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  • Open Access


    Improving Functionality of 2DOF Piezoelectric Cantilever for Broadband Vibration Energy Harvesting Using Magnets

    Junxiang Jiang1,2, Shaogang Liu1,*, Lifeng Feng3

    Energy Engineering, Vol.118, No.5, pp. 1287-1303, 2021, DOI:10.32604/EE.2021.015354

    Abstract This paper presents a 2DOF nonlinear piezoelectric energy harvester for improving the efficiency of energy harvesting in low frequency range. The device consisted of an L-shaped piezoelectric cantilever with a magnet at the tip of the first beam and two external magnets on the pedestal. The distance between the magnets which generated nonlinear magnetic attraction was adjusted such that the system can exhibit monostable or bistable characteristics. First, the model of this piezoelectric energy harvester was established and the dynamic equation was derived based on the magnetic attractive force. Then, the nonlinear dynamic responses of the system subject to harmonic… More >

  • Open Access


    A Weighted Combination Forecasting Model for Power Load Based on Forecasting Model Selection and Fuzzy Scale Joint Evaluation

    Bingbing Chen*, Zhengyi Zhu, Xuyan Wang, Can Zhang

    Energy Engineering, Vol.118, No.5, pp. 1499-1514, 2021, DOI:10.32604/EE.2021.015145

    Abstract To solve the medium and long term power load forecasting problem, the combination forecasting method is further expanded and a weighted combination forecasting model for power load is put forward. This model is divided into two stages which are forecasting model selection and weighted combination forecasting. Based on Markov chain conversion and cloud model, the forecasting model selection is implanted and several outstanding models are selected for the combination forecasting. For the weighted combination forecasting, a fuzzy scale joint evaluation method is proposed to determine the weight of selected forecasting model. The percentage error and mean absolute percentage error of… More >

  • Open Access


    Study of Polymer Flooding in Heterogeneous Porous Media by Using Nuclear Magnetic Resonance

    Xing Zhang*

    Energy Engineering, Vol.118, No.5, pp. 1453-1467, 2021, DOI:10.32604/EE.2021.015032

    Abstract Polymer has been successfully used to enhance crude oil recovery at high water cut stage. However, the application of polymer flooding is limited by the heterogeneity of reservoir. In this work, the role of polymer flooding in heterogeneous reservoir was explored by nuclear magnetic resonance (NMR) spectroscopy. Parallel core displacement experiments were carried out to study polymer flooding in heterogeneous formation. The results showed that the polymer flooding area was related to permeability and pore connectivity. At the end of the water flooding stage, the residual oil was not evenly distributed in porous media. The percent crude oil recovery increased… More >

  • Open Access


    The Multi-Objective Optimization of AFPM Generators with Double-Sided Internal Stator Structures for Vertical Axis Wind Turbines

    Dandan Song1,*, Lianjun Zhou1, Ziqi Peng2, Senhua Luo2, Jun Zhu3

    Energy Engineering, Vol.118, No.5, pp. 1439-1452, 2021, DOI:10.32604/EE.2021.015011

    Abstract The axial flux permanent magnet (AFPM) generator with double-sided internal stator structure is highly suitable for vertical axis wind turbines due to its high power density. The performance of the AFPM generator with double-sided internal stator structure can be improved by the reasonable design of electromagnetic parameters. To further improve the overall performance of the AFPM generator with double-sided internal stator structure, multivariable (coil width ωc, permanent magnet thickness h, pole arc coefficient αp and working air gap lg) and multi-objective (generator efficiency η, total harmonic distortion of the voltage THD and induced electromotive force amplitude EMF) functional relationships are… More >

  • Open Access


    Assessment of Electricity Productivity in China: Regional Differences and Convergence

    Pinjie Xie1,*, Ying Zhai1, Fan Yang1,2, Zhuowen Mu3, Chao Wang4

    Energy Engineering, Vol.118, No.5, pp. 1353-1374, 2021, DOI:10.32604/EE.2021.014970

    Abstract Electricity productivity is regarded as a major assessment indicator in the design of energy saving policies, given that China has entered a “New Normal” of economic development. In fact, enhancing electricity productivity in an all-round way, as is one of the binding indicators for energy and environmental issues, means that non-growth target of total electric energy consumption in the economic development is feasible. The Gini coefficient, Theil index, and Mean log deviation are utilized to measure regional differences in China’s electricity productivity from 1997 to 2016 in five regions, and conditional β convergence is empirically analyzed with the spatial Durbin… More >

  • Open Access


    An Experimental Study on Oxidized Mercury Adsorption by Bromide Blended Coal Combustion Fly Ash

    Mingyu Yu1, Mengyuan Liu1, Guangqian Luo1,2,*, Ruize Sun1, Jingyuan Hu1, Hailu Zhu1, Li Zhong3, Lipeng Han3, Xian Li1, Hong Yao1

    Energy Engineering, Vol.118, No.5, pp. 1277-1286, 2021, DOI:10.32604/EE.2021.014810

    Abstract The application of forced mercury oxidation technology would lead to an increase of Hg2+ concentration in the flue gas. Although Hg2+ can be easily removed in the WFGD, the mercury re-emission in the WFGD can decrease the total removal of mercury from coal-fired power plants. Hence, it is necessary to control Hg2+ concentration in the devices before the WFGD. Fly ash adsorbent is considered as a potential alternative for commercial activated carbon adsorbent. However, the adsorption efficiency of the original fly ash is low. Modification procedure is needed to enhance the adsorption performance. In this study, the adsorption of Hg2+More >

  • Open Access


    The Relationship between Urbanization and Domestic Energy Consumption: An Empirical Study of Shandong Province, China

    Doudou Liu1,*, Liang Qiao2,3, Feng Zhang4, Xueliang Yuan2

    Energy Engineering, Vol.118, No.5, pp. 1395-1409, 2021, DOI:10.32604/EE.2021.014697

    Abstract The rapid development of urbanization has led to a rapid increase in total energy consumption. The proportion of domestic energy consumption to total energy consumption has gradually increased and has become the major driving force for energy consumption. With the pressure from urbanization and domestic energy consumption, it is necessary to study the impact of urbanization on domestic energy consumption of the regional level and to explore the function paths of these two factors. The findings are helpful to realize sustainable development based on the actual situation analysis, horizontal survey data and statistical yearbook panel data. The current situation and… More >

  • Open Access


    Optimal Trading Decision-Making of Power Supply Chain under Renewable Portfolio Standards

    Hui Wang, Haocheng Xu*, Wenhui Zhao

    Energy Engineering, Vol.118, No.5, pp. 1375-1394, 2021, DOI:10.32604/EE.2021.014641

    Abstract Under the background of implementing renewable portfolio standards and the ever-improving tradable green certificate scheme, the increasingly environmentally-friendly preference of power users is leading to changes in electricity demand, which, in turn, is driving changes in the decision-making behaviors of various actors in the power supply chain. Based on this, with the goal of pursuing maximum profit, consumer-power-demand functions have been introduced with some consideration of the factors of consumer preference to establish an optimal profit model for each trading subject in non-cooperative states of the power supply chain, under the constraints of meeting renewable energy portfolio standards. Here, the… More >

  • Open Access


    Behaviours of Multi-Stakeholders under China’s Renewable Portfolio Standards: A Game Theory-Based Analysis

    Bing Wang1,2, Kailei Deng1, Liting He1, Zhenming Sun1,*

    Energy Engineering, Vol.118, No.5, pp. 1333-1351, 2021, DOI:10.32604/EE.2021.014258

    Abstract China has implemented both quantitative and policy incentives for renewable energy development since 2019 and is currently in the policy transition stage. The implementation of renewable portfolio standards (RPSs) is difficult due to the interests of multiple stakeholders, including power generation enterprises, power grid companies, power users, local governments, and the central government. Based on China’s RPS policy and power system reform documents, this research sorted out the core game decision problems of China’s renewable energy industry and established a conceptual game decision model of the renewable energy industry from the perspective of local governments, power generation enterprises and power… More >

  • Open Access


    Open-Circuit Faults Diagnosis in Direct-Drive PMSG Wind Turbine Converter

    Wei Zhang1,2, Qihui Ling1,2,*, Qiancheng Zhao1,2, Hushu Wu3

    Energy Engineering, Vol.118, No.5, pp. 1515-1535, 2021, DOI:10.32604/EE.2021.014162

    Abstract The condition monitoring and fault diagnosis have been identified as the key to achieving higher availabilities of wind turbines. Numerous studies show that the open-circuit fault is a significant contributor to the failures of wind turbine converter. However, the multiple faults combinations and the influence of wind speed changes abruptly, grid voltage sags and noise interference have brought great challenges to fault diagnosis. Accordingly, concerning the open-circuit fault of converters in direct-driven PMSG wind turbine, a diagnostic method for multiple open-circuit faults is proposed in this paper, which is divided into two tasks: The first one is the fault detection… More >

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