Jiangtao Li

Theoretical Analysis and Experimental Study on an Avalanche Transistor-Based Marx Generator

High-voltage, nanosecond, high-repetitive-frequency, and portable pulse generators are always required in many fields. Avalanche transistor-based Marx circuits have been widely studied to generate pulses satisfying the above requirements. However, the basic topology of an avalanche transistor-based circuit, configuration of circuit parameters, and optimal working performance (including output impedance matching) were still scarcely discussed. In this paper, the detailed process of analyzing and designing a compact Marx generator using avalanche transistors was described. Based on the conventional principles of avalanche transistors and Marx circuit, a list of useful and interesting conclusions was discovered by experiment. An example with specific parameter requirements was utilized for the clearness of illustration. The 12 cm × 4 cm Marx circuit could finally generate pulses with a 2.5-kV amplitude, 6.0-ns width, 10-kHz repetitive frequency, lower than a 100-ps jitter and ~125-kW maximum peak output power on a matched 50-Ω resistive load. The pulse amplitude could be adjusted from 1.5 to 2.5 kV and the pulse width could also be broadened. This paper may help to provide a reference to similar methods of producing high-voltage, nanosecond, and high-repetitive-frequency pulses.

Study on the Simplified Distributed Parameter Model for HTS Cables

Nowadays, the power demand has been dramatically rising in highly populated load areas. The high-temperature superconductor (HTS) cables are one possible solution for the electricity transmission due to their high transmission capacity and tremendously lower electrical loss compared with traditional power cables. A comprehensive and accurate model is very important to predict the working condition prediction for the purpose of power flow control, relay protection and overvoltage protection, especially for HTS cable which is highly expensive and lacking of operation experience. In this paper, a simplified analytical model of HTS cable is presented to further facilitate operating condition simulations. The inductances are derived and the result is verified with FEM software COMSOL. The self-, mutual inductances, capacitances between each layer are calculated to build the parameter matrixes. By appropriate transformation, electrical parameter matrixes can be converted into simplified PI sections. A simple simulation model for power system containing HTS cable can be built up by using EMTP-ATP program. The instructive guide for protection systems for HTS cables may be provided according to the simulation results. The simplified distributed parameters model described in the paper is also helpful for structure optimization to obtain uniform current distribution in superconductor layers.

Double Butterfly Coil for Transcranial Magnetic Stimulation Aiming at Improving Focality

It is important to improve the focality of the transcranial magnetic stimulation coil in order to minimize the undesired effects when the induced electric field exceeds the excitation threshold of the nontarget tissues. In this paper, a new double-butterfly coil was proposed and a simulation model as well as an experimental setup was developed to validate the performance of the new stimulation coil. Focality of the double-butterfly coil was compared with that of the butterfly coil via both simulation and experiment method. It is showed that the focality of the proposed coil has better focality than the butterfly coil. The effects of structural parameters on the focality performance of the induced electrical field were carefully studied.

Pulsed Power Regulation in Selective Passively Compensated Pulsed Alternator

The selective passively compensated pulsed alternator has wide applications in military and civil areas such as power source for electromagnetic launch, electrothermal chemical gun and plasma sprayed coating. It can produce wide range of current waveforms realized by shorted compensating windings. In this paper, two cases of winding arrangements and their corresponding circuit models are presented to further discuss on the power waveform regulations. The effects of the phase angles between different windings and the switching time on the pulsed power are presented in this paper as well. The results indicate that the output power waveform is possible to be regulated flexibly especially through the new winding arrangements proposed in this paper. This work may extend the applications of selective passively compensated pulsed alternator where different output waveforms are required.

A hybrid pulse combining topology utilizing the combination of modularized avalanche transistor Marx circuits, direct pulse adding, and transmission line transformer

Numerous applications driven by pulsed voltage require pulses to be with high amplitude, high repetitive frequency, and narrow width, which could be satisfied by utilizing avalanche transistors. The output improvement is severely limited by power capacities of transistors. Pulse combining is an effective approach to increase the output amplitude while still adopting conventional pulse generating modules. However, there are drawbacks in traditional topologies including the saturation tendency of combining efficiency and waveform oscillation. In this paper, a hybrid pulse combining topology was adopted utilizing the combination of modularized avalanche transistor Marx circuits, direct pulse adding, and transmission line transformer. The factors affecting the combining efficiency were determined including the output time synchronization of Marx circuits, and the quantity and position of magnetic cores. The numbers of the parallel modules and the stages were determined by the output characteristics of each combining method. Experimental results illustrated the ability of generating pulses with 2-14 kV amplitude, 7-11 ns width, and a maximum 10 kHz repetitive rate on a matched 50-300 Ω resistive load. The hybrid topology would be a convinced pulse combining method for similar nanosecond pulse generators based on the solid-state switches.

Development of a stereo-symmetrical nanosecond pulsed power generator composed of modularized avalanche transistor Marx circuits

Avalanche transistors have been widely studied and used in nanosecond high voltage pulse generations. However, output power improvement is always limited by the low thermal capacities of avalanche transistors, especially under high repetitive working frequency. Parallel stacked transistors can effectively improve the output current but the controlling of trigger and output synchronism has always been a hard and complex work. In this paper, a novel stereo-symmetrical nanosecond pulsed power generator with high reliability was developed. By analyzing and testing the special performances of the combined Marx circuits, numbers of meaningful conclusions on the pulse amplitude, pulse back edge, and output impedance were drawn. The combining synchronism of the generator was confirmed excellent and lower conducting current through the transistors was realized. Experimental results showed that, on a 50 Ω resistive load, pulses with 1.5-5.2 kV amplitude and 5.3-14.0 ns width could be flexibly generated by adjusting the number of combined modules, the supply voltage, and the module type.

Functional Magnetic Stimulation System and Pulsed Magnetic-Field Effect on Peripheral Nerve

This paper studies a pulsed magnetic-field generator which provides a noncontact way for functional nerve stimulation. Each component of the device, such as charging circuit, discharging circuit, and control circuit, is described in detail. The feasibility of the device is verified by simulation and experiments. The magnetic field and the induced electric field are produced by a figure-8 coil under excitation of pulsed discharging current. According to the Schwarz model, the action potentials of nerve fiber are simulated, and the neural dynamic response is predicted.

A distributed parameter model of transmission line transformer for high voltage nanosecond pulse generation

A transmission line transformer has potential advantages for nanosecond pulse generation including excellent frequency response and no leakage inductance. The wave propagation process in a secondary mode line is indispensable due to an obvious inside transient electromagnetic transition in this scenario. The equivalent model of the transmission line transformer is crucial for predicting the output waveform and evaluating the effects of magnetic cores on output performance. However, traditional lumped parameter models are not sufficient for nanosecond pulse generation due to the natural neglect of wave propagations in secondary mode lines based on a lumped parameter assumption. In this paper, a distributed parameter model of transmission line transformer was established to investigate wave propagation in the secondary mode line and its influential factors through theoretical analysis and experimental verification. The wave propagation discontinuity in the secondary mode line induced by magnetic cores is emphasized. Characteristics of the magnetic core under a nanosecond pulse were obtained by experiments. Distribution and formation of the secondary mode current were determined for revealing essential wave propagation processes in secondary mode lines. The output waveform and efficiency were found to be affected dramatically by wave propagation discontinuity in secondary mode lines induced by magnetic cores. The proposed distributed parameter model was proved more suitable for nanosecond pulse generation in aspects of secondary mode current, output efficiency, and output waveform. In depth, comprehension of underlying mechanisms and a broader view of the working principle of the transmission line transformer for nanosecond pulse generation can be obtained through this research.

Flexible multichannel transcranial magnetic stimulation coil array

Transcranial magnetic stimulation devices have been widely used for clinic and research purpose, and the design of coils is important for field distribution, focality and target locating. Nowadays, multichannel TMS coil become a research hotspot for its better performance than single coil. In this paper, several coil array types were studied, and their flexible working pattern make it easily to adapt various applications. Focaliy of some working patterns was found higher than single coils.

Novel remanence detection for power transformers based on modified J-A model

This paper proposes a novel remanence detection method for power transformers based on the modified Jiles-Atherton model. The residual flux can be determined accurately by inputting the same sources in DC tests to our simulation model. The value of remanence could be seen as the intercept on B axis of demagnetization curve in our Simulink model, and its polarity could be obtained by the current direction based on right-hand rule. The relative error of this detection method will not exceed 6.8% compared to experimental data.