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
随着“双碳”战略推进,我国大力发展风电、光伏等新能源。处于电网末端的新能源场站因缺乏交流电源支撑,需依赖柔性直流输电技术(modular multilevel converter-high voltage direct current,MMC-HVDC)实现并网,但电力电子变流器的广泛...随着“双碳”战略推进,我国大力发展风电、光伏等新能源。处于电网末端的新能源场站因缺乏交流电源支撑,需依赖柔性直流输电技术(modular multilevel converter-high voltage direct current,MMC-HVDC)实现并网,但电力电子变流器的广泛应用引发了高频谐振的问题。首先,针对新能源场站经柔直并网中的高频谐振问题,建立了包含电磁式电压/电流互感器及其二次电缆在内的MMC孤岛系统主回路与控制环节的数学模型。其次,用π型电路等效电磁式电压/电流互感器二次电缆并对其进行特性分析。然后,对综合考虑电磁式电压/电流互感器二次电缆的MMC孤岛系统展开稳定性分析,明确了电磁式电压/电流互感器二次电缆的传变特性导致孤岛系统发生高频谐振的机理。最后,在PSCAD/EMTDC中进行仿真验证。结合现场试验,证明了所提电磁式电压/电流互感器二次电缆引起孤岛系统高频谐振机理的准确性。展开更多
针对模块化多电平换流器型高压直流输电(modular multilevel converter-high voltage direct current,MMC-HVDC)系统,提出了一种创新的换流器桥臂保护方法。首先,分析了在换流器单桥臂接地以及单相桥臂间接地情况下电流的流通路径,构建...针对模块化多电平换流器型高压直流输电(modular multilevel converter-high voltage direct current,MMC-HVDC)系统,提出了一种创新的换流器桥臂保护方法。首先,分析了在换流器单桥臂接地以及单相桥臂间接地情况下电流的流通路径,构建了等值电路,并推导了换流器闭锁前后桥臂电流的表达式。基于此,剖析了故障后三相桥臂电流之和的独有特征,提出了通过检测三相桥臂和电流的基频分量是否为零来区分桥臂内部故障与外部故障的保护策略。鉴于现有桥臂保护方法无法有效应对换流器单相桥臂间短路的问题,进一步研究了此类短路情况下的特性,发现故障相上、下桥臂电流仅包含基频分量而不含直流分量,从而制定了相应的动作判据。将三相桥臂和电流保护与单相桥臂间短路保护判据进行,能够全面识别换流器桥臂上发生的各种故障,丰富和完善了换流器桥臂的保护原理。最终,通过在MATLAB/SimulinK中搭建双极MMC-HVDC系统仿真模型验证了所提出保护方法的有效性和可靠性。展开更多
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.
文摘随着“双碳”战略推进,我国大力发展风电、光伏等新能源。处于电网末端的新能源场站因缺乏交流电源支撑,需依赖柔性直流输电技术(modular multilevel converter-high voltage direct current,MMC-HVDC)实现并网,但电力电子变流器的广泛应用引发了高频谐振的问题。首先,针对新能源场站经柔直并网中的高频谐振问题,建立了包含电磁式电压/电流互感器及其二次电缆在内的MMC孤岛系统主回路与控制环节的数学模型。其次,用π型电路等效电磁式电压/电流互感器二次电缆并对其进行特性分析。然后,对综合考虑电磁式电压/电流互感器二次电缆的MMC孤岛系统展开稳定性分析,明确了电磁式电压/电流互感器二次电缆的传变特性导致孤岛系统发生高频谐振的机理。最后,在PSCAD/EMTDC中进行仿真验证。结合现场试验,证明了所提电磁式电压/电流互感器二次电缆引起孤岛系统高频谐振机理的准确性。
文摘针对模块化多电平换流器型高压直流输电(modular multilevel converter-high voltage direct current,MMC-HVDC)系统,提出了一种创新的换流器桥臂保护方法。首先,分析了在换流器单桥臂接地以及单相桥臂间接地情况下电流的流通路径,构建了等值电路,并推导了换流器闭锁前后桥臂电流的表达式。基于此,剖析了故障后三相桥臂电流之和的独有特征,提出了通过检测三相桥臂和电流的基频分量是否为零来区分桥臂内部故障与外部故障的保护策略。鉴于现有桥臂保护方法无法有效应对换流器单相桥臂间短路的问题,进一步研究了此类短路情况下的特性,发现故障相上、下桥臂电流仅包含基频分量而不含直流分量,从而制定了相应的动作判据。将三相桥臂和电流保护与单相桥臂间短路保护判据进行,能够全面识别换流器桥臂上发生的各种故障,丰富和完善了换流器桥臂的保护原理。最终,通过在MATLAB/SimulinK中搭建双极MMC-HVDC系统仿真模型验证了所提出保护方法的有效性和可靠性。
