This paper investigates a control and protection strategy for a four-terminal modular multilevel converter(MMC)based high-voltage direct current(HVDC)system under a converter-side AC fault.Based on the system operatin...This paper investigates a control and protection strategy for a four-terminal modular multilevel converter(MMC)based high-voltage direct current(HVDC)system under a converter-side AC fault.Based on the system operating condition,a control and protection strategy against the fault with normal blocking of the converter is proposed.In practical,applications encountering such a fault,the MMC at the fault side may experience different conditions of blocking failure.The blocking failures may occur on:①the whole converter;②one converter arm;③one sub-module(SM)/several SMs of one converter arm;④other conditions.The phenomenon of the multi-terminal HVDC(MTDC)system following the fault is analyzed under the first three conditions with real-time simulations using the real-time digital simulator(RTDS).Based on the impact of different conditions on the MTDC system,the necessity of utilizing special control and protection is discussed.A special control and protection strategy is proposed for emergency conditions,and its effectiveness is verified by real-time simulation results.展开更多
Energy storage systems with multilevel converters play an important role in modern electric power systems with large-scale renewable energy integration.This paper proposes a reverse-blocking modular multilevel convert...Energy storage systems with multilevel converters play an important role in modern electric power systems with large-scale renewable energy integration.This paper proposes a reverse-blocking modular multilevel converter for a battery energy storage system(RB-MMCBESS). Besides integrating distributed low-voltage batteries to medium or high voltage grids, with the inherited advantages of traditional MMCs, the RB-MMC-BESS also provides improved DC fault handling capability. This paper analyzes such a new converter configuration and its operating principles. Control algorithms are developed for AC side power control and the balancing of battery state of charge. The blocking mechanism to manage a DC pole-topole fault analyzed in depth. Comprehensive simulation results validate both the feasibility of the RB-MMC-BESS topology and the effectiveness of the control and fault handling strategies.展开更多
Multi-terminal direct current(MTDC)grids provide the possibility of meshed interconnections between regional power systems and various renewable energy resources to boost supply reliability and economy.The modular mul...Multi-terminal direct current(MTDC)grids provide the possibility of meshed interconnections between regional power systems and various renewable energy resources to boost supply reliability and economy.The modular multilevel converter(MMC)has become the basic building block for MTDC and DC grids due to its salient features,i.e.,modularity and scalability.Therefore,the MMC-based MTDC systems should be pervasively embedded into the present power system to improve system performance.However,several technical challenges hamper their practical applications and deployment,including modeling,control,and protection of the MMC-MTDC grids.This paper presents a comprehensive investigation and reference in modeling,control,and protection of the MMC-MTDC grids.A general overview of state-of-the-art modeling techniques of the MMC along with their performance in simulation analysis for MTDC applications is provided.A review of control strategies of the MMC-MTDC grids which provide AC system support is presented.State-of-the art protection techniques of the MMCMTDC systems are also investigated.Finally,the associated research challenges and trends are highlighted.展开更多
特高压直流（ultra-high voltage direct current,UHVDC）输电有助于我国实现能源资源的优化配置,因而发展十分迅速。UHVDC送电容量大,当其发生闭锁后,会对电网造成严重的影响。因此,建立合适的功率模型,进而准确地分析UHVDC闭锁对受端...特高压直流（ultra-high voltage direct current,UHVDC）输电有助于我国实现能源资源的优化配置,因而发展十分迅速。UHVDC送电容量大,当其发生闭锁后,会对电网造成严重的影响。因此,建立合适的功率模型,进而准确地分析UHVDC闭锁对受端电网的影响十分必要。该文首先分析了UHVDC闭锁后极间功率转移机理,以及建立了UHVDC逆变站的有功模型;其次分析了逆变站无功的消耗机理,并结合无功补偿设备投切策略,建立了闭锁后逆变站输出无功功率的模型;然后,采用所建立的模型,对天中直流＂6.14＂闭锁后逆变站的输出功率进行建模,并与实测逆变站的输出功率数据进行对比,验证所建模型的准确性较高。最后,将所建模型应用于河南电网仿真算例,仿真结果与实测数据进行对比,进一步验证了该模型的准确性。为适应UHVDC快速的发展,该文所提模型可为含UHVDC的实际电网的分析提供帮助。展开更多
直流故障穿越是柔性直流输电(voltage sourced converter based high voltage direct current transmission,VSCHVDC)技术面临的重要问题之一。全桥型模块化多电平换流器(full bridge modular multilevel converter,FBMMC)能够快速清除...直流故障穿越是柔性直流输电(voltage sourced converter based high voltage direct current transmission,VSCHVDC)技术面临的重要问题之一。全桥型模块化多电平换流器(full bridge modular multilevel converter,FBMMC)能够快速清除直流侧故障,是实现直流故障穿越的理想拓扑。该文首先分析现有换流阀闭锁保护策略下电容放电阶段和换流阀闭锁阶段的等效电路,推导电容电压和电流的解析式。针对实际工程中功率模块具有恒功率负载特性,换流站闭锁期间功率模块电容电压逐渐发散并最终导致交流断路器跳闸的问题,提出一种FBMMC-HVDC的故障穿越控制保护策略。在故障穿越期间,换流器处于可控状态,能够避免电容电压发散,无需切断交直流系统连接;在故障清除后能够立即恢复正常运行,具备暂时性和永久性直流故障穿越能力。在PSCAD/EMTDC软件中构建了FBMMC-HVDC仿真模型,对比上述两种保护策略,分析两种策略各自的优缺点。展开更多
基金This work is supported by UK EPSRC and UK National Grid.
文摘This paper investigates a control and protection strategy for a four-terminal modular multilevel converter(MMC)based high-voltage direct current(HVDC)system under a converter-side AC fault.Based on the system operating condition,a control and protection strategy against the fault with normal blocking of the converter is proposed.In practical,applications encountering such a fault,the MMC at the fault side may experience different conditions of blocking failure.The blocking failures may occur on:①the whole converter;②one converter arm;③one sub-module(SM)/several SMs of one converter arm;④other conditions.The phenomenon of the multi-terminal HVDC(MTDC)system following the fault is analyzed under the first three conditions with real-time simulations using the real-time digital simulator(RTDS).Based on the impact of different conditions on the MTDC system,the necessity of utilizing special control and protection is discussed.A special control and protection strategy is proposed for emergency conditions,and its effectiveness is verified by real-time simulation results.
基金supported by the State Key Laboratory of Large Electric Drive System and Equipment Technology(No.SKLLDJ042016005)the National Key Research and Development Program of China(No.2016YFE0131700)the National Natural Science Foundation of China(No.51577010)
文摘Energy storage systems with multilevel converters play an important role in modern electric power systems with large-scale renewable energy integration.This paper proposes a reverse-blocking modular multilevel converter for a battery energy storage system(RB-MMCBESS). Besides integrating distributed low-voltage batteries to medium or high voltage grids, with the inherited advantages of traditional MMCs, the RB-MMC-BESS also provides improved DC fault handling capability. This paper analyzes such a new converter configuration and its operating principles. Control algorithms are developed for AC side power control and the balancing of battery state of charge. The blocking mechanism to manage a DC pole-topole fault analyzed in depth. Comprehensive simulation results validate both the feasibility of the RB-MMC-BESS topology and the effectiveness of the control and fault handling strategies.
基金funded by SGCC Science and Technology Program under project Research on Electromagnetic Transient Simulation Technology for Large-scale MMC-HVDC Systems.
文摘Multi-terminal direct current(MTDC)grids provide the possibility of meshed interconnections between regional power systems and various renewable energy resources to boost supply reliability and economy.The modular multilevel converter(MMC)has become the basic building block for MTDC and DC grids due to its salient features,i.e.,modularity and scalability.Therefore,the MMC-based MTDC systems should be pervasively embedded into the present power system to improve system performance.However,several technical challenges hamper their practical applications and deployment,including modeling,control,and protection of the MMC-MTDC grids.This paper presents a comprehensive investigation and reference in modeling,control,and protection of the MMC-MTDC grids.A general overview of state-of-the-art modeling techniques of the MMC along with their performance in simulation analysis for MTDC applications is provided.A review of control strategies of the MMC-MTDC grids which provide AC system support is presented.State-of-the art protection techniques of the MMCMTDC systems are also investigated.Finally,the associated research challenges and trends are highlighted.
文摘特高压直流（ultra-high voltage direct current,UHVDC）输电有助于我国实现能源资源的优化配置,因而发展十分迅速。UHVDC送电容量大,当其发生闭锁后,会对电网造成严重的影响。因此,建立合适的功率模型,进而准确地分析UHVDC闭锁对受端电网的影响十分必要。该文首先分析了UHVDC闭锁后极间功率转移机理,以及建立了UHVDC逆变站的有功模型;其次分析了逆变站无功的消耗机理,并结合无功补偿设备投切策略,建立了闭锁后逆变站输出无功功率的模型;然后,采用所建立的模型,对天中直流＂6.14＂闭锁后逆变站的输出功率进行建模,并与实测逆变站的输出功率数据进行对比,验证所建模型的准确性较高。最后,将所建模型应用于河南电网仿真算例,仿真结果与实测数据进行对比,进一步验证了该模型的准确性。为适应UHVDC快速的发展,该文所提模型可为含UHVDC的实际电网的分析提供帮助。
文摘直流故障穿越是柔性直流输电(voltage sourced converter based high voltage direct current transmission,VSCHVDC)技术面临的重要问题之一。全桥型模块化多电平换流器(full bridge modular multilevel converter,FBMMC)能够快速清除直流侧故障,是实现直流故障穿越的理想拓扑。该文首先分析现有换流阀闭锁保护策略下电容放电阶段和换流阀闭锁阶段的等效电路,推导电容电压和电流的解析式。针对实际工程中功率模块具有恒功率负载特性,换流站闭锁期间功率模块电容电压逐渐发散并最终导致交流断路器跳闸的问题,提出一种FBMMC-HVDC的故障穿越控制保护策略。在故障穿越期间,换流器处于可控状态,能够避免电容电压发散,无需切断交直流系统连接;在故障清除后能够立即恢复正常运行,具备暂时性和永久性直流故障穿越能力。在PSCAD/EMTDC软件中构建了FBMMC-HVDC仿真模型,对比上述两种保护策略,分析两种策略各自的优缺点。
