The Experts below are selected from a list of 378147 Experts worldwide ranked by ideXlab platform
Peter A Busby - One of the best experts on this subject based on the ideXlab platform.
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electrode Impedance in adults and children using the nucleus 24 cochlear implant system
2002Co-Authors: Peter A Busby, Kerrie Plant, Lesley A WhitfordAbstract:AbstractThis study measured changes in electrode Impedance over time in 19 adults and 29 children implanted with the Nucleus 24 cochlear implant system, using common ground and three monopolar modes of stimulation, over a series of time intervals. Impedances increased from the intraoperative to the initial fitting session, decreased during the initial fitting session and for the following week, and were then stable. Impedances were lowest for the common ground mode, while for the monopolar modes, Impedances were related to the surface area of the return electrode. Impedances for children were higher than those for adults at the initial fitting session and for the following three weeks. The clinically measured Impedance values increased in a basal-to-apical direction. When these data were corrected for differences in electrode surface area, Impedances decreased in a basal-to-apical direction. Impedances were influenced by whether the electrodes were stimulated or unstimulated. Adults with higher electrode ...
Wei Rongjin - One of the best experts on this subject based on the ideXlab platform.
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a novel approach for busbar protection based on measured surge Impedance
2012Co-Authors: Wei RongjinAbstract:To avoid the influence of current transformer saturation on bus-bar protection,a measured surge Impedance based approach for busbar protection is proposed.The theoretical analysis on the faults occurred inside and outside the busbar protection zone shows that when the fault inside the protection zone occurs the polarity of all measured surge Impedances of all transmission lines are negative and their amplitudes are approximately equal,when the fault outside the protection zone occurs the polarity of all measured surge Impedance of all transmission lines are positive and their amplitudes are far less than the amplitudes of measured surge Impedances of non-faulty transmission lines,thus by means of comparing the polarities and amplitudes of measured Impedances of all transmission lines connected to the busbar the fault type occurred on busbar can be judged.Besides,the implementation of the proposed new approach for busbar protection is discussed and a feasible scheme to implement the proposed approach is achieved.Results of both theoretical analysis and simulation of EMTP show that the proposed approach based on measured surge Impedance is basically not affected by fault types,transition resistance,fault position and initial phase angle by which the fault occurs,so this approach is reliable and effective.
Lesley A Whitford - One of the best experts on this subject based on the ideXlab platform.
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electrode Impedance in adults and children using the nucleus 24 cochlear implant system
2002Co-Authors: Peter A Busby, Kerrie Plant, Lesley A WhitfordAbstract:AbstractThis study measured changes in electrode Impedance over time in 19 adults and 29 children implanted with the Nucleus 24 cochlear implant system, using common ground and three monopolar modes of stimulation, over a series of time intervals. Impedances increased from the intraoperative to the initial fitting session, decreased during the initial fitting session and for the following week, and were then stable. Impedances were lowest for the common ground mode, while for the monopolar modes, Impedances were related to the surface area of the return electrode. Impedances for children were higher than those for adults at the initial fitting session and for the following three weeks. The clinically measured Impedance values increased in a basal-to-apical direction. When these data were corrected for differences in electrode surface area, Impedances decreased in a basal-to-apical direction. Impedances were influenced by whether the electrodes were stimulated or unstimulated. Adults with higher electrode ...
Xiongfei Wang - One of the best experts on this subject based on the ideXlab platform.
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Impedance measurement of traction network and electric train for stability analysis in high speed railways
2018Co-Authors: Haitao Hu, Xiaowei Yang, Frede Blaabjerg, Xiongfei Wang, Zhengyou HeAbstract:Instability and oscillation issues have frequently occurred in high-speed railways due to the Impedance mismatch versus frequency between the four-quadrant converter (4QC)-based high-speed train and the traction network (hereinafter train–network). However, solely utilizing the mathematical deduction to quantify the Impedances seems to be difficult owing to unknown detailed parameters of both traction network and electric train. This paper proposes a method to measure the equivalent Impedances of the traction network and the 4QC of the electric train in the stationary frame for stability analysis. A disturbance circuit consisting of antiparallel insulated gate bipolar transistor (IGBT) modules and an excitation load is adopted by means of the pulsewidth modulation (PWM) signal to drive the IGBTs. Consequently, a desired broad spectral excitation is then generated to measure the output Impedance of the traction network. When injecting the harmonics twice, which are linearly independent at the same frequency, the input Impedance of the 4QC can be calculated at the corresponding frequency considering the frequency-coupled effect. The proposed method shows a good measurement accuracy. Additionally, the stability and oscillation issues of the train–network system can be then identified using measured Impedances. Both simulation and experimental results validate the effectiveness of the proposed measurement method.
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virtual Impedance based control for voltage source and current source converters
2015Co-Authors: Xiongfei Wang, Frede Blaabjerg, Poh Chiang LohAbstract:The virtual Impedance concept is increasingly used for the control of power electronic systems. Generally, the virtual Impedance loop can either be embedded as an additional degree of freedom for active stabilization and disturbance rejection, or be employed as a command reference generator for the converters to provide ancillary services. This paper presents an overview of the virtual-Impedance-based control strategies for voltage-source and current-source converters. The control output Impedance shaping attained by the virtual Impedances is generalized first using the Impedance-based models. Different virtual Impedances and their implementation issues are then discussed. A number of practical examples are demonstrated to illustrate the feasibility of virtual Impedances. Emerging applications and future trends of virtual Impedances in power electronic systems conclude this paper.
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an Impedance based stability analysis method for paralleled voltage source converters
2014Co-Authors: Xiongfei Wang, Frede Blaabjerg, Poh Chiang LohAbstract:This paper analyses the stability of paralleled voltage source converters in AC distributed power systems. An Impedance-based stability analysis method is presented based on the Nyquist criterion for multiloop system. Instead of deriving the Impedance ratio as usual, the system stability is assessed based on a series of Nyquist diagrams drawn for the terminal Impedance of each converter. Thus, the effect of the right half-plane zeros of terminal Impedances in the derivation of Impedance ratio for paralleled source-source converters is avoided. The interaction between the terminal Impedance of converter and the passive network can also be predicted by the Nyquist diagrams. This method is applied to evaluate the current and voltage controller interactions of converters in both grid-connected and islanded operations. Simulations and experimental results verify the effectiveness of theoretical analysis.
Poh Chiang Loh - One of the best experts on this subject based on the ideXlab platform.
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virtual Impedance based control for voltage source and current source converters
2015Co-Authors: Xiongfei Wang, Frede Blaabjerg, Poh Chiang LohAbstract:The virtual Impedance concept is increasingly used for the control of power electronic systems. Generally, the virtual Impedance loop can either be embedded as an additional degree of freedom for active stabilization and disturbance rejection, or be employed as a command reference generator for the converters to provide ancillary services. This paper presents an overview of the virtual-Impedance-based control strategies for voltage-source and current-source converters. The control output Impedance shaping attained by the virtual Impedances is generalized first using the Impedance-based models. Different virtual Impedances and their implementation issues are then discussed. A number of practical examples are demonstrated to illustrate the feasibility of virtual Impedances. Emerging applications and future trends of virtual Impedances in power electronic systems conclude this paper.
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an Impedance based stability analysis method for paralleled voltage source converters
2014Co-Authors: Xiongfei Wang, Frede Blaabjerg, Poh Chiang LohAbstract:This paper analyses the stability of paralleled voltage source converters in AC distributed power systems. An Impedance-based stability analysis method is presented based on the Nyquist criterion for multiloop system. Instead of deriving the Impedance ratio as usual, the system stability is assessed based on a series of Nyquist diagrams drawn for the terminal Impedance of each converter. Thus, the effect of the right half-plane zeros of terminal Impedances in the derivation of Impedance ratio for paralleled source-source converters is avoided. The interaction between the terminal Impedance of converter and the passive network can also be predicted by the Nyquist diagrams. This method is applied to evaluate the current and voltage controller interactions of converters in both grid-connected and islanded operations. Simulations and experimental results verify the effectiveness of theoretical analysis.
