Energies

316 KiB

Open AccessArticle

Modeling and Performance Analysis of State Transitions for Energy-Efficient Femto Base Stations

by YunWon Chung

Energies 2015, 8(5), 4629-4646; https://doi.org/10.3390/en8054629 - 21 May 2015

Cited by 2 | Viewed by 4004

Lowering the energy required by base stations (BSs) is one of the hot issues nowadays in order to achieve green cellular networks. The energy consumption of femto BSs can be reduced, by turning off the radio interface when there is no mobile station [...] Read more.

Lowering the energy required by base stations (BSs) is one of the hot issues nowadays in order to achieve green cellular networks. The energy consumption of femto BSs can be reduced, by turning off the radio interface when there is no mobile station (MS) under the coverage area of the femto BSs or MSs served by the femto BSs do not transmit or receive data packets for a long time, especially late at night. In the energy-efficient femto BSs, if MSs have any data packet to transmit and the radio interface of femto BSs is in the off state, MSs wake up the radio interface of femto BSs by using an additional low-power radio interface. In this paper, active (data), idle, active (signaling), sleep entering, sleep and waking up states are defined for the state model for the energy-efficient femto BSs, and the state transitions are modeled analytically. The steady-state probability of each state is derived thoroughly using a semi-Markov approach. Then, the performance of the energy-efficient femto BSs is analyzed in detail, from the aspects of energy consumption, cumulative average delay, cost and low-power radio signaling load. From the results, the tradeoff relationship between energy consumption and cumulative average delay is analyzed in detail, and it was concluded that an appropriate inactivity timer value should be selected to balance the tradeoff. Full article

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785 KiB

Open AccessArticle

Locational Pricing to Mitigate Voltage Problems Caused by High PV Penetration

by Sam Weckx, Reinhilde D'hulst and Johan Driesen

Energies 2015, 8(5), 4607-4628; https://doi.org/10.3390/en8054607 - 21 May 2015

Cited by 14 | Viewed by 5189

Abstract

In this paper, a locational marginal pricing algorithm is proposed to control the voltage in unbalanced distribution grids. The increasing amount of photovoltaic (PV) generation installed in the grid may cause the voltage to rise to unacceptable levels during periods of low consumption. [...] Read more.

In this paper, a locational marginal pricing algorithm is proposed to control the voltage in unbalanced distribution grids. The increasing amount of photovoltaic (PV) generation installed in the grid may cause the voltage to rise to unacceptable levels during periods of low consumption. With locational prices, the distribution system operator can steer the reactive power consumption and active power curtailment of PV panels to guarantee a safe network operation. Flexible loads also respond to these prices. A distributed gradient algorithm automatically defines the locational prices that avoid voltage problems. Using these locational prices results in a minimum cost for the distribution operator to control the voltage. Locational prices can differ between the three phases in unbalanced grids. This is caused by a higher consumption or production in one of the phases compared to the other phases and provides the opportunity for arbitrage, where power is transferred from a phase with a low price to a phase with a high price. The effect of arbitrage is analyzed. The proposed algorithm is applied to an existing three-phase four-wire radial grid. Several simulations with realistic data are performed. Full article

(This article belongs to the Collection Smart Grid)

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780 KiB

Open AccessArticle

Fast Charging Battery Buses for the Electrification of Urban Public Transport—A Feasibility Study Focusing on Charging Infrastructure and Energy Storage Requirements

by Matthias Rogge, Sebastian Wollny and Dirk Uwe Sauer

Energies 2015, 8(5), 4587-4606; https://doi.org/10.3390/en8054587 - 21 May 2015

Cited by 162 | Viewed by 14049

Abstract

The electrification of public transport bus networks can be carried out utilizing different technological solutions, like trolley, battery or fuel cell buses. The purpose of this paper is to analyze how and to what extent existing bus networks can be electrified with fast [...] Read more.

The electrification of public transport bus networks can be carried out utilizing different technological solutions, like trolley, battery or fuel cell buses. The purpose of this paper is to analyze how and to what extent existing bus networks can be electrified with fast charging battery buses. The so called opportunity chargers use mainly the regular dwell time at the stops to charge their batteries. This results in a strong linkage between the vehicle scheduling and the infrastructure planning. The analysis is based on real-world data of the bus network in Muenster, a mid-sized city in Germany. The outcomes underline the necessity to focus on entire vehicle schedules instead on individual trips. The tradeoff between required battery capacity and charging power is explained in detail. Furthermore, the impact on the electricity grid is discussed based on the load profiles of a selected charging station and a combined load profile of the entire network. Full article

(This article belongs to the Special Issue Electrical Power and Energy Systems for Transportation Applications)

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1675 KiB

Open AccessArticle

Experimental Results of a DC Bus Voltage Level Control for a Load-Controlled Marine Current Energy Converter

by Johan Forslund, Staffan Lundin, Karin Thomas and Mats Leijon

Energies 2015, 8(5), 4572-4586; https://doi.org/10.3390/en8054572 - 21 May 2015

Cited by 5 | Viewed by 5545

Abstract

This paper investigates three load control methods for a marine current energy converter using a vertical axis current turbine (VACT) mounted on a permanent magnet synchronous generator (PMSG). The three cases are; a fixed AC load, a fixed pulse width modulated (PWM) DC [...] Read more.

This paper investigates three load control methods for a marine current energy converter using a vertical axis current turbine (VACT) mounted on a permanent magnet synchronous generator (PMSG). The three cases are; a fixed AC load, a fixed pulse width modulated (PWM) DC load and DC bus voltage control of a DC load. Experimental results show that the DC bus voltage control reduces the variations of rotational speed by a factor of 3.5 at the cost of slightly increased losses in the generator and transmission lines. For all three cases, the tip speed ratio $\lambda$ can be kept close to the expected $\lambda_{opt}$. The power coefficient is estimated to be 0.36 at $\lambda_{opt}$; however, for all three cases, the average extracted power was about $\sim 19$\%. A maximum power point tracking (MPPT) system, with or without water velocity measurement, could increase the average extracted power. Full article

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3924 KiB

Open AccessArticle

Temporal and Spatial Variations in Provincial CO₂ Emissions in China from 2005 to 2015 and Assessment of a Reduction Plan

by Xuankai Deng, Yanhua Yu and Yanfang Liu

Energies 2015, 8(5), 4549-4571; https://doi.org/10.3390/en8054549 - 20 May 2015

Cited by 9 | Viewed by 5868

Abstract

This study calculated the provincial carbon dioxide (CO₂) emissions in China, analyzed the temporal and spatial variations in emissions, and determined the emission intensity from 2005 to 2015. The total emissions control was forecasted in 2015, and the reduction pressure of [...] Read more.

This study calculated the provincial carbon dioxide (CO₂) emissions in China, analyzed the temporal and spatial variations in emissions, and determined the emission intensity from 2005 to 2015. The total emissions control was forecasted in 2015, and the reduction pressure of the 30 provinces in China was assessed based on historical emissions and the 12th five-year (2011–2015) reduction plan. Results indicate that CO₂ emissions eventually increased and gradually decreased from east to west, whereas the emission intensity ultimately decreased and gradually increased from south to north. By the end of 2015, the total control of provincial emissions will increase significantly compared to the 2010 level, whereas the emission intensity will decrease. The provinces in the North, East, and South Coast regions will maintain the highest emission levels. The provinces in the Southwest and Northwest regions will experience a rapid growth rate of emissions. However, the national emission reduction target will nearly be achieved if all provinces can implement reduction targets as planned. Pressure indices show that the South Coast and Northwest regions are confronted with a greater reduction pressure of emission intensity. Finally, policy implications are provided for CO₂ reductions in China. Full article

(This article belongs to the Special Issue Energy Policy and Climate Change)

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2349 KiB

Open AccessArticle

Numerical Validation of a New Approach to Model Single Junction Low Concentration PV Cells under Non-Uniform Illumination

by Hang Zhou, Yuehong Su, Michele Bottarelli, Marco Bortoloni and Shenyi Wu

Energies 2015, 8(5), 4529-4548; https://doi.org/10.3390/en8054529 - 20 May 2015

Cited by 3 | Viewed by 5824

Abstract

This study presents a numerical validation of a new approach to model single junction PV cell under non-uniform illumination for low-concentration solar collectors such as compound parabolic concentrators (CPC). The simulation is achieved by finite element modelling (FEM). To characterize the results, the [...] Read more.

This study presents a numerical validation of a new approach to model single junction PV cell under non-uniform illumination for low-concentration solar collectors such as compound parabolic concentrators (CPC). The simulation is achieved by finite element modelling (FEM). To characterize the results, the model is simulated with five different non-uniform illumination profiles. The results indicate that increasing the non-uniformity of concentrated light will introduce more resistive losses and lead to a significant attenuation in the PV cell short-circuit current. The FEM modelling results are then used to validate the array modelling approach, in which a single junction PV cell is considered equivalent to a parallel-connected array of several cell splits. A comparison between the FEM and array modelling approaches shows good agreement. Therefore, the array modelling approach is a fast way to investigate the PV cell performance under non-uniform illumination, while the FEM approach is useful in optimizing design of fingers and bus-bars on a PV. Full article

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1059 KiB

Open AccessArticle

Lithium-Ion Battery Cell Cycling and Usage Analysis in a Heavy-Duty Truck Field Study

by Pontus Svens, Mårten Behm and Göran Lindbergh

Energies 2015, 8(5), 4513-4528; https://doi.org/10.3390/en8054513 - 20 May 2015

Cited by 5 | Viewed by 7365

Abstract

This paper presents results from a field test performed on commercial power-optimized lithium-ion battery cells cycled on three heavy-duty trucks. The goal with this study was to age battery cells in a hybrid electric vehicle (HEV) environment and find suitable methods for identifying [...] Read more.

This paper presents results from a field test performed on commercial power-optimized lithium-ion battery cells cycled on three heavy-duty trucks. The goal with this study was to age battery cells in a hybrid electric vehicle (HEV) environment and find suitable methods for identifying cell ageing. The battery cells were cycled on in-house developed equipment intended for testing on conventional vehicles by emulating an HEV environment. A hybrid strategy that allows battery usage to vary within certain limits depending on driving patterns was used. This concept allows unobtrusive and low-cost testing of battery cells under realistic conditions. Each truck was equipped with one cell cycling equipment and two battery cells. One cell per vehicle was cycled during the test period while a reference cell on each vehicle experienced the same environmental conditions without being cycled. Differential voltage analysis and electrochemical impedance spectroscopy were used to identify ageing of the tested battery cells. Analysis of driving patterns and battery usage was performed from collected vehicle data and battery cell data. Full article

(This article belongs to the Special Issue Advances in Plug-in Hybrid Vehicles and Hybrid Vehicles)

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844 KiB

Open AccessArticle

Adaptive Disturbance Observer-Based Parameter-Independent Speed Control of an Uncertain Permanent Magnet Synchronous Machine for Wind Power Generation Applications

by Seok-Kyoon Kim, Hwachang Song and Jang-Ho Lee

Energies 2015, 8(5), 4496-4512; https://doi.org/10.3390/en8054496 - 19 May 2015

Cited by 6 | Viewed by 4842

Abstract

This paper proposes a parameter-independent speed controller based on the classical cascade speed control strategy comprising an inner-loop current controller and an outer-loop speed controller for permanent magnet synchronous machines. The contribution of this paper is three-fold: the first is the proposal of [...] Read more.

This paper proposes a parameter-independent speed controller based on the classical cascade speed control strategy comprising an inner-loop current controller and an outer-loop speed controller for permanent magnet synchronous machines. The contribution of this paper is three-fold: the first is the proposal of a parameter-independent current controller in the inner loop with global asymptotic stability guarantee; the second is the presentation of a guideline for choosing stabilizing proportional-integral (PI) gains in the outer loop; and the third is designing an adaptive disturbance observer (ADOB) to predict the one step ahead state, so that this predicted state compensates the one-step time delay on the control input. The effectiveness of the proposed controller is demonstrated by simulating a wind power generation application using powerSIM (PSIM) software. Full article

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828 KiB

Open AccessArticle

Multi-Objective Dynamic Economic Dispatch of Microgrid Systems Including Vehicle-to-Grid

by Haitao Liu, Yu Ji, Huaidong Zhuang and Hongbin Wu

Energies 2015, 8(5), 4476-4495; https://doi.org/10.3390/en8054476 - 19 May 2015

Cited by 63 | Viewed by 7966

Abstract

Based on the characteristics of electric vehicles (EVs), this paper establishes the load models of EVs under the autonomous charging mode and the coordinated charging and discharging mode. Integrating the EVs into a microgrid system which includes wind turbines (WTs), photovoltaic arrays (PVs), [...] Read more.

Based on the characteristics of electric vehicles (EVs), this paper establishes the load models of EVs under the autonomous charging mode and the coordinated charging and discharging mode. Integrating the EVs into a microgrid system which includes wind turbines (WTs), photovoltaic arrays (PVs), diesel engines (DEs), fuel cells (FCs) and a storage battery (BS), this paper establishes multi-objective economic dispatch models of a microgrid, including the lowest operating cost, the least carbon dioxide emissions, and the lowest pollutant treatment cost. After converting the multi-objective functions to a single objective function by using the judgment matrix method, we analyze the dynamic economic dispatch of the microgrid system including vehicle-to-grid (V2G) with an improved particle swarm optimization algorithm under different operation control strategies. With the example system, the proposed models and strategies are verified and analyzed. Simulation results show that the microgrid system with EVs under the coordinated charging and discharging mode has better operation economics than the autonomous charging mode. Meanwhile, the greater the load fluctuation is, the higher the operating cost of the microgrid system is. Full article

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1962 KiB

Open AccessArticle

Adaptive Micro-Grid Operation Based on IEC 61850

by Wei Deng, Wei Pei, Ziqi Shen, Zhenxing Zhao and Hui Qu

Energies 2015, 8(5), 4455-4475; https://doi.org/10.3390/en8054455 - 18 May 2015

Cited by 24 | Viewed by 8031

Abstract

Automatically identifying the new equipment after its integration and adjusting operation strategy to realize “plug and play” functionality are becoming essential for micro-grid operations. In order to improve and perfect the micro-grid “plug and play” function with the increased amount of equipment with [...] Read more.

Automatically identifying the new equipment after its integration and adjusting operation strategy to realize “plug and play” functionality are becoming essential for micro-grid operations. In order to improve and perfect the micro-grid “plug and play” function with the increased amount of equipment with different information protocols and more diverse system applications, this paper presents a solution for adaptive micro-grid operation based on IEC 61850, and proposes the design and specific implementation methods of micro-grid “plug and play” function and system operation mode conversion in detail, by using the established IEC 61850 information model of a micro-grid. Actual operation tests based on the developed IED and micro-grid test platform are performed to verify the feasibility and validity of the proposed solution. The tests results show that the solution can automatically identify the IEC 61850 information model of equipment after its integration, intelligently adjust the operation strategies to adapt to new system states and achieves a reliable system operation mode conversion. Full article

(This article belongs to the Special Issue Microgrids)

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303 KiB

Open AccessArticle

A Methodology for Assessing Islanding of Microgrids: Between Utility Dependence and Off-Grid Systems

by Antonio Colmenar-Santos, Carlos De Palacio, Lorenzo Alfredo Enríquez-García and África López-Rey

Energies 2015, 8(5), 4436-4454; https://doi.org/10.3390/en8054436 - 18 May 2015

Cited by 10 | Viewed by 6051

Abstract

This paper presents a novel methodology for assessing islanding microgrids from the economical and functional perspective, for various stakeholders. The paper proposes the triggers for competitive deployment of microgeneration, storage, microgrid islanding, the market conditions that apply, and discusses the future tendencies and [...] Read more.

This paper presents a novel methodology for assessing islanding microgrids from the economical and functional perspective, for various stakeholders. The paper proposes the triggers for competitive deployment of microgeneration, storage, microgrid islanding, the market conditions that apply, and discusses the future tendencies and the policy recommendations to foster microgrid benefits. The validation of the proposed scheme is based on real market cases, where the triggers for autogeneration and islanding microgrids are present. Additionally, the new concept of grid independence cycle is presented and analyzed. The policy implications of a situation where grid consumption reduction leads to higher energy prices are presented and discussed. The paper concludes with a summary of prioritized technical and regulatory recommendations, proposed as a result of the assessment. Full article

(This article belongs to the Special Issue Microgrids)

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1368 KiB

Open AccessArticle

Graded-Bandgap Solar Cells Using All-Electrodeposited ZnS, CdS and CdTe Thin-Films

by Obi K. Echendu and Imyhamy M. Dharmadasa

Energies 2015, 8(5), 4416-4435; https://doi.org/10.3390/en8054416 - 15 May 2015

Cited by 65 | Viewed by 10273

Abstract

A 3-layer graded-bandgap solar cell with glass/FTO/ZnS/CdS/CdTe/Au structure has been fabricated using all-electrodeposited ZnS, CdS and CdTe thin layers. The three semiconductor layers were electrodeposited using a two-electrode system for process simplification. The incorporation of a wide bandgap amorphous ZnS as a buffer/window [...] Read more.

A 3-layer graded-bandgap solar cell with glass/FTO/ZnS/CdS/CdTe/Au structure has been fabricated using all-electrodeposited ZnS, CdS and CdTe thin layers. The three semiconductor layers were electrodeposited using a two-electrode system for process simplification. The incorporation of a wide bandgap amorphous ZnS as a buffer/window layer to form glass/FTO/ZnS/CdS/CdTe/Au solar cell resulted in the formation of this 3-layer graded-bandgap device structure. This has yielded corresponding improvement in all the solar cell parameters resulting in a conversion efficiency >10% under AM1.5 illumination conditions at room temperature, compared to the 8.0% efficiency of a 2-layer glass/FTO/CdS/CdTe/Au reference solar cell structure. These results demonstrate the advantages of the multi-layer graded-bandgap device architecture over the conventional 2-layer structure. In addition, they demonstrate the effective application of the two-electrode system as a simplification to the conventional three-electrode system in the electrodeposition of semiconductors with the elimination of the reference electrode as a possible impurity source. Full article

(This article belongs to the Special Issue Next Generation of Photovoltaic (PV) Technology)

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3368 KiB

Open AccessArticle

Online Internal Temperature Estimation for Lithium-Ion Batteries Based on Kalman Filter

by Jinlei Sun, Guo Wei, Lei Pei, Rengui Lu, Kai Song, Chao Wu and Chunbo Zhu

Energies 2015, 8(5), 4400-4415; https://doi.org/10.3390/en8054400 - 15 May 2015

Cited by 74 | Viewed by 9238

Abstract

The battery internal temperature estimation is important for the thermal safety in applications, because the internal temperature is hard to measure directly. In this work, an online internal temperature estimation method based on a simplified thermal model using a Kalman filter is proposed. [...] Read more.

The battery internal temperature estimation is important for the thermal safety in applications, because the internal temperature is hard to measure directly. In this work, an online internal temperature estimation method based on a simplified thermal model using a Kalman filter is proposed. As an improvement, the influences of entropy change and overpotential on heat generation are analyzed quantitatively. The model parameters are identified through a current pulse test. The charge/discharge experiments under different current rates are carried out on the same battery to verify the estimation results. The internal and surface temperatures are measured with thermocouples for result validation and model construction. The accuracy of the estimated result is validated with a maximum estimation error of around 1 K. Full article

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1243 KiB

Open AccessReview

Power Quality in DC Power Distribution Systems and Microgrids

by Stephen Whaite, Brandon Grainger and Alexis Kwasinski

Energies 2015, 8(5), 4378-4399; https://doi.org/10.3390/en8054378 - 15 May 2015

Cited by 98 | Viewed by 16811

Abstract

This review paper discusses power quality considerations for direct current (DC) electric power distribution systems, particularly DC microgrids. First, four selected sample DC architectures are discussed to provide motivation for the consideration of power quality in DC systems. Second, a brief overview of [...] Read more.

This review paper discusses power quality considerations for direct current (DC) electric power distribution systems, particularly DC microgrids. First, four selected sample DC architectures are discussed to provide motivation for the consideration of power quality in DC systems. Second, a brief overview of power quality challenges in conventional alternating current (AC) distribution systems is given to establish the field of power quality. Finally, a survey of literature addressing power quality issues in DC systems is presented, and necessary power quality considerations in DC distribution system design and operation are discussed. Full article

(This article belongs to the Special Issue Microgrids)

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2923 KiB

Open AccessArticle

The Development of Cloud Energy Management

by Chin-Chi Cheng, Dasheng Lee, Ching Hung Wang, Shu Fen Lin, Hung-Peng Chang and Shang-Te Fang

Energies 2015, 8(5), 4357-4377; https://doi.org/10.3390/en8054357 - 14 May 2015

Cited by 8 | Viewed by 6736

Abstract

The energy management service (EMS) has been utilized for saving energy since 1982 by managing the energy usage of site or facilities through the microprocessor, computer, Ethernet, internet, and wireless sensor network. The development and represented function groups of EMS are illustrated in [...] Read more.

The energy management service (EMS) has been utilized for saving energy since 1982 by managing the energy usage of site or facilities through the microprocessor, computer, Ethernet, internet, and wireless sensor network. The development and represented function groups of EMS are illustrated in the supplementary file of this paper. Along with this tendency, a cloud EMS, named the intelligent energy management network (iEN), was launched by Chunghwa Telecom in 2011 and tested during a pilot run from 2012 to 2013. The cloud EMS integrated three service modes together, including infrastructure as a service (IaaS), platform as a service (PaaS), and software as a service (SaaS). This cloud EMS could reduce the facility cost and enable a continuously improved service for energy conservation. From the literature review, 32 selected EMS cases of whole site and single facility were chosen for calculating the energy savings and payback rate. According to the literature, the average energy savings by applying EMS are 11.6% and 21.4% for the whole site and single facility, respectively. The iEN was applied on 55 demo sites with the similar scale, the same kind of machines and approaching conditions. The testing sites include a factory, a complex building, and a residual building, 12 lighting systems and 8 air conditioning systems. According to the testing results, the average energy savings by applying iEN are 10% and 23.5% for the whole site and single facility, respectively. Comparing with the reported EMS cases, it was found that the energy savings by adopting the cloud EMS were only 70%–80% compared with those using the traditional EMS. Although the cloud EMS presented less energy savings, it revolutionized the traditional EMS by its innovative business model. Compared with the averaged 1.7 years payback period of the traditional EMS, more than 70% of the cloud EMS cases could pay back immediately for the service fees and without the equipment investment. Full article

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893 KiB

Open AccessArticle

Modeling and Simulation of DC Microgrids for Electric Vehicle Charging Stations

by Fabrice Locment and Manuela Sechilariu

Energies 2015, 8(5), 4335-4356; https://doi.org/10.3390/en8054335 - 13 May 2015

Cited by 49 | Viewed by 10467

Abstract

This paper focuses on the evaluation of theoretical and numerical aspects related to an original DC microgrid power architecture for efficient charging of plug-in electric vehicles (PEVs). The proposed DC microgrid is based on photovoltaic array (PVA) generation, electrochemical storage, and grid connection; [...] Read more.

This paper focuses on the evaluation of theoretical and numerical aspects related to an original DC microgrid power architecture for efficient charging of plug-in electric vehicles (PEVs). The proposed DC microgrid is based on photovoltaic array (PVA) generation, electrochemical storage, and grid connection; it is assumed that PEVs have a direct access to their DC charger input. As opposed to conventional power architecture designs, the PVA is coupled directly on the DC link without a static converter, which implies no DC voltage stabilization, increasing energy efficiency, and reducing control complexity. Based on a real-time rule-based algorithm, the proposed power management allows self-consumption according to PVA power production and storage constraints, and the public grid is seen only as back-up. The first phase of modeling aims to evaluate the main energy flows within the proposed DC microgrid architecture and to identify the control structure and the power management strategies. For this, an original model is obtained by applying the Energetic Macroscopic Representation formalism, which allows deducing the control design using Maximum Control Structure. The second phase of simulation is based on the numerical characterization of the DC microgrid components and the energy management strategies, which consider the power source requirements, charging times of different PEVs, electrochemical storage ageing, and grid power limitations for injection mode. The simulation results show the validity of the model and the feasibility of the proposed DC microgrid power architecture which presents good performance in terms of total efficiency and simplified control. Full article

(This article belongs to the Special Issue Electrical Power and Energy Systems for Transportation Applications)

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Graphical abstract

1806 KiB

Open AccessArticle

A New Optimization Method for Centrifugal Compressors Based on 1D Calculations and Analyses

by Pei-Yuan Li, Chu-Wei Gu and Yin Song

Energies 2015, 8(5), 4317-4334; https://doi.org/10.3390/en8054317 - 12 May 2015

Cited by 49 | Viewed by 9120

Abstract

This paper presents an optimization design method for centrifugal compressors based on one-dimensional calculations and analyses. It consists of two parts: (1) centrifugal compressor geometry optimization based on one-dimensional calculations and (2) matching optimization of the vaned diffuser with an impeller based on [...] Read more.

This paper presents an optimization design method for centrifugal compressors based on one-dimensional calculations and analyses. It consists of two parts: (1) centrifugal compressor geometry optimization based on one-dimensional calculations and (2) matching optimization of the vaned diffuser with an impeller based on the required throat area. A low pressure stage centrifugal compressor in a MW level gas turbine is optimized by this method. One-dimensional calculation results show that D3/D2 is too large in the original design, resulting in the low efficiency of the entire stage. Based on the one-dimensional optimization results, the geometry of the diffuser has been redesigned. The outlet diameter of the vaneless diffuser has been reduced, and the original single stage diffuser has been replaced by a tandem vaned diffuser. After optimization, the entire stage pressure ratio is increased by approximately 4%, and the efficiency is increased by approximately 2%. Full article

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1660 KiB

Open AccessArticle

Fault Diagnosis and Fault-Tolerant Control of Wind Turbines via a Discrete Time Controller with a Disturbance Compensator

by Yolanda Vidal, Christian Tutivén, José Rodellar and Leonardo Acho

Energies 2015, 8(5), 4300-4316; https://doi.org/10.3390/en8054300 - 12 May 2015

Cited by 50 | Viewed by 8378

Abstract

This paper develops a fault diagnosis (FD) and fault-tolerant control (FTC) of pitch actuators in wind turbines. This is accomplished by combining a disturbance compensator with a controller, both of which are formulated in the discrete time domain. The disturbance compensator has a [...] Read more.

This paper develops a fault diagnosis (FD) and fault-tolerant control (FTC) of pitch actuators in wind turbines. This is accomplished by combining a disturbance compensator with a controller, both of which are formulated in the discrete time domain. The disturbance compensator has a dual purpose: to estimate the actuator fault (which is used by the FD algorithm) and to design the discrete time controller to obtain an FTC. That is, the pitch actuator faults are estimated, and then, the pitch control laws are appropriately modified to achieve an FTC with a comparable behavior to the fault-free case. The performance of the FD and FTC schemes is tested in simulations with the aero-elastic code FAST. Full article

(This article belongs to the Special Issue Wind Turbines)

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567 KiB

Open AccessArticle

Calculation of Efficiencies of a Ship Power Plant Operating with Waste Heat Recovery through Combined Heat and Power Production

by Mirko Grljušić, Vladimir Medica and Gojmir Radica

Energies 2015, 8(5), 4273-4299; https://doi.org/10.3390/en8054273 - 12 May 2015

Cited by 42 | Viewed by 10223

Abstract

The aim of this research was to investigate the possibility of a combined heat & power (CHP) plant, using the waste heat from a Suezmax-size oil tanker’s main engine, to meet all heating and electricity requirements during navigation. After considering various configurations, a [...] Read more.

The aim of this research was to investigate the possibility of a combined heat & power (CHP) plant, using the waste heat from a Suezmax-size oil tanker’s main engine, to meet all heating and electricity requirements during navigation. After considering various configurations, a standard propulsion engine operating at maximum efficiency, combined with a supercritical Organic Rankine cycle (ORC) system, was selected to supply the auxiliary power, using R245fa or R123 as the working fluid. The system analysis showed that such a plant can meet all heat and electrical power requirements at full load, with the need to burn only a small amount of supplementary fuel in a heat recovery steam generator (HRSG) when the main engine operates at part load. Therefore, it is possible to increase the overall thermal efficiency of the ship’s power plant by more than 5% when the main engine operates at 65% or more of its specified maximum continuous rating (SMCR). Full article

(This article belongs to the Special Issue Organic Rankine Cycle (ORC))

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492 KiB

Open AccessArticle

Evaluation of Fermentative Hydrogen Production from Single and Mixed Fruit Wastes

by Julius Akinbomi and Mohammad J. Taherzadeh

Energies 2015, 8(5), 4253-4272; https://doi.org/10.3390/en8054253 - 12 May 2015

Cited by 41 | Viewed by 8333

Abstract

The economic viability of employing dark fermentative hydrogen from whole fruit wastes as a green alternative to fossil fuels is limited by low hydrogen yield due to the inhibitory effect of some metabolites in the fermentation medium. In exploring means of increasing hydrogen [...] Read more.

The economic viability of employing dark fermentative hydrogen from whole fruit wastes as a green alternative to fossil fuels is limited by low hydrogen yield due to the inhibitory effect of some metabolites in the fermentation medium. In exploring means of increasing hydrogen production from fruit wastes, including orange, apple, banana, grape and melon, the present study assessed the hydrogen production potential of singly-fermented fruits as compared to the fermentation of mixed fruits. The fruit feedstock was subjected to varying hydraulic retention times (HRTs) in a continuous fermentation process at 55 °C for 47 days. The weight distributions of the first, second and third fruit mixtures were 70%, 50% and 20% orange share, respectively, while the residual weight was shared equally by the other fruits. The results indicated that there was an improvement in cumulative hydrogen yield from all of the feedstock when the HRT was five days. Based on the results obtained, apple as a single fruit and a fruit mixture with 20% orange share have the most improved cumulative hydrogen yields of 504 (29.5% of theoretical yield) and 513 mL/g volatile solid (VS) (30% of theoretical yield ), respectively, when compared to other fruits. Full article

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1074 KiB

Open AccessArticle

Enhanced Hydrogen Generation Properties of MgH₂-Based Hydrides by Breaking the Magnesium Hydroxide Passivation Layer

by Liuzhang Ouyang, Miaolian Ma, Minghong Huang, Ruoming Duan, Hui Wang, Lixian Sun and Min Zhu

Energies 2015, 8(5), 4237-4252; https://doi.org/10.3390/en8054237 - 11 May 2015

Cited by 104 | Viewed by 10587

Abstract

Due to its relatively low cost, high hydrogen yield, and environmentally friendly hydrolysis byproducts, magnesium hydride (MgH₂) appears to be an attractive candidate for hydrogen generation. However, the hydrolysis reaction of MgH₂ is rapidly inhibited by the formation of a [...] Read more.

Due to its relatively low cost, high hydrogen yield, and environmentally friendly hydrolysis byproducts, magnesium hydride (MgH₂) appears to be an attractive candidate for hydrogen generation. However, the hydrolysis reaction of MgH₂ is rapidly inhibited by the formation of a magnesium hydroxide passivation layer. To improve the hydrolysis properties of MgH₂-based hydrides we investigated three different approaches: ball milling, synthesis of MgH₂-based composites, and tuning of the solution composition. We demonstrate that the formation of a composite system, such as the MgH₂/LaH₃ composite, through ball milling and in situ synthesis, can improve the hydrolysis properties of MgH₂ in pure water. Furthermore, the addition of Ni to the MgH₂/LaH₃ composite resulted in the synthesis of LaH₃/MgH₂/Ni composites. The LaH₃/MgH₂/Ni composites exhibited a higher hydrolysis rate—120 mL/(g·min) of H₂ in the first 5 min—than the MgH₂/LaH₃ composite— 95 mL/(g·min)—without the formation of the magnesium hydroxide passivation layer. Moreover, the yield rate was controlled by manipulation of the particle size via ball milling. The hydrolysis of MgH₂ was also improved by optimizing the solution. The MgH₂ produced 1711.2 mL/g of H₂ in 10 min at 298 K in the 27.1% ammonium chloride solution, and the hydrolytic conversion rate reached the value of 99.5%. Full article

(This article belongs to the Special Issue Hydrides: Fundamentals and Applications)

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2697 KiB

Open AccessArticle

3-D CFD Modeling for Parametric Study in a 300-MWe One-Stage Oxygen-Blown Entrained-Bed Coal Gasifier

by Sang Shin Park, Hyo Jae Jeong and Jungho Hwang

Energies 2015, 8(5), 4216-4236; https://doi.org/10.3390/en8054216 - 11 May 2015

Cited by 39 | Viewed by 7442

Abstract

Three-dimensional computational fluid dynamics (CFD) modeling of the gasification performance in a one-stage, entrained-bed coal gasifier (Shell Coal Gasification Process (SCGP) gasifier) was performed, for the first time. The parametric study used various O₂/coal and steam/coal ratios, and the modeling used [...] Read more.

Three-dimensional computational fluid dynamics (CFD) modeling of the gasification performance in a one-stage, entrained-bed coal gasifier (Shell Coal Gasification Process (SCGP) gasifier) was performed, for the first time. The parametric study used various O₂/coal and steam/coal ratios, and the modeling used a commercial code, ANSYS FLUENT. CFD modeling was conducted by solving the steady-state Navier–Stokes and energy equations using the Eulerian–Lagrangian method. Gas-phase chemical reactions were solved with the Finite–Rate/Eddy–Dissipation Model. The CFD model was verified with actual operating data of Demkolec demo Integrated Gasification Combined Cycle (IGCC) facility in Netherlands that used Drayton coal. For Illinois #6 coal, the CFD model was compared with ASPEN Plus results reported in National Energy Technology Laboratory (NETL). For design coal used in the SCGP gasifier in Korea, carbon conversion efficiency, cold gas efficiency, temperature, and species mole fractions at the gasifier exit were calculated and the results were compared with those obtained by using ASPEN Plus-Kinetic. The optimal O₂/coal and steam/coal ratios were 0.7 and 0.05, respectively, for the selected operating conditions. Full article

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1169 KiB

Open AccessArticle

The Concept of EV’s Intelligent Integrated Station and Its Energy Flow

by Da Xie, Haoxiang Chu, Yupu Lu, Chenghong Gu, Furong Li and Yu Zhang

Energies 2015, 8(5), 4188-4215; https://doi.org/10.3390/en8054188 - 11 May 2015

Cited by 6 | Viewed by 7032

Abstract

The increasing number of electric vehicles (EVs) connected to existing distribution networks as time-variant loads cause significant distortions in line current and voltage. A novel EV’s intelligent integrated station (IIS) making full use of retired batteries is introduced in this paper to offer [...] Read more.

The increasing number of electric vehicles (EVs) connected to existing distribution networks as time-variant loads cause significant distortions in line current and voltage. A novel EV’s intelligent integrated station (IIS) making full use of retired batteries is introduced in this paper to offer a potential solution for accommodating the charging demand of EVs. It proposes the concept of generalized energy in IIS, based on the energy/power flow between IIS and EVs, and between IIS and the power grid, to systematically evaluate the energy capacity of IIS. In order to derive a unique and satisfactory operation mode, information from both the grid (in terms of load level) and IIS (in terms of its energy capacity and EVs battery charging/exchanging requests) is merged. Then, based on the generalized energy of different systems, a novel charging/discharging control strategy is presented and whereby the operating status of the grid and energy capacity of IIS are monitored to make reasonable operation plans for IIS. Simulation results suggest that the proposed IIS offers peak load shifting when EV battery charging/exchanging requests are satisfied compared to existing charging stations. Full article

(This article belongs to the Special Issue Advances in Plug-in Hybrid Vehicles and Hybrid Vehicles)

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995 KiB

Open AccessArticle

Probabilistic Agent-Based Model of Electric Vehicle Charging Demand to Analyse the Impact on Distribution Networks

by Pol Olivella-Rosell, Roberto Villafafila-Robles, Andreas Sumper and Joan Bergas-Jané

Energies 2015, 8(5), 4160-4187; https://doi.org/10.3390/en8054160 - 11 May 2015

Cited by 86 | Viewed by 10955

Abstract

Electric Vehicles (EVs) have seen significant growth in sales recently and it is not clear how power systems will support the charging of a great number of vehicles. This paper proposes a methodology which allows the aggregated EV charging demand to be determined. [...] Read more.

Electric Vehicles (EVs) have seen significant growth in sales recently and it is not clear how power systems will support the charging of a great number of vehicles. This paper proposes a methodology which allows the aggregated EV charging demand to be determined. The methodology applied to obtain the model is based on an agent-based approach to calculate the EV charging demand in a certain area. This model simulates each EV driver to consider its EV model characteristics, mobility needs, and charging processes required to reach its destination. This methodology also permits to consider social and economic variables. Furthermore, the model is stochastic, in order to consider the random pattern of some variables. The model is applied to Barcelona’s (Spain) mobility pattern and uses the 37-node IEEE test feeder adapted to common distribution grid characteristics from Barcelona. The corresponding grid impact is analyzed in terms of voltage drop and four charging strategies are compared. The case study indicates that the variability in scenarios without control is relevant, but not in scenarios with control. Moreover, the voltages do not reach the minimum voltage allowed, but the MV/LV substations could exceed their capacities. Finally, it is determined that all EVs can charge during the valley without any negative effect on the distribution grid. In conclusion, it is determined that the methodology presented allows the EV charging demand to be calculated, considering different variables, to obtain better accuracy in the results. Full article

(This article belongs to the Special Issue Electrical Power and Energy Systems for Transportation Applications)

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383 KiB

Open AccessArticle

System Identification and Resonant Control of Thermoacoustic Engines for Robust Solar Power

by Boe-Shong Hong and Tsu-Yu Lin

Energies 2015, 8(5), 4138-4159; https://doi.org/10.3390/en8054138 - 8 May 2015

Cited by 7 | Viewed by 7535

Abstract

It was found that thermoacoustic solar-power generators with resonant control are more powerful than passive ones. To continue the work, this paper focuses on the synthesis of robustly resonant controllers that guarantee single-mode resonance not only in steady states, but also in transient [...] Read more.

It was found that thermoacoustic solar-power generators with resonant control are more powerful than passive ones. To continue the work, this paper focuses on the synthesis of robustly resonant controllers that guarantee single-mode resonance not only in steady states, but also in transient states when modelling uncertainties happen and working temperature temporally varies. Here the control synthesis is based on the loop shifting and the frequency-domain identification in advance thereof. Frequency-domain identification is performed to modify the mathematical modelling and to identify the most powerful mode, so that the DSP-based feedback controller can online pitch the engine to the most powerful resonant-frequency robustly and accurately. Moreover, this paper develops two control tools, the higher-order van-der-Pol oscillator and the principle of Dynamical Equilibrium, to assist in system identification and feedback synthesis, respectively. Full article

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2048 KiB

Open AccessArticle

A Numerical Study on Combustion and Emission Characteristics of a Medium-Speed Diesel Engine Using In-Cylinder Cleaning Technologies

by Shuang He, Bao-Guo Du, Li-Yan Feng, Yao Fu, Jing-Chen Cui and Wu-Qiang Long

Energies 2015, 8(5), 4118-4137; https://doi.org/10.3390/en8054118 - 8 May 2015

Cited by 18 | Viewed by 6767

Abstract

In order to clarify the potential of internal purification methods on medium speed diesel engines to meet the IMO Tier III nitrogen oxide (NO_x) emission regulations, combined 1-D engine working cycle simulation and 3-D CFD simulation were conducted to predict the [...] Read more.

In order to clarify the potential of internal purification methods on medium speed diesel engines to meet the IMO Tier III nitrogen oxide (NO_x) emission regulations, combined 1-D engine working cycle simulation and 3-D CFD simulation were conducted to predict the performance and emissions of the engine under different valve close timings, geometric compression ratios, injection timings, and Exhaust Gas Recirculation (EGR) rates. The numerical results show that, as the inlet valve close timing is advanced, NO_x is reduced by as much as 27%, but the peak of premixed combustion heat release rate is increased; this can weaken the ability to reduce NO_x with the Miller cycle. Moreover, the peak of premixed combustion heat release rate is reduced when the geometric compression ratio is increased to 15.4, and linking with injection timing by delaying 6°CA can further reduce NO_x by 55.3% from the baseline. Finally, over 80% NO_x reduction can be achieved when the above schemes are combined with over 15% EGR. The NO_x and soot can be reduced simultaneously by using moderate Miller cycle combination with moderate EGR, and the results show a large reduction of NO_x and moderate reduction of soot. This can be a feasible technical solution to meet Tier III regulations. Full article

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1677 KiB

Open AccessArticle

Techno-Economic Analysis of Bioethanol Production from Lignocellulosic Biomass in China: Dilute-Acid Pretreatment and Enzymatic Hydrolysis of Corn Stover

by Lili Zhao, Xiliang Zhang, Jie Xu, Xunmin Ou, Shiyan Chang and Maorong Wu

Energies 2015, 8(5), 4096-4117; https://doi.org/10.3390/en8054096 - 8 May 2015

Cited by 87 | Viewed by 13485

Abstract

Lignocellulosic biomass-based ethanol is categorized as 2^nd generation bioethanol in the advanced biofuel portfolio. To make sound incentive policy proposals for the Chinese government and to develop guidance for research and development and industrialization of the technology, the paper reports careful techno-economic [...] Read more.

Lignocellulosic biomass-based ethanol is categorized as 2^nd generation bioethanol in the advanced biofuel portfolio. To make sound incentive policy proposals for the Chinese government and to develop guidance for research and development and industrialization of the technology, the paper reports careful techno-economic and sensitivity analyses performed to estimate the current competitiveness of the bioethanol and identify key components which have the greatest impact on its plant-gate price (PGP). Two models were developed for the research, including the Bioethanol PGP Assessment Model (BPAM) and the Feedstock Cost Estimation Model (FCEM). Results show that the PGP of the bioethanol ranges $4.68–$6.05/gal (9,550–12,356 yuan/t). The key components that contribute most to bioethanol PGP include the conversion rate of cellulose to glucose, the ratio of five-carbon sugars converted to ethanol, feedstock cost, and enzyme loading, etc. Lignocellulosic ethanol is currently unable to compete with fossil gasoline, therefore incentive policies are necessary to promote its development. It is suggested that the consumption tax be exempted, the value added tax (VAT) be refunded upon collection, and feed-in tariff for excess electricity (byproduct) be implemented to facilitate the industrialization of the technology. A minimum direct subsidy of $1.20/gal EtOH (2,500 yuan/t EtOH) is also proposed for consideration. Full article

(This article belongs to the Special Issue Bioenergy and Biorefining)

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2020 KiB

Open AccessArticle

Transport Mechanisms for CO₂-CH₄ Exchange and Safe CO₂ Storage in Hydrate-Bearing Sandstone

by Knut Arne Birkedal, Lars Petter Hauge, Arne Graue and Geir Ersland

Energies 2015, 8(5), 4073-4095; https://doi.org/10.3390/en8054073 - 8 May 2015

Cited by 45 | Viewed by 7719

Abstract

CO₂ injection in hydrate-bearing sediments induces methane (CH₄) production while benefitting from CO₂ storage, as demonstrated in both core and field scale studies. CH₄ hydrates have been formed repeatedly in partially water saturated Bentheim sandstones. Magnetic Resonance Imaging [...] Read more.

CO₂ injection in hydrate-bearing sediments induces methane (CH₄) production while benefitting from CO₂ storage, as demonstrated in both core and field scale studies. CH₄ hydrates have been formed repeatedly in partially water saturated Bentheim sandstones. Magnetic Resonance Imaging (MRI) and CH₄ consumption from pump logs have been used to verify final CH₄ hydrate saturation. Gas Chromatography (GC) in combination with a Mass Flow Meter was used to quantify CH₄ recovery during CO₂ injection. The overall aim has been to study the impact of CO₂ in fractured and non-fractured samples to determine the performance of CO₂-induced CH₄ hydrate production. Previous efforts focused on diffusion-driven exchange from a fracture volume. This approach was limited by gas dilution, where free and produced CH₄ reduced the CO₂ concentration and subsequent driving force for both diffusion and exchange. This limitation was targeted by performing experiments where CO₂ was injected continuously into the spacer volume to maintain a high driving force. To evaluate the effect of diffusion length multi-fractured core samples were used, which demonstrated that length was not the dominating effect on core scale. An additional set of experiments is presented on non-fractured samples, where diffusion-limited transportation was assisted by continuous CO₂ injection and CH₄ displacement. Loss of permeability was addressed through binary gas (N₂/CO₂) injection, which regained injectivity and sustained CO₂-CH₄ exchange. Full article

(This article belongs to the Special Issue Coastal Ocean Natural Gas Hydrate 2014)

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657 KiB

Open AccessArticle

Acceleration Slip Regulation Strategy for Distributed Drive Electric Vehicles with Independent Front Axle Drive Motors

by Lingfei Wu, Jinfang Gou, Lifang Wang and Junzhi Zhang

Energies 2015, 8(5), 4043-4072; https://doi.org/10.3390/en8054043 - 8 May 2015

Cited by 17 | Viewed by 7855

Abstract

This paper presents an acceleration slip regulation strategy for distributed drive electric vehicles with two motors on the front axle. The tasks of the strategy include controlling the slip ratio to make full use of the road grip and controlling the yaw rate [...] Read more.

This paper presents an acceleration slip regulation strategy for distributed drive electric vehicles with two motors on the front axle. The tasks of the strategy include controlling the slip ratio to make full use of the road grip and controlling the yaw rate to eliminate the lateral movement due to the difference between motor torques. The rate of the slip ratio change can be controlled by controlling the motor torque, so that the slip ratio can be controlled by applying a proportional-integral control strategy to control the rate of the slip ratio change. The yaw rate can be controlled to almost zero by applying torque compensation based on yaw rate feedback. A coordination control strategy for the slip ratio control and yaw rate control is proposed based on analysis of the priorities and features of the two control processes. Simulations were carried out using MATLAB/Simulink, and experiments were performed on a hardware-in-loop test bench with actual motors. The results of the simulations and experiments showed that the proposed strategy could improve the longitudinal driving performance and straight line driving stability of the vehicle. Full article

(This article belongs to the Special Issue Advances in Plug-in Hybrid Vehicles and Hybrid Vehicles)

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526 KiB

Open AccessArticle

Social Science Insights for the BioCCS Industry

by Anne-Maree Dowd, Michelle Rodriguez and Talia Jeanneret

Energies 2015, 8(5), 4024-4042; https://doi.org/10.3390/en8054024 - 8 May 2015

Cited by 34 | Viewed by 8545

Abstract

BioCCS is a technology gaining support as a possible emissions reduction policy option to address climate change. The process entails the capture, transport and storage of carbon dioxide produced during energy production from biomass. Globally, the most optimistic energy efficiency scenarios cannot avoid [...] Read more.

BioCCS is a technology gaining support as a possible emissions reduction policy option to address climate change. The process entails the capture, transport and storage of carbon dioxide produced during energy production from biomass. Globally, the most optimistic energy efficiency scenarios cannot avoid an average temperature increase of +2 °C without bioCCS. Although very much at the commencement stage, bioCCS demonstration projects can provide opportunity to garner knowledge, achieve consensus and build support around the technology’s properties. Yet many challenges face the bioCCS industry, including no guarantee biomass will always be from sustainable sources or potentially result in carbon stock losses. The operating environment also has no or limited policies, regulations and legal frameworks, and risk and safety concerns abound. Some state the key problem for bioCCS is cultural, lacking in a ‘community of support’, awareness and credibility amongst its own key stakeholders and the wider public. Therefore, the industry can benefit from the growing social science literature, drawing upon other energy and resource based industries with regard to social choice for future energy options. To this end, the following scoping review was conducted in order to ascertain gaps in existing public perception and acceptance research focusing on bioCCS. Full article

(This article belongs to the Special Issue Carbon Capture and Storage (CCS): Bio-Energy vs Fossil Fuels)

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Energies, Volume 8, Issue 5 (May 2015) – 67 articles , Pages 3292-4646

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