1991 Fiscal Year Final Research Report Summary
Basic Research on Very Low Temperature Power Electronics
| Project/Area Number |
01460131
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
電力工学
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| Research Institution | Osaka University |
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Principal Investigator |
MURAKAMI Yoshishige Osaka University, Osaka University Research Center for Superconducting Materials and Electronics, Professor, 超伝導エレクトロニクス研究センター, 教授 (70029015)
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| Co-Investigator(Kenkyū-buntansha) |
ISE Toshifumi Osaka University, Faculty of Eng. Dep. EE, Research Associate, 工学部, 助手 (00184581)
TSUJI Kiichirou Osaka University, Faculty of Eng. Dep. EE, Professor, 工学部, 教授 (30029342)
YAMAMOTO Junya National Institute for Fusion Science, Professor, 教授 (00029208)
SHIRAFUJI Junji Osaka University, Faculty of Eng. Dep. EE, Professor, 工学部, 教授 (70029065)
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| Project Period (FY) |
1989 – 1991
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| Keywords | Low Temperature Power Electronics / Superconducting Magnet / Low Temperature Characteristics of Semiconductor / Operation of Power Converter in Cold Environment |
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| Research Abstract |
We find several issues in power electronics which are composed of semiconductor devices for the control of superconducting magnets and machines. The7 are pointed out as follows : (1) Although superconducting machines are applied for the high efficiency and high integration, the ability of current conduction and break down voltages of semiconductor devices are inferior to those of superconducting machines. (2) Although superconducting machines are operated in the very cold environments, semiconductor devices are designed to be operated in room temperature.
From these points of view, this research has been studied in these three years from 1989 to 1991, which is oriented for the development of power electronics system and the semiconductor devices such that they are operated in the cold environments same as the superconducting machines. The obtained results are given in the followings.
(1) Power MOSFETs of the unipolar devices demonstrated the favorite characteristics in 80 degree Kelvin o
… More
f liquid nitrogen temperature, and the conduction resistance became 1/3.5 that of room temperature, although the bipolar devices could not conduct the currents due to freeze-out of carriers in these low temperatures. The averaged loss due to repeated switching was also decreased in the similar manner.
(2) For controlling life time of minority carriers of internal diodes in power MOSFETS, both electron irradiation and platinum diffusion are processed. However, the platinum diffusion invokes the carrier freeze-out and deteriorated the low temperature characteristics. On the contrary, the electron irradiation did not make such inferiority.
(3) We have composed the chopper circuits which consist of power MOSFETs and diodes such that they are installed in the same cryostat of superconducting magnet. High Tc superconductor was utilized as the power leads between the chopper and the magnet, and these control system are operated in the cold environment near liquid nitrogen temperature. The experimental results have verified the power conversion in such low temperature. The power loss converted to room temperature became larger than that of room temperature operation. We can expect the loss in cold environment converted to room temperature can be decreased to the level which is comparable the loss in room temperature by the improvement of the efficiency of refrigerator of liquid nitrogen together with the device design optimized in the cold environments.
(4) The current density and electric field distributions were analyzed by the two dimensional simulation based on finite element method. The design optimization in the low temperatures have been discussed. The break down voltage decreases accompanied with the decrease of on resistance by virtue of the increase of doping level. The compromise between the two will result in the optimization. Less
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