Bongseong Kim

Active Clamping Circuit to Suppress Switching Stress on a MOS-Gate-Structure-Based Power Semiconductor for Pulsed-Power Applications

Metal-oxide-silicon (MOS)-gate-structure-based power semiconductors, such as MOS field-effect transistors, insulated-gate bipolar transistors, and MOS controlled thyristors, are widely used as high-voltage switch and power modulator components in pulsed-power applications. The power semiconductors are generally connected in series and in parallel in order to increase their maximum switching voltage and current, respectively. It is important to suppress overvoltage or switching stress on power semiconductors connected in series and parallel during an extremely short switching time and at fast operating frequency. Generally, gate drive control techniques and methods for the suppression of high voltage are required. To suppress overvoltage and switching stress, this paper proposes a simple and effective active clamping method rather than the use of a snubber circuit with free switching condition modulation. Based on comparative switching experiments, the active clamping method is expected to suppress switching stress and overvoltage while load and switching conditions are changed without modification of the high-side auxiliary circuit for pulsed-power applications.

Optimal design of an elliptically graded permittivity spacer configuration in gas insulated switchgear

A functionally graded material (FGM) was investigated for use as an insulator in high voltage applications. The FGM was able to relax the electric field concentration around a high voltage electrode and along the gas-insulator surface. The FGM spacer, the permittivity of which was gradually changed, exhibited a considerable reduction in the maximum electric field when compared to a conventional spacer with a uniform permittivity. It is difficult to apply a gradual permittivity variation in the FGM spacer to real product processing due to its complicated shape. Thus, in this work, the electrode shape in the gas insulated switchgear was changed in order to increase the possibility of real FGM insulator manufacturing. To achieve this goal, optimization processes were used to modify the shape of both the electrode and the FGM spacer on a commercial gas insulated switchgear configuration. Especially, a modification of the spacer configuration was performed with the design of experiments (DOE). Consequently, the insulation capability of the switchgear with the optimally designed FGM spacer can be efficiently improved.

Study of Switching Characteristics of Static Induction Thyristor for Pulsed Power Applications

It is difficult to design a standard gate driver for optimal switching control of a static induction thyristor (SI-Thy) because of its unique internal structure and the direct commutation switching characteristic between the gate and cathode terminals during the transient turn-on and turn-off switching phases. Therefore, it is important to develop a simple and effective gate driver for achieving optimal fast turn-on and stable switching operations in an SI-Thy under hard-switching conditions. To achieve faster turn-on switching time with shorter gate delay time, impedance matching between the SI-Thy and the turn-on driving circuit component in the gate driver can be realized with additional circuit modification through this paper. To ensure higher stabilities in the turn-off switching phase, forced commutation techniques and additional auxiliary circuits in the gate driver have been devised to suppress the latchup and to eliminate potential ringing possibility. We have demonstrated that our designed and tested gate driver for realizing optimal switching characteristics of an SI-Thy is effective, particularly in the gate driving circuits for various pulsed-power switching applications.

Considerations on the DBD power supply for surface change of ozone reactor

It has been noticed that dielectric barrier discharging (DBD) has great potential as an ozone radical and light source in the medical and environmental industries. However, due to its operating pressure and the need for a sealed reactor to ensure its safety, it is impossible to measure its electrical characteristics in direct. First, it is preceded by an electrical modeling of the planer types of the DBD reactor using the 2-port circuit analysis method with a DBD discharging mechanism to estimate the electrical characteristics of the DBD reactor. Through the modeling of the DBD reactor, two types of power supplies are analyzed in order to achieve the high efficiency required to indicate impedance matching with the DBD reactor.

Investigation of simple graded permittivity solid spacer shape by electrode modification on gas insulated switchgear

It was investigated and proved that the Functionally Graded Material (FGM) as an insulation material for high voltage applications are able to relax the electric field concentration around the high voltage electrode and along the gas-insulator surface. Based on the previous numerical analysis, it was proved that the FGM spacer, which permittivity has gradually changed, with the modification of a spacer configuration by the Design of Experiment (DOE) showed considerable maximum electric field reduction in comparison with a conventional spacer which has uniform permittivity. However, it is hard to apply a gradual permittivity variation in the FGM spacer for a real product processing due to its complicated shape. Thus, through this paper, it is proceeded to change the electrode shape in the gas insulated switchgear in order to increase the possibility of real FGM insulator manufacturing. To achieve the goal, the optimization processes are used to modify the both shape of electrode and FGM spacer on a commercial gas insulated switchgear configuration. Consequently, the insulation capability of the switchgear with the optimally designed FGM spacer can be efficiently improved.

The Design of a Power Supply for Planer Type of the Dielectric Barrier Discharge Ozone Reactor with Impedance Matching

Dielectric Barrier Discharge (DBD) reactor with sinsodual AC type of power supply is very widely adopted for its compact size and effective discharging mechanism to generate high density of ozone radicals. However, at the aspect of design on power supply, its optimal switching conditions and topology is achieved by empirical test. Therefore, throughout this paper, it is proposed a design method of DBD power supply to guarantee a maximum ozone yield rate in accordance with DBD reactor modification and impedance variation when rapid gas discharging in the DBD reactor is proceeded.

An active voltage clamping method on series connected power semiconductors for pulsed hard switching application

There are commonly and widely used snubber, voltage clamping, and gate control circuit in series connection of IGBTs (Insulated Gate Bipolar Transistor) to relieve switching stresses induced by unbalanced voltage sharing in each of the IGBTs and overvoltage while that are occurred by rapid load condition varying, stray inductance, and delayed switching behavior in the power semiconductor switches. Due to easy design with simple structure and effective characteristics to suppress overvotage in the IGBTs, snubber circuit is preferred. But, high voltage switch that is composed by series connected IGBTs with snubber circuit has limitation in switching condition such as load condition, pulse duration, and operating frequency because capacitor of the snubber circuit is fixed and has to change its capacitance in proportion to operating frequency with pulse duration. Thus, focus of this paper is introducing newly designed active voltage clamping control method with passive network that consists of passive network circuit that is similar to the snubber circuit, BJT, and capacitor which is connected to the BJT to overcome shortcomings of the snubber circuit in narrow modulation of operation frequency and pulse duration in the series connected IGBTs.

The optimal design and comparison of power supply for dielectric barrier discharge ozone reactor

It has been noticed that Dielectric Barrier Discharging (DBD) has a great potential as ozone radical and light source in medical and environmental industry. But, due to its operating pressure, it is impossible to measure its electrical characteristics in direct. For the first step, it is proceeded electrical modeling of planer types of DBD reactor by using 2-port circuit analysis method with DBD discharging mechanism to estimate the electrical characteristics of DBD reactor. Through the modeling of DBD reactor, 2 types of power supplies of the DBD reactor for achieving high efficient that indicates impedance matching with DBD reactor are analyzed.

An implementation and switching characteristics comparison of power semiconductor based Marx generator using by SI-Thyristor and IGBT

An employment of power semiconductor switch on the pulsed power applications becomes a reasonable due to its faster repetitive operating frequency, semi-permanent life, good reliability, and simple switching control by low signal modulation. Especially, at hard switching condition on the pulsed power application, series connection control methods of power semiconductor are generally preferred. However, in a certain case of pulse power application such as IEC (Inertial Electrostatic Confinement), high voltage switch that is composed of series connected power semiconductor has possibility to be unstable because of rapid impedance change on the reactor. Thus, we studied switching characteristics of Marx generator using by IGBT and SI-Thyristor. The Marx generator used IGBT was constructed and experimented. And SI-Thyristor driving circuit was designed and tested.

Optimal design of a grid cathode structure in Spherically Convergent Beam Fusion device by response surface methodology combined with experimental design

To apply fusion energy through a spherically convergent beam fusion (SCBF) device as a portable neutron source, neutron production is very important. The rate of production is greatly dependent upon the ion current, which is closely related to the potential-well structure within a grid cathode. In this paper, we propose a design method by varying the cathode-ring sizes to produce an optimal grid-cathode structure in an SCBF device. The optimization is based on response-surface methodology (RSM); however, full factorial design is also applied to increase the precision of optimization and reduce experiment iteration in the application of RSM. The finite-element method, combined with the flux-corrected transport algorithm, is employed to calculate the ion current. From the optimized model, a higher ion current is calculated, resulting in a deeper potential well.