Time filter

Source Type

Xue Y.,Zhejiang University | Xu Z.,Zhejiang University | Huang Y.,China Southern Grid Research Center | Li X.,China Southern Grid Research Center
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering

Harmonic current calculation is the critical part in the design and configuration of AC filters in HVDC projects. A modified time domain piecewise algorithm was proposed, which can calculate both non-characteristic and characteristic harmonic currents in the AC side simultaneously. At first, based on the characteristics of HVDC systems, the harmonic voltages on the entrance of the DC line were assumed to be zero. This assumption decouples the harmonic current calculation process of the rectifier side and the inverter side, and avoids the modeling of the DC line in the harmonic current calculation. Secondly, the overlap angles were calculated accurately by considering the usual non-ideal factors, including the negative sequence fundamental voltage and the background harmonic voltages on the AC side, the unsymmetrical firing angles and the imbalance of converting transformer impedances. This ensures an exact partition of the commutation interval and the non-commutation interval, which has an important influence on the non-characteristic harmonic computation. The effect of the DC current ripple was also taken into account in the calculation of the AC side harmonic current. The validity of the proposed method was demonstrated by comparison with the simulation results of PSCAD/EMTDC. It shows the proposed method is fast and accurate, and can meet the requirement of HVDC filter design for practical projects. © 2010 Chinese Society for Electrical Engineering. Source

Lei J.,China Southern Grid Research Center | Dong X.,China Southern Grid Research Center | Wu H.,Hefei University of Technology
Advanced Materials Research

According to the principle of photovoltaic(PV) grid-connected generation, the maximum power point tracking (MPPT) and grid-connected control strategy were presented in this paper. Based on the V-I characteristic curve of photovoltaic array, it built the mathematic model of photovoltaic array and the MPPT algorithm. Through adopting the double-loop feedback control strategy, it achieved the unit power factor control. Lastly, with the example system, it implemented the simulations analysis including the sunlight changing and the temperature changing. The simulation results show that the proposed models and the control strategy are correct. © (2012) Trans Tech Publications, Switzerland. Source

Xu Z.,Zhejiang University | Qiu P.,Zhejiang University | Huang Y.,China Southern Grid Research Center | Li X.-L.,China Southern Grid Research Center
Gaodianya Jishu/High Voltage Engineering

The resonant characteristics of DC loop is important in the design of HVDC projects. Therefore, the DC loop impedance at any frequency is defined, and an approach to calculate the DC loop impedance is proposed, which is based on the test signal method and time domain simulation. Through a typical ±500 kV HVDC sample system, the impacts of some important factors on the DC loop resonant characteristics are studied. Those important factors include the short circuit ratio of the AC systems, the capacity and type of the AC filters, the short circuit voltage drop of the converter transformers, the firing angle of the converters, the transmitted power of the HVDC system, the inductance of the smoothing reactor, the number of the DC filters, the length of the DC transmission line, as well as the operation mode of the HVDC system. Furthermore, based on the proposed approach, the resonant characteristics of the DC loop of the Nuozhadu-Guangdong ±800 kV UHVDC project is analyzed. The results are very useful when the DC loop resonant characteristics needs to be changed through varying the parameters of some elements of the HVDC system. Source

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