Keiichi Hirose

Nagasaki University, Nagasaki, Nagasaki, Japan

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Publications (31)0.34 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this paper is to present the demonstration of digitally controlled peak current mode parallel dc-dc converter for the higher voltage direct current (HVDC) system. The peak current mode control circuit is only composed of the RC integrator and comparator. It can detect the peak current in real time. A prototype uses 800W phase-shifted full-bridge zero volt switching (ZVS) dc-dc converter. The digital control circuit is implemented by the field programmable gate array (FPGA) except the A-D conversion of output voltage. In this paper, the prototype tests the transient response by the experiment. Experimental results show that the prototype has superior transient response and it is suitable for switching power supplies for the HVDC system.
    Power Engineering, Energy and Electrical Drives (POWERENG), 2013 Fourth International Conference on; 01/2013
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    ABSTRACT: The interest in DC power supplies for efficiency in data centers, communication buildings, and microgrids has been increasing in recent years. The authors focus on wire and cable facilities and report experimental investigation of the effects of DC power on cable. The study is divided into verification of the permissible current of cable, comparison of the results for AC current and DC current, and verification of cable degradation under long??term DC use. It was confirmed that the permissible current for single-core cable is from 1% to 3% higher under DC operation than under AC operation. Tests of the lifetime of cable subjected to long-term use confirmed that cable that has be used for DC operation for five years exhibited no degradation. These results confirm that DC power has no practical effect on cable.
    Telecommunications Energy Conference 'Smart Power and Efficiency' (INTELEC), Proceedings of 2013 35th International; 01/2013
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    ABSTRACT: This paper presents a high speed soft-start dc-dc converter for energy management in the data center. The proposed con-trol method is constructed as the digital current-mode control dc-dc converter used in the higher voltage direct current (380V HVDC) system. In this system, power supplies are connected in parallel to obtain more high efficiency, safety and reliability in the data center. It is needed to balance between the each unit in parallel operation. In order to suppress the current imbalance between each unit, the maximum current tracking control is operated. The speed of the soft-start operation should be set up depending to the load conditions. In the proposed control method, the fastest speed of the soft-start is determined using the approximated liner function of output current which is obtained from the experiment results in advance. The proposed control method has the superior soft-start characteristics of the output voltage. As a result, the convergence time of the output voltage is improved.
    Telecommunications Energy Conference 'Smart Power and Efficiency' (INTELEC), Proceedings of 2013 35th International; 01/2013
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    ABSTRACT: This paper reports the experimental study of a DC microgrid for an office building that is now being constructed in Obihiro City, Hokkaido, Japan. The objective of this study is to develop a self-sustained distributed energy system by combining distribution energies, batteries, and appliances with DC power. This new DC energy system not only reduces the environment load and improves energy efficiency but also forms a community energy system that can become independent from utility grids and resistant to natural disasters. This paper describes the system configuration of the DC microgrid constructed in the city office, the characteristics of the developed equipment, the operational algorithm of the EMS. This research was conducted under the Technical Countermeasures to Global Warming Program of the Ministry of the Environment, Japan.
    Telecommunications Energy Conference 'Smart Power and Efficiency' (INTELEC), Proceedings of 2013 35th International; 01/2013
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    ABSTRACT: This paper describes a solution to a problem that occurs in the operation of data centers due to the disparity between the capacity of power supply equipment and the power consumption of information and communication technology (ICT) equipment. As a result of this disparity, the power supply modules and power supply units (PSUs) operate at a low load factor, which causes them to operate at low efficiency. Here we describe the operation of a supply management scheme depending on load factor for controlling the number of operating power supply modules in real time with a 380 V direct current distribution system and assess the performance of this scheme.
    Telecommunications Energy Conference 'Smart Power and Efficiency' (INTELEC), Proceedings of 2013 35th International; 01/2013
  • Tetsushi Tsumura, Keiichi Hirose, Masato Mino
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    ABSTRACT: A method applying a Markov process to compute the reliability of power systems that use storage batteries in facilities such as data centers and communications buildings is proposed. In conventional computations using series-parallel reliability blocks, each element is evaluated in terms of one of two exclusive states: normal or in failure. With the proposed Markov-process method, the supply failure frequency can also be computed, which was difficult with earlier methods. State changes due to control operations in various types of power supply system can also be evaluated, and in the future, it should be possible to perform further study, such as building repair models that incorporate many weaknesses and other changes in each state.
    Telecommunications Energy Conference 'Smart Power and Efficiency' (INTELEC), Proceedings of 2013 35th International; 01/2013
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    ABSTRACT: The purpose of this paper is to present the prototype of digital peak-current-mode and fast feedback control dc-dc converter system with the energy management. The prototype has been developed for the higher voltage direct current (HVDC) system in the data center. The proposed digital control circuit has two features for quick responses. One is a fast P control for quick feedback calculation of output voltage. Another one is a digital peak current mode control circuit which can detect the peak current in real time unlike the conventional method. In this paper, the power efficiency and transient response of prototype has been measured in the parallel operation using up to 4 prototypes. As a result, the efficiency of prototype can keep at least 91% in more than 11% load. Furthermore, the prototype shows a superior transient response. The convergence time of output voltage can be improved by 33% compared with the conventional digital control method.
    Telecommunications Energy Conference 'Smart Power and Efficiency' (INTELEC), Proceedings of 2013 35th International; 01/2013
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    ABSTRACT: The prototypes of the cut-off switch for 400 V direct current power distribution. They have functions of arc extinguishing and electric shock prevention. Evaluation of load switching is conducted with the prototypes and it is confirmed that they have enough capability of arc extinguishing. For future, it is scheduled that the product shape and specification will be reviewed for user??s needs and international standardization.
    Telecommunications Energy Conference 'Smart Power and Efficiency' (INTELEC), Proceedings of 2013 35th International; 01/2013
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    ABSTRACT: In recent years, the concepts of the smatt grid and the smatt community have received attention as a new infrastructure for more prudent use of energy, electricity in particular, with less waste and more convenience. Here, we describe a combined renewable energy system that optimizes energy use and increases robustness against disasters by integrating various distributed power sources such as the existing power grid, solar energy and storage batteries on the demand side and by using ICT.
    Telecommunications Energy Conference 'Smart Power and Efficiency' (INTELEC), Proceedings of 2013 35th International; 01/2013
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    ABSTRACT: The purpose of this paper is to present a novel digital peak current mode dc-dc converter and its control characteristics. The proposed method can detect the peak current in real time. The proposed peak current detection circuit is composed of RC integrator and comparator as the A-D converter. The design of RC integrator has a large effect on regulation characteristics and the transient response of the proposed method. In this paper, the influence of circuit parameters of the RC integrator is clarified. As a result, it is confirmed that the proposed method shows a superior transient response by selecting optimal parameters. The convergence time and undershoot are suppressed by 67% and 34% compared with the conventional digital voltage mode control method, respectively.
    Power Electronics and Drive Systems (PEDS), 2013 IEEE 10th International Conference on; 01/2013
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    ABSTRACT: This paper presents the performance of novel digital P-I-D control switching power supply with fast proportional control, which is compared with conventional digital control. The transient response is improved, while the transient response of proposed method is improved even with P-I-D parameters that are same to the conventional method. It is confirmed that it has the superior transient response, which is verified with 800W prototype.
    Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM), 2012 International Symposium on; 01/2012
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    ABSTRACT: This paper presents a fast response digitally controlled full bridge converter in parallel operation. The digital controlled circuit has some problem. One of the main problems is the delay time. The delay time includes the conversion time of A-D converter and processing time of digital controller. It exerts a bad influence on the dynamic characteristic. In the proposed method, the sample timing for P control is contrived, thus the delay time for P control is minimized. The proposed fast P control method is applied to the full bridge converters in parallel operation. It is confirmed that the proposed method has superior transient response compared to the conventional method. The proposed digitally controlled parallel full bridge converter is suitable to the power converter for automotive.
    Vehicle Power and Propulsion Conference (VPPC), 2012 IEEE; 01/2012
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    ABSTRACT: This paper presents a new digital peak current mode dc-dc converter using a FPGA delay circuit and a simple A-D converter. The peak current detection circuit is only composed of RC integrator and field programmable gate array (FPGA) delay circuit. The sampling point of detected current is changed by the feedback value of output voltage. The RC integrator is performed as the A-D converter for the current. The proposed method can detect the peak point of current in real time and shows a superior transient response. As a result, the convergence time and undershoot of output voltage are suppressed to one third and one fourth, respectively.
    Energy Conversion Congress and Exposition (ECCE), 2012 IEEE; 01/2012
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    ABSTRACT: The purpose of this paper is to present performance characteristics of a quick response digital peak-current-mode 380V dc-dc converter for the green IT system. A proto-type is constructed as the digital control dc-dc converter used in the higher voltage direct current (HVDC) system for the green IT. The proto-type uses the digital peak-current-mode control to show a superior transient response. A dc power supply uses 380V in above HVDC system. The transient response of proto-type is indicated in this paper. As a result, the convergence time and undershoot of output voltage are suppressed to one half and one fourth, respectively.
    Renewable Energy Research and Applications (ICRERA), 2012 International Conference on; 01/2012
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    ABSTRACT: This paper presents a novel digital P-I-D control FPGA for a switching power supply in the higher voltage direct-current (HVDC) power feeding system. At first, digital fast P control buck type converter is presented. Then, the appropriate number of sample point is determined. Then the fast P control is applied to the full bridge converter for HVDC. The acceptable delay time, with realizing superior dynamic response, is half of a switching cycle based on the appropriate number of sample points of buck converter. In the proposed method, the calculation processes of P and I-D controls are parallel. The delay time of P control is less than that of I-D control. The step change against the load will be discussed. It is revealed that the proposed circuit has the superior transient response. Then the proposed digitally controlled phase-shift full bridge dc-dc converter is verified with 800W proto type. The maximum power efficiency is about 92%. Then it is confirmed that proposed digital controlled phase-shift full bridge dc-dc converter achieves superior transient response compared to conventional one.
    Power Electronics for Distributed Generation Systems (PEDG), 2012 3rd IEEE International Symposium on; 01/2012
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    ABSTRACT: The purpose of this paper is to present a new digital control switching power supply for the HVDC system in data center. The two stage converters are proposed to address the problem of input voltage drop. It consists of the boost converter and the phase-shifted full bridge converter. Since the first stage boost converter make the output voltage constant, good regulation characteristics against the input voltage of the server as the load and superior transient response are achieved with keeping high efficiency in this proposed converter for HVDC. A digital peak current mode control and the existing fast P control are implemented. And then the transient responses of converters in parallel operation are discussed because it is needed in the data center. The digital control method presented in this paper achieves the superior response compared with the existing digital control. It is experimentally verified with 800W prototypes that this unit has superior static and dynamic characteristics.
    Telecommunications Energy Conference (INTELEC), 2012 IEEE 34th International; 01/2012
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    ABSTRACT: This paper proposes a novel quick soft-start method for the digital control dc-dc converter. To implement the energy management for energy saving, the power supply that can be operated in start-up and be shuttled down quickly and continually is necessary. It is the power supply added to the soft-start capability. It is important for the soft-start operation to detect the load resistor. In the conventional analog control method, the fixed large time constant of the soft-start circuit must be set corresponding to the worth condition. In the proposed digital control, the optimal time constant of the soft-start circuit can be decided with load resistor with the control processor. Therefore, it doesn't need to set the large value for the time constant. As a result, the convergence time of output voltage is suppressed. From simulation results, it is confirmed that the digital control method has superior soft- start characteristics compared to the analog one and the convergence time of output voltage is approximately 94% smaller than the analog one.
    01/2011;
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    ABSTRACT: om Abstract-This paper reports test results and reviews of the developed DC plug and socket-outlet. The developed item can be applied to the 400 Vdc power to improve energy efficiency in telecommunicatio n sites, data centers, commercial buildings, and smart energy. There are some safety issues to use the 400 Vdc power. The set of plug and socket-outlet has a mechanism which based on combination of a permanent magnet and mechanical contact in the limited small space. That should solve the problems such as both arc extinction and protection against electric shock known as critical DC power issue for a long time.
    01/2011;
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    ABSTRACT: This paper presents a novel 800W proto type digital P-I-D control switching power supply for the high voltage direct-current(HVDC) power feeding system The digital control circuit for HVDC power feeding system has some problems. Especially, the conversion time of A-D converter and the processing time of digital controller exert a bad influence upon the dynamic characteristics. In the proposed method, the calculation processes of P and I-D controls are parallel. The delay time of P control is less than that of I-D control. The results against the step change of load are discussed. As a result, it is revealed that the proposed circuit has the superior transient response.
    01/2011;
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    ABSTRACT: In recent years, higher voltage direct current (HVDC) distribution systems have been developed to reduce power consumption in telecommunication buildings and data centers. Thus, a demonstration test has been conducted to determine the energy efficiency, power stability, and safety of the HVDC system. The demonstration test was conducted in an in-service data center. The test results show that the HVDC system is 5.8% more efficient than the existing AC system. It was also found that servers that were altered for HVDC use could reduce the power consumption by up to 7%. According to the results of simulations including the effect of air conditioning, HVDC system could reduce the total power consumption by 15%. These test results also show that the HVDC system has no problem in operation in terms of power stability and safety.
    01/2011;