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
Detecting, real-time monitoring and early warning of underground water-bearing structures are critically important issues in prevention and mitigation of water inrush hazards in underground engineering. Direct current...Detecting, real-time monitoring and early warning of underground water-bearing structures are critically important issues in prevention and mitigation of water inrush hazards in underground engineering. Direct current （DC） resistivity method is a widely used method for routine detection, advanced detection and real-time monitoring of water-bearing structures, due to its high sensitivity to groundwater. In this study, the DC resistivity method applied to underground engineering is reviewed and discussed, including the observation mode, multiple inversions, and real-time monitoring. It is shown that a priori information constrained inversion is desirable to reduce the non-uniqueness of inversion, with which the accuracy of detection can be significantly improved. The focused resistivity method is prospective for advanced detection;with this method, the flanking interference can be reduced and the detection dis-tance is increased subsequently. The time-lapse resistivity inversion method is suitable for the regions with continuous conductivity changes, and it can be used to monitor water inrush in those regions. Based on above-mentioned features of various methods in terms of benefits and limitations, we propose a three-dimensional （3D） induced polarization method characterized with multi-electrode array, and introduce it into tunnels and mines combining with real-time monitoring with time-lapse inversion and cross-hole resistivity method. At last, the prospective applications of DC resistivity method are discussed as follows： （1） available advanced detection technology and instrument in tunnel excavated by tunnel boring machine （TBM）, （2） high-resolution detection method in holes, （3） four-dimensional （4D） monitoring technology for water inrush sources, and （4） estimation of water volume in water-bearing structures.展开更多
Due to the low impedance characteristic of the high voltage direct current(HVDC)grid,the fault current rises extremely fast after a DC-side fault occurs,and this phenomenon seriously endangers the safety of the HVDC g...Due to the low impedance characteristic of the high voltage direct current(HVDC)grid,the fault current rises extremely fast after a DC-side fault occurs,and this phenomenon seriously endangers the safety of the HVDC grid.In order to suppress the rising speed of the fault current and reduce the current interruption requirements of the main breaker(MB),a fault current limiting hybrid DC circuit breaker(FCL-HCB)has been proposed in this paper,and it has the capability of bidirectional fault current limiting and fault current interruption.After the occurrence of the overcurrent in the HVDC grid,the current limiting circuit(CLC)of FCL-HCB is put into operation immediately,and whether the protected line is cut off or resumed to normal operation is decided according to the fault detection result.Compared with the traditional hybrid DC circuit breaker(HCB),the required number of semiconductor switches and the peak value of fault current after fault occurs are greatly reduced by adopting the proposed device.Extensive simulations also verify the effectiveness of the proposed FCL-HCB.展开更多
Photovoltaics,energy storage,direct current and flexibility(PEDF)are important pillars of achievement on the path to manufacturing nearly zero energy buildings(NZEBs).HVAC systems,which are an important part of public...Photovoltaics,energy storage,direct current and flexibility(PEDF)are important pillars of achievement on the path to manufacturing nearly zero energy buildings(NZEBs).HVAC systems,which are an important part of public buildings,play a key role in adapting to PDEF systems.This research studied the basic principles and operational control strategies of a DC inverter heat pump using a DC distribution network with the aim of contributing to the development and application of small DC distribution systems.Along with the characteristics of a DC distribution network and different operating conditions,a DC inverter heat pump has the ability to adapt to changes in the DC bus voltage and adds flexibility to the system.Theoretical models of the DC inverter heat pump integrated with an ice storage unit were developed.The control strategies of the DC inverter heat pump system considered the influence of both room temperature and varied bus voltage.A simulation study was conducted using MATLAB&Simulink software with simulation results validated by experimental data.The results showed that:(1)The bus fluctuation under the rated working voltage had little effect on the operation of the unit;(2)When the bus voltage was fluctuating from 80%-90%or 105%-107%,the heat pump could still operate normally by reducing the frequency;(3)When the bus voltage was less than 80%or more than 107%,the unit needed to be shut down for the sake of equipment safety,so that the energy storage device could adjust to the sharp decrease or rise of voltage.展开更多
针对高压直流(high voltage direct current,HVDC)输电网直流故障处理中存在的耗时长且影响范围较广等问题,提出了基于形态学梯度与故障阻断换流器(fault blocking converter,FBC)的HVDC输电网故障处理方法。首先,利用多分辨形态学梯度...针对高压直流(high voltage direct current,HVDC)输电网直流故障处理中存在的耗时长且影响范围较广等问题,提出了基于形态学梯度与故障阻断换流器(fault blocking converter,FBC)的HVDC输电网故障处理方法。首先,利用多分辨形态学梯度算法提取故障电流信号特征,并进行滤波处理以消除噪音干扰;然后,设计了基于FBC的HVDC直流网故障处理策略,结合FBC与高速开关实现快速且有选择性地处理直流故障;最后,利用PSCAD模拟HVDC输电网直流故障。试验结果表明,所提方法的故障处理耗时仅为10 ms,准确率高达95%,能够高效且准确地处理故障。展开更多
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supported by the National Program on Key Basic Research Project of China (973 Program) (Nos. 2013CB036002 and 2014CB046901)the National Key Technology R&D Program of the Ministry of Science and Technology of China (No. 2013BAK06B01)the National Natural Science Foundation of China (No. 51139004)
文摘Detecting, real-time monitoring and early warning of underground water-bearing structures are critically important issues in prevention and mitigation of water inrush hazards in underground engineering. Direct current （DC） resistivity method is a widely used method for routine detection, advanced detection and real-time monitoring of water-bearing structures, due to its high sensitivity to groundwater. In this study, the DC resistivity method applied to underground engineering is reviewed and discussed, including the observation mode, multiple inversions, and real-time monitoring. It is shown that a priori information constrained inversion is desirable to reduce the non-uniqueness of inversion, with which the accuracy of detection can be significantly improved. The focused resistivity method is prospective for advanced detection;with this method, the flanking interference can be reduced and the detection dis-tance is increased subsequently. The time-lapse resistivity inversion method is suitable for the regions with continuous conductivity changes, and it can be used to monitor water inrush in those regions. Based on above-mentioned features of various methods in terms of benefits and limitations, we propose a three-dimensional （3D） induced polarization method characterized with multi-electrode array, and introduce it into tunnels and mines combining with real-time monitoring with time-lapse inversion and cross-hole resistivity method. At last, the prospective applications of DC resistivity method are discussed as follows： （1） available advanced detection technology and instrument in tunnel excavated by tunnel boring machine （TBM）, （2） high-resolution detection method in holes, （3） four-dimensional （4D） monitoring technology for water inrush sources, and （4） estimation of water volume in water-bearing structures.
基金This project is funded by the Dongying Science Development Fund Project(DJ2021013).
文摘Due to the low impedance characteristic of the high voltage direct current(HVDC)grid,the fault current rises extremely fast after a DC-side fault occurs,and this phenomenon seriously endangers the safety of the HVDC grid.In order to suppress the rising speed of the fault current and reduce the current interruption requirements of the main breaker(MB),a fault current limiting hybrid DC circuit breaker(FCL-HCB)has been proposed in this paper,and it has the capability of bidirectional fault current limiting and fault current interruption.After the occurrence of the overcurrent in the HVDC grid,the current limiting circuit(CLC)of FCL-HCB is put into operation immediately,and whether the protected line is cut off or resumed to normal operation is decided according to the fault detection result.Compared with the traditional hybrid DC circuit breaker(HCB),the required number of semiconductor switches and the peak value of fault current after fault occurs are greatly reduced by adopting the proposed device.Extensive simulations also verify the effectiveness of the proposed FCL-HCB.
基金funded by State Grid Science&Technology Project“Research and Demonstration of Key Technologies on Electric-Heating Collaboration Cross-Network Mutual Supply for Typical Regional Clean Energy”,Grant Number 5400-202111575A-0-5-SF.
文摘Photovoltaics,energy storage,direct current and flexibility(PEDF)are important pillars of achievement on the path to manufacturing nearly zero energy buildings(NZEBs).HVAC systems,which are an important part of public buildings,play a key role in adapting to PDEF systems.This research studied the basic principles and operational control strategies of a DC inverter heat pump using a DC distribution network with the aim of contributing to the development and application of small DC distribution systems.Along with the characteristics of a DC distribution network and different operating conditions,a DC inverter heat pump has the ability to adapt to changes in the DC bus voltage and adds flexibility to the system.Theoretical models of the DC inverter heat pump integrated with an ice storage unit were developed.The control strategies of the DC inverter heat pump system considered the influence of both room temperature and varied bus voltage.A simulation study was conducted using MATLAB&Simulink software with simulation results validated by experimental data.The results showed that:(1)The bus fluctuation under the rated working voltage had little effect on the operation of the unit;(2)When the bus voltage was fluctuating from 80%-90%or 105%-107%,the heat pump could still operate normally by reducing the frequency;(3)When the bus voltage was less than 80%or more than 107%,the unit needed to be shut down for the sake of equipment safety,so that the energy storage device could adjust to the sharp decrease or rise of voltage.
文摘针对高压直流(high voltage direct current,HVDC)输电网直流故障处理中存在的耗时长且影响范围较广等问题,提出了基于形态学梯度与故障阻断换流器(fault blocking converter,FBC)的HVDC输电网故障处理方法。首先,利用多分辨形态学梯度算法提取故障电流信号特征,并进行滤波处理以消除噪音干扰;然后,设计了基于FBC的HVDC直流网故障处理策略,结合FBC与高速开关实现快速且有选择性地处理直流故障;最后,利用PSCAD模拟HVDC输电网直流故障。试验结果表明,所提方法的故障处理耗时仅为10 ms,准确率高达95%,能够高效且准确地处理故障。
