This paper aims at specifying the optimal allocation of a vanadium redox flow battery (VRB) energy storage system (ESS) for maintaining power balance of active distribution networks for wind power applications. Correspondingly, an optimal allocation approach for the VRB ESS was proposed. Different with the previous researches, the dynamic efficiency and life of VRB are considered in the proposed mathematical framework. Also, this proposed mathematical framework made a comprehensive assessment of the total benefits including the consumption of wind power, the reduced load interruption, greenhouse gas emission, network loss, and the capital cost of VRB ESS. These economic indicators are used to evaluate the penetration of VRB ESS and the economy of ADNs can achieve to the optimal with the designed VRB ESS. Finally, the proposed optimal allocation approach was validated and tested by a modified IEEE 33-bus system and IEEE 123 node system. Test results have demonstrated the effectiveness of the proposed optimal allocation approach associated with the power flow operation characteristics of active distribution networks.

Wind power has achieved great development in Northern China, but abundant wind power is dissipated, rather than utilized, due to inflexible electricity production of combined heat and power (CHP) units. In this paper, an integrated CHP system consisting of CHP units, wind power plants, and condensing power plants is investigated to decouple the power and heat production on both the power supply side and heat supply side, by incorporating electrical energy storage (EES) and thermal energy storage (TES). Then the integrated CHP system dispatch (ICHPSD) model is formulated to reach the target of reducing wind power curtailment and primary energy consumption. Finally, the feasibility and effectiveness of the proposed ICHPSD model are verified by the six-bus system, and the simulation results show that EES has a better effect on wind power integration than TES. The annual net benefits by incorporating EES and TES increase with increasing wind penetration, but they gradually approach saturation. Introducing both EES and TES can largely increase the amount of wind power integration and improve the operation efficiency of the system. Energies 2016, 9, 474 2 of 17 technologies which are suitable for large-scale applications, conventional battery storage is efficient but the investment would be very high. Pumped hydro is fit for large-scale applications but it is applicable only in certain locations [11]. Nowadays, hydrogen storage is emerging as a promising alternative due to high energy density, clean fuel, and relatively low capital cost [12,13]. Adding hydrogen storage to a CHP system could improve the accommodation of wind power, as well as primary energy saving, since the wind energy curtailed in off-peak hours could be used to split water into hydrogen and oxygen. Hydrogen would be stored and then transformed to electrical energy, when necessary, by various ways.Thermal energy storage (TES) is another attractive option for wind energy integration. Although thermal storage is not directly related with electrical energy production, introducing TES is an efficient solution to relieve the mismatch between heat/power demand and supply, by decoupling the generation of electricity and heat [14]. The surplus thermal energy is stored during the operating periods for a later use when electrical demand is low, leading to a decrease in heat production of CHP plants, along with a reduction in electricity production, as a result, wind power would be better integrated. Under the influence of real-time electricity pricing, a large number of TES units have been installed in European countries which have a large percentage of wind power [15]. For example, in Denmark, TES systems have been an important part of its 100% renewable energy system plan [16].Many studies have been involved in the flexible operation of integrated CHP systems recently. In [17], heat pumps and thermal inertia of buildings and thermal comfort of end users are considered to increase the wind power integration. In [18], electric boilers and heat storage tanks are...

Abstract:With the penetration of distributed generators (DGs), operation planning studies are essential in maintaining and operating a reliable and secure power system. Appropriate siting and sizing of DGs could lead to many positive effects forthe distribution system concerned, such as the reduced total costs associated with DGs, reduced network losses, and improved voltage profiles and enhanced power-supply reliability. In this paper, expected load interruption cost is used as the assessment of operation risk in distribution systems, which is assessed by the point estimate method (PEM). In light with the costs of system operation planning, a novel mathematical model of chance constrained programming (CCP) framework for optimal siting and sizing of DGs in distribution systems is proposed considering the uncertainties of DGs. And then, a hybrid genetic algorithm (HGA), which combines the GA with traditional optimization methods, is employed to solve the proposed CCP model. Finally,the feasibility and effectiveness of the proposed CCP model are verified by the modified IEEE 30-bus system, and the test results have demonstrated that this proposed CCP model is more reasonable to determine the siting and sizing of DGs compared with traditional CCP model.

Summary This paper aims at specifying the optimal allocation of a hybrid supercapacitor‐vanadium redox flow battery (VRB) energy storage system (ESS) for maintaining power balance of active distribution networks (ADNs) for wind power applications. Correspondingly, an optimal allocation approach for the hybrid ESS considering the application scenarios of supercapacitor ESS and VRB ESS was proposed. The supercapacitor ESS was used for restraining the high‐frequency components of net load power and a net load power spectrum analysis method based on dividing the variations of net load power was used to obtain the optimal capacity of supercapacitor ESS. For the allocation of hybrid ESS, a mathematical framework was proposed considering both the economy and reliability of ADNs associated with VRB′ dynamic operation characteristics. Finally, the proposed optimal allocation approach was validated and tested by a modified IEEE 33‐bus system. Test results have demonstrated the effectiveness of the proposed optimal allocation approach associated with the power flow operation characteristics of ADNs.

To meet the increasing need for clean combustion, improve the combustion efficiency of fuels, and reduce the pollutants produced in the combustion process, it is necessary to systematically study the combustion of hydrocarbon fuels. An accurate and detailed chemical kinetic model is an important prerequisite for understanding the combustion performance of hydrocarbon fuels and studying complex chemical reaction networks. Therefore, based on ReaxGen, new detailed mechanisms for the lowtemperature combustion of n-nonane are proposed and verified in detail in this study. Meanwhile, some international mainstream combustion models such as the LLNL model and the JetSurf 2.0 model are compared with ours, showing that the proposed new mechanisms can better predict the ignition delay combustion characteristics of n-nonane, and they also hold in a wide range of conditions. In addition, the numerical simulation results of the concentration curve calculated for the new mechanisms, especially Model v2, are in good agreement with the experimental data, and the mechanisms can reproduce the performance of the negative-temperaturecoefficient behavior toward n-nonane ignition. The numerical simulation results of the laminar flame propagation velocity varying with the equivalence ratio are also in good agreement with the available experimental data. Finally, the ignition delay sensitivity of nnonane is analyzed by the sensitivity analysis method; the key reactions affecting the ignition mechanism are investigated; and the reaction path analysis is conducted to better understand the models' predicted performance. In a word, the new mechanisms are helpful to understand the ignition properties of large hydrocarbon fuels for high-speed aircrafts.

This study aims at specifying the operational risk assessment of active distribution networks (ADNs). Correspondingly, an operational risk assessment model based on point estimate method (PEM) considering probabilistic uncertainties of distributed generators-loads and power management of vanadium redox flow battery (VRB) energy storage systems (ESSs) was proposed. The probabilistic uncertainties of distributed generators and loads growth are mathematically modelled and discretised by PEM. Also, the distributed VRB ESSs are maximally used for the consumption of renewable energy and power supply of loads by the power management of VRB ESSs. The risk assessment indexes of expected energy not supplied and severity index for ADNs are constructed and the 2m + 1 PEM was used for the calculation. Finally, the case studies verified the effectiveness of PEM as the relative error is less than 1.75% and the excellent advantage on fast calculation. In addition, both the power management of distributed VRB ESSs and the dispersion of DGs or VRB ESSs have a significant influence on the operational risk assessment of ADNs.

This paper used a Vanadium Redox flow Battery (VRB) as the storage battery and designed a two-stage topology of a VRB energy storage system in which a phase-shifted full bridge dc-dc converter and three-phase inverter were used, considering the low terminal voltage of the VRB. Following this, a model of the VRB was simplified, according to the operational characteristics of the VRB in this designed topology of a VRB energy storage system (ESS). By using the simplified equivalent model of the VRB, the control parameters of the ESS were designed. For effectively estimating the state of charge (SOC) of the VRB, a traditional method for providing the SOC estimation was simplified, and a simple and effective SOC estimation method was proposed in this paper. Finally, to illustrate the proper design of the VRB ESS and the proposed SOC estimation method, a corresponding simulation was designed by Simulink. The test results have demonstrated that this proposed SOC estimation method is feasible and effective for indicating the SOC of a VRB and the proper design of this VRB ESS is very reasonable for VRB applications.

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