Tonghai Ding

Design of a 135 MW Power Supply for a 50 T Pulsed Magnet

The National High Magnetic Field Laboratory at Los Alamos designs a magnet that produces magnetic fields of up to 60 T for as long as 100 ms. The power and energy to operate the magnet is provided by a 1430 MVA, 24 kV energy storage generator. Three modular design power supplies convert the AC-power produced by the generator into controlled DC-power needed by the three coil groups of the eight coil magnet. The modules are rated at 4 kV no-load voltage and 20 kA full-load current for up to 2 seconds once every hour, each including a 12-pulse, line-commutated rectifier designed to operate in the 66 Hz to 42 Hz pulse operation range of the generator. A short description of the overall 60 T/100 ms magnet system is given, followed by a detailed description of the the power converter system design. >

A 35 kA Disc-Shaped Thyristor DC Switch for Batteries Power Supply of Flat-Top Pulsed Magnetic Field

A 35 kA thyristor DC switch which consists of 8 paralleled high power thyristors installed in a disc-shaped aluminum bus to get a symmetrical structure is developed in order to meet the requirement of the DC power supply using lead-acid batteries in pulsed magnetic field with maximum flat-top current 35 kA, pulse width 1 s. This thyristor DC switch will be turned on at the beginning of experiment, and turned off by forced commutation technology which uses charged capacitors to output inverse current to extinguish the current of thyristor switch at the end. Every branch of 8 thyristors is in series with a stainless steel resistor 1.4 and a fast-fuse to achieve parallel current sharing and overload protection of the thyristors. The detail design of the thyristor switch is described and the validity of this design is proved by simulation using MATLAB R2008a in consideration of the actual parameters of pulsed magnet with crowbar. At present the manufacturing and assembling of the switch has been completed, and primary short pulse test is finished. Finally the DC switch will be used in two-coil or three-coil 40 T/0.5 s flat-top pulsed magnet for some special science experiments by the end of 2012.

Prototype Test and Manufacture of a Modular 12.5 MJ Capacitive Pulsed Power Supply

A new Pulsed High Magnetic Field Facility (PHMFF) is under construction at the Huazhong University of Science and Technology (HUST) in Wuhan, China. In order to provide a wide spectrum range, a modular capacitive pulsed power supply is designed to energize 12.5 MJ at 25 kV and a large variety of coils are designed for magnetic fields in the 50-80 T with pulse duration 15-200 ms, respectively. In order to energize multi-coil systems, the 12.5 MJ power supply is divided into 11 independent 1 MJ modules with a short circuit current of 44.7 kA each and 2 independent 0.75 MJ modules for 61.2 kA each. Each module is provided with its own protection inductor, thyristor switch, crowbar circuit, dump circuit, polarity-changing circuit, charging unit and switchgear. The current pulses can be modified in shape, amplitude and duration by varying the charging voltage, the number of modules and the crowbar resistors. For verifying the design scheme and gaining experience in the construction and operation of pulsed power supply, a 1 MJ prototype that is used to energize pulsed magnets for 50-72 T fields with reversible polarity has been developed. In this paper, after the introduction of the system configuration with different module types and system settings, the design of both the 1 MJ and 0.75 MJ modules is described in detail. Finally, test results of the 1 MJ prototype are presented.

Development of a High-Stability Flat-Top Pulsed Magnetic Field Facility

A high stability flat-top pulsed magnetic field has both high field strength and high field stability simultaneously, which can be used for the high precision scientific experiments. In this paper, we present such a high stability flat-top pulsed magnetic field facility developed in the Wuhan National High Magnetic Field Center. A passive bypass circuit is developed to regulate current up to tens of thousands amperes, as well as a 25 T/200 ms flat-top pulsed magnetic field with a ripple of 250 ppm (0.025%). The main circuit scheme of the facility as well as the preliminary experimental results will be presented in this paper.

Short and Long Pulse High Magnetic Field Facility at the Wuhan National High Magnetic Field Center

The pulsed high magnetic field facility funded by the Chinese National Development and Reformation Committee has been developed at the Wuhan National High Magnetic Field Center (WHMFC). Magnets of short pulse, long pulse and the combination of both with bore sizes from 12 to 34 mm have been developed and are operational for electric transport, magnetization, magneto-optics and electron spin resonance at temperatures in the range from 100 mK to 350 K. The power supplies for these magnets consist of a capacitor bank with 12 modules of 1 MJ/25 kV each and 2 modules of 0.8 MJ/25 kV each, a 100 MVA/100 MJ flywheel pulse generator and a 771 V/180 kAh battery bank. A dual-coil magnet driven by the capacitor banks has successfully generated 86.3 T field with a total pulse duration over 350 ms in a 12-mm bore. A dual-coil long pulse magnet wound from soft copper wire energized by the flywheel generator produces 50 T peak field with a 100 ms flat-top and a total 1.1 s pulse duration in a 22 mm bore. A battery bank driven long pulse magnet composed by the series connection of two nested coils generates 32 T peak field with the pulse duration of 1.5 s in a 21-mm bore.

Design of Multipulse Power Supply for Small Pulsed High Magnetic Field Device

Three small pulsed high magnet field devices (SPHMF) which can continuously operate 20 times in rated power with different maximum magnetic field intensity from 10 T~40 T were developed in Wuhan High Magnet Field Center(WHMFC). The SPHMF systems are used to investigate the sterilization of fruit juice, magnetization of permanent magnet for wind power generator, some industrial applications and so on. The SPHMF consists of pulsed capacitor power supply, charger, control & measurement system, cryogenic system and pulsed magnet. These systems can accommodate sample room size from ¿12 mm to ¿18 mm and hold sample room in indoor temperature 300 K for different scientific researches and high magnetic field industrial applications. In this paper, power supply, magnet, control system and cryogenic system are presented. The total experiment results of SPHMF show that the devices are feasible, steady and reliable.

The Development of High Performance Pulsed Magnets of the Prototype Facility of WHMFC

Coils for pulsed magnets in the range of 50-75 T are developed with optimized combinations of conductors and reinforcement for the prototype laboratory of the Wuhan High Magnetic Field Center (WHMFC). The basic design tool is a Pulsed Magnet Design Software package (PMDS) for calculating the capacitor discharge, conductor heating, mechanical stresses and the residual stress, including plastic deformation and winding tension. A 1 MJ capacitor bank is equipped with a thyristor switch, a mechanical switch, polarity reversal switches, a current limiting inductor and a diode crowbar. The design and the test results of the magnets, of the protection inductance and of the capacitor bank are presented and discussed in this paper.

Design of a Novel Pulsed Power System for Repetitive Pulsed High Magnetic Fields

A repetitive pulsed high magnetic field is a useful tool for scientific research and industrial applications. In this paper, a novel repetitive pulsed power system (RPPS) adopted to generate repetitive pulsed high magnetic fields (RPHMF) at the Wuhan National High Magnetic Field Center (WHMFC) is designed. The capacitors serve as the energy storage elements in the pulsed power system, and the key issue of the RPHMF system is to decrease the loss and to charge the capacitors quickly, safely and efficiently. For this purpose, a new discharge topology is used to feed the energy stored in the magnet back to the capacitor by an additional choke coil and a resonant capacitor. The energy lost during each pulse will be replenished to the capacitor through a high frequency series-parallel resonant capacitor charging power supply (CCPS).

Fabrication and Test of a 40 T Long-Pulse Magnet Driven by Battery Bank

A 40 T long-pulse magnet has been constructed and tested to 32 T with total pulse width of 1.5 s at the Wuhan National High Magnetic Field Center (WHMFC). The magnet is energized by a battery bank power source consisting of 900 12 V/200 Ah lead-acid battery cells. The magnet consists of a polyhelix inner coil and an outer coil wound with copper foil. We made some improvements by adding axial slots on the helices due to the eddy current electromagnetic force, and each layer of helices is reinforced by Zylon-epoxy composite. The copper foil coil is insulated with polyimide film extending over the sides of the foil. The copper bar electrode is silver brazed on the ends of copper foil and has been proved to be quite feasible. In this paper, the calculated results of the electromagnetic force caused by eddy current will be presented. The magnet manufacture techniques will be described and the magnet test results will be listed and analyzed.

Analysis and Experiment of Battery Bank Power Supply System for Long Pulse Helical Magnet in WHMFC

Traditionally, pulse capacitor and pulse generator power supply are frequently used to energize pulse high magnet up to 100 T, but they are not the ideal power supply for long pulse and low ripple high magnetic field so that they cannot meet higher requirement of science research and wider application in industry. In Wuhan National High Magnetic Field Center (WHMFC), a new type power supply system which uses lead-acid batteries has been developed to output more energy and longer pulse than capacitor bank, and also output more steady voltage and smaller current ripple than pulse generator using ac/dc convertor. The battery power supply is a new application that valve-regulated lead-acid battery (VRLA) is used in high-rate discharge with pulse current 2 kA/2 s or peak 2.5 kA/1 s, and it is not unnecessary to analyze the changes of internal resistance and main factors which influence the battery life under the high current discharge. Based on the simulation analysis of the battery bank system, the structure and parameters including charge and discharge circuit of battery bank which can output maximum 35 kA/1 s under 770 V are designed. The tests of battery bank discharge, current sharing among the 15 parallel branches, and experiment of the helical magnet 32 T/1.5 s as battery bank outputs 34.5 kA/0.8 s are presented.