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The electricity demand and thus the amount of transmitted power are continuously growing in recent year while extensions of transmission systems have kept relatively slow. These results in larger stress of transmission systems that are operated much closer to stability boundaries than ever. This creates a demand for tools allowing very accurate and rapid monitoring of power system voltage stability margin with regard to load demand. This paper deals with applying quasi-steady-state analysis to study long term voltage stability problems resulting from small disturbances or load increase. The long term evolution is traced by successive equilibrium points, hence offering a good compromise between efficiency and accuracy. First a simple case is discussed, where only static load model is adopted and long term load restoration is considered by OLTC tap changing, then load models with long term restoration is dealt. The novel approach provides good convergence when system approaches the critical point by choosing continuation parameter. The accurate load demand margin and high simulation speed are also achieved at the same time. Numerical results are illustrated on a test system.

Abstract With the increase in the share of energy from new energy sources such as photovoltaics and wind power, the development and application of integrated energy systems are becoming more and more rapid. However, if energy is not coordinated and optimized, wind and solar abandonment may occur. This is to achieve a variety of energy sources. The integration, complementarity and flexible regulation of the company have brought great challenges. The fifth-generation district heating and cooling system, as a new direction of comprehensive energy development, can greatly improve the energy efficiency of sources and networks and the convenience of user-side energy consumption, but its adjustment potential for the user-side is insufficient. This paper explores the thermal inertia of the existing infrastructure in the system, that is, the user-side building cluster in the regional thermal system, and uses the thermal inertia of the building cluster to improve the overall potential flexibility of the regional-level integrated energy system and realize the optimized operation of the regional integrated energy system, then improve the flexibility and economy of system operation.

Abstract In this study, batch tests were performed to evaluate the effects of different thermal pretreatment temperatures (55–160 °C) and durations (15–120 min) on the anaerobic digestion of kitchen waste (KW). Two commonly used approaches, namely the modified Gompertz model and the approach developed by Koch and Drewes, were applied to assess the effects of the different pretreatment parameters on the biomethane yield, lag time and hydrolysis rate constant via data fitting. The subsequent anaerobic digestion of KW pretreated at 55–120 °C presented greater efficiency, and longer treatment durations resulted in increased methane production and higher hydrolysis rate constants. These findings were obtained due to the lower nutrient loss observed in KW treated at lower temperature treatments compared with that found with higher temperature treatments. In general, the effects of thermal pretreatment on the lag phase and hydrolysis rate differed depending on the treatment parameters leading to the variations in the KW compositions. The soundness of the two model results was evaluated, and higher statistical indicators (R2) were found with the modified Gompertz model than with the approach developed by Koch and Drewes.

Construction contract management is an important research field in engineering. However, in construction contract management courses, student learning interest is decreasing because of unreasonable course design and management. Consequently, the use of project-based teaching (PBT) has increased in recent years. Nevertheless, there has been little research conducted to provide evidence that highlights the role of PBT among the factors of learning interest. This study aimed to investigate the factors that promote learning interest in PBT courses. First, we identified research gaps with a literature review and developed a potential research model. Second, a PBT course was carried out where 71 Tsinghua University students who attended the course were surveyed via 5-point Likert-scale questionnaires. Third, data were analyzed using the Wilcoxon signed-rank test and the ordinal logistic regression model. Finally, the results were interpreted and discussed. Our findings show that there is a significant improvement in students’ learning interest towards the related course after the PBT method was adopted and that pedagogical factors, specifically (1) curriculum scope and sequence, (2) collaboration and communication, and (3) workload are the most salient factors that can influence student learning interest. None of the dispositional factors were found to significantly affect student interest. These results underpin the theoretical validity of PBT and can be used to improve PBT in engineering education management.

The deepening penetration of renewables in power systems has contributed to the increasing needs for generation scheduling flexibility. Specifically, for short-term operations, flexibility here indicates that sufficient ramp capacities should be reserved to respond to the expected changes in the load and intermittent generation, also covering a certain amount of their uncertainty. To address the growing requirements for flexible ramp capacity, markets for ramp products have been launched in practice such as the ones in California ISO and Midcontinent ISO. Some-times, to guarantee sufficient ramp capacity, expensive fast start units have to be committed in real-time. Moreover, with higher penetration of renewable generation, the flexibility provided by the conventional units might not be enough. Actually, wind power producers are physically capable of offering flexibility, which is sometimes also economically efficient to the entire system. In this paper, we aim to explore the mechanism and possibility of including wind power producers as ramp providers to increase the supply of flexibility. To conduct the anal-yses, a two-stage stochastic real-time unit commitment model considering ramp capacity adequacy is formulated. Case studies indicate that both the system and the wind power producers can benefit if the wind power is allowed to provide flexible ramp products. Submitted to a journal

As an important index to measure the reliability of interchange power trading, available transfer capability (ATC) has been widely employed and investigated in existing studies and projects. With the rapid development of energy storage (ES) technology, ES can take advantage of responsive capability to flexibly shift peak load to valley hours, thus effectively enhancing regional ATC. However, the impacts of ES on ATC have not yet been systematically explored. To fill this gap, we evaluate the contributions of energy storage to ATC enhancement in this paper. A two-stage ATC evaluation framework is developed considering the load shifting capability of ES. In the first stage, a day-ahead unit commitment model is formulated to schedule generators and ES. Scenario-based stochastic programming is adopted to depict the uncertainty in renewable power and load. In the second stage, a real-time ATC model is used to quantify the maximal capacity of further interchange power trading. Case studies based on IEEE 14-bus system demonstrate the impacts of ES on enhancing realtime ATC while facilitating renewable energy accommodation.

Iron-based oxygen carriers (OCs) have received much attention due to their low costs, high mechanical strengths and high-temperature stabilities in the chemical looping gasification (CLG) of biomass, but their chemical reactivity is very ordinary. Converter steel slags (CSSs) are steelmaking wastes and rich in Fe2O3, CaO and MgO, which have good oxidative ability and good stability as well as catalytic effects on biomass gasification. Therefore, the composite OCs prepared by mechanically mixing CSSs with iron-based OCs are expected to be used to increase the hydrogen production in the CLG of biomass. In this study, the catalytic performance of CSS/Fe2O3 composite OCs prepared by mechanically mixing CSSs with iron-based OCs on the gasification of brewers’ spent grains (BSGs) were investigated in a tubular furnace experimental apparatus. The results showed that when the weight ratio of the CSSs in composite OCs was 0.5, the relative volume fraction of hydrogen reached the maximum value of 49.1%, the product gas yield was 0.85 Nm3/kg and the gasification efficiency was 64.05%. It could be found by X-ray diffraction patterns and scanning electron microscope characterizations that the addition of CSSs helped to form MgFe2O4, which are efficient catalysts for H2 production. Owing to the large and widely distributed surface pores of CSSs, mixing them with iron-based OCs was beneficial for catalytic steam reforming to produce hydrogen.

Under the development of information and communication technologies, this paper discusses a cloud-based user-side integrated energy management to improve the energy utilization efficiency in a smart community, for which a two-level model is proposed that relies on an energy hub and load aggregators. Furthermore, to address the issue of preserving confidentiality for the cloud service, an information-masking mechanism is designed based on linear mapping functions, whose information-masking requirements and processes are specified accordingly. Numerical results demonstrate the effectiveness of the proposed model and of the method for cloud computing.