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Nishida K.,National Institute of Technology, Ube College | Ahmed T.,Assiut University | Nakaoka M.,Kyungnam University
IEEE Transactions on Industry Applications | Year: 2011

In this paper, a novel grid integration system for a variable-speed wind turbine using an interior permanent-magnet synchronous generator (IPMSG) is developed. The power conditioner system (PCS) consists of a series-type 12-pulse uncontrolled diode rectifier powered by a phase-shifting transformer and then cascaded to a pulsewidth-modulated (PWM) voltage source inverter. The active current of the grid-side PWM inverter is only controlled to follow the optimal active current reference which is determined by using a simple maximum power point tracking (MPPT) control strategy. The MPPT algorithm requires only three sensors in order to track the maximum power of the wind turbine. The most significant advantage of the proposed system is that the passive filter together with a series-type 12-pulse rectifier provides high efficiency by compensating the power factor angle of the IPMSG and suppresses distortions presented in the IPMSG voltages and currents. The laboratory results indicate that the proposed construction and scheme are simple, cheap, and efficient. © 2010 IEEE.

Ishikawa S.,Kyushu Institute of Technology | Kubota R.,National Institute of Technology, Ube College | Horio K.,Kyushu Institute of Technology
Expert Systems with Applications | Year: 2015

In this paper, we propose a new optimization technique, the hierarchical multi-space competitive distributed genetic algorithm (HmcDGA), which is effective for the hierarchical optimization problem. It is an extension of the multi-space competitive distributed genetic algorithm (mcDGA), which was proposed by the authors. The mcDGA efficiently finds an optimal solution with a low computational cost by increasing the number of individuals in a solution space in which it is likely to exist. An optimization method that is divided into several levels of hierarchy is called a hierarchical optimization. Several hierarchical optimization techniques have been proposed, including the hierarchical genetic algorithm (HGA). In hierarchical optimization, a complex problem is divided into a hierarchical collection of simpler problems, and each level is optimized independently. In this way, complex problems can be solved without the need to develop problem-specific operators. However, in the conventional HGA, this results in a high computational cost because the genetic algorithm (GA) is repeated many times at upper and lower level. The HmcDGA is a hybrid of the mcDGA and HGA, and it has some of the advantages of each one; for example, the HmcDGA can find an optimal solution at low computational cost and without requiring special operations. This allows it to be applied to a wide variety of optimization problems. Therefore, the HmcDGA may become the powerful optimization algorithm that can solve various problems. In this paper, we apply the proposed HmcDGA to the flexible job-shop scheduling problem (FJSP) which is one of the complex combinational optimization problem and confirm its effectiveness. Simulation results show that the HmcDGA can find solutions that are comparable to those found by using GAs developed specifically for the FJSP, the HmcDGA is not required a lot of computational costs comparing to the HGA. © 2015 Elsevier Ltd. All rights reserved.

Yoshida M.,National Institute of Technology, Ube College
Materials Transactions | Year: 2012

Titanium diboride (TiB 2) has been sintered using spark plasma sintering (SPS) with the addition of titanium tri-aluminide (Al 2Ti) at the temperature between 1273 and 1573 K. By the X-ray diffraction measurements, it has been shown that TiB 2Al 2Ti composites can be obtained by the sintering at 1273 K. Vickers hardness of the specimen increases as the amount of Al 2Ti increases up to 30% by the sintering at 1273 K, and TiB 230 mass% Al 2Ti composite has the relative density of around 96% and Vickers hardness as high as 2100 Hv. On the other hand, Al 2Ti evaporates during sintering above 1473 K. TiB 2 sintered with 10 mass% Al 2Ti at 1573K has the relative density of 94% and Vickers hardness 2100 Hv, while TiB 2 sintered without Al 2Ti has the relative density as low as 76%. This fact indicates that Al 2Ti accelerates the diffusion of TiB 2 causing densification of sintered TiB 2 specimens in the sintering above 1473 K. © 2012 The Japan Institute of Metals.

Nishida K.,National Institute of Technology, Ube College | Ahmed T.,Assiut University | Nakaoka M.,Kyungnam University
IEEE Transactions on Industry Applications | Year: 2014

This paper proposes appropriate analytical expressions for a deadbeat control system to be implemented in the output inductor-capacitor-inductor (LCL) filter of a grid-connected inverter. Unlike in a conventional analysis, the proposed control algorithm with a settling time of three sampling periods is derived from the system transfer function in the discretized time domain instead of the Laplace s-domain. Furthermore, when introducing the deadbeat control, the independent control of the integrated active power and that of the reactive power are also made possible. The experimental results of the proposed deadbeat control system indicate that the feedbacks from both grid and inverter currents have similarly high capabilities in attenuating switching frequency components and damping resonance. Such proficiency is brought about because the remaining two undetected control variables of the LCL filter are taken as estimates in the DSP when introduced to the state observer. However, feedback from the grid currents can be seen to significantly reduce the total harmonic distortion of the actual grid currents themselves. © 1972-2012 IEEE.

Kubota R.,National Institute of Technology, Ube College | Suetake N.,Yamaguchi University
Journal of the Franklin Institute | Year: 2011

We present a novel switching median filter for the removal of random-valued impulse noise on a color image. The present filter consists of a new noise detector with auto-tuning function, and a vector type noise remover avoiding the occurrence of the color artifacts after the noise removal. The detector has a parameter, which is automatically tuned only by using the distribution information of the noise signal without any training signals, and detects the pixel corrupted by the random-valued impulse noise with the parameter. And the detector operates in each channel independently. As a noise remover, the ordinary vector median filter is employed to interpolate only the pixel which is detected as noisy one by the detector. Through the experiments using some digital color images, the validity and the effectiveness of the present method are verified. © 2011 The Franklin Institute.

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