Akiyoshi Komura

Output Power Smoothing and Hydrogen Production by Using Variable Speed Wind Generators

This paper presents a combination system of wind energy conversion and hydrogen production. Hydrogen is expected as an alternative energy source in the future, and this is the best way to produce it from renewable energy like wind energy. On the other hand, the output of a wind generator, in general, fluctuates greatly due to wind speed variations, and thus the output fluctuations can have a serious influence on the power system operation. In the proposed system, a variable speed wind generator is adopted, and an electrolyzer is installed in parallel with it for hydrogen production. Output power from the wind generator is smoothed and supplied to the power system as well as to the electrolyzer based on the cooperative control method. The performance of the proposed system is evaluated by simulation analyses, in which simulations are performed by using PSCAD/EMTDC.

A study on optimal coil configurations in a split-type superconducting MRI magnet

Optimal coil configurations in a split-type superconducting MRI magnet have been investigated, and the feasibility of the compact and high performance magnet is presented. A highly homogeneous magnetic field of about 10 ppm/50 cm diameter spherical volume (DSV) is attainable by eliminating error fields of higher orders and, moreover, the radius of the outermost coil can be reduced to about 70 percent of that of the magnet with positive current simply by alternately arranging coils with positive and negative currents.

Three-dimensional optimization of correction iron pieces for open high field MRI system

We have developed a new magnet for open high field (0.7 T) MRI systems. In order to homogenize magnetic fields in the field of view, an optimization method to determine initial configurations of large correction iron pieces was developed. In our method, we combined linear programming (LP) and 3D magnetic FEA and, using analytic formulae for LP, we computed field harmonics due to the volume of magnetized iron.

Shielding stray magnetic fields of open high field MRI magnets

We have developed a new magnet for open high field (0.7 T) MRI systems. Since MRI systems are installed in hospital sites, it is important to reduce stray magnetic fields of the magnets. We studied passive, active and hybrid shielding methods and compared them. In order to study feasibility of active shielding, we considered higher order multipole stray fields. We present details of the calculation method and the results.

A cooperative control method for output power smoothing and hydrogen production by using variable speed wind generator

This paper presents a combination system of wind energy conversion and hydrogen production. Hydrogen is expected as alternative energy sources in the future, and it is the best way to produce it from renewable energy like wind energy. On the other hand, the output of a wind generator, in general, fluctuates greatly due to wind speed variations, and thus the output fluctuations can have a..serious influence on the power system. In the proposed system, a variable speed wind generator is adopted, and an electrolyzer is installed in parallel with it for hydrogen production. Output power from the wind generator is smoothed and supplied to the power system as well as to the electrolyzer based on the cooperative control method. The performance of the proposed system is evaluated by simulation analyses, in which simulations are performed by using PSCAD/EMTDC.

Calculation method of circulating current in parallel armature windings in consideration of magnetic circuit

Recently, the capacity of turbo generators used in power plants is increasing in order to keep up with the growth of electric power consumption in the world. Turbo generators are consequently experiencing problems, including increasing electromagnetic force, temperature rise of armature coils, etc., as we try to increase the armature current to keep pace with the capacity increase. One way of avoiding these problems is to increase the number of parallel armature windings for decreasing the armature current per coil. However, the circulating current in the parallel windings is generated by the difference of the linkage flux of each winding, when the number of parallel windings is not a divisor of pole numbers. In this paper, we propose a simple method to calculate the circulating current by using a magnetic circuit in the design phase. We confirmed the proposed method has a similar accuracy and faster performance in comparison with the finite element method (FEM) analysis. And then we applied the proposed method to a calculation of the circulating current in 2- and 4-pole generators and considered the factors affecting the circulating current.

A new wind generation system cooperatively controlled with hydrogen electrolyzer

This paper presents a cooperative control method of the wind generation system composed of multiple wind genera1tors and hydrogen generator. In this system, some part of the output power from the wind generators is consumed by hydrogen generator, and the other part, which is smoothed by the cooperative control between the wind generators and the hydrogen generator, is supplied to the grid. In this system, Doubly-Fed Induction Generator (DFIG) is adopted as a wind generator, which can be operated at adjustable speed. Each electrolyzer in the hydrogen generator is operated only at the rated power consumption mode (“ON condition”) or at zero power consumption mode (“OFF condition”), because fractional power operation can have a bad influence on the service life of electrolyzers. Therefore, since the hydrogen generator cannot smooth the fluctuating power from the wind generators completely, the smoothing control is performed by controlling the kinetic energy of DFSGs in this system. As a result, in the proposed system, smoothed power can be supplied to the grid system without using any energy storage device as well as hydrogen can be produced.