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Tetsuji Okamura
Tokyo Institute of Technology, 13290 Yokohama, Kanagawa, Japan

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Journal article
Published: 01 February 2021 in IEEE Transactions on Applied Superconductivity
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As a high-efficiency cooling technology for HTS coils, we have begun research and development to examine the feasibility of a cooling assist technology that maintains a cryogenic state by combining the magnetic force generated by the superconducting coil with magnetic refrigeration technology. Magnetic refrigeration requires the magneto caloric material to change the magnetic field. It was considered that the magnetic field change can be obtained if the magnetic force can be controlled by the magnetic shield. In the experiment, the temperature change obtained when a magnetic shield was inserted into the air gap was measured by a simple test device using an iron-based magneto caloric material. The principle verification confirmation test was performed using several types of magnetic shielding materials such as Permalloy bulks and the electrical steel sheets. In addition, numerical analysis is performed on the magnetic shielding effect, and the shielding effect is improved by increasing the thickness of the shielding material and the possibility of using HTS as magnetic shielding materials were also analyzed. In this study, we report the possibility of cooling the high-temperature superconducting coil with high efficiency by combining the magnetic field created by the superconducting coil and magnetic refrigeration.

ACS Style

Naoki Hirano; Yuta Onodera; Toshiyuki Mito; Setsura Nagai; Yodai Okazaki; Tetsuji Okamura. Feasibility study of high-efficiency cooling of high-temperature superconducting coils by magnetic refrigeration. IEEE Transactions on Applied Superconductivity 2021, PP, 1 -1.

AMA Style

Naoki Hirano, Yuta Onodera, Toshiyuki Mito, Setsura Nagai, Yodai Okazaki, Tetsuji Okamura. Feasibility study of high-efficiency cooling of high-temperature superconducting coils by magnetic refrigeration. IEEE Transactions on Applied Superconductivity. 2021; PP (99):1-1.

Chicago/Turabian Style

Naoki Hirano; Yuta Onodera; Toshiyuki Mito; Setsura Nagai; Yodai Okazaki; Tetsuji Okamura. 2021. "Feasibility study of high-efficiency cooling of high-temperature superconducting coils by magnetic refrigeration." IEEE Transactions on Applied Superconductivity PP, no. 99: 1-1.

Journal article
Published: 16 October 2020 in IEEE Transactions on Power Electronics
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This paper presents an interleaved bidirectional chopper with auxiliary converters for onboard energy storage systems that is capable of achieving a significant reduction in the mass and volume of the current-smoothing inductors. The proposed chopper consists of multiple interleaved sub-converters, where each sub-converter consists of a bidirectional chopper cell, a current-smoothing inductor at the low-voltage side, and an auxiliary converter that is formed by the cascade connection of multiple full-bridge cells. Each auxiliary converter is connected in series with its respective inductor to suppress the ac voltage component that produces ripple current in the inductor of each sub-converter; hence, a smaller inductor can be used to meet the ripple current requirement when compared with the conventional bidirectional chopper. In addition, auxiliary converters can be used as dc-circuit breakers to protect the low-voltage side against faults in the power devices of the bidirectional chopper cells. This paper discusses the operating principles and control method of the proposed chopper, followed by experiments using a downscaled experimental model.

ACS Style

Hamzeh J. Ahmad; Makoto Hagiwara. Interleaved Bidirectional Chopper With Auxiliary Converters for DC Electric Railways. IEEE Transactions on Power Electronics 2020, 36, 5336 -5347.

AMA Style

Hamzeh J. Ahmad, Makoto Hagiwara. Interleaved Bidirectional Chopper With Auxiliary Converters for DC Electric Railways. IEEE Transactions on Power Electronics. 2020; 36 (5):5336-5347.

Chicago/Turabian Style

Hamzeh J. Ahmad; Makoto Hagiwara. 2020. "Interleaved Bidirectional Chopper With Auxiliary Converters for DC Electric Railways." IEEE Transactions on Power Electronics 36, no. 5: 5336-5347.

Original paper
Published: 26 July 2018 in Electrical Engineering
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In this paper, a new and efficient global optimization method known as teaching–learning-based optimization is adopted to optimally design the parameters of a passive RC-damped LCL filter for grid-connected voltage source inverters. The novel proposed objective function of the optimization algorithm is to minimize the values of inductors and capacitors. The proposed design improves inverter efficiency and minimizes filter stored energy at a predefined operating and switching frequencies. Moreover, the proposed design procedure may reduce the complexity of the passive RC-damped LCL filter by removing one inductor or one capacitor. The optimal design procedure is built based on an accurate mathematical model and description of the filter topology. A detailed comparison between the results of the proposed work and related work in the literature is thoroughly discussed. The optimized filter is designed, built, and validated analytically and experimentally for verification based on a hardware prototype.

ACS Style

Saher Albatran; Ahmed Koran; Issam A. Smadi; Hamzeh J. Ahmad. Optimal design of passive RC-damped LCL filter for grid-connected voltage source inverters. Electrical Engineering 2018, 100, 2499 -2508.

AMA Style

Saher Albatran, Ahmed Koran, Issam A. Smadi, Hamzeh J. Ahmad. Optimal design of passive RC-damped LCL filter for grid-connected voltage source inverters. Electrical Engineering. 2018; 100 (4):2499-2508.

Chicago/Turabian Style

Saher Albatran; Ahmed Koran; Issam A. Smadi; Hamzeh J. Ahmad. 2018. "Optimal design of passive RC-damped LCL filter for grid-connected voltage source inverters." Electrical Engineering 100, no. 4: 2499-2508.

Journal article
Published: 09 February 2018 in Energies
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The performance optimization of the two-level, three-phase, grid-feeding, voltage-source inverter (VSI) is studied in this paper, which adopts an online adaptive switching frequency algorithm (OASF). A new degree of freedom has been added to the employed OASF algorithm for optimal selection of the weighting factor and overall system optimization design. Toward that end, a full mathematical formulation, including the impact of the coupling inductor and the controller response time, is presented. At first, the weighting factor is selected to favor the switching losses, and the controller gains are optimized by minimizing the integral time-weighted absolute error (ITAE) of the output active and reactive power. Different loading and ambient temperature conditions are considered to validate the optimized controller and its fast response through online field programmable gate array (FPGA)-in-the-loop. Then, the weighting factor is optimally selected to reduce the cost of the L-filter and the heat-sink. An optimization problem to minimize the cost design at the worst case of loading condition for grid-feeding VSI is formulated. The results from this optimization problem are the filter inductance, the thermal resistance of the heat-sink, and the optimal switching frequency with the optimal weighting factor. The VSI test-bed using the optimized parameters is used to verify the proposed work experimentally. Adopting the OASF algorithm that employs the optimal weighting factor for grid-feeding VSI, the percentages of the reductions in the slope of the steady state junction temperature profile compared to fixed frequencies of 10 kHz, 14.434 kHz, and 20 kHz are about 6%, 30%, and 18%, respectively.

ACS Style

Issam A. Smadi; Saher Albatran; Hamzeh J. Ahmad. On the Performance Optimization of Two-Level Three-Phase Grid-Feeding Voltage-Source Inverters. Energies 2018, 11, 400 .

AMA Style

Issam A. Smadi, Saher Albatran, Hamzeh J. Ahmad. On the Performance Optimization of Two-Level Three-Phase Grid-Feeding Voltage-Source Inverters. Energies. 2018; 11 (2):400.

Chicago/Turabian Style

Issam A. Smadi; Saher Albatran; Hamzeh J. Ahmad. 2018. "On the Performance Optimization of Two-Level Three-Phase Grid-Feeding Voltage-Source Inverters." Energies 11, no. 2: 400.

Journal article
Published: 15 December 2017 in Electronics
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Enhancing the performance of the voltage source inverters (VSIs) without changing the hardware structure has recently acquired an increased amount of interest. In this study, an optimization algorithm, enhancing the quality of the output power and the efficiency of three-phase grid connected VSIs is proposed. Towards that end, the proposed algorithm varies the switching frequency (fsw) to maintain the best balance between switching losses of the insulated-gate-bipolar-transistor (IGBT) power module as well as the output power quality under all loading conditions, including the ambient temperature effect. Since there is a contradiction with these two measures in relation to the switching frequency, the theory of multi-objective optimization is employed. The proposed algorithm is executed on the platform of Altera® DE2-115 field-programmable-gate-array (FPGA) in which the optimal value of the switching frequency is determined online without the need for heavy offline calculations and/or lookup tables. With adopting the proposed algorithm, there is an improvement in the VSI efficiency without degrading the output power quality. Therefore, the proposed algorithm enhances the lifetime of the IGBT power module because of reduced variations in the module’s junction temperature. An experimental prototype is built, and experimental tests are conducted for the verification of the viability of the proposed algorithm.

ACS Style

Saher Albatran; Issam A. Smadi; Hamzeh J. Ahmad; Ahmed Koran. Online Optimal Switching Frequency Selection for Grid-Connected Voltage Source Inverters. Electronics 2017, 6, 110 .

AMA Style

Saher Albatran, Issam A. Smadi, Hamzeh J. Ahmad, Ahmed Koran. Online Optimal Switching Frequency Selection for Grid-Connected Voltage Source Inverters. Electronics. 2017; 6 (4):110.

Chicago/Turabian Style

Saher Albatran; Issam A. Smadi; Hamzeh J. Ahmad; Ahmed Koran. 2017. "Online Optimal Switching Frequency Selection for Grid-Connected Voltage Source Inverters." Electronics 6, no. 4: 110.