Junxiang Jiang^1,2, Shaogang Liu^1,*, 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 >

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 >

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 >

Dandan Song^1,*, 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 ω_c, permanent magnet thickness h, pole arc coefficient α_p and working air gap l_g) and multi-objective (generator efficiency η, total harmonic distortion of the voltage THD and induced electromotive force amplitude EMF) functional relationships are… More >

Pinjie Xie^1,*, Ying Zhai¹, Fan Yang^1,2, 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 >

Mingyu Yu¹, Mengyuan Liu¹, Guangqian Luo^1,2,*, 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 >

Doudou Liu^1,*, Liang Qiao^2,3, 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 >

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 >

Bing Wang^1,2, Kailei Deng¹, Liting He¹, Zhenming Sun^1,*

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 >

Wei Zhang^1,2, Qihui Ling^1,2,*, Qiancheng Zhao^1,2, 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 >