variety of engineering applications. In the power and energy area, a basic structure in designing the majority of available single-phase FLLs is the second-order generalized integrator-based FLL (SOGI-FLL), which is a nonlinear feedback control system. This nonlinearity makes the SOGI-FLL analysis complicated. To deal with this problem, some attempts to derive linear models for the SOGI-FLL have been made in very recent years. The available linear models, however, are not able to accurately predict the dynamic behavior, stability region, and robustness metrics of the SOGI-FLL. The situation is even worse for close variants of the SOGI-FLL because some of them have no linear model at all. Filling these gaps in research is the main goal of this article. To this end, the structural relationship among the SOGI-FLL and its variants is identified first. Based on this information and deriving the linear time-periodic (LTP) model of a recently proposed extended SOGI-FLL, the LTP models of the standard SOGI-FLL and its close variants are obtained. The accuracy assessment of these LTP models, discussion about their limitations, and performing the stability analysis using them are other contributions of this article.

Recent advances in using renewable energy resources make them more accessible and prevalent in microgrids (MGs) and nano grids (NGs) applications. Accordingly, much attention has been paid during the past few years to design and operate MGs with high renewable energy sources (RESs) penetration. Energy storage (ES) is the crucial enabler for reliable MG operation to help MGs become more resistant to disruptions, particularly with the increased penetration of RESs. In this regard, this paper formulates a two-stage optimization framework to improve a grid-connected MG performance. Firstly, the optimal allocation decisions of the battery ES systems (BESSs) are provided to enhance the self-consumption rate of the RESs and the hosting capacity (HC) of the MG. Secondly, an operation strategy with the results (number, location, and capacity) of the BESSs obtained from the first stage is handled as an objective function to minimize the MG&rsquo, s total operation cost. The IEEE 33-bus radial system is modified to act as the MG with high RESs penetration. The problem is solved using a recent swarm intelligence optimization algorithm called the Harris hawks optimization (HHO) algorithm. The proposed optimal operation strategy considers numerous constraints, such as the charge-discharge balance, number and capacity limitations of the BESSs, and the different technical performance constraints of the MG. The results obtained verify the proposed optimization framework&rsquo, s effectiveness for grid-connected MGs and validate the benefits gained from the appropriate allocation of BESSs. The results also indicate that oversized storage or using many unneeded storage units may adversely influence the MG&rsquo, s total power losses.

This paper proposes an enhanced energy management system (EEMS) for a residential AC microgrid. The renewable energy-based AC microgrid with hybrid energy storage is broken down into three distinct parts: a photovoltaic (PV) array as a green energy source, a battery (BT) and a supercapacitor (SC) as a hybrid energy storage system (HESS), and apartments and electric vehicles, given that the system is for residential areas. The developed EEMS ensures the optimal use of the PV arrays’ production, aiming to decrease electricity bills while reducing fast power changes in the battery, which increases the reliability of the system, since the battery undergoes fewer charging/discharging cycles. The proposed EEMS is a hybrid control strategy, which is composed of two stages: a state machine (SM) control to ensure the optimal operation of the battery, and an operating mode (OM) for the best operation of the SC. The obtained results show that the EEMS successfully involves SC during fast load and PV generation changes by decreasing the number of BT charging/discharging cycles, which significantly increases the system’s life span. Moreover, power loss is decreased during passing clouds phases by decreasing the power error between the extracted power by the sources and the required equivalent; the improvement in efficiency reaches 9.5%.

This paper proposes an enhanced modular multilevel converter as an alternative to the conventional half-bridge modular multilevel converter that employs a reduced number of medium-voltage cells, with the aim of improving waveforms quality in its AC and DC sides. Each enhanced modular multilevel converter arm consists of high-voltage and low-voltage chain-links. The enhanced modular multilevel converter uses the high-voltage chain-links based on medium-voltage half-bridge cells to synthesize the fundamental voltage using nearest level modulation. Although the low-voltage chain-links filter out the voltage harmonics from the voltage generated by the high-voltage chain-links, which are rough and stepped approximations of the fundamental voltage, the enhanced modular multilevel converter uses the nested multilevel concept to dramatically increase the number of voltage levels per phase compared to half-bridge modular multilevel converter. The aforementioned improvements are achieved at the cost of a small increase in semiconductor losses. Detailed simulations conducted in EMPT-RV and experimental results confirm the validity of the proposed converter.

This study presents types 1 and 2 hybrid converters with reduced power circuit complexity compared with the mixed cell modular multilevel converter (MC-MMC). The type 1 converter is formed by replacing the director switches of the alternate arm converter by high-voltage (HV) half-bridge (HB) cells rated for half of the dc-link voltage. Also, it resembles special case of MC-MMC, where the entire HB cells of each arm are lumped into a single HV HB cell, with both capacitors of the half- and full-bridge cells are exposed to fundamental current as in the conventional MMC. The upper and lower arms of the type 2 converter resemble a front-to-front connection of two three-phase hybrid cascaded two-level converters, where the cell capacitors of the three-phase two-level converters that act as director switches do not experience fundamental currents. Therefore, the type 2 converter offers compact design compared with type 1 converter and the MC-MMC. The technical viabilities of the proposed hybrid converters are assessed using simulations, with both converters modelled in MATLAB-Simulink using electromagnetic transient simulation approach, considering normal and transient conditions. Experimental results obtained from single-phase type 1 converter confirm the practical viability of the proposed converters.

The design of reliable power filters that mitigate current and voltage harmonics to meet the power quality requirements of the utility grid is a major requirement of present-day power systems. In this paper, a detailed systematic approach to design a shunt active power filter (SAPF) for power quality enhancement is discussed. A proportional&ndash, integral (PI) controller is adopted to regulate the DC-link voltage. The instantaneous reactive power theory is employed for the reference current&rsquo, s extraction. Hysteresis current control is used to obtain the gate pulses that control the voltage source inverter (VSI) switches. The detailed SAPF is developed and simulated for balanced nonlinear loads and unbalanced nonlinear loads using MATLAB/Simulink. The simulation results indicate that the proposed filter can minimize the harmonic distortion to a level below that deployed by the Institute of Electrical and Electronics Engineers (IEEE) standards.

The SOGI-FLL (Second-Order Generalized Integrator&ndash, Frequency-Locked Loop) is a well-known and simple adaptive filter that allows for estimating the parameters of grid voltage with a small computational burden. However, the SOGI-FLL has been shown to be especially sensitive to voltage sags and voltage swells, which deeply distort the estimated parameters, especially the frequency. This problem can be alleviated by simply using a saturation block at the Frequency-Locked Loop (FLL) output to limit the impact of distortion on the estimated frequency. Improving upon this straightforward approach, in this paper we propose the use of a finite state machine (FSM) for the definition of the different states of the SOGI-FLL frequency response during a voltage sag or swell fault. The FSM approach allows for applying different gains during the fault, enhancing the SOGI-FLL transient response. The performance of the FSM-based SOGI-FLL is evaluated by using simulation results, which show a better and faster response to these kinds of faults.

All-pass filter (APF) passes all frequency components of a signal without altering their amplitude, but changes their phase. This feature has made the APF a versatile building block in different signal processing applications. The focus of this article is on APF-based phase-locked loops (PLLs), where the APF is required for creating a $\text{90}^\circ$ phase shift at the fundamental frequency. Such a phase shift is needed for generating a fictitious orthogonal signal in single-phase applications and rejecting the grid voltage imbalance in three-phase systems. To the best of authors’ knowledge, none of the APF-based PLLs have an accurate model yet. This gap in knowledge makes the analysis of these synchronization systems and identifying their advantages/disadvantages compared to state-of-the-art structures complicated. The main objective of this article is to bridge this knowledge gap.

The second-order-generalized-integrator-based freq-uency-locked loop (SOGI-FLL) is a well-known tool for filtering and synchronization purposes in the power and energy applications. The SOGI-FLL, nevertheless, has a limited ability in rejecting the grid voltage disturbances. To deal with this problem, two advanced SOGI-FLLs have been proposed recently. In the first one, a SOGI-based filter is included inside the standard SOGI-FLL control loop, and in the second one, a SOGI-based filter is employed as the prefiltering stage of the SOGI-FLL. The small-signal modeling, tuning procedure, and detailed performance comparison of these advanced SOGI-FLLs have not been carried out yet. The aim of this paper is to cover these issues.

This paper employs an amplitude modulation with sinusoidal plus third harmonic injection instead of trapezoidal modulation to operate a controlled transition bridge (CTB) converter as ac/dc and dc/ac converter terminals. With such an operation, the CTB converter may require small ac filters; thus attractive for high-voltage direct current (HVDC) transmission systems. To facilitate ac voltage control over a wide range and black-start capability, the injected 3rd harmonic allows the cell capacitor voltages of the CTB converter to be regulated independent of the modulation index and power factor. The insertion of 3rd harmonic into modulating signals achieves two objectives: extends the regions around voltage zeros so that the total voltage unbalanced can be distributed between the cell capacitors, thereby exploiting the bipolar capability of the full-bridge cells in each limb; and to ensure that each limb can be clamped to the positive and negative dc rails every half fundamental period independent of the modulation index to allow recharge of the cell capacitors from the active dc link. The suitability of the CTB converter for HVDC type applications is demonstrated using a two-terminal HVDC link that employs a 21-cell CTB converter, considering normal operation and ac faults.

In power and energy applications, implementing a large number of phase-locked loops (PLLs) involves using transfer delays. These delays are employed for different control and filtering purposes, such as creating a fictitious orthogonal signal (which is required for the frame transformation in single-phase PLLs) and filtering harmonics, dc offset, and other disturbances. Depending on the application in hand and the expected variation range of the grid frequency, the length of these delays may be variable or fixed. Roughly speaking, the variable-length delays are often preferred for applications where large frequency drifts are anticipated and a high accuracy is required. To the best of authors’ knowledge, the small-signal modeling of a variable-length delay-based PLL has not yet been conducted. The main aim of this paper is to cover this gap. The tuning procedure and analysis of these PLLs are also presented. As design examples, some well-known single-phase and three-phase PLLs are considered.

This paper applies the adaptive gradient descent method to the second-order generalized integrator (SOGI) filter in order to find an online estimation algorithm for the grid frequency, which leads to the proposal of three possible estimators. One of them is identical to the frequency-locked loop algorithm reported in the literature, which proves that it should be understood as a gradient descent estimation algorithm and not as a “frequency locked loop.” The proposed gradient descent estimators are simple and suitable to be implemented into a digital processor with small computational burden. However, due to the SOGI characteristics, the estimators show to be especially sensitive to subharmonic and dc-offset voltage distortion. These problems are removed adopting a cascaded double SOGI approach, which strongly increases the rejection capability to harmonics and enhances the response to voltage sags. Simulation and experimental results are provided to validate the proposed contribution.

The available controller chips for power electronic systems are used for specific transient and steady-state performances. In such systems, the parameter ranges for stable operation are delimited by slow-timescale as well as fast-timescale instabilities. The usual practice is to design the control loop based on the state-space averaging technique, which cannot predict the fast-timescale instabilities. In this study, the first attempt has been made to propose a new design of the controller chip that can suppress these instabilities, thus extending the stable operating range in the parameter space. For this, the authors make use of the Filippov method which can effectively predict both types of instabilities. In this approach, the stability of the system is obtained in terms of the state transition matrices across each subsystem and saltation matrices across each switching event. The basic idea is to exercise control over the saltation matrices to increase the stability margin of the periodic orbit. Since in the Filippov approach an increase in the number of switching events in a cycle does not increase the complexity of the analysis, the proposed controller chip will be particularly useful in complex power electronic systems such as interconnected converters, multi-input multi-output converters, resonant converters, micro-grids and so on.

Frequency-locked loops (FLLs) create a rather large category of closed-loop synchronization techniques, which have received considerable attention in different engineering applications, particularly for synchronization, signal processing, and control purposes. Focusing on single-phase grid applications, designing FLLs is often based on a second-order generalized integrator (SOGI), and the SOGI-FLL is regarded as a standard structure. Using the linear Kalman filter (LKF), complex bandpass filter (CBF), and circular limit-cycle oscillator (CLO) are some alternative approaches. FLLs based on these filters/elements, which are briefly referred to as the LKF-FLL, $1\phi$-CBF-FLL, and CLO-FLL, have not been well analyzed in the literature, and limited knowledge about their real advantages/disadvantages compared to the SOGI-FLL exists. Covering this gap is the objective of this paper.

This paper presents a techno-economic feasibility evaluation for a grid-connected photovoltaic energy conversion system on the rooftop of a typical residential building in Jeddah, one of the major cities in Saudi Arabia. In Saudi Arabia, electric energy consumption is the highest in the domestic sector, with 48.1% of the total electricity consumption. As the power generation in Saudi Arabia mainly relies on conventional resources, environmental pollution and energy sustainability are major concerns. To minimize these issues, the Saudi government is in the process of maximizing the utilization of renewable energy resources for power generation. Investing in solar energy in Saudi Arabia is important because the country is witnessing a rapid increase in load demand, with annual growth rates of 6%. In this paper, the system advisor model software for renewable energy modeling has been utilized to perform a techno-economic feasibility analysis of a residential grid-connected solar photovoltaic (PV) system, which is proposed for a typical apartment in Saudi Arabia, on the basis of various key performance indicators, namely: yield factor, capacity factor, performance ratio, levelized cost of energy, net present value, internal rate of return, and payback period. A sensitivity analysis that investigates the impact of varying techno-economic parameters on system performance and feasibility is also discussed. The size of the PV system for a typical Saudi Arabian apartment is estimated to be 12.25 kW. Results have shown that the proposed system can generate 87% of the electricity needs of an apartment. The technical analysis showed that the capacity factor and the performance ratio were 22% and 78% respectively. The levelized cost of energy and net present value revealed competitive figures of 0.0382 $/kWh and $4378, respectively. The investigations indicate that residential PV installations are an effective option for energy management in the country.

This paper proposes a critical analysis of the literature addressed to modelling and simulations of human crowds with the aim of selecting the most appropriate scale out of the microscopic (individual based), mesoscopic (kinetic), and macroscopic (hydrodynamical) approaches. The selection is made focusing on possible applications of the model. In particular, model validation and safety problems, where validation consists of studying the ability of models to depict empirical data and observed emerging behaviors. The contents of the paper look forward to computational applications related to the flow crowds on the Jamarat bridge.

In this research, sinusoidal tank including inner circular cylinder was considered and to expedite the solidification, radial fins were installed over the inner cold cylinder. To improve the conduction, CuO nano sized material was added and effects of size of particles were involved. The governing equations consist of energy equation with one source term of solid fraction and equation for distribution of ice fraction. To fins the solution, Galerkin approach was applied and different mesh configuration in various time step helps to capture the phenomena more accurate. Validation with experimental data shows the nice accommodation. So, influence of fins length and diameter of particles were imposed. As longer fins were employed, the solidification time reduces about 3.74% when dp = 40. As dp rises from 40 to 50, temperature augments and greater energy has been achieved because of augmentation of needed time from 175.44 to 264.05 s. Impact of dp on isotherms is more significant than fins length.

The present experimental investigation describes the impact of surfactants (such as Benzalkonium chloride (BAC), Cetrimonium chloride (CTAC), Ammonium lauryl sulphate (ALS), PLS (Pottasium lauryl sulphate), Brij 700, and Span 80), sonication time (30–240 min.), and temperature (55 °C ~ 80 °C), on the stability and viscosity of hybrid nanoparticle (CeO2 + MWCNT) for different base fluids (water, silicone oil, EG, and therminol VP-I). The results of Zeta potential analysis indicated that BAC surfactant shows the best impact on hybrid nanofluid stability (HNF). The observed optimum sonication time is 60, 120, 90, and 120 min, respectively, for silicon oil, EG, water, and therminol VP-I for which HNF yields maximum zeta potential value. With the increment in operating temperature range, the stability of prepared HNF using different base fluids and adding six different surfactants has decreased. Furthermore, it is found that with the increase in sonication time, the viscosity of HNF firstly decreases up to an optimum time, after which it increases gradually. The rheological behavior of working HNF for various practical applications of the current suspensions is also reported. From 3S analysis such as sonication, surfactant, and stability, De-Ionized (DI) Water is advisable to be used as a base fluid for the particle combination of CeO2 + MWCNT with 80:20 mixture ratio as it provides long-term stability and marginal viscosity enhancement. Finally, results show that the CeO2 + MWCNT (80,20)/ DI water nano colloidal behaves as a Non-Newtonian fluid as there is no linear agreement found between shear stress and shear rate.

Parallel configuration is the main common and conventional structure of the plate heat exchangers. However, this paper focuses on non-parallel configuration for these types of heat exchangers and clarifies whether these configurations are more thermally efficient compared to the parallel plates. Besides, frictional and exergetic behavior of non-parallel structures are investigated as well. As shown in the graphical abstract, eight configurations are possible for non-parallel structures all of which are comprehensively studied in this research using a validated 3-D numerical simulation. The results show that the non-parallel plates provide higher Nusselt number and thermal performance factor compared to the common parallel plates. In the same value of inlet mass flow rate, case “e” in which hot fluid moves though the converge channel and cold fluid moves through the divergent channel obtains the maximum Nu number. Obtained thermal performance factors higher than unity show the positive role of non-parallel structures with consideration of both Nusselt number and friction factor. Generally, it is concluded that non-parallel structures can be considered as an efficient method to augment the efficiency of plate heat exchangers. Many other parameters in term of second law of thermodynamics are studied for all structures as well in this study.