The main objective of this paper was to study a bidirectional direct current to direct current converter (BDC) topology with a high voltage conversion ratio for electric vehicle (EV) batteries connected to a dc-microgrid system. In this study, an unregulated level converter (ULC) cascaded with a two-phase interleaved buck-boost charge-pump converter (IBCPC) is introduced to achieve a high conversion ratio with a simpler control circuit. In discharge state, the topology acts as a two-stage voltage-doubler boost converter to achieve high step-up conversion ratio (48 V to 385 V). In charge state, the converter acts as two cascaded voltage-divider buck converters to achieve high voltage step-down conversion ratio (385 V to 48 V). The features, operation principles, steady-state analysis, simulation and experimental results are made to verify the performance of the studied novel BDC. Finally, a 500 W rating prototype system is constructed for verifying the validity of the operation principl... [more]

A physics-based explicit mathematical model for the external voltage-dependent forward dark current in bulk heterojunction (BHJ) organic solar cells is developed by considering Shockley-Read-Hall (SRH) recombination and solving the continuity equations for both electrons and holes. An analytical model for the external voltage-dependent photocurrent in BHJ organic solar cells is also proposed by incorporating exponential photon absorption, dissociation efficiency of bound electron-hole pairs (EHPs), carrier trapping, and carrier drift and diffusion in the photon absorption layer. Modified Braun’s model is used to compute the electric field-dependent dissociation efficiency of the bound EHPs. The overall net current is calculated considering the actual solar spectrum. The mathematical models are verified by comparing the model calculations with various published experimental results. We analyze the effects of the contact properties, blend compositions, charge carrier transport properties... [more]

Repowering is a process for transforming an old power plant for greater capacity and/or higher efficiency. As a consequence, the repowered plant is characterized by higher power output and less specific CO₂ emissions. Usually, repowering is performed by adding one or more gas turbines into an existing steam cycle which was built decades ago. Thus, traditional repowering results in combined cycles (CC). High temperature fuel cells (such as solid oxide fuel cell (SOFC)) could also be used as a topping cycle, achieving even higher global plant efficiency and even lower specific CO₂ emissions. Decreasing the operating temperature in a SOFC allows the use of less complex materials and construction methods, consequently reducing plant and the electricity costs. A lower working temperature makes it also suitable for topping an existing steam cycle, instead of gas turbines. This is also the target of this study, repowering of an existing power plant with SOFC as well as gas turbines. Different... [more]

A novel modular arc-linear flux-switching permanent-magnet motor (MAL-FSPM) used for scanning system instead of reduction gearboxes and kinematic mechanisms is proposed and researched in this paper by the finite element method (FEM). The MAL-FSPM combines characteristics of flux-switching permanent-magnet motor and linear motor and can realize the direct driving and limited angular movement. Structure and operation principle of the MAL-FSPM are analyzed. Cogging torque model of the MAL-FSPM is established. The characteristics of cogging torque and torque ripple are investigated for: (1) distance (dend) between left end of rotor and left end of stator is more than two rotor tooth pitch (τp); and (2) dend is less than two rotor tooth pitch. Cogging torque is an important component of torque ripple and the period ratio of the cogging torque to the back electromotive force (EMF) equals one for the MAL-FSPM before optimization. In order to reduce the torque ripple as much as possible and af... [more]

With the recent shale gas boom, the U.S. is expected to have very large natural gas resources. In this respect, the key question is would it be better to rely completely on free market resource allocations which would lead to large exports of natural gas or to limit natural gas exports so that more could be used in the U.S.. After accounting for the cost of liquefying the natural gas and shipping it to foreign markets, the current price difference leaves room for considerable profit to producers from exports. In addition, there is a large domestic demand for natural gas from various sectors such as electricity generation, industrial applications, and the transportation sector etc. A hybrid modeling approach has been carried out using our version of the well-known MARket ALlocation (MARKAL)-Macro model to keep bottom-up model richness with macro effects to incorporate price and gross domestic product (GDP) feedbacks. One of the conclusion of this study is that permitting higher natural... [more]

Rising demand, climate change, growing fuel costs, outdated power system infrastructures, and new power generation technologies have made renewable distribution generators very attractive in recent years. Because of the increasing penetration level of renewable energy sources in addition to the growth of new electrical demand sectors, such as electrical vehicles, the power system may face serious problems and challenges in the near future. A revolutionary new power grid system, called smart grid, has been developed as a solution to these problems. The smart grid, equipped with modern communication and computation infrastructures, can coordinate different parts of the power system to enhance energy efficiency, reliability, and quality, while decreasing the energy cost. Since conventional distribution networks lack smart infrastructures, much research has been recently done in the distribution part of the smart grid, called smart distribution grid (SDG). This paper surveys contemporary l... [more]

Voltage source converter (VSC)-based high voltage direct current (VSC-HVDC) interconnectors can realize accurate and fast control of power transmission among AC networks, and provide emergency power support for AC networks. VSC-HVDC interconnectors bring exclusive fault characteristics to AC networks, thus influencing the performance of traditional protections. Since fault characteristics are related to the control schemes of interconnectors, a fault ride-through (FRT) strategy which is applicable to the interconnector operating characteristic of working in four quadrants and capable of eliminating negative-sequence currents under unbalanced fault conditions is proposed first. Then, the additional terms of measured impedances of distance relays caused by fault resistances are derived using a symmetrical component method. Theoretical analysis shows the output currents of interconnectors are controllable after faults, which may cause malfunctions in distance protections installed on line... [more]

This paper investigated the prospects of biodiesel production from macadamia oil as an alternative fuel for diesel engine. The biodiesel was produced using conventional transesterification process using the base catalyst (KOH). A multi-cylinder diesel engine was used to evaluate the performance and emission of 5% (B5) and 20% (B20) macadamia biodiesel fuel at different engine speeds and full load condition. It was found that the characteristics of biodiesel are within the limit of specified standards American Society for Testing and Materials (ASTM D6751) and comparable to diesel fuel. This study also found that the blending of macadamia biodiesel⁻diesel fuel significantly improves the fuel properties including viscosity, density (D), heating value and oxidation stability (OS). Engine performance results indicated that macadamia biodiesel fuel sample reduces brake power (BP) and increases brake-specific fuel consumption (BSFC) while emission results indicated that it reduces the averag... [more]

The effects of using a wind acceleration device (wind lens) with vertical-axis wind turbines in wind tunnel experiments were examined. A wind lens consists of a diffuser and flanges, and this study investigated the optimum parameters of their configuration with regard to the power augmentation of the turbines. The wind lens with a flat-panel-type diffuser demonstrated power augmentation by a factor of 2.0 compared with an open wind turbine. An increase from 5° to 20° in the semi-open angle of the diffuser made it possible to generate a 30% high power output over a wide range of tip speed ratios. On that basis, an optimum semi-open angle was determined. For the flat-panel-type diffuser, a recommended diffuser length is the half of the throat width, and its semi-open angle is 20°.The inlet enhanced power augmentation over a wide range of tip speed ratios. The optimum location for the wind lens in the streamwise direction was aligned with the center of the vertical-axis wind turbines. The... [more]

The investigation of various aspects of the wave climate at a wave energy test site is essential for the development of reliable and efficient wave energy conversion technology. This paper presents studies of the wave climate based on nine years of wave observations from the 2005⁻2013 period measured with a wave measurement buoy at the Lysekil wave energy test site located off the west coast of Sweden. A detailed analysis of the wave statistics is investigated to reveal the characteristics of the wave climate at this specific test site. The long-term extreme waves are estimated from applying the Peak over Threshold (POT) method on the measured wave data. The significant wave height and the maximum wave height at the test site for different return periods are also compared. In this study, a new approach using a mixed-distribution model is proposed to describe the long-term behavior of the significant wave height and it shows an impressive goodness of fit to wave data from the test site.... [more]

The estimation and policy use of spatially explicit discrete choice models has yet to receive serious attention from practitioners. In this study we aim to analyze how geographical variables influence individuals’ sensitivity to key features of heating systems, namely investment cost and CO₂ emissions. This is of particular policy interest as heating systems are strongly connected to two major current environmental issues: emissions of pollutants and increased use of renewable resources. We estimate a mixed logit model (MXL) to spatially characterize preference heterogeneity in the mountainous North East of Italy. Our results show that geographical variables are significant sources of variation of individual’s sensitivity to the investigated attributes of the system. We generate maps to show how the willingness to pay to avoid CO₂ emissions varies across the region and to validate our estimates ex-post. We discuss why this could be a promising approach to inform applied policy decision... [more]

The proposed framework enables innovative power management in smart campuses, integrating local renewable energy sources, battery banks and controllable loads and supporting Demand Response interactions with the electricity grid operators. The paper describes each system component: the Energy Management System responsible for power usage scheduling, the telecommunication infrastructure in charge of data exchanging and the integrated data repository devoted to information storage. We also discuss the relevant use cases and validate the framework in a few deployed demonstrators.

Functionally-graded electrodes (FGEs) have shown great potential in improving solid oxide fuel cells’ (SOFCs) performance. In order to produce predictions of real FGE operations, a comprehensive numerical model that takes into account all the microstructure parameters, together with two sub model correlations, i.e., porosity-tortuosity, and porosity-particle size ratio, is utilized, aiming to provide a novel approach to demonstrate the advantages of FGEs for SOFCs. Porosity grading and particle size grading are explored by using this implemented model as a baseline. Multiple types of grading cases are tested in order to study the FGEs at a micro-scale level. Comparison between the FGEs and conventional non-graded electrodes (uniform random composites) is conducted to investigate the potential of FGEs for SOFCs. This study essentially focuses on presenting a new perspective to examine the real-world FGEs performance by involving the correlations of physically connected micro-structural... [more]

In this paper, we propose a chemically grown titanium oxide (TiO₂) on Si to form a heterojunction for photovoltaic devices. The chemically grown TiO₂ does not block hole transport. Ultraviolet photoemission spectroscopy was used to study the band alignment. A substantial band offset at the TiO₂/Si interface was observed. X-ray photoemission spectroscopy (XPS) revealed that the chemically grown TiO₂ is oxygen-deficient and contains numerous gap states. A multiple-trap-assisted tunneling (TAT) model was used to explain the high hole injection rate. According to this model, the tunneling rate can be 10⁵ orders of magnitude higher for holes passing through TiO₂ than for flow through SiO₂. With 24-nm-thick TiO₂, a Si solar cell achieves a 33.2 mA/cm² photocurrent on a planar substrate, with a 9.4% power conversion efficiency. Plan-view scanning electron microscopy images indicate that a moth-eye-like structure formed during TiO₂ deposition. This structure enables light harvesting for a high... [more]

In power system control unicontrol with single storage units or centralized control with multiple storage units to meet different level targets is challenging. Considering the charge and discharge characteristics of storage devices, this paper proposes a hierarchical configuration structure of a battery and supercapacitor mixed storage scenario, and develops a convenient control method for accessing various DC loads and can central manage mass batteries in one place. Aiming at the optimal management of large scale battery storage, the paper proposes a three-layer battery hierarchical control structure and the control objects and control circuits are discussed. Simulation studies are used to verify the control effect of the hierarchical storage system and the results show that the strategy can effectively decrease photovoltaic output fluctuation.

Latent heat thermal energy storage (TES) plays an important role in the advocation of TES in contrast to sensible energy storage because of the large storage energy densities per unit mass/volume possible at a nearly constant thermal energy. In the current study, a heat exchange device with a zigzag configuration containing multiple phase-change-materials (m-PCMs) was considered, and an experimental system was built to validate the model for a single PCM. A two-dimensional numerical model was developed using the ANSYS Fluent 14.0 software program. The energy fractions method was put forward to calculate the average Ste number and the influence of Re and Ste numbers on the discharge process were studied. The influence of phase change temperature among m-PCMs on the solidification process has also been studied. A new boundary condition was defined to determine the combined effect of the Re and Ste numbers on the discharging process. The modelling results show that for a given input power... [more]

In this paper, natural convection from vertical cylinders with inclined plate fins is investigated experimentally for use in cooling electronic equipment. Extensive experimental investigations are performed for various inclination angles, fin numbers, and base temperatures. From the experimental data, a correlation for estimating the Nusselt number is proposed. The correlation is applicable when the Rayleigh number, inclination angle, and fin number are in the ranges 100,000⁻600,000, 30°⁻90°, and 9⁻36, respectively. Using the correlation, a contour map depicting the thermal resistance as a function of the fin number and fin thickness is presented. Finally, the optimal thermal resistances of cylinders with inclined plate fins and conventional radial plate fins are compared. It is found that that the optimal thermal resistance of the cylinder with inclined fins is 30% lower than that of the cylinder with radial plate fins.

Organic Rankine cycle (ORC) power systems have recently emerged as promising solutions for waste heat recovery in low- and medium-size power plants. Their performance and economic feasibility strongly depend on the expander. The design process and efficiency estimation are particularly challenging due to the peculiar physical properties of the working fluid and the gas-dynamic phenomena occurring in the machine. Unlike steam Rankine and Brayton engines, organic Rankine cycle expanders combine small enthalpy drops with large expansion ratios. These features yield turbine designs with few highly-loaded stages in supersonic flow regimes. Part A of this two-part paper has presented the implementation and validation of the simulation tool TURAX, which provides the optimal preliminary design of single-stage axial-flow turbines. The authors have also presented a sensitivity analysis on the decision variables affecting the turbine design. Part B of this two-part paper presents the first applic... [more]

A computational tool is developed for the estimation of the energy requirements of Miscanthus x giganteus on individual fields that includes a detailed analysis and account of the involved in-field and transport operations. The tool takes into account all the individual involved in-field and transport operations and provides a detailed analysis on the energy requirements of the components that contribute to the energy input. A basic scenario was implemented to demonstrate the capabilities of the tool. Specifically, the variability of the energy requirements as a function of field area and field-storage distance changes was shown. The field-storage distance highly affects the energy requirements resulting in a variation in the efficiency if energy (output/input ratio) from 15.8 up to 23.7 for the targeted cases. Not only the field-distance highly affects the energy requirements but also the biomass transportation system. Based on the presented example, different transportation systems a... [more]

Despite the increasing interest in organic Rankine cycle (ORC) systems and the large number of cycle models proposed in the literature, charge-based ORC models are still almost absent. In this paper, a detailed overall ORC simulation model is presented based on two solution strategies: condenser subcooling and total working fluid charge of the system. The latter allows the subcooling level to be predicted rather than specified as an input. The overall cycle model is composed of independent models for pump, expander, line sets, liquid receiver and heat exchangers. Empirical and semi-empirical models are adopted for the pump and expander, respectively. A generalized steady-state moving boundary method is used to model the heat exchangers. The line sets and liquid receiver are used to better estimate the total charge of the system and pressure drops. Finally, the individual components are connected to form a cycle model in an object-oriented fashion. The solution algorithm includes a prec... [more]

Reliable and quick response fault diagnosis is crucial for the wind turbine generator system (WTGS) to avoid unplanned interruption and to reduce the maintenance cost. However, the conditional data generated from WTGS operating in a tough environment is always dynamical and high-dimensional. To address these challenges, we propose a new fault diagnosis scheme which is composed of multiple extreme learning machines (ELM) in a hierarchical structure, where a forwarding list of ELM layers is concatenated and each of them is processed independently for its corresponding role. The framework enables both representational feature learning and fault classification. The multi-layered ELM based representational learning covers functions including data preprocessing, feature extraction and dimension reduction. An ELM based autoencoder is trained to generate a hidden layer output weight matrix, which is then used to transform the input dataset into a new feature representation. Compared with the t... [more]

The integration of renewable power sources with power grids presents many challenges, such as synchronization with the grid, power quality problems and so on. The shunt active power filter (SAPF) can be a solution to address the issue while suppressing the grid-end current harmonics and distortions. Nonetheless, available SAPFs work somewhat unpredictably in practice. This is attributed to the dependency of the SAPF controller on nonlinear complicated equations and two distorted variables, such as load current and voltage, to produce the current reference. This condition will worsen when the plant includes wind turbines which inherently produce 3rd, 5th, 7th and 11th voltage harmonics. Moreover, the inability of the typical phase locked loop (PLL) used to synchronize the SAPF reference with the power grid also disrupts SAPF operation. This paper proposes an improved synchronous reference frame (SRF) which is equipped with a wavelet-based PLL to control the SAPF, using one variable such... [more]

In a parallel-connected battery group (PCBG), capacity degradation is usually caused by the inconsistency between a faulty cell and other normal cells, and the inconsistency occurs due to two potential causes: an aging inconsistency fault or a loose contacting fault. In this paper, a novel method is proposed to perform online and real-time capacity fault diagnosis for PCBGs. Firstly, based on the analysis of parameter variation characteristics of a PCBG with different fault causes, it is found that PCBG resistance can be taken as an indicator for both seeking the faulty PCBG and distinguishing the fault causes. On one hand, the faulty PCBG can be identified by comparing the PCBG resistance among PCBGs; on the other hand, two fault causes can be distinguished by comparing the variance of the PCBG resistances. Furthermore, for online applications, a novel recursive-least-squares algorithm with restricted memory and constraint (RLSRMC), in which the constraint is added to eliminate the “i... [more]

Implementation of microbial fuel cells (MFCs) for electricity production requires effective current generation from waste products via robust cathode reduction. Three cathode types using dissolved oxygen cathodes (DOCs), ferricyanide cathodes (FeCs) and air cathodes (AiCs) were therefore assessed using bioethanol effluent, containing 20.5 g/L xylose, 1.8 g/L arabinose and 2.5 g/L propionic acid. In each set-up the anode and cathode had an electrode surface area of 88 cm², which was used for calculation of the current density. Electricity generation was evaluated by quantifying current responses to substrate loading rates and external resistance. At the lowest external resistance of 27 Ω and highest substrate loading rate of 2 g chemical oxygen demand (COD) per L·day, FeC-MFC generated highest average current density (1630 mA/m²) followed by AiC-MFC (802 mA/m²) and DOC-MFC (184 mA/m²). Electrochemical impedance spectroscopy (EIS) was used to determine the impedance of the cathodes. It w... [more]

Redox mediators based on cobalt complexes allowed dye-sensitized solar cells (DSCs) to achieve efficiencies exceeding 14%, thus challenging the emerging class of perovskite solar cells. Unfortunately, cobalt-based electrolytes demonstrate much lower long-term stability trends if compared to the traditional iodide/triiodide redox couple. In view of the large-scale commercialization of cobalt-based DSCs, the scientific community has recently proposed various approaches and materials to increase the stability of these devices, which comprise gelling agents, crosslinked polymeric matrices and mixtures of solvents (including water). This review summarizes the most significant advances recently focused towards this direction, also suggesting some intriguing way to fabricate third-generation cobalt-based photoelectrochemical devices stable over time.