柔性直流输电系统中,直流故障的分析与判别是柔直系统中亟待解决的重要问题。为了更好地分析故障特征,推导出一种多端柔性直流输电网(modular multilevel converter-high voltage direct current,MMC-MTDC)的母线侧简化电路故障计算方法...柔性直流输电系统中,直流故障的分析与判别是柔直系统中亟待解决的重要问题。为了更好地分析故障特征,推导出一种多端柔性直流输电网(modular multilevel converter-high voltage direct current,MMC-MTDC)的母线侧简化电路故障计算方法,并分析了母线侧单极接地故障和极间短路故障的故障特征,在此基础上设计了一种适用于多端柔性直流输电网的故障判别方案和保护措施。该判别方案通过故障启动判据、故障区域判别和故障类型判别3个模块进行故障判定,采用了故障电压瞬时跌落值与系统电压之差及故障线路电流值作故障特征量,整套判别方案不受其他元件参数、故障位置等因素的影响,将Spearman相关性分析与传统电气故障区域判别相结合,准确判定系统区内外故障的同时,解决了故障区域判别中受线路各参数干扰导致误判的问题,仿真测试验证了本保护方案的可行性。展开更多
Bidirectional interlinking converter(BIC)is the core equipment in a hybrid AC/DC microgrid connected between AC and DC sub-grids.However,the variety of control modes and flexible bidirectional power flow complicate th...Bidirectional interlinking converter(BIC)is the core equipment in a hybrid AC/DC microgrid connected between AC and DC sub-grids.However,the variety of control modes and flexible bidirectional power flow complicate the influence of AC faults on BIC itself and on DC sub-grid,which potentially threaten both converter safety and system reliability.This study first investigates AC fault influence on the BIC and DC bus voltage under different BIC control modes and different pre-fault operation states,by developing a mathematical model and equivalent sequence network.Second,based on the analysis results,a general accommodative current limiting strategy is proposed for BIC without limitations to specific mode or operation condition.Current amplitude is predicted and constrained according to the critical requirements to protect the BIC and relieving the AC fault influence on the DC bus voltage.Compared with conventional methods,potential current limit failure and distortions under asymmetric faults can also be avoided.Finally,experiments verify feasibility of the proposed method.展开更多
It is difficult to detect and extinguish direct current(DC)arc in power electronics systems,and the arc could easily lead to a fire and cause great damage to surrounding equipment.A DC arc generation simulation unit i...It is difficult to detect and extinguish direct current(DC)arc in power electronics systems,and the arc could easily lead to a fire and cause great damage to surrounding equipment.A DC arc generation simulation unit is established,in which DC series arcs are generated by dragging the moving electrode away from the fixed one with the help of the stepper motor.In addition,a ferrite rod antenna is used to receive the electromagnetic radiation signals induced by the arcs.Based on experiments using the unit,the general characteristics of DC arc,including the pulse characteristics of arc current and source output in corresponding time window,and the frequency-domain characteristics of arc current,are studied.With discussion on three detection methods,it is concluded that the variation of current and voltage of arc,the spectrum of the arc current during the discontinuous intervals and the radiating electromagnetic signal are all features that can be adopted for detecting DC series arc.Therefore,a synthetic judgment method is suggested for further study.展开更多
The hybrid dc circuit breaker(HCB)has the advantages of fast action speed and low operating loss,which is an idealmethod for fault isolation ofmulti-terminal dc grids.Formulti-terminal dc grids that transmit power thr...The hybrid dc circuit breaker(HCB)has the advantages of fast action speed and low operating loss,which is an idealmethod for fault isolation ofmulti-terminal dc grids.Formulti-terminal dc grids that transmit power through overhead lines,HCBs are required to have reclosing capability due to the high fault probability and the fact that most of the faults are temporary faults.To avoid the secondary fault strike and equipment damage that may be caused by the reclosing of the HCB when the permanent fault occurs,an adaptive reclosing scheme based on traveling wave injection is proposed in this paper.The scheme injects traveling wave signal into the fault dc line through the additionally configured auxiliary discharge branch in the HCB,and then uses the reflection characteristic of the traveling wave signal on the dc line to identify temporary and permanent faults,to be able to realize fast reclosing when the temporary fault occurs and reliably avoid reclosing after the permanent fault occurs.The test results in the simulation model of the four-terminal dc grid show that the proposed adaptive reclosing scheme can quickly and reliably identify temporary and permanent faults,greatly shorten the power outage time of temporary faults.In addition,it has the advantages of easiness to implement,high reliability,robustness to high-resistance fault and no dead zone,etc.展开更多
针对具有故障穿越策略的永磁风电场经多端柔性直流(Voltage Source Converter Based Multi-terminal Direct Current,VSC⁃MTDC)输电系统外送的交直流混联系统,分析故障穿越控制目标下受端交流电网故障和考虑输电线路频变特性的直流系统...针对具有故障穿越策略的永磁风电场经多端柔性直流(Voltage Source Converter Based Multi-terminal Direct Current,VSC⁃MTDC)输电系统外送的交直流混联系统,分析故障穿越控制目标下受端交流电网故障和考虑输电线路频变特性的直流系统输电线路故障发生后的故障特征,以及大时间尺度下,直流系统对交流故障的响应。研究结果表明:基于实时数字仿真(Real Time Digital Simulation,RTDS)搭建的交直流混联系统模型在有效控制故障发展的前提下,不同故障条件、控制策略下具有相对应的故障特征,如:交流并网线路故障时,负序电流将被抑制,换流站仅向故障点提供有限的正序电流,且优先输出无功功率,直流线路累积不平衡功率出现直流过电压现象,计及直流电压波动引起受端换流站的dq轴电流发生变化,造成交流线路故障电流短时间内增大约20%。直流线路发生单极接地故障时,故障极电压以最大700 kV/ms的速率迅速下降到0,非故障极电压上升为原来的两倍,且故障电流会随着接地电阻的增大而减小;当发生双极故障时,故障电流能够在数毫秒内达到额定电流的几十倍,最大速率可达8.25 kA/ms,严重威胁电力电子器件的安全,并且电压迅速降至0,此时通过混合直流断路器快速动作,在故障电流上升至额定电流2倍前切除故障线路,使系统满足N-1运行原则。仿真结果与理论分析结论相符。展开更多
文摘柔性直流输电系统中,直流故障的分析与判别是柔直系统中亟待解决的重要问题。为了更好地分析故障特征,推导出一种多端柔性直流输电网(modular multilevel converter-high voltage direct current,MMC-MTDC)的母线侧简化电路故障计算方法,并分析了母线侧单极接地故障和极间短路故障的故障特征,在此基础上设计了一种适用于多端柔性直流输电网的故障判别方案和保护措施。该判别方案通过故障启动判据、故障区域判别和故障类型判别3个模块进行故障判定,采用了故障电压瞬时跌落值与系统电压之差及故障线路电流值作故障特征量,整套判别方案不受其他元件参数、故障位置等因素的影响,将Spearman相关性分析与传统电气故障区域判别相结合,准确判定系统区内外故障的同时,解决了故障区域判别中受线路各参数干扰导致误判的问题,仿真测试验证了本保护方案的可行性。
文摘Bidirectional interlinking converter(BIC)is the core equipment in a hybrid AC/DC microgrid connected between AC and DC sub-grids.However,the variety of control modes and flexible bidirectional power flow complicate the influence of AC faults on BIC itself and on DC sub-grid,which potentially threaten both converter safety and system reliability.This study first investigates AC fault influence on the BIC and DC bus voltage under different BIC control modes and different pre-fault operation states,by developing a mathematical model and equivalent sequence network.Second,based on the analysis results,a general accommodative current limiting strategy is proposed for BIC without limitations to specific mode or operation condition.Current amplitude is predicted and constrained according to the critical requirements to protect the BIC and relieving the AC fault influence on the DC bus voltage.Compared with conventional methods,potential current limit failure and distortions under asymmetric faults can also be avoided.Finally,experiments verify feasibility of the proposed method.
基金Project supported by International Cooperation Project in Shaanxi Province of China(2012KW-01)
文摘It is difficult to detect and extinguish direct current(DC)arc in power electronics systems,and the arc could easily lead to a fire and cause great damage to surrounding equipment.A DC arc generation simulation unit is established,in which DC series arcs are generated by dragging the moving electrode away from the fixed one with the help of the stepper motor.In addition,a ferrite rod antenna is used to receive the electromagnetic radiation signals induced by the arcs.Based on experiments using the unit,the general characteristics of DC arc,including the pulse characteristics of arc current and source output in corresponding time window,and the frequency-domain characteristics of arc current,are studied.With discussion on three detection methods,it is concluded that the variation of current and voltage of arc,the spectrum of the arc current during the discontinuous intervals and the radiating electromagnetic signal are all features that can be adopted for detecting DC series arc.Therefore,a synthetic judgment method is suggested for further study.
基金supported by the Science and Technology Project of State Grid Corporation of China under Grant 520201210025。
文摘The hybrid dc circuit breaker(HCB)has the advantages of fast action speed and low operating loss,which is an idealmethod for fault isolation ofmulti-terminal dc grids.Formulti-terminal dc grids that transmit power through overhead lines,HCBs are required to have reclosing capability due to the high fault probability and the fact that most of the faults are temporary faults.To avoid the secondary fault strike and equipment damage that may be caused by the reclosing of the HCB when the permanent fault occurs,an adaptive reclosing scheme based on traveling wave injection is proposed in this paper.The scheme injects traveling wave signal into the fault dc line through the additionally configured auxiliary discharge branch in the HCB,and then uses the reflection characteristic of the traveling wave signal on the dc line to identify temporary and permanent faults,to be able to realize fast reclosing when the temporary fault occurs and reliably avoid reclosing after the permanent fault occurs.The test results in the simulation model of the four-terminal dc grid show that the proposed adaptive reclosing scheme can quickly and reliably identify temporary and permanent faults,greatly shorten the power outage time of temporary faults.In addition,it has the advantages of easiness to implement,high reliability,robustness to high-resistance fault and no dead zone,etc.
文摘针对具有故障穿越策略的永磁风电场经多端柔性直流(Voltage Source Converter Based Multi-terminal Direct Current,VSC⁃MTDC)输电系统外送的交直流混联系统,分析故障穿越控制目标下受端交流电网故障和考虑输电线路频变特性的直流系统输电线路故障发生后的故障特征,以及大时间尺度下,直流系统对交流故障的响应。研究结果表明:基于实时数字仿真(Real Time Digital Simulation,RTDS)搭建的交直流混联系统模型在有效控制故障发展的前提下,不同故障条件、控制策略下具有相对应的故障特征,如:交流并网线路故障时,负序电流将被抑制,换流站仅向故障点提供有限的正序电流,且优先输出无功功率,直流线路累积不平衡功率出现直流过电压现象,计及直流电压波动引起受端换流站的dq轴电流发生变化,造成交流线路故障电流短时间内增大约20%。直流线路发生单极接地故障时,故障极电压以最大700 kV/ms的速率迅速下降到0,非故障极电压上升为原来的两倍,且故障电流会随着接地电阻的增大而减小;当发生双极故障时,故障电流能够在数毫秒内达到额定电流的几十倍,最大速率可达8.25 kA/ms,严重威胁电力电子器件的安全,并且电压迅速降至0,此时通过混合直流断路器快速动作,在故障电流上升至额定电流2倍前切除故障线路,使系统满足N-1运行原则。仿真结果与理论分析结论相符。
