The unified power flow controller(UPFC)based on modular multilevel converter(MMC) is the most creative flexible ac transmission system(FACTS) device. In theory, the output voltage of the series MMC in MMCUPFC can be r...The unified power flow controller(UPFC)based on modular multilevel converter(MMC) is the most creative flexible ac transmission system(FACTS) device. In theory, the output voltage of the series MMC in MMCUPFC can be regulated from 0 to the rated value. However,there would be relatively large harmonics in the output voltage if the voltage modulation ratio is small. In order to analyze the influence of MMC-UPFC on the harmonics of the power grid, the theoretical calculation method and spectra of the output voltage harmonics of MMC are presented. Subsequently, the calculation formulas of the harmonics in the power grid with UPFC are proposed. Based on it, the influence of UPFC on the grid voltage harmonics is evaluated, when MMC-UPFC is operated with different submodular numbers and voltage modular ratios. Eventually, the proposed analysis method is validated using digital simulation. The study results would provide guideline for the design and operation of MMC-UPFC project.展开更多
Based on orthogonal experiments,the effects of voltage,frequency,duty ratio and their interactions on the thickness and corrosion resistance of coatings prepared by plasma electrolytic oxidation(PEO)on aluminum in an ...Based on orthogonal experiments,the effects of voltage,frequency,duty ratio and their interactions on the thickness and corrosion resistance of coatings prepared by plasma electrolytic oxidation(PEO)on aluminum in an alkaline silicate-containing electrolyte were investigated.The thicknesses of these coatings were obtained by measuring their cross-section using Image J software.Their corrosion resistances were evaluated in HCl and NaCl media through spot test and electrochemical test.The results show that the experimental design of this study is the key to investigate the interactions among these electrical parameters.Additionally,not only each independent factor,but also their interactions exhibit a remarkable influence on the coatings.The combination of high voltage,low frequency and large duty ratio significantly increases the coating thickness and content of the corrosion resistance phase,and thus improves the corrosion resistance of the coating in HNO3 medium.Conversely,the coating possessing the densest microstructure and best corrosion resistance in NaCl medium is obtained when low voltage and high frequency match with a small duty ratio.展开更多
解决110 k V阳山变电站两台主变压器并列运行时产生环流的问题。基于主变压器并列运行时环流产生的机理,对阳山变电站两台并列运行主变压器的运行台账、负荷数据、技术参数等进行分析,得出环流产生的主要原因是两台变压器35k V侧电压档...解决110 k V阳山变电站两台主变压器并列运行时产生环流的问题。基于主变压器并列运行时环流产生的机理,对阳山变电站两台并列运行主变压器的运行台账、负荷数据、技术参数等进行分析,得出环流产生的主要原因是两台变压器35k V侧电压档位不一致使得电压变比不同。现场检查结果显示:1号、2号主变压器35 k V侧电压档位分别处于5档和3档位置,由此验证了分析的准确性。在运行过程中,如发现两台并列运行的主变压器中压侧档位不一致,应尽快将主变压器分列运行或转检修后进行档位调整,以及时消除环流。展开更多
基金supported by State Grid Corporation of China(SGCC)’s Major Science and Technology Demonstrative Project of UPFC in West Nanjing Power Grid(No.SGCC-2015-011)
文摘The unified power flow controller(UPFC)based on modular multilevel converter(MMC) is the most creative flexible ac transmission system(FACTS) device. In theory, the output voltage of the series MMC in MMCUPFC can be regulated from 0 to the rated value. However,there would be relatively large harmonics in the output voltage if the voltage modulation ratio is small. In order to analyze the influence of MMC-UPFC on the harmonics of the power grid, the theoretical calculation method and spectra of the output voltage harmonics of MMC are presented. Subsequently, the calculation formulas of the harmonics in the power grid with UPFC are proposed. Based on it, the influence of UPFC on the grid voltage harmonics is evaluated, when MMC-UPFC is operated with different submodular numbers and voltage modular ratios. Eventually, the proposed analysis method is validated using digital simulation. The study results would provide guideline for the design and operation of MMC-UPFC project.
基金Project(1111RJDA011)supported by the Creative Research Group Fund of Gansu Province,ChinaProject(SKLAB02015006)supported by the State Key Laboratory Open Fund of Advanced Processing and Recycling of Nonferrous Metals,China。
文摘Based on orthogonal experiments,the effects of voltage,frequency,duty ratio and their interactions on the thickness and corrosion resistance of coatings prepared by plasma electrolytic oxidation(PEO)on aluminum in an alkaline silicate-containing electrolyte were investigated.The thicknesses of these coatings were obtained by measuring their cross-section using Image J software.Their corrosion resistances were evaluated in HCl and NaCl media through spot test and electrochemical test.The results show that the experimental design of this study is the key to investigate the interactions among these electrical parameters.Additionally,not only each independent factor,but also their interactions exhibit a remarkable influence on the coatings.The combination of high voltage,low frequency and large duty ratio significantly increases the coating thickness and content of the corrosion resistance phase,and thus improves the corrosion resistance of the coating in HNO3 medium.Conversely,the coating possessing the densest microstructure and best corrosion resistance in NaCl medium is obtained when low voltage and high frequency match with a small duty ratio.
文摘解决110 k V阳山变电站两台主变压器并列运行时产生环流的问题。基于主变压器并列运行时环流产生的机理,对阳山变电站两台并列运行主变压器的运行台账、负荷数据、技术参数等进行分析,得出环流产生的主要原因是两台变压器35k V侧电压档位不一致使得电压变比不同。现场检查结果显示:1号、2号主变压器35 k V侧电压档位分别处于5档和3档位置,由此验证了分析的准确性。在运行过程中,如发现两台并列运行的主变压器中压侧档位不一致,应尽快将主变压器分列运行或转检修后进行档位调整,以及时消除环流。
