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We attempted to evaluate a 400 VDC appliance coupler by performing a test with the inrush current and test circuit defined in IEC TS 62735-1, an international standard covering plugs and socket-outlets for 400 VDC appliance couplers published in 2015 [1]. However, we were unable to obtain the specified inrush current waveform with a test circuit constructed according to the specification. We identified problems in the specified test circuit and analytically determined a method for approximating the specified inrush current waveform with an actual test circuit. Specifically, we used circuit simulator to reproduce the parasitic capacitance and equivalent series resistance of the circuit wiring and components and analyzed their parameter sensitivity. The result was a more accurate reproduction of the specified inrush current waveform with an actual test circuit that produced good results when used to test a 400 VDC appliance coupler.

The basic characteristics of a 400 VDC appliance coupler for use in the power input module of ICT equipment in data centers and similar facilities are reported. When ICT equipment is powered at 400 VDC, the electrical characteristics differ from when conventional AC power is used and greater safety considerations are required. To maintain safety, the appliance coupler used in this evaluation is equipped with an arc extinguishing function that uses a permanent magnet. Other concerns when DC power is used include the need for evaluation of specifications for control of the temperature rise when voltage is increased and current interrupt when a circuit is opened. Without products that have an arc extinguishing function or standards for a 400 VDC appliance coupler, there were no clear criteria to be used for evaluation of safety. We therefore evaluated the 400 VDC appliance coupler with reference to the IEC standards related to plugs and socket-outlets. Temperature tests showed that the temperature increase was 45 K or less when a current of 15 A was applied to the appliance coupler for one hour. The current breaking test showed that was possible to interrupt the current normally and no abnormality of the internal contacts was seen after 5000 insertions and extractions under a current of 12 A and supplied voltage of 400 VDC with a resistance load connected.

To promote the widespread use of HVDC power supply systems, this paper proposes high-efficiency downsized power conversion (380 V to −48 V) equipment for HVDC use having a size small enough for mounting in the dead space of a rack and describes its performance. Configuring 380 V/−48 V conversion equipment with existing technology lowers the efficiency of the entire power supply system and increases the installation area. To solve these problems, it has become necessary to develop equipment with an efficiency of 97 % or greater and with dimensions (W43 × H400 × D80 mm) small enough for mounting in the dead space of a rack. To this end, we have achieved high efficiency and small size by adopting a circuit configuration that uses a compact, high-efficiency chip converter as used on motherboards in ICT equipment and that disconnects the voltage step-up circuit during normal operation. However, a chip converter incorporated in a power supply system may not necessarily operate in a stable manner. To achieve stable use, we performed a stability evaluation while establishing and verifying input/output conditions and taking chip-converter control characteristics into account. We used the results of this evaluation to equip the equipment with the necessary measures to ensure stability.

A new power supply topology is proposed for using various types of power supply systems together in data centers and telecom buildings. In this topology, the power supply chain from the building power receiving point to the IC chips in the ICT equipment is organized into blocks to simplify the number of DC bus conversion steps. Two types of voltage for the DC bus are proposed; 380 V and 48 V. This topology is expected to enable the design of power supply systems that are highly efficient, highly reliable, and less expensive and that can be flexibly applied in buildings that are large or small according to reliability requirements.