柔性直流电网的故障检测与保护研究是当前电力领域的关键技术。直流电网发生故障时,故障电流迅速上升导致电网系统设备损坏且稳定性下降,因此对故障保护系统的快速性和可靠性要求极高。通过比较线路上限流电感电压值在故障前后的变化,...柔性直流电网的故障检测与保护研究是当前电力领域的关键技术。直流电网发生故障时,故障电流迅速上升导致电网系统设备损坏且稳定性下降,因此对故障保护系统的快速性和可靠性要求极高。通过比较线路上限流电感电压值在故障前后的变化,提出一种利用限流电感两端电压比值实现线路故障识别的方法。在PSCAD/EMTDC仿真平台建立四端模块化多电平换流器型柔性直流输电(modular multilevel converter high voltage direct current,MMC-HVDC)电网模型,对所提出的方法进行故障启动、类型识别和极线选择验证。在故障被正确识别后,相应的直流断路器(DC circuit breaker,DCCB)能够正确动作并隔离故障。此外,还对系统的性能指标以及故障过渡电阻值、故障后系统的噪声、故障距离和通信误差方面因素进行可行性分析。研究结果表明,所提出的故障保护方案能够准确识别并且快速隔离故障,从而保障电网安全稳定运行。展开更多
To enhance power flow regulation in scenarios involving large-scale renewable energy transmission via high-voltage direct current(HVDC)links and multi-infeed DC systems in load-center regions,this paper proposes a hyb...To enhance power flow regulation in scenarios involving large-scale renewable energy transmission via high-voltage direct current(HVDC)links and multi-infeed DC systems in load-center regions,this paper proposes a hybrid modular multilevel converter–capacitor-commutated line-commutated converter(MMC-CLCC)HVDC transmission system and its corresponding control strategy.First,the system topology is constructed,and a submodule configuration method for the MMC—combining full-bridge submodules(FBSMs)and half-bridge submodules(HBSMs)—is proposed to enable direct power flow reversal.Second,a hierarchical control strategy is introduced,includingMMCvoltage control,CLCC current control,and a coordinationmechanism,along with the derivation of the hybrid system’s power flow reversal characteristics.Third,leveraging the CLCC’s fast current regulation and theMMC’s negative voltage control capability,a coordinated power flow reversal control strategy is developed.Finally,an 800 kV MMC-CLCC hybrid HVDC system is modeled in PSCAD/EMTDC to validate the power flow reversal performance under a high proportion of full-bridge submodule configuration.Results demonstrate that the proposed control strategy enables rapid(1-s transition)and smooth switching of bidirectional power flow without modifying the structure of primary equipment:the transient fluctuation ofDC voltage from the rated value(UdcN)to themaximumreverse voltage(-kUdcN)is less than 5%;the DC current strictly follows the preset characteristic curve with a deviation of≤3%;the active power reverses continuously,and the system maintains stable operation throughout the reversal process.展开更多
本文作者提出了一种含储能的混合式配电变压器(Hybrid Distribution Transformer,HDT)电路拓扑,并重点研究了双向DC/DC变换器的设计。该拓扑结合储能电池和超级电容,通过双向DC/DC变换器实现HDT与储能装置之间的双向电能流动。本文推导...本文作者提出了一种含储能的混合式配电变压器(Hybrid Distribution Transformer,HDT)电路拓扑,并重点研究了双向DC/DC变换器的设计。该拓扑结合储能电池和超级电容,通过双向DC/DC变换器实现HDT与储能装置之间的双向电能流动。本文推导了双向DC/DC变换器的小信号模型,详细阐述了电路参数选取方法,并设计了相应的控制器。在Matlab/Simulink中实现了仿真验证,结果表明所设计的系统能够实现功率的双向传递,验证了所提出拓扑和控制策略的有效性和可行性。展开更多
In modern ZnO varistors,traditional aging mechanisms based on increased power consumption are no longer relevant due to reduced power consumption during DC aging.Prolonged exposure to both AC and DC voltages results i...In modern ZnO varistors,traditional aging mechanisms based on increased power consumption are no longer relevant due to reduced power consumption during DC aging.Prolonged exposure to both AC and DC voltages results in increased leakage current,decreased breakdown voltage,and lower nonlinearity,ultimately compromising their protective performance.To investigate the evolution in electrical properties during DC aging,this work developed a finite element model based on Voronoi networks and conducted accelerated aging tests on commercial varistors.Throughout the aging process,current-voltage characteristics and Schottky barrier parameters were measured and analyzed.The results indicate that when subjected to constant voltage,current flows through regions with larger grain sizes,forming discharge channels.As aging progresses,the current focus increases on these channels,leading to a decline in the varistor’s overall performance.Furthermore,analysis of the Schottky barrier parameters shows that the changes in electrical performance during aging are non-monotonic.These findings offer theoretical support for understanding the aging mechanisms and condition assessment of modern stable ZnO varistors.展开更多
文摘柔性直流电网的故障检测与保护研究是当前电力领域的关键技术。直流电网发生故障时,故障电流迅速上升导致电网系统设备损坏且稳定性下降,因此对故障保护系统的快速性和可靠性要求极高。通过比较线路上限流电感电压值在故障前后的变化,提出一种利用限流电感两端电压比值实现线路故障识别的方法。在PSCAD/EMTDC仿真平台建立四端模块化多电平换流器型柔性直流输电(modular multilevel converter high voltage direct current,MMC-HVDC)电网模型,对所提出的方法进行故障启动、类型识别和极线选择验证。在故障被正确识别后,相应的直流断路器(DC circuit breaker,DCCB)能够正确动作并隔离故障。此外,还对系统的性能指标以及故障过渡电阻值、故障后系统的噪声、故障距离和通信误差方面因素进行可行性分析。研究结果表明,所提出的故障保护方案能够准确识别并且快速隔离故障,从而保障电网安全稳定运行。
基金supported by Science and Technology Project of the headquarters of the State Grid Corporation of China(No.5500-202324492A-3-2-ZN).
文摘To enhance power flow regulation in scenarios involving large-scale renewable energy transmission via high-voltage direct current(HVDC)links and multi-infeed DC systems in load-center regions,this paper proposes a hybrid modular multilevel converter–capacitor-commutated line-commutated converter(MMC-CLCC)HVDC transmission system and its corresponding control strategy.First,the system topology is constructed,and a submodule configuration method for the MMC—combining full-bridge submodules(FBSMs)and half-bridge submodules(HBSMs)—is proposed to enable direct power flow reversal.Second,a hierarchical control strategy is introduced,includingMMCvoltage control,CLCC current control,and a coordinationmechanism,along with the derivation of the hybrid system’s power flow reversal characteristics.Third,leveraging the CLCC’s fast current regulation and theMMC’s negative voltage control capability,a coordinated power flow reversal control strategy is developed.Finally,an 800 kV MMC-CLCC hybrid HVDC system is modeled in PSCAD/EMTDC to validate the power flow reversal performance under a high proportion of full-bridge submodule configuration.Results demonstrate that the proposed control strategy enables rapid(1-s transition)and smooth switching of bidirectional power flow without modifying the structure of primary equipment:the transient fluctuation ofDC voltage from the rated value(UdcN)to themaximumreverse voltage(-kUdcN)is less than 5%;the DC current strictly follows the preset characteristic curve with a deviation of≤3%;the active power reverses continuously,and the system maintains stable operation throughout the reversal process.
文摘本文作者提出了一种含储能的混合式配电变压器(Hybrid Distribution Transformer,HDT)电路拓扑,并重点研究了双向DC/DC变换器的设计。该拓扑结合储能电池和超级电容,通过双向DC/DC变换器实现HDT与储能装置之间的双向电能流动。本文推导了双向DC/DC变换器的小信号模型,详细阐述了电路参数选取方法,并设计了相应的控制器。在Matlab/Simulink中实现了仿真验证,结果表明所设计的系统能够实现功率的双向传递,验证了所提出拓扑和控制策略的有效性和可行性。
文摘In modern ZnO varistors,traditional aging mechanisms based on increased power consumption are no longer relevant due to reduced power consumption during DC aging.Prolonged exposure to both AC and DC voltages results in increased leakage current,decreased breakdown voltage,and lower nonlinearity,ultimately compromising their protective performance.To investigate the evolution in electrical properties during DC aging,this work developed a finite element model based on Voronoi networks and conducted accelerated aging tests on commercial varistors.Throughout the aging process,current-voltage characteristics and Schottky barrier parameters were measured and analyzed.The results indicate that when subjected to constant voltage,current flows through regions with larger grain sizes,forming discharge channels.As aging progresses,the current focus increases on these channels,leading to a decline in the varistor’s overall performance.Furthermore,analysis of the Schottky barrier parameters shows that the changes in electrical performance during aging are non-monotonic.These findings offer theoretical support for understanding the aging mechanisms and condition assessment of modern stable ZnO varistors.
