Tadahito Aoki

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.

Guidelines for power-supply systems for datacom equipment in NTT

This paper describes the guidelines for power-supply systems for datacom equipment in NTT that were established at the beginning of 2002, to prevent accidents in power-supply systems. The guidelines indicate that the -48 VDC power-supply system is preferable for supplying power to the datacom equipment. They specify that the input capacitor in a DC-DC converter used in datacom equipment should have a value of at least 0.3 /spl mu/F/W and that a capacitor should be connected to the input of the power distribution frame to prevent the oscillation in a -48 VDC system. They also prescribe that a pre-charge circuit should be installed to prevent inrush current to datacom equipment. If power-supply systems for datacom equipment follow these guidelines, there will be fewer serious accidents.

Characteristics of a quasi-resonant DC link PWM inverter

A quasi-resonant DC link PWM inverter using a series resonant DC link (SRDCL) circuit is proposed and a 10 kW prototype inverter is described. The SRDCL circuit adjusts the input voltage of the PWM inverter to zero for a short period whenever the conditions of the inverter switches change. The design method for reducing the peak voltage stress and peak current stress on the SRDCL circuit devices is discussed. Experimental results verified the operation of the proposed inverter. The electromagnetic interference (EMI) noise levels met the CISPR Pub. 22 standard requirement and the efficiency characteristics were similar to those of a conventional PWM inverter; efficiency is 93% at output power above 5 kW.

Energy-saving effects of super computers by using on-site solar power and direct HVDC feeding systems

Power consumption of the ICT sector of information and communication facilities and data centers has grown, and this has led to a need to improve energy efficiency of these facilities. DC distribution systems employing 380 VDC as the supply voltage is one promising approach to address this problem, countries around the world and are progressing to develop and deploy commercial services. We demonstrated a 380 VDC power distribution system interconnected with a solar power generation system. This demonstration showed that the 380 VDC power supply system saves more energy than the AC power supply system and showed how carbon dioxide emissions are reduced by integrating the solar power generation system.

4.5-kW fuel cell system based on PEFCs

We have developed a prototype 4.5-kW fuel cell system that is powered by polymer electrolyte fuel cells (PEPCs). It consists of two parts: a generator unit and a hydrogen cylinder box. The generator contains a fuel cell stack, an inverter, a control unit, and other components. The volume of the unit is 657 l and the weight is 190 kg. The system can supply 3.5 kW of AC 100 V power for about three hours using eight 10 l hydrogen gas cylinders or two 47 l hydrogen gas cylinders. The warm-up time is about four minutes. The system generates electric power from the reaction between hydrogen and oxygen in air, so it does not emit harmful gases or carbon dioxide. We tested this prototype 4.5 kW fuel cell system and we found that the amount of steam expelled into the air needs to be reduced for indoor use.

Characteristics of a high-frequency link resonant inverter

The authors describe the configuration and operation of a high frequency link resonant inverter. In this inverter, a resonant link high frequency voltage generated in a primary resonant inverter is isolated by a high frequency transformer, then directly converted into a resonant link low-frequency voltage by a cycloconverter. The switching losses and surge voltage levels can be reduced by making all switches in the primary inverter and the cycloconverter operate at zero voltage. The relationship between the characteristic impedance of the resonant circuit and the conversion efficiency, and the output voltage characteristics are discussed by comparing analytical and experimental results.<<ETX>>

Effect of system parameters when fuse blows in High Voltage Direct Current (HVDC) power supply systems

In this thesis, we discuss the effects of system parameters on a High Voltage Direct Current (HVDC) power supply system when a fuse blows. We then use a new fuse model which we have created, to simulate voltages and currents when a fuse blows and evaluate the risks that other Information and Communications Technology (ICT) equipment will fail, or that fuses in the equipment will also blow. From these results, we create a risk map, and offer measures that can be used for construction of electrically safe systems.

A resonant DC link inverter with low-noise and high-output power

A resonant DC link inverter that provides high efficiency with low noise for uninterruptible power supplies has been developed. This paper describes the noise radiation, efficiency, and output voltage characteristics of a prototype resonant DC link inverter. It has 300 V DC input, and 200 V (1/spl phi/) and 10 kVA AC output. The noise radiation level meets the CISPR Pub. 22 standard and its efficiency and output voltage characteristics make it usable for practical applications.<<ETX>>

Improving Input Current Waveforms in a Switching Mode Rectifier with a High Frequency Transformer

In recent years, switching mode rectifiers (SMRs) which are composed of a capacitor input type rectifier and a DC-DC converter have been used to supply DC power to various electronic systems. Despite their desirable features such as small-size, light-weight, and high-efficiency, there is a disadvantage in that their input current waveforms include many harmonic components, which could severely influence other systems that AC power lines in common with the SMR. Conventional method to improve the waveforms uses bidirectional switch modules or three full bridge conversion circuits. However, this method cannot decrease the size, because the number of the switching devices increase.To solve this problem, a novel SMR with a high frequency transformer has been studied. In it, input 3-phase AC voltage is directly converted into high frequency AC, then rectified. Futhermore, low order harmonics in the input current waveforms can be eliminated by controlling the conduction intervals of switches, proportional to the instantaneous input line to line voltage.This paper describes the configuration of the novel SMR and its operating principle for obtaining sinusoidal input current waveforms as well as discusses the distortion factor characteristics of the input current waveforms.