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Chen W.,Donghua University | Shi J.,Donghua University | Zhu T.,Donghua University | Wang Q.,Songjiang Power Supply Company | And 3 more authors.
Electrochimica Acta | Year: 2015

Nitrogen and sulfur dual-doped mesoporous carbons (NSMCs) have been fabricated through a facile template-mediated pyrolyzing method using poly(ethyleneimine) (PEI) as sources of nitrogen (N) and carbon (C), ferrous sulfate(FeSO4 7H2O) as both precursor of sulfur (S) and activation reagent along with nanoscaled silica as sacrificial supports. The composition, morphology, and microstructure of the products are characterized using X-ray diffraction, scanning electron microscopy, nitrogen sorption analysis and X-ray photoelectron spectroscopy. It reveals that these NSMCs possess a BET surface area over 1064 m2 g-1and abundant mesoporous structure with pore size ranged from 4 to 20 nm. The atomic percentages of N and S functionalities are found to be 4.00 at.% N and 0.83 at.% S, indication of successful incorporation of both nitrogenand sulfur into carbon network. Benefiting from the aforementioned characteristics, these NSMCs show perfect supercapacitive performances, which have been demonstrated by cyclic voltammetry and constant-current charge/discharge cycling techniques. In 0.5 M H2SO4 electrolyte, the specific capacitance (SC) of the as-prepared NSMCs electrode can reach 280 F/g at a current density of 1 A/g. Even at a high rate capability of 100 A/g, the NSMCs electrode still shows the SC value as high as 232 F/g, retaining 83% of that at 1 A/g. Also, the electrode exhibits excellent charge/discharge cycling stability, and no measurable capacitance losses is observed even after 5000 cycles, making them potentially promising for high-performance energy storage devices. © 2015 Elsevier Ltd

Liang R.,China University of Mining and Technology | Sun S.,State Grid Corporation of China | Jin Z.,Songjiang Power Supply Company | Ma C.,China University of Mining and Technology
Gaodianya Jishu/High Voltage Engineering | Year: 2014

To improve fault location in power distribution networks in both accuracy and feasibility, we propose a combined method for radial power grids, which takes into account the characteristics and application of two-terminal location methods and one terminal location methods. Since two-terminal method is relatively easier, it is firstly adopted to recognize the fault distance approximately. Then, the accurate arriving times of wave fronts are obtained by analyzing the relationship between this approximate distance and the line parameters, which involve the reflected wave fronts from the fault point and the opposite terminal of fault line. Finally, accurate results are obtained. The method not only evades errors caused by synchronization system in global position system (GPS), but also overcomes the difficulty in recognizing traveling-wave fronts. Moreover, we establish a 35 kV radial network model in PSCAD to simulate variable parameters including fault distances, grounding resistance, and fault types. The arriving times of wave fronts in the results are compared with the fault location results from two-terminal method, which indicates that the distance error is less than 100 m. It is concluded that, while confirming the one and two-terminal methods mutually, the proposed method successively improves the fault location accuracy of one-terminal methods.

Lu T.,Jiangsu University | Gao C.,Jiangsu University | Su W.,Songjiang Power Supply Company | Li Y.,Jiangsu University
Dianwang Jishu/Power System Technology | Year: 2014

Based on the idea of delicacy management for ordered power utilization and taking both fairness and reasonableness as the general guidelines and taking the demand in economy into account, a draft procedure for the preset scheme of peak averting is designed, and a concept of classification and grouping of the preset scheme of peak averting is put forward. Firstly, utilizing the method of comprehensive evaluation the priorities of all power consumers to participate the peak averting are determined and the ordering list for peak averting is formed; then according the ordering of peak averting and the capacity of avertable peak load the power customers are grouped; finally according to the sequential arrangement of power customer groups and taking the minimized social loss due to peak averting as the objective, the composition of power customer groups of various levels of peak averting load is optimized. Results of case study analysis show that above-mentioned drafting method for the preset scheme of peak averting can ensure that the power customers with smaller comprehensive evaluation values of peak averting priorities possess the priority right to participate the peak averting, thus both reasonableness and fairness of the preset scheme can be improved; the policy orientation such as industrial restructuring, energy saving and emission reduction of power customer and environment protection can be effectively reflected; meanwhile the excessive loss of partial large customers due to peak averting under traditional peak averting patterns can be prevented.

Zhang M.,Tongji University | Du Z.,Shanghai Electrical Group Co. | Lin X.,Tongji University | Chen J.,Songjiang Power Supply Company
IEEE Transactions on Smart Grid | Year: 2015

The circulating current among the paralleled solid state transformers (SSTs) originated by the line parameter and mismatched output impedance comes into appearance in the islanded operation of the novel microgrid, the future renewable electric energy delivery and management system. In this regard, the aggregated control strategy of both virtual inductance and external inductance is proposed in this paper to suppress circulating current. The 'matching concept' regarding the parameter selection of virtual and external inductance is proposed to ensure the reliable operation of the system through constructing the complete small-signal model of SST. On the basis of aggregated control strategy and small-signal model, the adaptive virtual impedance control strategy is finally proposed by introducing the feedback of circulating current into the conventional virtual impedance control. The virtual impedance is adjusted adaptively according to the judgment algorithm to regulate the equivalent output impedance of SST. With this modification, the adjustment ability of virtual impedance control against sudden disturbance is improved and the circulating current is further reduced. The simulation results with nonlinear loading are presented to prove that the proposed control strategy, and the parameters determined by the matching concept substantially reduce the circulating current among SSTs and improve the accuracy of load sharing among SSTs. © 2010-2012 IEEE.

Liang R.,Chongqing University | Liang R.,China University of Mining and Technology | Jin Z.,Songjiang Power Supply Company | Liu J.-H.,China University of Mining and Technology
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2013

The transient characteristic propagates to both ends of line from fault point when a fault occurs in the distribution networks. A determined mathematical relationship is obtained between characteristic frequencies and distance from the fault point to observation point. The identification of wave front is unnecessary when using transient signal analysis based on characteristic frequencies, so that fault location error is avoided due to waveform distortion of time domain analysis. Some achievements and shortcomings are summarized from former papers, and a new single-ended fault location method is proposed and applied to medium distribution networks, which improves signal frequencies resolution and fault location accuracy. The proposed procedure builds an fault-waveform-inferred mother wavelets firstly, which enhances the adaptability of mother wavelets and resolution of characteristic frequencies; then characteristic frequencies are corrected by scalogram in time domain based on determined frequencies on the former step. Many simulations show the new method has good adaptability and high fault location accuracy.

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