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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Energy Science and Technology".

Deadline for manuscript submissions: closed (15 July 2018) | Viewed by 51140

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Prof. Dr. Tomonobu Senjyu

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Department of Electrical and Electronics Engineering, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan
Interests: high-efficiency energy conversion system; renewable energy in small islands; optimization of power system operation and control
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Special Issue Information

Dear Colleagues,

The Guest Editor is inviting submissions for a Special Issue of Applied Sciences on the subject area of "Renewable Energy 2018". Renewable energy is being introduced globally. Renewable energy is a promising and/or alternative energy resource in the world. This kind of energy reduces greenhouse gas compared with fossil resources. The introduction of renewable energy is environmental friendly and comprehensive in our society. However, highly-efficient and economic usage of renewable energy is a challenging task. We need to know the wide variety of knowledge for control, power electronics, power systems, etc. This Special Issue deals with recent state-of-the-art technology for renewable energy. These technologies increase the introduction of renewable energy in the world.

This Special Issue will focus on renewable energy and its applications. Topics of interest for publication include, but are not limited to:

• Wind energy;
• Solar energy;
• Tidal energy;
• Wave energy;
• Biomass energy;
• Energy storage;
• Energy transportation;
• Electrical power transmission;
• Energy distribution;
• Energy conversions;
• Control technique for renewable energy;
• Optimization technique for renewable energy;
• Reduction of CO2 emission;
• Economic issues in renewable energy;
• Hydrogen production from renewable energy.

Prof. Dr. Tomonobu Senjyu
Guest Editor

Manuscript Submission Information

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Published Papers (10 papers)

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Research

23 pages, 924 KiB

Open AccessFeature PaperArticle

Optimal Operation Method for Distribution Systems Considering Distributed Generators Imparted with Reactive Power Incentive

by Ryuto Shigenobu, Mitsunaga Kinjo, Paras Mandal, Abdul Motin Howlader and Tomonobu Senjyu

Appl. Sci. 2018, 8(8), 1411; https://doi.org/10.3390/app8081411 - 20 Aug 2018

Cited by 7 | Viewed by 4978

Abstract

In order to solve urgent energy and environmental problems, it is essential to carry out high installation of distributed generation using renewable energy sources (RESs) and environmentally-friendly storage technologies. However, a high penetration of RESs usually leads to a conventional power system unreliability, instability and low power quality. Therefore, this paper proposes a reactive power control method based on the demand response (DR) program to achieve a safe, reliable and stable power system. This program does not enforce a change in the active power usage of the customer, but provides a reactive power incentive to customers who participate in the cooperative control of the distribution company (DisCo). Customers can achieve a reduction in their total energy purchase by gaining a reactive power incentive, whilst the DisCo can achieve a reduction of its total procurement of equipment and distribution losses. An optimal control schedule is calculated using the particle swarm optimization (PSO) method, and also in order to avoid over-control, a modified scheduling method that is a dual scheduling method has been adopted in this paper. The effectiveness of the proposed method was verified by numerical simulation. Then, simulation results have been analyzed by case studies. Full article

(This article belongs to the Special Issue Renewable Energy 2018)

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19 pages, 3875 KiB

Open AccessArticle

Multi-Phase Under Voltage Load Shedding Scheme for Preventing Delayed Voltage Recovery by Induction Motor Power Consumption Characteristics

by Yunhwan Lee and Hwachang Song

Appl. Sci. 2018, 8(7), 1115; https://doi.org/10.3390/app8071115 - 10 Jul 2018

Cited by 2 | Viewed by 4753

Abstract

This paper aims to develop a multi-phase under voltage load shedding (MUVLS) strategy that effectively sheds the load to mitigate delayed voltage recovery (DVR). The major cause of the DVR phenomenon is related to the dynamic characteristics of induction motor (IM) loads. The deaccelerating and stalling of the IM load during disturbances is the main driving force of short-term voltage instability, resulting in an amount of reactive power consumption and excessive current draw. With the economic efficiency of energy use, the proportion of IM loads is gradually increasing, and this trend might deteriorate system stability. This paper focuses on the impact of IM loads in the Korean power system and analyzes the parameter sensitivity of IM loads and the proportion of appropriate IM loads. The proposed procedure for under voltage load shedding (UVLS) applies voltage stability criteria to decide the most efficient load shedding scheme. The determined MUVLS scheme can offer new and more effective remedial actions to maintain voltage stability, considering the characteristics of IM loads. Case studies on the Korean power system have validated the performance of the proposed MUVLS scheme under severe contingency scenarios, showing that the proposed strategy effectively mitigates DVR. Full article

(This article belongs to the Special Issue Renewable Energy 2018)

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27 pages, 4967 KiB

Open AccessArticle

Research on Distributed PV Storage Virtual Synchronous Generator System and Its Static Frequency Characteristic Analysis

by Xiangwu Yan, Xueyuan Zhang, Bo Zhang, Yanjun Ma and Ming Wu

Appl. Sci. 2018, 8(4), 532; https://doi.org/10.3390/app8040532 - 30 Mar 2018

Cited by 14 | Viewed by 5603

Abstract

The increasing penetration rate of grid connected renewable energy power generation reduces the primary frequency regulation capability of the system and poses a challenge to the security and stability of the power grid. In this paper, a distributed photovoltaic (PV) storage virtual synchronous generator system is constructed, which realizes the external characteristics of synchronous generator/motor. For this kind of input/output bidirectional devices (e.g., renewable power generation/storage combined systems, pumped storage power stations, battery energy storage systems, and vehicle-to-grid electric vehicles), a synthesis analysis method for system power-frequency considering source-load static frequency characteristics (S-L analysis method) is proposed in order to depict the system’s power balance dynamic adjustment process visually. Simultaneously, an inertia matching method is proposed to solve the problem of inertia matching in the power grid. Through the simulation experiment in MATLAB, the feasibility of the distributed PV storage synchronous virtual machine system is verified as well as the effectiveness of S-L analysis method and inertia matching method. Full article

(This article belongs to the Special Issue Renewable Energy 2018)

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19 pages, 5138 KiB

Open AccessArticle

A Novel Distributed Large-Scale Demand Response Scheme in High Proportion Renewable Energy Sources Integration Power Systems

by Shuai Fan, Guangyu He, Kunqi Jia and Zhihua Wang

Appl. Sci. 2018, 8(3), 452; https://doi.org/10.3390/app8030452 - 16 Mar 2018

Cited by 19 | Viewed by 4429

Abstract

Large-scale demand response (DR) is a useful regulatory method used in high proportion renewable energy sources (RES) integration power systems. Current incentive-based DR schemes are unsuitable for large-scale DR due to their centralized formulation. This paper proposes a distributed scheme to support large-scale implementation of DR. To measure DR performance, this paper proposes the customer directrix load (CDL), which is a desired load profile, to replace the customer baseline load (CBL). The uniqueness of CDL makes it more suitable for distributed schemes, while numerous CBLs have to be calculated in a centralized manner to ensure fairness. To allocate DR tasks and rebates, this paper proposes a distributed approach, where the load serving entity (LSE) only needs to publish a total rebate and corresponding CDL. As for each customer, s/he needs to claim an ideal rebate ratio that ranges from 0 to 1, which indicates the proportion of rebate s/he wants to get from LSE. The rebate value for each customer also determines his or her DR task. Then, the process of customer claims for the ideal rebate ratio is modeled as a non-cooperative game, and the Nash equilibrium is proved to exist. The Gossip algorithm is improved in this paper to be suitable for socially connected networks, and the entire game process is distributed. Finally, a large-scale DR system is formulated. The simulation results show that the proposed DR can promote the consumption of RES. Additionally, this scheme is suitable for large-scale customer systems, and the distributed game process is effective. Full article

(This article belongs to the Special Issue Renewable Energy 2018)

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20 pages, 952 KiB

Open AccessArticle

Hybrid Genetic Algorithm Fuzzy-Based Control Schemes for Small Power System with High-Penetration Wind Farms

by Mohammed Elsayed Lotfy, Tomonobu Senjyu, Mohammed Abdel-Fattah Farahat, Amal Farouq Abdel-Gawad, Liu Lei and Manoj Datta

Appl. Sci. 2018, 8(3), 373; https://doi.org/10.3390/app8030373 - 4 Mar 2018

Cited by 29 | Viewed by 4894

Abstract

Wind is a clean, abundant, and inexhaustible source of energy. However, wind power is not constant, as windmill output is proportional to the cube of wind speed. As a result, the generated power of wind turbine generators (WTGs) fluctuates significantly. Power fluctuation leads to frequency deviation and voltage flicker inside the system. This paper presents a new methodology for controlling system frequency and power. Two decentralized fuzzy logic-based control schemes with a high-penetration non-storage wind–diesel system are studied. First, one is implemented in the governor of conventional generators to damp frequency oscillation, while the other is applied to control the pitch angle system of wind turbines to smooth wind output power fluctuations and enhance the power system performance. A genetic algorithm (GA) is employed to tune and optimize the membership function parameters of the fuzzy logic controllers to obtain optimal performance. The effectiveness of the suggested controllers is validated by time domain simulation for the standard IEEE nine-bus three-generator test system, including three wind farms. The robustness of the power system is checked under normal and faulty operating conditions. Full article

(This article belongs to the Special Issue Renewable Energy 2018)

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15 pages, 1801 KiB

Open AccessArticle

Thermal Pre-Treatment of Sewage Sludge in a Lab-Scale Fluidized Bed for Enhancing Its Solid Fuel Properties

by Sujeeta Karki, Jeeban Poudel and Sea Cheon Oh

Appl. Sci. 2018, 8(2), 183; https://doi.org/10.3390/app8020183 - 26 Jan 2018

Cited by 14 | Viewed by 4927

Abstract

Thermal pre-treatment of non-lignocellulosic biomass, sewage sludge, using a lab-scale fluidized bed reactor was carried out in order to enhance its solid fuel properties. The influence of the torrefaction temperature range from 200–350 °C and 0–50 min residence time on the physical and chemical properties of the torrefied product was investigated. Properties of the torrefied product were analyzed on the basis of the degree of torrefaction, ultimate and proximate analysis, and gas analysis. An attempt was made to obtain the chemical exergy of sewage sludge. An elevated torrefaction temperature presented a beneficial impact on the degree of torrefaction and chemical exergy. Moreover, the effect of the torrefaction temperature and residence time on the elemental variation of sewage sludge exhibited an increase in the weight percentage of carbon while the H/C and O/C molar ratios deteriorated. Additionally, the product gas emitted during torrefaction was analyzed to study the pathway of hydrocarbons and oxygen containing compounds. The compounds with oxygen were emitted at higher temperatures in contrast to hydrocarbon gases. In addition, the study of various correlations for predicting the calorific value of torrefied sewage sludge was made. Full article

(This article belongs to the Special Issue Renewable Energy 2018)

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18 pages, 6507 KiB

Open AccessArticle

Low-Voltage Ride-Through Control Strategy for a Grid-Connected Energy Storage System

by Yeongsu Bak, June-Seok Lee and Kyo-Beum Lee

Appl. Sci. 2018, 8(1), 57; https://doi.org/10.3390/app8010057 - 2 Jan 2018

Cited by 38 | Viewed by 7224

Abstract

This paper presents a low-voltage ride-through (LVRT) control strategy for grid-connected energy storage systems (ESSs). In the past, researchers have investigated the LVRT control strategies to apply them to wind power generation (WPG) and solar energy generation (SEG) systems. Regardless of the energy source, the main purpose of the LVRT control strategies is to inject reactive power into the grid depending on the grid-code regulations using the grid-side inverter; the proposed LVRT control strategy for grid-connected ESSs also has the same purpose. However, unlike the WPG and SEG systems having unidirectional power flow, grid-connected ESSs have a bidirectional power flow. Therefore, the charging condition of the grid-connected ESSs should be considered for the LVRT control strategy. The proposed LVRT control strategy for grid-connected ESSs determines the injection quantity of the active and reactive currents, and the strategy depends on the voltage drop ratio of the three-phase grid. Additionally, in this paper, we analyzed the variations of the point of common coupling (PCC) voltage depending on the phase of the reactive current during the charging and discharging conditions. The validity of the proposed LVRT control strategy is verified and the variations of the PCC voltage of the grid-connected ESS are analyzed by simulation and experimental results. Full article

(This article belongs to the Special Issue Renewable Energy 2018)

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706 KiB

Open AccessArticle

Robust Control Examples Applied to a Wind Turbine Simulated Model

by Silvio Simani and Paolo Castaldi

Appl. Sci. 2018, 8(1), 29; https://doi.org/10.3390/app8010029 - 26 Dec 2017

Cited by 13 | Viewed by 4120

Abstract

Wind turbine plants are complex dynamic and uncertain processes driven by stochastic inputs and disturbances, as well as different loads represented by gyroscopic, centrifugal and gravitational forces. Moreover, as their aerodynamic models are nonlinear, both modeling and control become challenging problems. On the one hand, high-fidelity simulators should contain different parameters and variables in order to accurately describe the main dynamic system behavior. Therefore, the development of modeling and control for wind turbine systems should consider these complexity aspects. On the other hand, these control solutions have to include the main wind turbine dynamic characteristics without becoming too complicated. The main point of this paper is thus to provide two practical examples of the development of robust control strategies when applied to a simulated wind turbine plant. Extended simulations with the wind turbine benchmark model and the Monte Carlo tool represent the instruments for assessing the robustness and reliability aspects of the developed control methodologies when the model-reality mismatch and measurement errors are also considered. Advantages and drawbacks of these regulation methods are also highlighted with respect to different control strategies via proper performance metrics. Full article

(This article belongs to the Special Issue Renewable Energy 2018)

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2302 KiB

Open AccessArticle

Utilizing Downdraft Fixed Bed Reactor for Thermal Upgrading of Sewage Sludge as Fuel by Torrefaction

by Sujeeta Karki, Jeeban Poudel and Sea Cheon Oh

Appl. Sci. 2017, 7(11), 1189; https://doi.org/10.3390/app7111189 - 18 Nov 2017

Cited by 1 | Viewed by 4333

Abstract

A lab-scale downdraft fixed bed reactor was used for the study of sewage sludge, a non-lignocellulosic biomass, torrefaction to enhance the thermochemical properties of sewage sludge. The torrefaction was carried out for a temperature range of 200–350 °C and a residence time of 0–50 min. Degree of torrefaction, torrefaction index, chemical exergy, gas analysis, and molar ratios were taken into account to analyze the torrefied product with respect to torrefaction temperature. The effect of torrefaction temperature was very pronounced and the temperature range of 250–300 °C was considered to be the optimum torrefaction temperature range for sewage sludge. Chemical exergy, calorific value and torrefaction index were significantly influenced by the change in the relative carbon content resulting in decrease of the O/C and H/C molar ratios. Full article

(This article belongs to the Special Issue Renewable Energy 2018)

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804 KiB

Open AccessArticle

Spectral Correction of CPV Modules Equipped with GaInP/GaInAs/Ge Solar Cells and Fresnel Lenses

by Marios Theristis, Eduardo F. Fernández, Florencia Almonacid and George E. Georghiou

Appl. Sci. 2017, 7(8), 842; https://doi.org/10.3390/app7080842 - 16 Aug 2017

Cited by 9 | Viewed by 3933

Abstract

Photovoltaic (PV) devices are spectrally selective, and their performance is influenced by unavoidable spectral variations. In addition, multijunction-based concentrating photovoltaic (CPV) devices show a strong spectral dependence due to the series connection of various junctions with different absorption bands, and also due to the use of concentrator optics. In this work, the accuracy of a new set of analytical equations that quantify the spectral impact caused by the changes in air mass (AM), aerosol optical depth (AOD) and precipitable water (PW) is discussed. Four different CPV devices based on lattice-matched and metamorphic triple-junction solar cells and a poly(methyl methacrylate) (PMMA) and silicon-on-glass (SoG) Fresnel lenses are considered. A long-term outdoor experimental campaign was carried out at the Centre for Advanced Studies on Energy and Environment (CEAEMA) of the University of Jaén, Spain. Results show a high accuracy in the estimations of the spectral factor (SF), with an average mean absolute percentage error (MAPE) within 0.91% and a mean relative error (MRE) within −0.32%. Full article

(This article belongs to the Special Issue Renewable Energy 2018)

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