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RISS 인기검색어
- 검색키워드
- 저자 : Jiabing Hu (검색결과 5 건)
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Pole-to-Ground Fault Analysis for MMC-HVDC Grid
Zhen He,Jiabing Hu,Lei Lin,Zhiyuan He 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
Pole-to-ground (PTG) fault analysis is of vital importance for HVDC grid. However, many factors are not considered in the existing studies, such as the asymmetrical property of PTG fault, the coupling issue between dc transmission lines and the complexity of dc grid’s structure. This paper presents a PTG fault analysis method, which is based on common- and differential-mode (CDM) transformation. Similar to the symmetrical component method in ac system, the transformation decomposes the HVDC grid into CDM networks at first. Then, under the perspective of CDM components, a transfer impedance based analysis is performed to obtain the analytical expressions of PTG fault characteristics. The proposed PTG fault analysis method is applicable to arbitrary HVDC grid topologies. And the analytical expressions can give theoretical guidance for fault protection. The validity of the proposed PTG fault analysis method is verified by comparison with the simulation results in PSCAD/EMTDC.
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Fault Current Analysis of Type-3 Wind Turbine Considering Dynamic Influence of Phase Locked Loop
Xiaomeng Yu,Yuanzhu Chang,Jiabing Hu,Lei Shang 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
As Type-3 wind turbine (WT) has already become a vital source in power system, analyzing its fault current is necessary. Although phase-angle jump of stator voltage always occurs during short circuit, it is neglected in existing research and the influence of phase locked loop (PLL) on fault current is still unclear. In this paper, an analytical model of Type-3 WT considering both magnitude drop and phase-angle jump is first developed. Then, the variable-frequency phenomenon of fault current component is discovered by comparing the results of modal analysis and Hilbert-Huang Transformation (HHT). Moreover, the dominant branch causing this phenomenon is extracted so that the whole system can be decomposed into a linear subsystem and a nonlinear subsystem. Based on these subsystems, an analytical expression of fault current is deduced and validated. The conclusion of this paper indicates that the variable-frequency phenomenon may result in protective relays’ maloperation.
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Time-Varying Amplitude-Frequency Characteristics Analysis of VSC Internal Voltage under Grid Fault
Jingyi Liu,Yuanzhu Chang,Jiabing Hu,Lei Shang 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
As the voltage source converters (VSCs) are widely used as the important interface between the new energy applications and the power systems, the transient characteristics of VSC have great influence on the operation of the modern power systems. In this paper, internal voltage concept is introduced to represent the external characteristics of VSC. The amplitude/frequency characteristics of VSC internal voltage under non-severe grid fault and severe grid fault are analyzed and compared. The results show that under non-severe grid fault, the amplitude/frequency characteristics of VSC internal voltage are periodic time-varying. And the amplitude and frequency are the linear combination of modes of the close-loop system, while in severe grid fault, the characteristics of amplitude and frequency are aperiodic time-varying and are decided by the modes and the nonlinear elements. The results and conclusion are validated in Matlab/Simulink.
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Zhenhai Xie,Yuanzhu Chang,Jiabing Hu 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
During an AC fault, voltage source converter (VSC) has a different excitation-response characteristic compared with the synchronous generator (SG). As a result, for power systems with a high penetration of VSC-based equipment, the network response behaviors are mainly determined by the VSCs’ internal voltage whose amplitude and frequency are time-varying. However, the lumped parameter π-equivalent circuit model is established based on a sine steady-state signal. Thus, in order to analyze the network response behavior, an excitation-response relation model of AC network is proposed. Then, the response behaviors of node-voltage vectors are compared when using two different types line model in electromagnetic transient program (EMTP). Finally, the determinants of network response behaviors are analyzed. The conclusions of this paper indicate that the π-equivalent circuit model is improper and the distributed parameter line model is suggested to simulate the transient behaviors of a power system with high penetration of VSCs.
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Meiqing Zhang,Xiaoming Yuan,Jiabing Hu 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
Voltage-source converter (VSC) high voltage direct current (HVDC) connected to islanded grid is becoming a normal system operation mode. However, there is little research on the stability analysis of VSC-HVDC connected to islanded grid. On the basis of previous work, this paper analyzes the stability and adaptability of PLL-synchronized VSC-HVDC adopted with the additional frequency regulation scheme (FRS) under islanded grid. By defining the instantaneous frequency and regarding it as a state variable, the small-signal model of PLL-synchronized VSC under both grid-islanded mode and grid-connected mode is synthetically established. On this basis, the impact of FRS on the stability of PLL-synchronized VSC under islanded grid is analyzed, and then the adaptability of FRS to different grid strengths is investigated via considering different short current ratios (SCRs), including islanded grid (SCR=0), weak grid (SCR<2) and strong grid (SCR>5). The analysis results show that the FRS has important role on enhancing the small signal stability of the islanded grid, and also has excellent adaptability to the wide change of grid conditions, so as to further improve the possibility of the FRS applied in practical projects. These results finally are verified by time-domain simulations.
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