Hongfa Ding

An Analytical Steady-State Model of LCC type Series–Parallel Resonant Converter With Capacitive Output Filter

A piecewise analytical function is proposed and applied to investigate the steady-state behavior of series-parallel resonant converter operated in a discontinuous current mode. The converter shows two sequences of the equivalent circuits alternatively operated in the discontinuous current mode with different output voltages. To get the response time of current in one resonance, a successive solving process based on the state-space method is presented analytically in each sequence. This solving process can describe the complicated behavior resulting from the load rectifier, which makes the output capacitor appear or disappear several times in one switching period. By introducing the output voltage coefficient and the principle of energy transmission balance, the steady-state model is deduced afterward. This model is accurate and simple, making it helpful to design and optimize the converter conveniently. An excellent agreement is obtained when comparing numerical values calculated by the proposed model to the simulation and to the experimental results.

The Pulsed High Magnetic Field Facility at HUST, Wuhan, China and Associated Magnets

A pulsed high magnetic field laboratory has been funded to be established at the Huazhong University of Science and Technology (HUST), Wuhan, China by the National Development and Reform Committee. The facility is planned to be open for external users in 2011 with the implementation of various experimental techniques in pulsed magnetic fields up to 80 T. Pulse durations are in the range from 15 to 1000 ms with the magnet bore sizes from 12 to 34 mm. The pulsed power supplies are a 12 MJ, 25 kV capacitor bank and a 100 MVA/100 MJ flywheel pulse generator. The design and analysis of the power supplies and the magnets of short and long pulse durations and the multi-stage pulsed magnets with controllable waveforms are presented in this paper.

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. >

Design and Experiments of a High Field Electromagnetic Forming System

The concept of capacity coefficient is introduced to evaluate the processing capacity of electromagnetic forming (EMF). An EMF system design method, including capacity coefficient design, inductance design and strength design, is developed by a finite element method. The geometry and size of the driving coil are optimized by the capacity coefficient design. The inductance design is aimed at obtaining a reasonable pulse width of EMF. Finally, the strength design of the driving coil is presented with respect to the reinforcement. With this design method, a high strength driving coil is designed and wound. The height, inner radius, and outer radius of the driving coil are 25 mm, 5 mm, and 50 mm respectively. The number of turns is 40, resulting in reasonable pulse width of 380 . Experiments with different driving coils and pulse width were carried out. The results show that the processing capability of EMF is improved due to the high strength driving coil.

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.

Study on a Highly Stabilized Pulsed Power Supply for High Magnetic Fields

This paper proposes a pulsed power supply scheme to generate highly stabilized high magnetic fields (ripple less than 10 ppm), which are needed for some kinds of scientific experiments (such as the nuclear magnetic resonance experiment). The power supply presented in this paper consists of a large-capacity pulse-forming network (PFN) power supply and a small-capacity power electronics power supply (PEPS). The PFN provides a background field, and the PEPS compensates for the flattop of the background field to get a highly stabilized magnetic field.

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.