Kefu Liu

A repetitive high voltage pulse adder based on solid state switches

A repetitive high voltage pulse modulator based on solid state switches with insolated recharge is described. All capacitors in the modulator are recharged by a corresponding transformer separately through magnetic core transformers by a common high frequency power supply. This configuration simplifies the isolation design and arrangement. This scheme is suitable for work at high repetitive rate discharge due to its high charge efficiency. At the same time it retains the inherent switch protection capability of a solid-state Marx modulator. In our present work, a 22-stage test modulator has been built and has been successfully operated at repetitive rate of 20kHz, output voltage of 20kV, rise time of 150ns and pulse width of 3μs. The primary experiments verified the system feasibility. A system with higher parameters is under way.

All-Solid-State Repetitive Pulsed-Power Generator Using IGBT and Magnetic Compression Switches

By utilizing power semiconductor switches, especially high-voltage insulated gate bipolar transistors (IGBTs), as main switches, Marx modulators have demonstrated many advantages such as variable pulse length and pulse-repetition frequency, snubberless operation, and inherent redundancy. However, the relatively slow turn-on speed of the IGBT influences the pulse rise time of the Marx modulator. In this paper, a newly developed all-solid-state pulsed-power generator is proposed. This generator consists of a Marx modulator based on discrete IGBTs and a magnetic pulse-sharpening circuit, which is employed to compress the rising edge of the Marx output pulse. The experimental results are presented with a maximum voltage of 20 kV, a rise time of 200 ns, a pulse duration of 500 ns (full-width at half-maximum), and a repetition rate of 5 kHz on a 285- resistive load. The output power of the generator is 2.5 kW, and the average power in one pulse is 1 MW. The design methods of the IGBT drive circuits and the parameter calculation of the magnetic pulse-sharpening circuit are introduced in detail in this paper. The factors influencing the performance of the generator are also discussed.

All-solid-state pulse adder with bipolar high voltage fast narrow pulses output

A newly developed bipolar high voltage adder is proposed for generating fast narrow pulses. The new circuit topology enables the use of typical half-bridge semiconductor structures on the basis of conventional unipolar all-solid-state pulse adder. Magnetic ring transformers were employed for isolating the charge loop from the high-voltage pulse discharge loop, which simplified the isolation arrangement. Certain measures were implemented to resolve the EMI caused by the pulse adder arrangement. A laboratory prototype was assembled with 8 stages and each stage was made of 800 V MOSFETs. The modulator operating at 21 kHz repetition rate gives 2 kV bipolar pulses, with 200 ns positive/negative pulse widths, 37 ns rise time, 50 ns fall time, and 40 ns relaxation time into a 50 Ω resistive load. The adopted design is an all-solid-state approach with a simple control method, long maintenance-free lifetime, and high reliability.

Microstructure and properties of aging Cu–Cr–Zr alloy

The crystallography and morphology of precipitate particles in a Cu matrix were studied using an aged Cu–Cr–Zr alloy by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The tensile strength and electrical conductivity of this alloy after various aging processes were tested. The results show that two kinds of crystallographic structure associated with chromium-rich phases, fcc and bcc structure, exist in the peak-aging of the alloy. The orientation relationship between bcc Cr precipitate and the matrix exhibits Nishiyama–Wasserman orientation relationship. Two kinds of Zr-rich phases (Cu4Zr and Cu5Zr) can be identified and the habit plane is parallel to {111}Cu plane during the aging. The increase in strength is ascribed to the precipitation of Cr- and Zr-rich phase.

A Pulsed Power Supply Based on Power Semiconductor Switches and Transmission Line Transformer

Transmission line transformers (TLTs) as pulse transformers have received increasingly more attention due to their excellent frequency response characteristics over conventional wound transformers. This transformer basically consists of equal lengths of transmission line (normally coaxial cables are used) connected in parallel at the input side of the transformer, and in series at the output side so that the output voltage can be boosted in proportion. Because the reactance of the outer conductor increases with the rise of the frequency of the input voltage, the output voltage of each transmission line can be isolated mutually when the frequency is high enough. Then, the output voltage will be amplified through the voltage superposition. To minimize the substantial loss of voltage gain and obtain a low pulse droop rate, one stage transformer is entwined together as a unit, the number of stages of the transformer can increase easily by piling units one by one. This spiral construction makes the transmission line transformers much more compact. On the other hand, with the development of modern semiconductor technology, high voltage, fast rise time power semiconductor devices have been produced, the collector emitter breakdown voltage of one IGBT is to 1.7 kV and the rise time is 100 ns. This paper describes a kind of compact pulse power supply constructed by combining transmission line transformer and modern power semiconductor devices-IGBTs. High voltage IGBTs (VCES=1.7 kV) have been used as charge switches, short pulses can be obtained at the input port of the transformer, then the output pulse amplitude is 10 kV through a 10-stage transmission line transformer. Finally, the output voltage pulse waveforms are given in the paper.

A Novel All Solid-State Sub-Microsecond Pulse Generator for Dielectric Barrier Discharges

This paper presents the design for a novel all solid-state sub-microsecond pulse generator for dielectric barrier discharges (DBDs). This generator consists of a MARX generator, Blumlein transmission lines (BTLs) and one magnetic switch (MS). As a power supply, the all solid-state MARX generator is capable of outputting nanosecond-pulses with a voltage peak of up to 20 KV. The key elements are BTLs which are charged by the MARX generator. Due to the unmatched impedance of DBD load, energy stored in BTLs begins to oscillate through DBD load after the MS turns on. The violent oscillation lasts until all the energy is consumed. During the violent oscillation, over ten discharges are excited in 5 μs under a single-shot condition. Thus, extremely intense plasma can be produced due to the accumulation effect. The alternating-current decaying voltage over the MS has a demagnetization effect, and DC reset circuit can therefore be spared. Experiments with matched resistor load were also carried out, and rectangular pulses with voltage up to 20 kV and duration of 220 ns were obtained. The ratio of the energy consumed by the resistor from the energy stored in the BTLs is 84.9%. The DBD images under a single shot and 100 Hz are presented.

An all solid-state pulsed power generator based on Marx generator

High voltage pulsed power supply with high repetitive rate has found wide applications in industry, and military such as plasma source for ion implantation, microwave generator and high pulsed power laser. The conventional pulsed power supply is limited by gas switch with short lifetime and low repetitive frequency. In recent years Marx generator based on solid state switches has proposed. It has dual functions by combining high repetitive rate from semiconductor switch with voltage adder from Marx generator principle. The solid state switches can be MOSFET , IGBT or SCR. This all-solid-state pulsed power supply has multifold advantages such as flexibility of pulse voltage amplitude, pulse width and repetitive rate and long lifetime and compactness.

All solid-state pulsed power generator with semiconductor and magnetic compression switches

Conventional pulsed power sources using gas switches suffer from short lifetime, low PRF and expensive maintenance cost. Many all solid-state generator topologies have been developed to replace them. Marx modulator utilizing IGBTs as main switches has many advantages, such as variable pulse length and PRF, snubberless operation, inherent redundancy. However, the relatively slow turn-on speed of IGBT influences the pulse rise time of the Marx modulator. In this paper, a newly developed all solid-state pulsed power generator is proposed. This generator consists of a Marx modulator based on IGBT half bridge modules and a magnetic pulse sharpening circuit, which is employed to compress the rising edge of the Marx output pulse. The pulse sharpening circuit is composed of two magnetic compression switches and one peaking capacitor. The experimental results demonstrated the effectiveness of pulse sharpening. The design of IGBT drive circuits and magnetic switches is introduced in detail in this paper.

High-voltage pulse waveform modulator based on solid-state Marx generator

Many research fields need special high-voltage pulses in pulsed power applications, which are different from typical rectangular pulses. In this paper, a high-voltage waveform modulator of two methods using a solid-state Marx generator has been developed and tested. Instead of manufacturing a generator with a specialized structure, the modulator can control a general Marx generator by low-voltage programmable logic devices to produce an irregular but controllable high-voltage triangular pulse with pulse length of ~4.5 μs and peak voltage of ~123 kV.

Repetitive high voltage rectangular waveform pulse adder for pulsed discharge of capacitive load

When connected to capacitive loads, pulses with steep falling edge are hardly obtained by using conventional pulsed power modulators, which also leads them not suitable for operation at high repetitive frequency. In this paper, a repetitive high voltage pulse adder is described, which can generate rectangular pulses even with capacitive loads. This pulse adder is based on solid-state switches, and each power stage contains two MOSFETs: one of them outputs high voltage pulses and the other is used to dissipate charges stored in load and distributed capacitor. Testing the proposed pulse adder with dielectric barrier discharge (DBD) load, nearly rectangular pulses are obtained. In our present work, a 40-stage modulator has been built and successfully operates at output voltage of 30 kV, repetitive frequency of 20 kHz, both rise time and fall time less than 250 ns, and minimum pulse width of 6 us. This prototype has been applied to DBD experiment research.