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( T. Igarashi ),( A. Komatsu ),( T. Motooka ),( F. Ueno ),( M. Yamamoto ) 한국부식방식학회 2021 Corrosion Science and Technology Vol.20 No.3
In oxidizing nitric acid solutions, stainless steel undergoes intergranular corrosion accompanied by grain dropping and changes in the corrosion rate. For the safe operation of reprocessing plants, this mechanism should be understood. In this study, we constructed a three-dimensional computational model using a cellular automata method to simulate the intergranular corrosion propagation of stainless steel. The computational model was constructed of three types of cells: grain (bulk), grain boundary (GB), and solution cells. Model simulations verified the relationship between surface roughness during corrosion and dispersion of the dissolution rate of the GB. The relationship was investigated by simulation applying a constant dissolution rate and a distributed dissolution rate of the GB cells. The distribution of the dissolution rate of the GB cells was derived from the intergranular corrosion depth obtained by corrosion tests. The constant dissolution rate of the GB was derived from the average dissolution rate. Surface roughness calculated by the distributed dissolution rates of the GBs of the model was greater than the constant dissolution rates of the GBs. The cross-sectional images obtained were comparable to the corrosion test results. These results indicate that the surface roughness during corrosion is associated with the distribution of the corrosion rate.
Development of 1700V Hybrid Module with Si-IGBT and SiC-SBD for High Efficiency
T. Takaku,H. Wang,N. Matsuda,S. Igarashi,T. Nishimura,S. Miyashita,O. Ikawa 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
This paper describes about newly developed 1700V/400A hybrid module which consists of Si-IGBT and SiC-SBD. The static and dynamic characteristics were evaluated and the turn-on loss is 38% lower and the reverse recovery loss is 83% lower than the conventional all-Si IGBT module because of the reverse recovery current of SiC-SBD is very small to be an unipolar device. The radiation noise on hybrid module becomes higher with increasing collector current, but the peak value of the noise from hybrid module is almost same as the all-Si module if the collector current is less than 300A. In AC690V PWM inverter, the total power dissipation of hybrid module is 8% lower at 1 kHz and 29% lower at 10 kHz compare to the all Si module. Therefore the 1700V hybrid module is useful as a power module for an AC690V high efficiency inverter system such as wind power generation system and high voltage solar power generation system. This paper reports about the static and dynamic characteristics and the radiation noise measurement results on the 400A/1700V hybrid module.
T. Mori,T.Igarashi,H. Funato,S. Ogasawara,M. Hara,F.Okazaki,Y. Hirota 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
Recently, high performance power switching device realize high performance power converter. However, high speed turn-on and turn-off cause electromagnetic interference (EMI). EMI filters or wire shields decrease EMI. However, they take over space of automotive, and cost is expense. Authors have proposed a new method to decrease high-frequency noise at specific frequency band with modification of switching transient slope. In order to realize a step-down converter with modified switching slope, there are several problems such as generating PWM signal with modified slope, feasibility in a real chopper circuit, switching loss and so on. In this paper, a step-down converter applied proposed modified switching slope was successfully realized using MT (Modified Transient)-PWM generator. The operational characteristics were analyzed for resistive load.