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Tang Q.,Hunan University | Teng Z.,Hunan University | Gao Y.,Hunan University | Zhou Y.,Guangxi Electric Power Research Institute
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2012

To realize high-accuracy measurement of voltage flicker, a kind of voltage flicker measurement method using the square demodulation method based on S-transform was presented. S-transform principles were briefly introduced; the computational process of voltage flicker using the square demodulation method was simplified; and the voltage flicker measurement scheme using the S-transform-based square demodulation method was given. The S-transform is applied for the time-frequency analysis of voltage flicker signals. The frequency domain characteristic given in S-matrix was used for computing the magnitude of the voltage flicker. Based on the high frequency spectrum amplitude, the starting and ending moments of the voltage flicker were estimated. Simulation experiment results verify the feasibility and accuracy of this algorithm. Furthermore, a voltage flickermeter based on virtual instrument technology was developed, and its structure and main front panel were given. The operation results show that the meter has advantages of convenient operation and reliable measurement. © 2012 Chinese Society for Electrical Engineering. Source

Zeng B.,Hunan University | Teng Z.,Hunan University | Cai Y.,Huawei | Guo S.,Hunan University | Qing B.,Guangxi Electric Power Research Institute
IEEE Transactions on Smart Grid | Year: 2011

An approach for power system harmonic phasor analysis under asynchronous sampling is proposed in this paper. It is based on smoothing sampled data by windowing the signal with the four-term fifth derivative Nuttall (FFDN) window, and then calculating harmonic phasors in the frequency domain with an improved fast Fourier transform (IFFT) algorithm. The applicable rectification formulas of the IFFT are obtained by using the polynomial curve fitting, dramatically reducing the computation load. The FFDN window can effectively inhibit the spectral leakage and the picket fence effect can be modified by the IFFT algorithm under asynchronous sampling, and the overall algorithm can easily be implemented in embedded systems. The effectiveness of the proposed method was analyzed by means of simulations and practical experiments for multifrequency signals with the fluctuation of the fundamental frequency and with the presence of white noise and interharmonics. © 2010 IEEE. Source

Lu Z.,Hunan University | Luo A.,Hunan University | Jiang W.,Guangxi Electric Power Research Institute | Xu X.,Hunan University
Diangong Jishu Xuebao/Transactions of China Electrotechnical Society | Year: 2012

The new method of operating an inverter to imitate a synchronous generator for circulating current restraint is motivated and developed. Based on the comparison with the traditional droop control method, detail analysis is done on the principles of decoupling between the equivalent line impedance and output reactive power and the advantage of the new method to improving the accuracy of the load power distribution is described. In order to reduce voltage and frequency difference between the paralleled inverters when no-load operating, minor amendment is used to the droop control coefficient to meet the demand of load power distribution between different rated power inverters and circulation suppression and adding differential link to improve the control delays caused by power calculation. Simulation and experiment are done in a small-scale experimental micro-grid system which contains two inverters in parallel. The results are given to verify that the circulation inhibitory is effective in a variety of conditions. Source

Liu Y.,CAS Wuhan Institute of Rock and Soil Mechanics | Li H.,CAS Wuhan Institute of Rock and Soil Mechanics | Xiao K.,Guangxi Electric Power Research Institute | Li J.,CAS Wuhan Institute of Rock and Soil Mechanics | And 2 more authors.
Computers and Geotechnics | Year: 2014

In general, the determination of the factor of safety and the location of the critical slip surface are two major challenges in seismic slope stability analysis. In this paper, a new approach for determining the factor of safety and the corresponding critical slip surface of a layered rock slope subjected to seismic excitations is presented, through a case study based on the combination of the shear strength reduction technique and distinct element method. According to this proposed method, the seismic factor of safety and the critical slip surface of the slope are estimated and compared with those obtained by the pseudo-static approach, combined with the limit equilibrium method. It is found that the factor of safety obtained from the proposed method is slightly greater than that computed by the pseudo-static analysis, with a difference of 4.2%, and that the critical slip surface obtained from the two methods is identical, which confirms the reasonability and feasibility of the proposed method. © 2013 Elsevier Ltd. Source

Zeng B.,Guangxi Electric Power Research Institute | Teng Z.,Hunan University | Zhou Y.,Guangxi Electric Power Research Institute
Diangong Jishu Xuebao/Transactions of China Electrotechnical Society | Year: 2012

In this paper, the spectral characteristics of the cosine window are analyzed and an improved FFT method for harmonic analysis based on the even order cosine window (EOCW) is proposed. The rectification formulae of the frequency, amplitude and phase of the fundamental and harmonics are obtained by using the least squares fitting method. Simulation results indicate that, the precision in calculating harmonic parameters can be highly improved by the proposed algorithm, no matter with the fundamental frequency varies and the presence of interharmonics. The proposed algorithm is suitable for harmonic analysis under nonstationary situations and the correctness of which is verified by the application in embedded system. Source

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