• Energy Research
• BD close
• Southeast University close

More and more renewable energy sources are integrated into power grids, leading to a power electronic-based low-inertia power system. The grid-forming (GFM) inverter is an effective method for improving the inertia of the system. However, with the increased GFM inverters in the system, how the multiple control parameters affect the frequency response is still not clear. In this study, first, the power-phase model of the power grid is established; then, a small-signal distributed frequency model of the GFM inverter-based power system is established associating with the power-phase model of the power grid and the power-frequency model of the GFM inverter. Based on the proposed model, the influence of the multiple parameters to the frequency response is analyzed. It is concluded that both the inertia and damping coefficient affect the settling time, overshoot, and oscillation of the frequency. Finally, the simulation results verify the proposed model and the conclusion.

With the rapid aging population, the number of elderly passengers using bus services for daily travel will increase. Thus, it is increasingly more important for bus companies to understand the specific service requirements and expectations of elderly passengers. However, we are not aware of any dedicated studies on service requirement and travel satisfaction of the elderly. As an inclusive society is considered a key aspect of sustainable development, guaranteeing travel satisfaction is a sine qua non for sustainable transportation. Therefore, this study develops a customer satisfaction index (CSI) for the elderly. Assuming that perceived service quality affects passenger satisfaction, a structural equation model (SEM) is estimated to derive the importance of 10 dimensions of perceived service quality: reliability, time schedule, route characteristics, ticketing, driver service, convenience, safety and security, cleanliness, comfort, and information services. Furthermore, the effect of satisfaction on loyalty and filing complaints against the service company is examined. SEM is developed using data from a bus passenger survey, administered in 2017 in Harbin, China. The results show while some service dimensions such as time schedule and reliability are less important to the elderly (possibly due to their less strict time constraints) other dimensions such as service and security, convenience and driver service are in need of improvement due to the fact that they are very important for the elderly but their perceived performance from the elderly’s perspective is low.

The widespread use of Voltage Source Converter based High Voltage Direct Current Transmission (VSC-HVDC) technology has significantly increased the complexity of grid configuration and operation, which demands higher quality of AC/DC state estimation. The bad data detection and identification plays a vital role in ensuring the accuracy of state estimation outcomes. This paper presents a new approach to bad data in hybrid AC/DC grids based on the combined deep belief network (DBN) and K-means clustering method. First, the DBNs are trained separately for active and reactive power given the characteristics of VSC-HVDC by which the bad data can be detected. Then, an improved K-means is used for clustering the DBN outputs by setting the mean and the number of the samples within the clusters as two metrics for bad data identification. Finally, the case study is performed in a modified IEEE 14-bus system and the results demonstrate the effectiveness of the proposed method in terms of both the accuracy and efficiency. DOI: 10.5755/j01.eie.25.2.23206

As a natural working fluid, carbon dioxide (CO2) has been extensively applied to produce power and cooling in thermodynamic cycles. So far, various combined CO2 power and cooling systems have been proposed to enhance the energy conversion efficiency and reduce the cost further. However, how to evaluate the performance of different combined systems for a practical application scenario is still an open question. Thus, in this work, four representative systems are considered to investigate and compare the energy, exergy, and economic performances under design conditions. The corresponding models are established, and various performance parameters are calculated. According to the obtained results, the total products of four systems are 6831.36 kW, 4421.73 kW, 6252.81 kW, and 6978.69 kW, respectively. The minimum total cost is obtained by System 2. Thereafter, in order to maximize the total product (the sum of net work and refrigerating capacity), and simultaneously minimize the total cost, key system parameters are optimized by a multi-objective optimization algorithm, namely, NSGA-Ⅱ. The optimization results show that System 1 provides the highest total product (7345.4 kW), while System 2 has the lowest cost (27.51 $/h). After comprehensive comparisons for the net work, cooling capacity, efficiencies, and total cost, System 1 is regarded as the best among the considered four systems.

Characterized by increasing surface air temperature, global warming has altered the hydrological cycle at global and regional scales. In order to adapt water resources management under the context of global warming, attribution analysis on regional differentiation of water resources in the Yangtze River basin (YRB) was conducted in this study. Meteoro-hydrological variations across the basin were examined for the period 1960–2013, and then a statistic-based method was applied in quantifying the contributions of climate variability and human activities on annual runoff variations in different tributary sub-basins in the YRB. Our observation indicates that both the annual increasing rate and the inter-annual fluctuations of temperature in China and in the YRB were higher than that of the global average since the turn of the century. Climate change analysis indicates that the YRB experienced a hot-wet period during 1994–2002 and a hot-dry period during 2003–2013, since the step change of temperature in 1993. Contributions of climate change and human activities on runoff variations varied spatially in the basin. With reference to the baseline period of 1960–1993, the contribution of climate change played a dominant role in most regions of the basin, especially in those upstream sub-basins. The effect of human activities in the basin was quite complicated, not only its regional differentiation, but also its contribution were opposite during the hot-wet period and the hot-dry period in some sub-basins. The result of this study is helpful in understanding the impacts of climate change and human activities on water resources variation in both temporal and spatial scales.

Bien que l'utilisation des plastiques varie selon les régions, l'Afrique est classée deuxième après l'Asie en tant que consommateur indiscernable de plastiques qui se décomposent en microplastiques. De plus, on sait peu de choses sur l'impact de ces microplastiques sur le continent africain. Cette revue donne un aperçu de ce que sont les microplastiques et de leur impact sur l'environnement en Afrique. La mauvaise gestion des déchets plastiques est à son apogée en Afrique, car le continent gère mal plus de 70 % des déchets générés quotidiennement en moyenne par le biais d'activités telles que le tourisme, la pêche et le transport des déchets d'un bout à l'autre par les voies navigables. En ce qui concerne l'impact des microplastiques sur l'environnement, nous avons constaté qu'ils facilitent de graves conséquences environnementales, telles que le développement de la toxicité des métaux au sein des organismes aquatiques et terrestres, les perturbations de la chaîne alimentaire dans l'écosystème et les problèmes de santé publique pour les humains qui consomment des fruits de mer. Alternativement, les bioplastiques sont des matériaux plastiques biodégradables et respectueux de l'environnement prometteurs qui pourraient être cruciaux pour l'expansion de l'industrie du plastique en Afrique. En outre, le continent dispose de matières premières renouvelables biosourcées largement répandues qui peuvent être exploitées pour développer des bioplastiques. Par conséquent, les polymères à base de biomasse sont des matières premières plastiques alternatives prometteuses pour la production de plastiques, car ils peuvent facilement se biodégrader et se décomposer dans les installations de compostage industriel. Aunque el uso de plásticos varía según las diferentes regiones, África ocupa el segundo lugar después de Asia como un consumidor indiscernible de plásticos que se descomponen en microplásticos. Además, se sabe poco sobre el impacto de estos microplásticos en todo el continente africano. Esta revisión proporciona información sobre qué son los microplásticos y su impacto en el medio ambiente en toda África. La mala gestión de los residuos plásticos está en su apogeo en África, ya que el continente gestiona mal más del 70% de los residuos generados diariamente en promedio a través de actividades como el turismo, la pesca y el transporte de residuos de un extremo a otro a través de vías fluviales. Con respecto al impacto de los microplásticos en el medio ambiente, encontramos que facilitan graves consecuencias ambientales, como el desarrollo de toxicidad por metales dentro de organismos acuáticos y terrestres, interrupciones de la cadena alimentaria en el ecosistema y desafíos de salud pública para los humanos que consumen mariscos. Alternativamente, los bioplásticos prometen materiales plásticos biodegradables y respetuosos con el medio ambiente que podrían ser cruciales en la expansión de la industria plástica de África. Además, el continente tiene algunas materias primas renovables de base biológica ampliamente difundidas que se pueden aprovechar para desarrollar bioplásticos. Por lo tanto, los polímeros a base de biomasa son materias primas plásticas alternativas prometedoras para la producción de plásticos porque pueden biodegradarse y descomponerse fácilmente en instalaciones de compost industrial. Although the use of plastics varies across different regions, Africa is ranked second after Asia as an indiscernible consumer of plastics that break down into microplastic. Moreover, little is known about the impact of these microplastics across the African continent. This review provides insight into what microplastics are and their impact on the environment across Africa. The mismanagement of plastic waste is at its peak in Africa, as the continent mismanages over 70% of daily generated waste on average through activities such as tourism, fishing, and waste transport from one end to the other through waterways. Regarding the impact of microplastics on the environment, we found that they facilitate severe environmental consequences, such as the development of metal toxicity within aquatic and terrestrial organisms, disruptions of the food chain in the ecosystem, and public health challenges to humans who consume seafood. Alternatively, bioplastics are promising biodegradable and environmentally friendly plastic materials that could be crucial in expanding Africa's plastic industry. Furthermore, the continent has some widely spread biobased renewable raw materials that can be harnessed for developing bioplastics. Therefore, biomass-based polymers are promising alternative plastic feedstocks for producing plastics because they can readily biodegrade and break down in industrial compost facilities. على الرغم من أن استخدام البلاستيك يختلف باختلاف المناطق، إلا أن أفريقيا تحتل المرتبة الثانية بعد آسيا كمستهلك غير ملحوظ للبلاستيك الذي يتحلل إلى بلاستيك دقيق. علاوة على ذلك، لا يُعرف سوى القليل عن تأثير هذه المواد البلاستيكية الدقيقة في جميع أنحاء القارة الأفريقية. توفر هذه المراجعة نظرة ثاقبة حول ماهية المواد البلاستيكية الدقيقة وتأثيرها على البيئة في جميع أنحاء إفريقيا. يبلغ سوء إدارة النفايات البلاستيكية ذروته في أفريقيا، حيث تسيء القارة إدارة أكثر من 70 ٪ من النفايات المتولدة يوميًا في المتوسط من خلال أنشطة مثل السياحة وصيد الأسماك ونقل النفايات من طرف إلى آخر عبر المجاري المائية. فيما يتعلق بتأثير المواد البلاستيكية الدقيقة على البيئة، وجدنا أنها تسهل العواقب البيئية الوخيمة، مثل تطور سمية المعادن داخل الكائنات المائية والبرية، واضطرابات السلسلة الغذائية في النظام البيئي، وتحديات الصحة العامة للبشر الذين يستهلكون المأكولات البحرية. وبدلاً من ذلك، فإن البلاستيك الحيوي يعد بمواد بلاستيكية قابلة للتحلل الحيوي وصديقة للبيئة يمكن أن تكون حاسمة في توسيع صناعة البلاستيك في إفريقيا. علاوة على ذلك، تمتلك القارة بعض المواد الخام المتجددة الحيوية المنتشرة على نطاق واسع والتي يمكن تسخيرها لتطوير البلاستيك الحيوي. لذلك، فإن البوليمرات القائمة على الكتلة الحيوية تعد بمواد أولية بلاستيكية بديلة لإنتاج البلاستيك لأنها يمكن أن تتحلل وتتحلل بسهولة في مرافق السماد الصناعي.

Very limited information is available on the drought tolerance of European beech and silver fir in mixed cultivation, both for mature forests and natural regeneration. Particularly, little information is available regarding the significance on memory effects of drought exposure. Therefore, drought memory was analyzed in seedlings of these species grown in mixed cultivation in the present study. The results showed that previous-year drought hardening mediated enhanced biomass accumulation of beech leaves and root in the subsequent year, but did not impact fir growth. Total carbon (C) content was decreased by drought hardening in both the leaves and roots of beech and previous-year needles and roots of fir, in beech probably as a consequence of increased growth. Previous-year drought hardening had no significant effect on relative water contents, total nitrogen (N), or soluble protein contents in leaves and roots of beech and fir, but resulted in decreased total amino acid contents of beech leaves and fir needles. It further reduced structural N in current-year fir needles and decreased C/N ratios in roots of both beech and silver fir seedlings. Generally, the number of interspecific neighbors had no considerable effect on biomass or total C or N contents, as well as N partitioning in leaves and roots of beech and fir seedlings. The present study highlights that drought hardening induces memory effects in European beech and silver fir seedlings in their mixture in the subsequent year of growth, but these memory effects are stronger in beech than in fir.