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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.

Energy systems, in general, and power systems, in particular, are undergoing a changing landscape in terms of generation and demand portfolios. These transitions, although offering new economic and labor market opportunities, bring forth a suite of unprecedented technical implications and challenges in the interim. According to experts, our planet's population will reach 9.3 billion in the next four decades. A fundamental and granular outlook on global energy systems (prior to the COVID-19 outbreak) predicted that electricity consumption will double by 2050, with electrified transportation and higher living standards in buildings being among the principal components of this increase.

A second-order generalized integrator (SOGI) is a resonant regulator with a pair of complex-conjugate poles, and therefore, with infinite magnitude at its center frequency. Thanks to this property, one can put together a set of m SOGIs in an elegant way and decompose a single-phase signal into its constituent frequency components and detect their amplitude and phase angle. Such a configuration, which is often referred to as the multi-SOGI (MSOGI) structure, requires a frequency estimator to adapt the center frequency of SOGIs to frequency changes. This frequency estimation is often provided by interconnecting the MSOGI structure with a basic frequency-locked loop (FLL) or phase-locked loop (PLL). The resulting structures are known as the MSOGI-FLL and MSOGI-PLL. These structures and their close variants are mathematically difficult to analyze probably because of the lack of a linear model for these systems. This article aims to bridge this research gap. First, it is shown how linear time-periodic (LTP) models of the MSOGI-FLL and MSOGI-PLL can be obtained. The model verification, obtaining open-loop harmonic transfer function from the LTP model, and LTP stability assessment of MSOGI-based synchronization systems are the next parts of this article. Finally, some close variants of the MSOGI-FLL/PLL are considered and their modeling and stability assessment are briefly discussed.

With the increased installation of voltage source converters (VSCs) into the power grid, concerns about resonance/stability issues associated with interactions among converters, and between them and the ac grid is growing. The prevailing method for investigating these issues is the impedance modeling of VSCs, which involves linearizing all their control elements, such as their current control and grid synchronization system among others. In this process, most often a phase-locked loop (PLL) is considered for the grid synchronization of VSCs in the literature. The available options for the grid synchronization, however, are not limited to PLLs; a large number of frequency-locked loops (FLLs) for the grid synchronization of VSCs may also be found in the literature. The impedance modeling of three-phase VSCs equipped with FLL-based grid synchronization systems can be quite challenging as FLLs have different structures compared to PLLs. This article aims to address this difficulty. The general idea is obtaining the PLL counterparts of FLLs, which makes the VSC impedance modeling very straightforward. To make this idea clear, several case studies are presented and investigated.

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 thermal conversion of biomass plays an important role in the development of energy reaping technologies and fire engineering. The study investigates the bioenergy potential of Reed Canary (Phalaris arundinacea) through investigating the combustion kinetics and thermal behavior. Reed Canary samples were collected from various rural areas of Ontario, Canada. Four heating rates (10, 20, 30, and 40 °C min−1) were utilized to perform the thermal degradation analysis using a thermogravimetric analyzer. Three different stages were identified ranging from 25 °C to 800 °C in which major degradation stage had two regions from 210 °C to 530 °C where most of the biomass changed into products. Furthermore, iso-conversional models including Kissenger-Akahira-Sunose (KSA), Starink and Flynn–Wall–Ozawa (FWO) were used to evaluate the reaction kinetics such as the activation energy and the pre-exponential factor. The reported kinetics parameters demonstrate the promising potential of Reed Canary for bioenergy production. Moreover, the low cost and the abundance of Reed Canary facilitate the possibility of introducing the biomass as a cost efficient and environmentally friendly natural resource for renewable bioenergy production.

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 this paper, a 1D model of direct contact membrane distillation is presented in which all fluid properties are temperature-dependent. In addition, a Nusselt number (Nu) relationship for developing flow in ducts (accounting for both thermal and hydrodynamic effects) is used to obtain the convective heat transfer coefficient at each side of the membrane. Simulated mass flux shows very good agreement with experimental measurements at various feed temperature, flow rate and concentration. A comprehensive sensitivity analysis of all operational and geometrical parameters, as well as Nu estimation parameters on water mass flux across the membrane $$(J_{\text{m}} )$$ and thermal efficiency, is also done. To determine the relative importance of each parameter, a multi-parameter sensitivity analysis (MPSA) based on the Monte Carlo method is applied, and the sensitivity index of each parameter at the defined range is computed. Results show that $$J_{\text{m}}$$ is highly sensitive to bulk feed inlet temperature ( $$T_{{{\text{in}},{\text{f}}}}$$ ) while both $$J_{\text{m}}$$ and thermal efficiency are highly sensitive to membrane porosity. Results show that among all parameters, just membrane porosity is highly sensitive which affects both mass flux and thermal efficiency especially at low $$T_{{{\text{in}}.{\text{f}}}}$$ .

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.

Now-a-days many protective problems have been encountered due to the existence of distributed generators. The major problem is unintentional islanding phenomenon. This can cause hazardous conditions for people who are working and equipment connected to it. So it is required to detect the phenomena of islanding within 2 sec according to IEEE 1547 standards. In this paper, a new hybrid islanding detection method to identify islanding states has been proposed based on combined changes of the rate of change of active power (ROCOAP) and rate of change of reactive power (ROCORP) at the point of common coupling (PCC). Due to hybrid nature, the performance of this method is better compared with previous methods. To validate the performance of the proposed detection techniques simulations are carried out on PSCAD/EMTDC. From the simulation results, it has been observed that the proposed technique can detect islanding faster which is less than 2 sec.

The paper proposes a new 0.8Voc model technique for medium voltage megawatt photovoltaic (PV) system integration. The power-voltage characteristic of photovoltaic (PV) modules shows multiple of local maximum power point when the modules are exposed to different irradiance levels. It is predicted that the local peaks are located near the multiples of 0.8 V oc , where V oc is .the open circuit voltage of the PV module. However, this prediction is not necessary correct especially with long string of PV modules exposed to lower irradiance level. It is most likely that the algorithm will deviate from the original peak locations and unnecessary scanning will be essential. Therefore, a new 0.8Voc model is proposed, which estimates the voltage at global maximum power point. By scanning the PV current on I-V characteristic curve to map out solar irradiance pattern, peak voltage and related deviation correction expressions are calculated. Afterwards, the position of the global peak voltage is estimated. The proposed algorithm is capable of exploiting the advantages of conventional 0.8Voc model, while improving its performance. The principles of design and theoretical analysis of the proposed algorithm are presented and its feasibility also validated by simulation for medium voltage megawatt photovoltaic (PV) system integration.

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.

In a power conditioning fuel cell system, the application of a single phase voltage source inverter (VSI) generates a second harmonic (100/120 Hz) ripple current. The harmonic current reduces life,...

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.

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.

The objective of the current paper is to study the two-dimensional, incompressible nanofluid flow over a curved stretching sheet coiled in a circle. Further, the impact of dispersion of nanoparticle CuO in base liquid water on the performance of flow, thermal conductivity and mass transfer using KKL model in the presence of Cattaneo-Christov heat flux and activation energy is deliberated. A curvilinear coordinate system is used to develop the mathematical model describing the flow phenomena in the form of partial differential equations. Further, by means of apt similarity transformations the governing boundary value problems are reduced to ordinary differential equations. Mathematical computations are simplified using Runge-Kutta-Fehlberg-45(RKF-45) process by adopting shooting method. Graphical illustrations of velocity, temperature, concentration gradients for various pertinent parameters are presented. The result reveals that, the heightening of porosity parameter heightens the thermal gradient but converse trend is depicted in velocity gradient. The enhancing values of Schmidt number and chemical reaction rate parameter declines concentration gradient whereas converse trend is depicted for upsurge in activation energy parameter.

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.

This paper discusses maximum power point tracking (MPPT) methods of PV system for normal and partial shading conditions (PSC). The selected MPPT methods were classified as artificial intelligent, hybrid, and other MPPT methods. The comparison of researches on MPPT methods under normal condition and PSC reveals that researchers have concentrated more on shading conditions since the last few years mainly due to the need of power output and efficiency improvements. It is believed that the information contained in this piece of work will be of great use for the researchers in the field under consideration.

Certain environmental conditions such as accumulation of dust and change in weather conditions affect the amount of solar radiation received by photovoltaic (PV) panel surfaces and thus have a significant effect on panel efficiency. This study conducted an experimental investigation in Surabaya, Indonesia, on the effect of these factors on output PV power reduction from the surface of a PV module. The module was exposed to outside weather conditions and connected to a measurement system developed using a rule-based model to identify different environmental conditions. The rule-based model, a clear sky solar irradiance model that included solar position, and a PV temperature model were then used to estimate the PV output power, and tests were also conducted using an ARM Cortex-M4 microcontroller STM32F407 as a standalone digital controller equipped with voltage, current, temperature, and humidity sensors to measure real time PV output power. In this system, humidity was monitored to identify dusty, cloudy, and rainy conditions. Validated test results demonstrate that the prediction error of PV power output based on the model is 3.6% compared to field measurements under clean surface conditions. The effects of dust accumulation and weather conditions on PV panel power output were then analyzed after one to four weeks of exposure. Results revealed that two weeks of dust accumulation caused a PV power output reduction of 10.8% in an average relative humidity of 52.24%. Results of the experiment under rainy conditions revealed a decrease in PV output power of more than 40% in average relative humidity of 76.32%, and a decrease in output power during cloudy conditions of more than 45% in an average relative humidity of 60.45% was observed. This study reveals that local environmental conditions, i.e., dust, rain, and partial cloud, significantly reduce PV power output.

The tilt angle of photovoltaic (PV) panels is a major factor affecting the amount of solar radiation falling on the panel surface. The optimum tilt angle depends on the position of the sun, latitude and local geographical characteristics. This paper investigates PV panel optimum tilt angles for various cities in the Kingdom of Saudi Arabia. For simulation purposes, horizontal solar radiation data for the study cities was obtained from NASA. MATLAB software was used to optimize tilt angle by maximizing solar radiation. Experiments were conducted to validate the theoretical requirement for negative tilt angles during summer. Results demonstrate that adjusting tilt angles six times per year harvests 99.5% of the solar radiation that could be attained with daily PV panel adjustment.

Current source inverters (CSIs) have increasingly become popular because of their inherent advantages over voltage source inverter. In a single phase system, the operation of multilevel current source inverter (MCSI) requires large and bulky DC link inductor and the employment of switching state redundancy to balance the inductor currents limit the advantages of MCSI. This study proposed a new configuration for parallel MCSI. The proposed energy-recovery scheme provides a major path to release its stored energy in order to balance the sharing inductor currents and introduces a novel single state switching technique for the generation of MCSI output current. In addition, a chopper circuit with smaller inductor size is employed to replace the large and bulky input DC link inductor. An integration of five-level MCSI and a chopper based DC-current source with energy recovery scheme circuits produce a five-level MCSI with a simple converter structure. The performance of the proposed MCSI is analysed through MATLAB and is verified by constructing a prototype. The results demonstrate that the proposed circuit with the balancing inductor current scheme significantly reduces the input DC link inductor size, eliminate the control complexity in balancing the inductor currents and has excellent sharing inductor current characteristics.