A fractional frequency transmission system(FFTS)is a promising solution to offshore wind power integration,for which the hexagonal modular multilevel converter(Hexverter)is an attractive choice for power conversion.Th...A fractional frequency transmission system(FFTS)is a promising solution to offshore wind power integration,for which the hexagonal modular multilevel converter(Hexverter)is an attractive choice for power conversion.The Hexverter has recently been proposed to directly connect two three-phase systems of different frequencies and voltage amplitudes,with only six branches in the FFTS in that case.This paper examines for the first time the control scheme of the Hexverter when applied to offshore wind power integration via a FFTS.Firstly,the frequency-decoupled mathematical model of the Hexverter is deduced by introducing the double dq transformation.Then the branch energy of the Hexverter is analyzed in detail and the reactive power constraint equation is obtained.The corresponding control scheme is thoroughly discussed,including the inner loop current control,the outer loop voltage control in both grid-connected mode and passive mode,and a novel optimization method to minimize the circulating current in the Hexverter.Finally,a simulation model of offshore wind power integration via a 4-terminal FFTS based on the Hexverter is built in MATALB/Simulink to verify the feasibility of Hexverter and the effectiveness of the control scheme proposed in this paper.展开更多
为观察不同消毒法对手术室空气消毒效果,采用现场消毒试验方法比较了3种空气消毒方法对空气中自然菌消毒效果。结果,在无人条件下,用含1500 mg/L二氧化氯消毒液气溶胶喷雾消毒,密闭作用15 m in,对手术室内空气中自然菌消亡率达到96.9%;...为观察不同消毒法对手术室空气消毒效果,采用现场消毒试验方法比较了3种空气消毒方法对空气中自然菌消毒效果。结果,在无人条件下,用含1500 mg/L二氧化氯消毒液气溶胶喷雾消毒,密闭作用15 m in,对手术室内空气中自然菌消亡率达到96.9%;用紫外线照射60 m in,对空气中自然菌消亡率为93.0%;用多功能循环风消毒机连续运行60 m in,可使空气中自然菌消亡率达到96.3%。在手术室有人条件下,三种消毒方法消毒处理60 m in后,空气中细菌总数均在卫生标准规定范围内;但在人员进入手术后,气溶胶喷雾消毒和紫外线照射都处于停止状态,随时间延长,细菌数不断增加;多功能循环风消毒机可继续运行,能保持细菌总数符合要求。结论,3种消毒方法在无人条件下,对室内空气中自然菌具有很好的杀灭效果;在有人条件下,只有多功能循环风消毒机可持续消毒,保持室内空气细菌总数符合规定标准。展开更多
基金supported by a grant from the National Natural Science Foundation of China (No.51677142)State Grid Science and Technology Project (No.52094016000C)
文摘A fractional frequency transmission system(FFTS)is a promising solution to offshore wind power integration,for which the hexagonal modular multilevel converter(Hexverter)is an attractive choice for power conversion.The Hexverter has recently been proposed to directly connect two three-phase systems of different frequencies and voltage amplitudes,with only six branches in the FFTS in that case.This paper examines for the first time the control scheme of the Hexverter when applied to offshore wind power integration via a FFTS.Firstly,the frequency-decoupled mathematical model of the Hexverter is deduced by introducing the double dq transformation.Then the branch energy of the Hexverter is analyzed in detail and the reactive power constraint equation is obtained.The corresponding control scheme is thoroughly discussed,including the inner loop current control,the outer loop voltage control in both grid-connected mode and passive mode,and a novel optimization method to minimize the circulating current in the Hexverter.Finally,a simulation model of offshore wind power integration via a 4-terminal FFTS based on the Hexverter is built in MATALB/Simulink to verify the feasibility of Hexverter and the effectiveness of the control scheme proposed in this paper.
文摘为观察不同消毒法对手术室空气消毒效果,采用现场消毒试验方法比较了3种空气消毒方法对空气中自然菌消毒效果。结果,在无人条件下,用含1500 mg/L二氧化氯消毒液气溶胶喷雾消毒,密闭作用15 m in,对手术室内空气中自然菌消亡率达到96.9%;用紫外线照射60 m in,对空气中自然菌消亡率为93.0%;用多功能循环风消毒机连续运行60 m in,可使空气中自然菌消亡率达到96.3%。在手术室有人条件下,三种消毒方法消毒处理60 m in后,空气中细菌总数均在卫生标准规定范围内;但在人员进入手术后,气溶胶喷雾消毒和紫外线照射都处于停止状态,随时间延长,细菌数不断增加;多功能循环风消毒机可继续运行,能保持细菌总数符合要求。结论,3种消毒方法在无人条件下,对室内空气中自然菌具有很好的杀灭效果;在有人条件下,只有多功能循环风消毒机可持续消毒,保持室内空气细菌总数符合规定标准。
