Jong-Soo Kim

Development and Optimization of High-Voltage Power Supply System for Industrial Magnetron

This paper describes the design and analysis of a 42-kW (14 kV, 3 A) high-voltage power supply for a 30-kW industrial magnetron drive. The design is based on a series resonant converter in discontinuous conduction mode (DCM) to take advantage of both the superior arc protection stemming from the current source characteristics and the high power density owing to the use of parasitic elements such as the leakage inductance in the high-voltage transformer. The detailed design procedure for the resonant tank and high-voltage transformer with respect to the input and output specifications is described on the basis of a simplified analysis of the DCM series resonant converter. Special considerations for designing high-power high-voltage power supplies are provided, such as series stacking of diodes for a voltage doubling rectifier and insulation between each winding of the high-voltage transformer. In addition, a comparative study using theoretical equations, simulation, and experimental results was carried out. This study yielded the output voltage and current characteristics at different switching frequencies and verified the advantages of this topology, such as arc protection without an additional protection circuit and high efficiency due to zero-current or zero-voltage switching. Moreover, the parallel operation of two converters with phase shifted gating signal is proposed to reduce the output current ripple and increase power capability for higher power magnetron drive. Additionally, the design considerations of two auxiliary power supplies (a filament power supply: 15 V, 150 A and a magnet power supply: 50 V, 5 A) are also provided and optimized for effective driving industrial magnetron. Finally, the developed power supply was tested with a 30-kW industrial magnetron, and the results prove the reliability and robustness of the proposed scheme.

Development of Rectangle-Pulse Marx Generator Based on PFN

In this paper, two designs of the rectangle-pulse Marx generator based on pulse-forming network (PFN) for pulse-power application are reported. The PFN is composed of inductors and capacitors. Proposed schemes consist of several identical PFNs that are connected according to Marx generator scheme. PFN Marx generators can output rectangle pulse several hundreds of nanoseconds in duration and several tens of nanoseconds in rising time. The effect of component parameter to the waveform is studied. Prototypes made of four PFNs have been tested. One of the prototypes is designed according to classical Marx mode, while another is designed as an L-C Marx generator in which only one command switch and one isolating switch is needed. In a 500-ns duration, 65-ns rising-time rectangle pulse has been achieved on the matching load.

Design and performance of a 300 kJ pulsed power module for ETC application

In order to support the Korean electrothermal chemical (ETC) launcher program, a 2.4 MJ pulsed power supply system is scheduled to be constructed for the ETC launcher driver. The overall power system consists of eight capacitive 300 kT energy storage banks. In this paper we describe the design features, setup and test operation result of the 300 kJ pulsed power module. Each capacitor bank of the 300 kT module consists of six 22 kV 50 kJ capacitors. A triggered vacuum switch (TVS-43) was adopted as the main pulse power-closing switch and operation characteristics were investigated. Crowbar diode circuits, variable multi-tap inductors and energy dumping systems are connected to each high power capacitor bank via bus-bars and coaxial cables. A parallel crowbar diode stack is fabricated in coaxial structure with two series 13.5 kV, 60 kA avalanche diodes. The main design parameters of the 300 Kj module are a maximum current of 180 kA and a pulse width of 0.5-3 ms. The electrical performances of each component and current output variations into resistive loads have been investigated.

Evaluation of a RVU-43 switch as the closing switch for a modular 300 kJ pulse power supply for ETC application

Eight 300 kJ capacitor bank modules are being assembled for the Korean ETC program. Six self-healing capacitors (22 kV, 50 kJ) are used as a capacitor bank module and an RVU-43 switch is used as the main pulse power closing switch for each module. Pulse power inductors of 20 /spl mu/H to 160 /spl mu/H are used to obtain the required current pulse width and each module is crowbarred by three parallel crowbar diode stacks. Several kinds of high current switch for capacitive pulse power system were considered. The RVU-43 switch was selected because it is much cheaper than thyristors and has rectifying capability after passing the current zero. Performance test for the Russian-made RVU-43 (max rating: 25 kV, 200 kA, 120 Coulomb) switch have been conducted and the results for self-breakdown voltage, minimum operating voltage, turn-on delay, reverse current blocking ability and switch loss are presented.

A constant current high voltage capacitor charging power supply for pulsed power applications

This paper describes a power supply for a rapid pulsed power charging system designed for charging a 0.25 /spl mu/F capacitor up to 20 kV in approximately 3 ms. It is capable of charging the load capacitor at repetition rate of 300 pps. This power supply is based on a series resonant three phase inverter followed by step-up transformers. Experimental results carried out at different repetition rates and charging voltage are included along with the system descriptions.

Development of 2.4-MJ capacitor bank for electrothermal propulsion technology

A pulsed-power supply of a 2.4-MJ capacitor bank has been developed to investigate electric gun technology by the Agency for Defense Development and some Research Institutes. This is made up of eight 300-kJ modules and can supply various shapes of high-current pulse by controlling the charging voltage, inductance, capacitance, and firing time of each module. The unit module has been designed and fabricated for the maximum operating voltage of 22 kV, the peak current of 150 kA, the pulse duration of 1 ms, and the stored energy of 300 kJ. After the consideration of the characteristics of the main switch, crowbar diode, and the capacitor, the circuit topology of the module was determined. The experiments and the analysis were performed to evaluate the circuit topology. All the modules showed good performance under the condition of the charging voltage of 22 kV, the inductance of 20 /spl mu/H, and the shorted load. The experiments were performed to verify the parallel operation performances of the modules with the inductance of 20 /spl mu/H and the load resistance of 100 m/spl Omega/, where the modules were discharged simultaneously and/or sequentially. The value of 20 /spl mu/H was chosen for the permissible peak current and the value of 100 m/spl Omega/ was chosen as the practical maximum value of the load. The results of the experiments were analyzed. The 2.4-MJ capacitor bank is used for the pulsed power supply for the electrothermal chemical gun.

Fast high-voltage pulse generation using nonlinear capacitors

Many pulsed power applications require short high-voltage pulses with a high-repetition rate. Conventional high-voltage discharge pulse-switches such as thyratrons, spark gap switches, and vacuum tube switches have a short lifetime, whereas the semiconductor switches have a long lifetime and high reliability. The semiconductor switches, however cannot be directly applied to fast high-voltage pulsed power generation due to their limited operating voltage ratings despite their relatively long switching times. Therefore, they are used with voltage amplification and a pulse compression stage. This paper describes two pulse generators that use the semi-conductor switches and nonlinear capacitors: one is based on an opening switch (IGBT) and inductive energy storage, the other is a combination of a closing switch (RSD) and capacitive energy storage.

High current pulse forming by modularized capacitor banks

For use as a driver for a electrothermal-chemical (ETC) gun, a 2.4 MJ pulse power system (PPS) has been developed and built up. The 2.4 MJ PPS consists of 8 modular capacitor banks (CB) with energy of 300 kJ each. The 300 kJ CB modules are designed to operate separately and have a charging voltage of 22 kV and a current capability of 150 kA. Prior to the ETC gun application, various shapes of current pulse have been tried to a dummy resistive load by the multiple CB modules. Investigations on a multimodule operation revealed that the Triggered Vacuum Switch (TVS) in the module are triggered simultaneously when other module fires (sympathetic triggering), and some TVSs cannot block the reverse current (failure in diode function). The analysis of these malfunctions of the TVS and some countermeasures have been performed. As another problem, an overvoltage surge has been observed during multiple modules operations. The peak of surge voltage can be higher than the charging voltage, and it can cause the breakdown of crowbar circuits in the module. Solutions to protect the crowbar against the surge voltage have been suggested and some modifications of CB module have been carried out. The experiments on a multi-module operation confirmed that our PPS consisting of improved CB modules has a sufficient pulse forming capability required for the ETC gun load.

Status of KERI's Pulsed Power Research and Development

This paper reviews the research and development results achieved in the Korea Electrotechnology Research Institute (KERI) in a decade. KERI develops pulsed power technology and its applications are mostly based on power electronics. KERIs research and development activity covers components, military systems, and industry applications. High-voltage switching means developed in KERI are a rotary arc gap (RAG) switch (11 kV and 400 kAp), a vacuum RAG (20 kV and 150 kAp), an inverse pinch switch (20 kV and 150 kAp), and 10-kV semiconductor switch stacks made of thyristors and Insulated Gate Bipolar Transistors (IGBTs). The IGBT and thyristor stacks consist of 10 or 12 1.2-kV discrete devices and are operated by only one active drive circuit installed in the groundside. Some ferromagnetic opening switch schemes are also researched on trial bases. Some of KERIs research and development works from devices to application systems will be described.

A novel crowbar scheme for capacitive pulsed power systems

Summary form only given, as follows. Capacitive pulsed power systems are based on the RLC circuits. According to the magnitude of the load resistance and the circuit characteristic impedance, the load current or capacitor voltage may swing or not. The current or voltage oscillation is often not allowed due to the load property or the voltage reversal limit of the energy storage capacitors. Crowbar circuits are inserted for the suppression of the oscillation in these cases. Usually diodes are used as a crowbar switch but when the system voltage and current become high it is not a practical system because the cost of the diodes goes up enormously. A novel crowbar scheme using a spark gap or vacuum gap switch which was triggered at a proper time after the current peak was proposed, implemented and tested. A Rogowski coil was used for sensing the current peak. Because the output of a Rogowski coil shows generally the time derivative of the current waveform, a diode inserted in parallel to the output signal can clamp the positive part of the induced voltage signal of the Rogowski coil. When the voltage arrives at a proper negative value, a square pulse voltage signal of 15 V which triggers the trigger generator for the gap switch for crowbarring can be produced through an amplifier circuit. The implemented circuit shows successful crowbarring actions at a RLC circuit of 1236 /spl mu/F, 160 /spl mu/H, 100 mOhm with the capacitor charged up to 17 kV, the peak current of 34 kA and the capacitor voltage reversal of 1.8 kV.