Tadatoshi Babasaki

Developing of higher voltage direct-current power-feeding prototype system

High efficiency power feeding systems are effective solutions for reducing ICT power consumption of ICT equipment, such as routers and servers, or high efficiency cooling systems. We developed a higher voltage direct current (HVDC) power feeding system prototype. This system is composed of a rectifier, power distribution cabinet, batteries, and ICT equipment. The configuration is similar to a −48 V DC power supply system. The output of the rectifier is 100 kW, and the output voltage is 401.4 V. We describe the advantage of an HVDC power feeding system and show that its basic characteristics are stable.

Grounding concept considerations and recommendations for 400VDC distribution system

400VDC is becoming a new voltage interface for telecommunication buildings and data centers as well as for ICT equipment. 400VDC interface covers applications for up to 400VDC with a typical nominal voltage of 380VDC. Key drivers for utilizing a higher DC voltage are overall efficiency and reliability gains vs present solutions. However, introduction of a new 400VDC interface brings up some questions about personnel safety and implementation of system grounding. Although DC is considered safer than AC, till now datacom operators have been hesitant to deploy 400VDC because its not as commonly used and well understood as AC. This paper addresses 400VDC grounding issues and recommends high resistance midpoint grounding concept, as an effective way to provide safe operation of 400VDC distribution systems. Today Europe, North America (NA), and Japan telecom/ datacom installations employ slightly different grounding concepts, practices, codes, or regulations. This paper also reviews different grounding models and their implementation praxis in Europe, NA, and Japan. Benefits and the disadvantages of different grounding concepts are discussed and explanation of the reasons for selection of high resistance midpoint grounding as a preferable model for 400VDC distribution system is provided.

Development of power distribution cabinet for higher-voltage direct-current power feeding system

Reducing the feeding loss of information and communications technology equipment, such as servers and routers, is very effective for reducing the total power consumption in data centers and telecommunication buildings. In this paper, the structure and function of a higher-voltage direct-current (HVDC) power feeding system prototype is presented. This system was developed to reduce power delivery and conversion losses by using 380 V DC. For operational safety, a floating ground system with an earth detector is applied and a fuse and circuit breaker in the power distribution cabinet work in cooperation. The system voltage is around 380 V, and the output power of the rectifier is 100 kW. We describe the advantages of an HVDC power feeding system and show that its basic characteristics are stable.

A new high performance auto-tuning digital control circuit for buck-boost converter

The purpose of this paper is to present the dynamic characteristics of the new high performance auto-tuning digital control circuit for buck-boost converter when the step change of the load resistance R from 20 Ω to 10Ω. The buck-boost dc-dc converter is used with wide input voltage changing. At the same time, the suitable proportional gain and bias value are changing against the input voltage and the load resistance of the converter. So, we took two methods that changing proportional gain automatically and changing bias value against the input voltage, the load resistance and the loss of the converter. As a result, using this proposed method it is revealed that not only the dynamic characteristic but also regulation characteristic can be improved and it is effective for wide range input voltage. Especially, the steady-state error is improved from 470mV to 50mV when the input voltage is 5V, 700mV to 40mV when the input voltage is 15V, respectively.

Development of higher-voltage direct current power feeding system in telecommunications buildings and data centers

This paper describes the fuse-blowing characteristics for higher-voltage direct current (HVDC) power feeding systems. We developed a new fuse model, and evaluated the fuse-blowing characteristics and the effect of cable length. From the results, the electrical stability of HVDC power feeding system when a shorting accident or an overcurrent occurs is discussed.

Modeling of fuses for DC power supply systems including arcing time analysis

This paper describes a fuse model that can calculate the fuse current and voltage fluctuations from the start of a shorting accident to the completion of the fuse blowing. In the previous paper, the melting time and fuse current were calculated by considering the detectors current and diffusion factor during the melting period. Here, we extend the model to calculate the arcing time. Our model has a capacitor model that can represent the level of voltage fluctuation and waveforms of decreasing current. It also has an arc switch that can represent the voltage drop when the fuse becomes completely isolated from the circuit. Simulation results are in good agreement with the experimental results. We can calculate these characteristics easily, automatically, and accurately. Once we have obtained the fuse blowing parameters by performing only one experiment, we can calculate these characteristics even if the system is changed.

380-VDC power distribution system for 4-MW-scale cloud facility

In February 2014, the NTT Group officially announced that it has launched a high voltage direct current (HVDC) (380-VDC) with a 4-MW-scale power supply system for the Tokyo metropolitan area. Activities, such as international standardization, has led to the commercial commencement of a full-fledged 380-VDC power supply system, demonstration projects, and technology development, which took more than 10 years. For the completion of the 380-VDC power supply system, evaluation, analysis and development, and demonstration of power supply system parts and equipment were necessary. The 380-VDC power supply system is a novel concept completely different from that of AC or 48-VDC systems. There are some technology gaps to provide breakthrough solutions. Prior to development, technology must be codified for the introduction of a safe optimal power supply method, grounding scheme, protection against electric shock, such as overcurrent protection, and stability and noise immunity. Recently, there have been many excellent reports from around the world. This paper focuses on promoting the introduction of our 380-VDC supply system into business and the long-term (over 10 years) development of the 380-VDC power supply system by the NTT Group.

Basic study on grounding system for high-voltage direct current power supply system

The relationship between grounding systems and a high-voltage direct current (HVDC, 380-V DC) power supply system is presented. To assess the effect of grounding system configurations, a simple model of the HVDC power supply system was assumed, and two typical grounding models were evaluated. The noise emission level (conductive disturbance) was measured by using a prototype HVDC rectifier. By use of the measurement results and evaluations, the advantages and disadvantages of these grounding systems are discussed.

Examination progress and development of HVDC power feeding system

A higher voltage direct-current (HVDC) power feeding system for data centers has many advantages and is presently being studied in many countries. This system is composed of a rectifier, power distribution cabinet (PDC), batteries, and ICT equipment, and the configuration is similar to a –48-V DC power feeding system. The power feeding voltage is about 400 V. We developed a prototype of an HVDC power feeding system using commercial fuses in 2008. A prototype of a power distribution cabinet and fuses were developed in 2009. We conducted a basic experiment and confirmed that the characteristics of our prototype are stable. In this paper, we describe the advantages and development of an HVDC power feeding system and the examination progress of standardization.

A new approach to improve dynamic characteristics of digitally controlled buck-boost dc-dc converter

This paper presents a new digital control buck-boost dc-dc converter with bias model to improve dynamic characteristics. The buck- boost converter needs to respond appropriately to changing input voltage and load change with wide input voltage. This approach makes adjustment to the bias value by input voltage and output current. As a result, it is revealed that not only the dynamic characteristics but also static characteristics can be improved and it is effective for wide range input voltage.