Electricity being a basic national infrastructure for a country, its security, reliability and quality are the most important parameters for the network managers. Several methods are generally used to improve the volt...Electricity being a basic national infrastructure for a country, its security, reliability and quality are the most important parameters for the network managers. Several methods are generally used to improve the voltage quality more and more. However, most of the means implemented depend on external factors independent of the network managers or require huge regular financial resources. The method used in this paper is the loopback, applied to the Southern Interconnected Grid (SIG) of Cameroon, which is the largest net</span><span style="font-family:Verdana;">work in the country. The procedure used takes into account nodes experiencing huge voltage drops and network constraints. The chosen loopback</span><span style="font-family:Verdana;"> scenario results in a clear improvement of the voltage plan in this network, and also a discharge of the transformers, a considerable decongestion of the lines, a reduction of the power losses and a significant reduction of the thermal placement used for improvement of the voltage profile.展开更多
Low voltage start-up was realized in HT-7 discharges under the assistance of lower hybrid (LH) waves. The use of a strong LH wavet which can Change its N// spectrum in a large range of several milliseconds, made the l...Low voltage start-up was realized in HT-7 discharges under the assistance of lower hybrid (LH) waves. The use of a strong LH wavet which can Change its N// spectrum in a large range of several milliseconds, made the loop voltage for start-up reduce from around 20 V to less than 5 V. It means that the electric field for HT-7 start-up decreases from 2.5-3 V/m to 0.6 V/m. Some physical phenomena such as the consumption of magnetic flux in start-up phase and the radiation from the initial plasma were observed in this kind of low voltage start-up discharges.展开更多
为提高单相动态电压恢复器（dynamic voltage restorer,DVR）的补偿性能,提出一种基于等效基波及奇次谐波谐振器组的数字控制方法。采用可等效为一组谐振器的延时模块,能够有效抑制电网基波和谐波扰动。给出一种包含两个控制参数和一组...为提高单相动态电压恢复器（dynamic voltage restorer,DVR）的补偿性能,提出一种基于等效基波及奇次谐波谐振器组的数字控制方法。采用可等效为一组谐振器的延时模块,能够有效抑制电网基波和谐波扰动。给出一种包含两个控制参数和一组零相移陷波滤波器的结构及其设计方法,使系统在保证稳定性的同时,获得较大的谐振增益。其中,延时环节衰减系数可增加谐振器组鲁棒性;控制器比例增益可解决零相移陷波器中使用延时带来的问题;零相移陷波器组既能对消LC谐振峰,也能解决等效谐振器组高增益在高频处的稳定性问题。同时,引入电源电压和负载电流双前馈来保证响应速度,增加了对扰动的抑制能力。所提控制策略结构简单,谐波补偿能力强,动态响应快,易于实现。在2kW单相DVR实验装置上的实验结果验证了该控制方法的正确性。展开更多
Increasing the number of atoms that interact with microwave fields represents a promising strategy for enhancing the sensitivity of Rydberg atom-based superheterodyne receivers.Nevertheless,the practical implementatio...Increasing the number of atoms that interact with microwave fields represents a promising strategy for enhancing the sensitivity of Rydberg atom-based superheterodyne receivers.Nevertheless,the practical implementation of this approach is impeded by adverse effects such as excitation saturation of Rydberg atoms and power broadening.Here,we demonstrate enhanced microwave field measurements based on two specific velocity groups of atoms,simultaneously addressed by dual-channel probe beams in a Sagnac loop interferometer.The application of resonance detuning in two-photon excitation enables selective addressing of atoms moving along the beam direction,thereby significantly mitigating atomic transit noise.At 7.97 GHz,our method yields a 3 dB improvement in signal-to-noise ratio(SNR),achieving a sensitivity of 10.7 nV·cm^(−1)·Hz^(−1/2).This approach offers a viable pathway to further improve the sensitivity of Rydberg atom-based microwave electrometers.展开更多
合环转供电是提高供电可靠性的关键手段,但直接合环可能产生较大冲击电流影响电网运行安全性。采用旋转潮流控制器(rotary power flow controller,RPFC)的方式能够实现台区的零感知合环,但电压调节轨迹不当将会带来RPFC接入点的电压越...合环转供电是提高供电可靠性的关键手段,但直接合环可能产生较大冲击电流影响电网运行安全性。采用旋转潮流控制器(rotary power flow controller,RPFC)的方式能够实现台区的零感知合环,但电压调节轨迹不当将会带来RPFC接入点的电压越限问题。对此,提出一种基于两阶段最优路径的RPFC配电网柔性合环方法。首先,对输出电压运行轨迹进行合理规划,将其分为两阶段:第1阶段要求合环点两端电压相位一致并约束电压幅值相等,实现端电压的平稳过渡;第2阶段在相位一致的基础上,控制RPFC输出电压至目标值,使合环点两端电压幅值一致。然后,采用分相量夹角计算和旋转角协调控制,选择就近的旋转角设定值作为目标值,从而实现合环点两端电压无差调节;最后,仿真和实验对比分析所提方法将电压越限至少降低至30%,展示RPFC在实现配电网柔性合环中的重要应用价值。展开更多
【目的】跟网型换流器(grid-following converter,GFL)被广泛应用于新能源并网系统。电网发生故障引起电压跌落时,系统进入低电压穿越(low voltage ride-through,LVRT)过程。传统锁相环(phase-locked loop,PLL)的二阶模型因忽略电流暂...【目的】跟网型换流器(grid-following converter,GFL)被广泛应用于新能源并网系统。电网发生故障引起电压跌落时,系统进入低电压穿越(low voltage ride-through,LVRT)过程。传统锁相环(phase-locked loop,PLL)的二阶模型因忽略电流暂态过程,难以准确描述LVRT期间系统的动态特性,导致暂态同步稳定性的提升效果受限。为此,针对对称故障场景,提出一种适用于LVRT过程的电流内环协同控制策略,以增强系统暂态同步稳定性。【方法】基于PLL四阶动态方程,结合暂态能量函数法,分析PLL输出频率突变以及电流内环与PLL耦合作用对系统暂态同步稳定性的影响,并设计相应的控制策略:根据最优阻抗比动态调整电流参考值,以抑制故障期间暂态能量累积;通过在电流内环前馈解耦项中引入频率偏差补偿机制,加速暂态能量耗散过程。两者协同作用,提升系统在LVRT期间的暂态同步稳定性。【结果】PSCAD/EMTDC对称故障时域仿真结果表明:故障瞬间PLL输出频率突变量与电网电压跌落幅值成正比,增大系统失稳风险;所提控制策略能够有效抑制故障期间PLL输出频率偏差,显著降低虚拟功角首摆幅度,缩短故障清除后系统恢复时间,在不同电网参数下均表现出良好的适应性。【结论】所提电流内环协同控制策略,能够在对称故障期间有效抑制暂态能量累积,在故障清除后加速暂态能量耗散,有效提升了GFL并网系统在此类LVRT过程中的暂态同步稳定性。展开更多
Increasing penetration of power electronic(PE)grid-tied devices has caused more and more dynamic problems with unknown mechanisms.Since grid operation asks for a certain voltage amplitude and frequency level when ther...Increasing penetration of power electronic(PE)grid-tied devices has caused more and more dynamic problems with unknown mechanisms.Since grid operation asks for a certain voltage amplitude and frequency level when there is a power imbalance,roles of the PE grid-tied devices during dynamics must be characterized as internal voltage response under power excitation,in which the voltage vector evolves through its timevarying amplitude and frequency.Existing modeling works,unfortunately,fail to recognize amplitude and frequency modulation essence of grid voltage during dynamics,so corresponding linear models are inapplicable to small-perturbation grid dynamic analysis.Thus,taking current control timescale of grid-tied voltage source converter(VSC)for example,this paper establishes a model with active and reactive current excitation and internal voltage amplitude and frequency response.Especially,the role of the terminal voltage detection-based phase-locked loop(PLL)in the excitation-response relationship is revealed.Linearization is conducted by clarifying amplitude and frequency operating points and corresponding increments of AC signals.This model intuitively reflects the evolution of internal voltage amplitude and frequency excited by active and reactive currents,which represents characteristics of the device during dynamics.Then,simulations for verification of the linear model and time-varying nature of amplitude and frequency are presented.Features of the characteristics of VSC are preliminarily discussed.展开更多
As a new composite welding heat source introduced in recent years, the cross-coupling arc uses a non-consumable electrode arc(plasma arc) and a consumable electrode arc(inter-wire arc) in cross-coupling, in which the ...As a new composite welding heat source introduced in recent years, the cross-coupling arc uses a non-consumable electrode arc(plasma arc) and a consumable electrode arc(inter-wire arc) in cross-coupling, in which the plasma arc is the main arc and the inter-wire arc is the vice arc, to realize the separate control of the heat input to the workpiece,arc force, and droplet transfer. To reveal the electrical characteristics of the inter-wire arc under the action of the plasma arc, in this study, rotating probes are used to sweep across the plasma arc. When the probes rotate into the plasma arc, a circuit is formed, and the electrical characteristics of the inter-wire arc are indirectly analyzed according to the circuit: the probe centering current and input voltage are used as the physical quantities. The results show that at a certain wire feed rate, the inter-wire arc current increases with increasing input voltage. When the input voltage is low, the wire feed rate has no obvious e ect on the inter-wire arc current. At a higher input voltage, where the wire feed rate is high, the inter-wire arc current decreases. With the increase in the plasma arc current, the inter-wire arc current first increases quickly and then increases slowly, and simultaneously, the striking arc time becomes longer.With the increase in the interval between the nozzle and the workpiece, the inter-wire arc current increases, but when the arc length increases to a certain limit, the slope of the welding current clearly declines.展开更多
Fe-10 at.%Cr alloy was implanted with hydrogen ions at room temperature, followed by annealing at high temperatures.The annealing process made the defects develop into large dislocation loops. The nature of the disloc...Fe-10 at.%Cr alloy was implanted with hydrogen ions at room temperature, followed by annealing at high temperatures.The annealing process made the defects develop into large dislocation loops. The nature of the dislocation loops formed after annealing was studied by the evolution of loops under in situ electron irradiation in high-voltage electron microscope.It indicated that only interstitial-type loops were observed when annealed at 550 °C and below, but vacancy-type loops started to form at the temperature higher than 600 °C. According to the previous study of our group, the presence of chromium element made the formation temperature of vacancy-type loops higher than that in pure iron. The effect of alloying elements on the formation temperature of the vacancy-type loops was discussed.展开更多
文摘Electricity being a basic national infrastructure for a country, its security, reliability and quality are the most important parameters for the network managers. Several methods are generally used to improve the voltage quality more and more. However, most of the means implemented depend on external factors independent of the network managers or require huge regular financial resources. The method used in this paper is the loopback, applied to the Southern Interconnected Grid (SIG) of Cameroon, which is the largest net</span><span style="font-family:Verdana;">work in the country. The procedure used takes into account nodes experiencing huge voltage drops and network constraints. The chosen loopback</span><span style="font-family:Verdana;"> scenario results in a clear improvement of the voltage plan in this network, and also a discharge of the transformers, a considerable decongestion of the lines, a reduction of the power losses and a significant reduction of the thermal placement used for improvement of the voltage profile.
基金This work is supported by Chinese National Nature Science Foundation, contract No.19975048.
文摘Low voltage start-up was realized in HT-7 discharges under the assistance of lower hybrid (LH) waves. The use of a strong LH wavet which can Change its N// spectrum in a large range of several milliseconds, made the loop voltage for start-up reduce from around 20 V to less than 5 V. It means that the electric field for HT-7 start-up decreases from 2.5-3 V/m to 0.6 V/m. Some physical phenomena such as the consumption of magnetic flux in start-up phase and the radiation from the initial plasma were observed in this kind of low voltage start-up discharges.
文摘为提高单相动态电压恢复器（dynamic voltage restorer,DVR）的补偿性能,提出一种基于等效基波及奇次谐波谐振器组的数字控制方法。采用可等效为一组谐振器的延时模块,能够有效抑制电网基波和谐波扰动。给出一种包含两个控制参数和一组零相移陷波滤波器的结构及其设计方法,使系统在保证稳定性的同时,获得较大的谐振增益。其中,延时环节衰减系数可增加谐振器组鲁棒性;控制器比例增益可解决零相移陷波器中使用延时带来的问题;零相移陷波器组既能对消LC谐振峰,也能解决等效谐振器组高增益在高频处的稳定性问题。同时,引入电源电压和负载电流双前馈来保证响应速度,增加了对扰动的抑制能力。所提控制策略结构简单,谐波补偿能力强,动态响应快,易于实现。在2kW单相DVR实验装置上的实验结果验证了该控制方法的正确性。
基金supported by the National Key R&D Program of China(Grant No.2022YFA1404003)the National Natural Science Foundation of China(Grant Nos.T2495252,12104279,and 123B2062)+2 种基金the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302100)the Fund for Shanxi“1331 Project”Key Subjects Constructionthe Bairen Project of Shanxi Province。
文摘Increasing the number of atoms that interact with microwave fields represents a promising strategy for enhancing the sensitivity of Rydberg atom-based superheterodyne receivers.Nevertheless,the practical implementation of this approach is impeded by adverse effects such as excitation saturation of Rydberg atoms and power broadening.Here,we demonstrate enhanced microwave field measurements based on two specific velocity groups of atoms,simultaneously addressed by dual-channel probe beams in a Sagnac loop interferometer.The application of resonance detuning in two-photon excitation enables selective addressing of atoms moving along the beam direction,thereby significantly mitigating atomic transit noise.At 7.97 GHz,our method yields a 3 dB improvement in signal-to-noise ratio(SNR),achieving a sensitivity of 10.7 nV·cm^(−1)·Hz^(−1/2).This approach offers a viable pathway to further improve the sensitivity of Rydberg atom-based microwave electrometers.
文摘合环转供电是提高供电可靠性的关键手段,但直接合环可能产生较大冲击电流影响电网运行安全性。采用旋转潮流控制器(rotary power flow controller,RPFC)的方式能够实现台区的零感知合环,但电压调节轨迹不当将会带来RPFC接入点的电压越限问题。对此,提出一种基于两阶段最优路径的RPFC配电网柔性合环方法。首先,对输出电压运行轨迹进行合理规划,将其分为两阶段:第1阶段要求合环点两端电压相位一致并约束电压幅值相等,实现端电压的平稳过渡;第2阶段在相位一致的基础上,控制RPFC输出电压至目标值,使合环点两端电压幅值一致。然后,采用分相量夹角计算和旋转角协调控制,选择就近的旋转角设定值作为目标值,从而实现合环点两端电压无差调节;最后,仿真和实验对比分析所提方法将电压越限至少降低至30%,展示RPFC在实现配电网柔性合环中的重要应用价值。
文摘【目的】跟网型换流器(grid-following converter,GFL)被广泛应用于新能源并网系统。电网发生故障引起电压跌落时,系统进入低电压穿越(low voltage ride-through,LVRT)过程。传统锁相环(phase-locked loop,PLL)的二阶模型因忽略电流暂态过程,难以准确描述LVRT期间系统的动态特性,导致暂态同步稳定性的提升效果受限。为此,针对对称故障场景,提出一种适用于LVRT过程的电流内环协同控制策略,以增强系统暂态同步稳定性。【方法】基于PLL四阶动态方程,结合暂态能量函数法,分析PLL输出频率突变以及电流内环与PLL耦合作用对系统暂态同步稳定性的影响,并设计相应的控制策略:根据最优阻抗比动态调整电流参考值,以抑制故障期间暂态能量累积;通过在电流内环前馈解耦项中引入频率偏差补偿机制,加速暂态能量耗散过程。两者协同作用,提升系统在LVRT期间的暂态同步稳定性。【结果】PSCAD/EMTDC对称故障时域仿真结果表明:故障瞬间PLL输出频率突变量与电网电压跌落幅值成正比,增大系统失稳风险;所提控制策略能够有效抑制故障期间PLL输出频率偏差,显著降低虚拟功角首摆幅度,缩短故障清除后系统恢复时间,在不同电网参数下均表现出良好的适应性。【结论】所提电流内环协同控制策略,能够在对称故障期间有效抑制暂态能量累积,在故障清除后加速暂态能量耗散,有效提升了GFL并网系统在此类LVRT过程中的暂态同步稳定性。
基金supported by the National Key Research and Development Program of China(2017YFB0902901)and National Natural Science Foundation of China(51627811).
文摘Increasing penetration of power electronic(PE)grid-tied devices has caused more and more dynamic problems with unknown mechanisms.Since grid operation asks for a certain voltage amplitude and frequency level when there is a power imbalance,roles of the PE grid-tied devices during dynamics must be characterized as internal voltage response under power excitation,in which the voltage vector evolves through its timevarying amplitude and frequency.Existing modeling works,unfortunately,fail to recognize amplitude and frequency modulation essence of grid voltage during dynamics,so corresponding linear models are inapplicable to small-perturbation grid dynamic analysis.Thus,taking current control timescale of grid-tied voltage source converter(VSC)for example,this paper establishes a model with active and reactive current excitation and internal voltage amplitude and frequency response.Especially,the role of the terminal voltage detection-based phase-locked loop(PLL)in the excitation-response relationship is revealed.Linearization is conducted by clarifying amplitude and frequency operating points and corresponding increments of AC signals.This model intuitively reflects the evolution of internal voltage amplitude and frequency excited by active and reactive currents,which represents characteristics of the device during dynamics.Then,simulations for verification of the linear model and time-varying nature of amplitude and frequency are presented.Features of the characteristics of VSC are preliminarily discussed.
基金Supported by National Natural Science Foundation of China(Grant No.51875004)Beijing Municipal Natural Science Foundation of China(Grant No.3172004)State Key Lab of Advanced Welding and Joining,Harbin Institute of Technology(Grant No.AWJ-16-M06)
文摘As a new composite welding heat source introduced in recent years, the cross-coupling arc uses a non-consumable electrode arc(plasma arc) and a consumable electrode arc(inter-wire arc) in cross-coupling, in which the plasma arc is the main arc and the inter-wire arc is the vice arc, to realize the separate control of the heat input to the workpiece,arc force, and droplet transfer. To reveal the electrical characteristics of the inter-wire arc under the action of the plasma arc, in this study, rotating probes are used to sweep across the plasma arc. When the probes rotate into the plasma arc, a circuit is formed, and the electrical characteristics of the inter-wire arc are indirectly analyzed according to the circuit: the probe centering current and input voltage are used as the physical quantities. The results show that at a certain wire feed rate, the inter-wire arc current increases with increasing input voltage. When the input voltage is low, the wire feed rate has no obvious e ect on the inter-wire arc current. At a higher input voltage, where the wire feed rate is high, the inter-wire arc current decreases. With the increase in the plasma arc current, the inter-wire arc current first increases quickly and then increases slowly, and simultaneously, the striking arc time becomes longer.With the increase in the interval between the nozzle and the workpiece, the inter-wire arc current increases, but when the arc length increases to a certain limit, the slope of the welding current clearly declines.
基金supported by the National Natural Science Foundation of China (Grant No. 51471026)
文摘Fe-10 at.%Cr alloy was implanted with hydrogen ions at room temperature, followed by annealing at high temperatures.The annealing process made the defects develop into large dislocation loops. The nature of the dislocation loops formed after annealing was studied by the evolution of loops under in situ electron irradiation in high-voltage electron microscope.It indicated that only interstitial-type loops were observed when annealed at 550 °C and below, but vacancy-type loops started to form at the temperature higher than 600 °C. According to the previous study of our group, the presence of chromium element made the formation temperature of vacancy-type loops higher than that in pure iron. The effect of alloying elements on the formation temperature of the vacancy-type loops was discussed.
