Tatsuya Matsukawa

Application of parallel connected power-MOSFET elements to high current d.c. power supply

The low aspect ratio spherical torus (ST), which has single turn toroidal field coil, requires the extremely high d.c. current like as 20 MA to energize the coil. Considering the ratings of such extremely high current and low voltage, power-MOSFET element is employed as the switching device for the a.c./d.c. converter of power supply. One of the advantages of power-MOSFET element is low on-state resistance, which is to meet the high current and low voltage operation. Recently, the capacity of power-MOSFET element has been increased and its on-state resistance has been decreased, so that the possibility of construction of high current and low voltage a.c./d.c. converter with parallel connected power-MOSFET elements has been growing. With the aim of developing the high current d.c. power supply using power-MOSFET, the basic characteristics of parallel operation with power-MOSFET elements are experimentally investigated. And, the synchronous rectifier type and the bi-directional self commutated type a.c./d.c. converters using parallel connected power-MOSFET elements are proposed.

Basic study on conductive characteristics of SiC power device for its application to AC/DC converter

Recently, the SiC-based power electronics device has been under development, which has more advanced electrical characteristics than conventional Si-based device. Main electrical characteristics of SiC-based power electronics device are high operational temperature, high withstanding voltage, low on-state resistance and fast switching frequency. Especially, forward voltage, including on-state resistance characteristics, is the important conductive feature on operational loss reduction of SiC-based power electronics device. To study SiC-based device experimentally, SiC-based Schottky barrier diode (SBD), as an example of SiC-based power electronics device, is examined on its temperature dependence of forward voltage in comparison with Si-based SBD. The application of SiC-based power electronics device to large capacity AC/DC converter is also discussed.

Low voltage, high current DC power supply with self commutated converter using power-MOSFET

The DC power supply for a nuclear fusion experimental system based on the low aspect ratio spherical torus requires a low voltage and high current output to power a toroidal field coil consisting of a single turn center conductor. To meet such requirements, the self-commutated converter using a power-MOSFET, which is more efficient than the conventional thyristor or diode converter, is proposed. The converter has the advantage of fast switching speed, low on-state resistance and voltage gate signal. The operating characteristics of a power-MOSFET and the switching unit using four MOSFET elements are also discussed.

Synchronous rectifier using power-MOSFET for high current AC/DC converter system

To supply high DC current to a single turn toroidal field coil of a spherical torus machine, it is an important engineering aspect that the operational losses should be minimized for the power supply system. As a switching element of an AC/DC converter, instead of a thyristor or diode, a power-MOSFET is a desirable component to be applied to a high current power supply system. The lowered resistance of parallel connected and pre-cooled power-MOSFET elements makes it possible to reduce the AC/DC converter power supply system losses. To output high DC current in one direction, the synchronous rectifier type AC/DC converter with parallel connected power-MOSFET elements is proposed as the power supply system for single turn toroidal field coil.

Application of SiC-based power element to high current AC/DC converter system

Abstract It is proposed that SiC-based power-MOSFET is applied to the high current AC/DC converter system. The possibility of using SiC-based power-MOSFET depends on operational loss reduction and circuit configuration simplification of the high current AC/DC converter system. Concerning the operational loss reduction, the lower on-state resistance of SiC-based power-MOSFET can decrease the conduction loss of switching unit, and it means that the temperature rise of switching unit in operation period is lowered. Therefore, the auxiliary cooling equipment for AC/DC converter will be minimized. The higher operational temperature of SiC-based power-MOSFET will allow also the cooling capacity minimization. As many parallel connected power-MOSFET elements are required for high current operation, the parallel connected elements should be cooled down to liquid nitrogen temperature for on-state resistance reduction.

Advanced application of power-MOSFET to large capacity converter

Advanced application of power-MOSFET to a large capacity novel converter system is studied. Parallel operation of many power-MOSFET elements is investigated in room and liquid nitrogen temperatures. The total on-state resistance shows lowered value in parallel connected and cooled down conditions, and the reduced resistance is effective for operational loss reduction of the converter circuit. The bi-directional switching unit with four power-MOSFET elements is proposed, which can be applied to the self commutated type AC/DC converter. Another type of AC/DC converter using power-MOSFET consists of a three phase synchronous rectifier circuit, which is suitable to output one directional high DC current.

Low Loss and Compact Grid Connecting Converter for Superconducting Magnet Using MERS

This paper proposes a new circuit topology for SMES (superconducting magnetic energy storage), which is based on a pulse link concept of two converters. A two quadrant dc chopper and a dc/ac converter connected via high frequency dc pulse link voltage. This concept has two advantages. All semi-conductor switches operate under soft-switching condition, which results in low loss generation and possibility to increase switching frequency. The other advantage is eliminating smoothing capacitor between two conversion stages. By these advantages, the proposed converter has possibility to achieve high efficiency and power density with rich controllability. This paper describes operation principles of the proposed converter. First experimental verification of this concept was conducted with small scale setup.

Application of Magnetic Energy Recovery Switch (MERS) to power supply systems of nuclear fusion device

Electric power circuits applied with Magnetic Energy Recovery Switch (MERS) are proposed to be used for power supply systems of nuclear fusion device. MERS basically consists of four self-commutated power electronics elements as switching unit and one capacitor. MERS can be operated with on-off switching of four power electronics elements by controlling their gate signals to output its electric power in DC or AC. As poloidal ield coil power supply, it is required that the coil current is slightly high DC one and controlled to sustain plasma current and/or configuration. When MERS assist the conventional AC/DC converter of poloidal field coil power supply, it is expected that the voltage rating of AC/DC converter would be reduced and the controllability of coil current would be also improved. As RWM (Resistive Wall Mode) suppressing coil power supply, it is required that the coil current should be pulsatile one in wide frequency range and controlled more rapidly to stabilize the plasma instability. When MERS is applied to RWM suppressing coil power supply, it will be promised that the controllability of coil current is improved with resonant operation of MERS and RWM suppressing coil itself.

Operational loss reduction using power-MOSFET for magnetic field coil power supplies of nuclear fusion experimental machine

To meet the requirement of supplying extremely high DC current to the magnetic field coil of nuclear fusion experimental machine, the AC/DC converter system of power supplies should be designed to reduce the operational loss. An attractive power electronics element of power-MOSFET has the advantage of low on state resistance, and is suitable as the switching device for low voltage and high current AC/DC converter. To make the on state resistance of power-MOSFET lower for loss reduction, the static and DC characteristics of on-state resistance are investigated in the conditions of pre-cooled down temperature and in parallel connection for power-MOSFET.

Conceptual design of SMES system equipped for IPP plant

The superconducting magnetic energy storage system (SMES) has been studied on its advantages over another type of energy storage system. Considering the advantages of SMES, it is recognized that SMES is one of the advanced energy storage systems for future power plants. In this paper, a SMES system equipped for an independent power producer (IPP) power plant is proposed and the operational scenario of the total plant is discussed. Also, some types of SMES coil for this study are designed in size or other parameters and the quantitative comparison among them is mentioned.