sexta-feira, 20 de dezembro de 2013
quinta-feira, 19 de dezembro de 2013
China's moon rover separates from moon lander
CHINA ATERIZOU COM SUCESSO SUA PRIMEIRA SONDA ESPACIAL NÃO TRIPULADA NA LUA,CHINA E APENAS O TERCEIRO PAIS A POUSAR NA LUA,SEGUINDO OS EUA E A ANTIGA UNIÃO SOVIETICA,QUE TANTO REALIZOU AS TAREFAS DECADAS ATRAS. "E UMA CONQUISTA DIGNA DE RESPEITO",DISSE JOHN LOGSDON,PROFESSOR EMERITO DA UNIVERSIDADE DE GEORGE WASHINGTON,QUE HA MUITO TEM MONITORADO POLITICA ESPACIAL.
'CHANG-3 E IMPRESSIONANTE COMO O PRIMEIRO POSSO NA LUA EM QUASE QUATRO DECADAS,CAINDO EM UM LUGAR QUE NÃO FOI EXPLORADO E USANDO INSTRUMENTAÇÃO CIENTIFICA RELATIVAMENTE AVANÇADA.
terça-feira, 17 de dezembro de 2013
Analysis of the Internal Electrical Characteristics of Electronic Power Transformers Yang Yi*, Cheng-Xiong Mao*, Dan Wang†, and Ji-Ming Lu**
Analysis of the Internal Electrical Characteristics of
Electronic Power Transformers
Yang Yi*, Cheng-Xiong Mao*, Dan Wang†, and Ji-Ming Lu**
*State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science
and Technology, Wuhan, China
†**College of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan,
China.
Abstract The modularized subunit of an electronic power transformer (EPT) is a series connection of two H-bridge voltage-source converters and a DC–DC converter with a high-frequency isolation transformer (HFIT). On the basis of cascading and paralleling the modularized subunits, EPT can be used in high-voltage and large-current applications in the power system. This paper discusses the steady state analysis of the modularized subunit of EPT. Theoretical analysis considers the influences of the two H-bridge voltage-source converters on the two sides of the DC–DC converter. We deduce the formulas of the theoretical calculation on the internal electrical characteristics of EPT (e.g., the voltages of the DC-bus capacitor and the primary side peak current of the HFIT). This paper provides guidance on the design and selection of EPT key elements (e.g., the DC-bus capacitors and HFIT). Experimental results are obtained from a single subunit of a laboratory model rated at 962 V, 15 kVA. All calculations, simulations,and experiments confirm the theoretical analysis of the subunit of EPT.
LINK
http://jpe.or.kr/archives/view_articles.asp?seq=776
Abstract The modularized subunit of an electronic power transformer (EPT) is a series connection of two H-bridge voltage-source converters and a DC–DC converter with a high-frequency isolation transformer (HFIT). On the basis of cascading and paralleling the modularized subunits, EPT can be used in high-voltage and large-current applications in the power system. This paper discusses the steady state analysis of the modularized subunit of EPT. Theoretical analysis considers the influences of the two H-bridge voltage-source converters on the two sides of the DC–DC converter. We deduce the formulas of the theoretical calculation on the internal electrical characteristics of EPT (e.g., the voltages of the DC-bus capacitor and the primary side peak current of the HFIT). This paper provides guidance on the design and selection of EPT key elements (e.g., the DC-bus capacitors and HFIT). Experimental results are obtained from a single subunit of a laboratory model rated at 962 V, 15 kVA. All calculations, simulations,and experiments confirm the theoretical analysis of the subunit of EPT.
LINK
http://jpe.or.kr/archives/view_articles.asp?seq=776
New Isolated Single-Phase AC-DC Converter for Universal Input Voltage Ming-Rong Lee*, Lung-Sheng Yang†, and Chia-Ching Lin*
LINK
http://jpe.or.kr/archives/view_articles.asp?seq=760
Modeling and Control Method for High-power Electromagnetic Transmitter Power Supplies Fei Yu† and Yi-ming Zhang*
Modeling and Control Method for High-power Electromagnetic Transmitter Power Supplies Fei Yu† and Yi-ming Zhang* †*College of Electronic Information and Control Engineering, Beijing University of Technology, Beijing, China
LINK
http://jpe.or.kr/archives/view_articles.asp?seq=769
Study on the Influence of Distribution Lines to Parallel Inverter Systems Adopting the Droop Control Method Xuan Zhang*, Jinjun Liu*, Zhiyuan You†, and Ting Liu*
Study on the Influence of Distribution Lines to Parallel Inverter Systems Adopting the Droop Control Method Xuan Zhang*, Jinjun Liu*, Zhiyuan You†, and Ting Liu* *†Dept. of Electronic Engineering, Xi’an Jiaotong University, Xi'an, China Abstract This paper takes into account the influence of the different impedances of distribution lines on power distribution among inverters when the inverters are paralleled with the droop control method. The impact of distribution lines on the power distribution of inverters can be divided into two aspects. Firstly, since the distributed generators are in low voltage grids, there is resistive impedance in the distribution lines, which will cause control coupling and reduce system stability. The virtual negative resistive impedance of inverters is adopted in this paper to neutralize the resistive element of distribution lines and thus make the distribution line impedance purely inductive. Secondly, after solving the resistive impedance problem, the difference in the inductive impedance value of distribution lines due to the low density of distributed generators will cause an unequal share of reactive power. With regards to this problem, modification is put forward for the droop control strategy to share the reactive power equally. The feasibility of the design is validated by simulation and experimental results.
LINK
http://jpe.or.kr/archives/view_articles.asp?seq=771
Control Method for Reducing the THD of Grid Current of Three-Phase Grid-Connected Inverters Under Distorted Grid Voltages
Control Method for Reducing the THD of Grid Current of Three-Phase Grid-Connected Inverters Under Distorted Grid Voltages Thanh-Vu Tran*, Tae-Won Chun†, Hong-Hee Lee*, Heung-Geun Kim**, and Eui-Cheol Nho*** *†Dept. of Electrical Engineering, University of Ulsan, Ulsan, Korea **Dept. Of Electrical Engineering, Kyungpook National University, Daegu, Korea ***Dept. of Electrical Engineering, Pukyong National University, Busan, Korea
Abstract This paper proposes a control method for reducing the total harmonic distortion (THD) of the grid current of three-phase grid-connected inverter systems when the grid voltage is distorted. The THD of the grid current caused by grid voltage harmonics is derived by considering the phase delay and magnitude attenuation due to the hardware low-pass filter (LPF). The Cauchy-Schwarz inequality theory is used in order to search more easily for the minimum point of the THD. Both the gain and angle of the compensation voltage at the minimum point of the THD of the grid current are derived with the variation of cut-off frequencies of the hardware LPF. Simulation and experimental results show the validity of the proposed control methods.
LINK
http://jpe.or.kr/archives/view_articles.asp?seq=772
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