Young-Maan Cho

Charging-balancing circuit design of series-connected electric double-layer capacitors in high power applications

The high power source which is included Electric-Double Layer Capacitors (EDLC) has been configured to generate power higher than limited power. Rated voltage of EDLC has low maximum value thats why it must need series-connection in high power applications. When EDLCs are series-connected, each cell has an unbalance voltage by each tolerance. Unbalance phenomenon is one of the facts reducing their life expectancy. Balancing or equalization is much studied in past years, but it is mostly not for high power applications. Hence, charging-balancing circuit of series-connected EDLCs is designed to equalize each cell and module voltages in this paper. It is not only discussion of circuit behavior but EDLC modeling of equivalent circuit which is considered parasitic elements causing voltage unbalance. Proposed balancing circuit mitigates voltage unbalance of EDLCs, as a result of charging-balancing circuit verified with simulation. Through the results, EDLC could be utilized in high power applications such as pulsed power, prime power source, hybrid electric vehicle.

In-line circuit modeling for damage analysis of RF front end system affected by high power electromagnetic pulse

Output of microwave have been increased with development of pulsed power system. The risk of RF front end system is dramatically increasing as the output of high power electromagnetic (HPEM) pulse increases. There are largely two ways of coupling HPEM pulse: (i) Front door coupling, which is through antennas and sensors to receive signals (ii) Back-door coupling, which is through unintended way such as punctures and slots. Compared to back-door coupling, front-door coupling is more risky and hazardous since it is coupled with intended parts. The simulation studies of this problem are conducted by numerical method. However it takes too many times in computation. In this paper, the in-line circuit modeling for damage analysis of the RF front end system affected by HPEM pulse is proposed. This integrated circuit modeling is simulated by the Electro Magnetic Transient Program (EMTP). It is simulated from the output of the HPEM system to the RF front end system. The target RF system of the study is the antenna. Passive circuit elements are used to model for antenna efficiency, propagation attenuation and etc.

Adjustable circuit model of vircator according to its characteristics

A virtual cathode oscillator (vircator) is one of the most important microwave generators, because it has advantages in simple structure, giga-watt level power and low impedance. Because of these advantages, it is widely used in high power electromagnetic (HPEM) pulse applications. The main disadvantage of the vircator is its low efficiency and it is complemented by simulation studies. Many of simulation studies are conducted by numerical method. Considering the connection to the pulse power part, a circuit modeling is needed. In this paper, the adjustable circuit model of the vircator according to its characteristics is proposed. Through the circuit model of the vircator, HPEM system can be handled as an integrated system, which contains a prime power part, a pulsed power part, a microwave source part, and others. This circuit analysis is simulated by the electromagnetic transient program (EMTP). Passive elements and switch are used to model for space-charge limitation, absorptions, oscillation and etc, which are derived from simulation condition (structure, input power). The vircator emission in the air is represented by the load. This study is helpful to efficiency researches because circuit elements are derived by the simulation conditions.

Damage Modeling of a Low-Noise Amplifier in an RF Front-End Induced by a High Power Electromagnetic Pulse

The RF front-end is a very vulnerable part of the coupling paths that are induced by a high power electromagnetic (HPEM) pulse. Existing studies found through experiment or simulation that low-noise amplifiers (LNAs) often break down or are damaged, which causes the malfunction of the RF front-end. To protect the RF front-end, the damage process of LNAs based on theory is required in detail. This paper summarizes the damage process, and a new library is developed describing the damage phenomenon of LNAs by using user-defined elements. The model can be combined with other circuit models, and can also offer variation of the internal parameters of LNAs by HPEM pulse. Existing physical protection methods have high costs and complexity, and it is difficult to provide perfect protection. Thus, the proposed model can contribute to protection studies utilizing a circuit model.

Design for Compression Improvement of a Magnetic Pulse Compressor by Using a Multiwinding Magnetic Switch

In a magnetic pulse compressor (MPC), the saturation inductance of the magnetic switch (MS) determines the energy transfer time. Thus, in general, the number of windings on the MS is modulated to vary the saturation inductance. Changing the number of windings also changes the energy transfer time and the saturation time. In this paper, we propose and analyze an MS with multiwindings to modulate the pulse width without affecting the saturation time of the MS. The parallel structure of the multiwindings on the MS decreases the energy transfer time without affecting the saturation time. Through experiments, we show that the energy transfer time is decreased by 13% via a double winding MS. Therefore, an MS with multiwindings can be used to modulate the pulse width at the last stage of the MPC without affecting the saturation time of the MS.

A 25-F Electric Double-Layer Capacitor Bank and DC Power Supply for Portable High-Current Applications

A portable dc power supply based on electric double-layer capacitor (EDLC) bank was established for high-power applications. EDLC bank needs a dc–dc converter to maintain a constant output voltage and current. Especially, a low-impedance load makes the voltage of capacitors discharge faster, and their discharging time is determined by RC time constant. The proposed system is designed as a fundamental concept, and deals with some issues occurring in a large-scale system. Also, this paper provides detailed information and consideration for a real establishment. Last, we performed a full-scale experiment using basic techniques.

Experimental analysis on hazardness of RF front-end system damaged by high power electromagnetic pulse

The high power electromagnetic(HPEM) is one of the major issue on military area in several years. Contrary to other direct weapons, it is nonlethal weapon that destroy or deceive electronic device but minimize the harm to human1. Commonly, there are two coupling path of electronic device damaged by HPEM pulse. One is the front-door coupling and the other is the back-door coupling2. Due to the front-door coupling is induced a lot more power than the back-door coupling, it is difficult to protect perfectly. Thus it needs to study the damage prediction and the protection method of RF front-end system affected by HPEM pulse.

Effects of electron beam focusing on virtual cathode formation in virtual cathode oscillator

As a high power microwave (HPM) source, virtual cathode oscillator has been studied due to its simplicity. A lot of experiments on virtual cathode oscillator has been conducted and reported to study the characteristics and to increase its efficiency. In order to increase its efficiency, ballistic focusing of an electron diode has been studied. And it is reported that the efficiency of virtual cathode oscillator is somewhat increased through the ballistic focusing.

Circuit models for band pass filter of RF front-end system damaged by high power electromagnetic pulse

Summary form only given. In present days, the effect of high power electromagnetic(HPEM) threats become increased. This HPEM threats cause critical damaging to electronic equipment. There are two ways of electronic equipment damaged by HPEM pulse: front-door coupling and back-door coupling1. Since front-door coupling is intended to transmit and to receive the electromagnetic wave, a lot more power is induced to it than back-door coupling and it is difficult to shield perfectly due to its purpose, transmitting and receiving electromagnetic waves. Because of these problems, it is necessary to study the damage and shield of RF systems affected by HPEM pulse.

Study on Measurement Method of Dielectric Recovery Voltage to analysis Dielectric Recovery Characteristic of Molded Case Circuit Breaker

Molded Circucit Breaker(MCCB) is a most widely used device to protect loads from the over-current in low power level distribution system. When the MCCB interrupts the over-current, the arc discharge occurred between fixed contact and moving contact to create hot gas. By the Lorentz force due to arc current, the occurred arc is bent to the grids. The grids extend and cool and divide it for arc extinguish. In the majority cases, the MCCB protects loads by interrupting the over-current successfully but in some cases the re-ignition is occurred by hot-gas created during process of interruption. The re-ignition arises when the recovery voltage(RV) is more higher than the recovery strength between contacts and it leads to interruption fault. Therefore to find out the dielectric recovery characteristics of protecting device has a great importance for preventing interruption fault. In this paper, we studies measurement method of the dielectric recovery characteristics considering inherent attribute of the MCCB. To measure the dielectric recovery characteristic of MCCB, we makes an experiment circuit for applying the over-current and the randomly recovery voltage. The measurement methode to find out the dielectric recovery voltage of the MCCB was established and the result was based on experiment results.