Choon-Sam Kim

A study on novel buck-boost AC-DC converter of high performance by partial resonance technique

The system efficiency of the proposed buck-boost AC-DC converter is increased by soft switching method. The converter includes to merit of power factor correction (PFC) from sinusoidal control of input current. The switching behavior of control switches operates with soft switching by partial resonance technique, and then the proposed converter has high system efficiency with decrement of switching power loss. The input current waveform in proposed converter is got to be a sinusoidal form of discontinuous quasi-pulse row in proportion to magnitude of AC input voltage under the constant duty cycle switching. Therefore, the input power factor is nearly unity. The output voltage of the converter is regulated by PWM control technique. The discontinuous mode action of current flowing into inductor makes to simplify control method and control components. The proposed novel buck-boost AC-DC converter is analyzed to compare with the conventional PFC buck-boost converter. Some computer simulative results and experimental results confirm to the validity of the analytical results.

High-voltage power supply using series-connected full-bridge PWM converter for pulsed power applications

This paper presents a capacitor charging power supply (CCPS) using high-voltage dc/dc converter for pulsed power applications. For the main converter, it used full-bridge phase-shifted (FBPS) pulse-width modulation (PWM) converter. The proposed CCPS has modularity concept, and the output voltage was boosted by a high-voltage high-frequency (HVHF) transformer included in FBPS PWM converter. The control method is used a phase-shifted PWM to reduce the losses caused by switching. To solve the voltage unbalancing problem of the output capacitors, synchronization algorithm is selected. Also Thermal characteristics are analyzed by theoretical calculation and simulation. Experimental results of the single module and CCPS are provided to validate the effectiveness of the proposed system and it was carried out the 20-kV 160-kW prototype.

A study on isolated DC-DC converter of soft switching with discontinuous conduction mode

In this paper, we study on a new isolated DC-DC converter of soft switching with discontinuous conduction mode (DCM). The switching devices in the proposed converter are operated by soft switching technique using a new quasi-resonant circuit, and are driven with DCM according to pulse width modulation (PWM). The quasi-resonant circuit uses a step-up inductor and a loss-less snubber capacitor. The proposed converter with DCM also simplifies the requirement of control circuits and reduces the number of control components, and the switching control technique of the converter is simplified for the switches to drive in a constant switching frequency. As a result, the proposed converter exhibits low switching power loss and high power efficiency. The validity of the analytical findings is confirmed by some simulation results and experimental results.

An Efficiency Improvement of Secondary-Side Rectifier for Minimizing 2nd Coil-Making in Contact-less Power Supply

The Spiral coil is made considering primary, secondary side coil inductance, turn number, size, thickness, and shielding area with the litz wire-type in case of manufacturing a coil, and at this time, the semi-automation winding machine is used. When deciding on primary and secondary side coil specification and manufacturing a coil, the spiral coil of a specification varied in the various litz wire of a specification is required, and at this time, a difficulty is generated by the manufacture cost, period which during, and failure the manufacture is generated in the coil sample making. A difficulty is in the desired coil quality control of a specification. Since improving the rectifier of the secondary side in order to improve this kind of problem, the range of the coil design and the during the manufacture, various coil manufacture specifications can be comprehensively made.

An Assessment on Voltage and Power Quality in Load Facility during the Islanding of Residential Fuel Cell System

Recently, due to the excessive use of fossil fuels, many studies about the fossil fuels such as solar and fuel cell energy source are progressing. Fuel cell system has high energy conversion efficiency. Also, fuel cell system is environmentally friendly system because the carbon emission is almost not occur. Therefore, the fuel cell system is considered as the core technology of in the fields of the future energy and environmental. Fuel cell system has an effect on distribution power system because another power source of other than large power plants. So, fuel cell system can be reason of power quality in the power system. In this paper, we constructed the system for an assessment on Islanding. The system is composed with power source, Impedance coordination load and linear load, fuel cell system. we are performed assessment on voltage and power quality in customer and the distributed power system during the Islanding of residential fuel cell system. In addition, no change in the impedance of power system, we made a islanding condition only using the actual load, As a variation of generation and load current under islanding, an analysis results based on assessment system showed that the power qualities of distribution system became more aggravation as effect of voltage sag and voltage swell phenomena.

The research of sensor node power management

Wireless sensor networks consist of small sensor nodes and are able to sense the environment in a distributed fashion. And embedded system is a kind of special computer system which is suitable for application system with strict requirements on the functionality, cost, size and power consumption. Hence the application of embedded systems will become increasingly important. Also the amount of data to be dealt with in the embedded system will continue to increase, so database processing technology is needed to the embedded system. In other words we need embedded database to manage large amount of data. In this paper, we present effective management method of sensor nodes are installed in various locations to collect environmental information. This method can monitor whether sensor node passes wrong environmental information or sensor node to lack of battery power. On this basis, we design sensor node power management system based on embedded system and use SQLite as database.

The Metal Detection using Primary Current in Contact-less Power Supply

The impurity detection method applied to existing discriminated the normality(R, L, C) and impurity(Metal) load using mutual RFID/ID method in the contactless power supply in which the primary side and the secondary side are completely separation by using the contactless transformer. However, this kind of system is caused the high cost of the system and complexity of control. Therefore, in this paper was proposed the contact-less power transfer using the primary current that determine normality or impurity load by compare the primary current Amplitude to reference quantity value and design the 3[W] contact-less power transfer and conduct an experiment for demonstrate the validity.

A Study on Instantaneous Voltage Compensation of UPS using on Ultracapacitor

This paper proposed UPS system parallel connected in battery and ultracapacitor to compensate instantaneous voltage drop. Ultracapacitor parallel connected with battery compensate instantaneous voltage drop at failure and it`s reduced the voltage regulation of output voltage. We are produced for fast instantaneous voltage drop compensation of ultracapacitor at UPS system and experiments are achieved. Experimental result was verified that the ultracapacitor indicated the fast compensation characteristics and regulation of the output voltage satisfied within 5[%] by using ultracapacitor.

Boost AC-DC Converter of High Power Factor and High Efficiency

This paper is studied on boost AC-DC converter of high power factor and high efficiency for discontinuous current control. The converter operated in discontinuous current control eliminates the complicated circuit control requirement, and reduces a number of components. The input current waveform in proposed circuit is got to be a discontinuous sinusoidal form in proportion to magnitude of ac input voltage under the constant duty cycle switching. Therefore, the input power factor is nearly unity and the control circuit is simple. Also the switching devices in a proposed circuit are operated with soft switching by the partial resonant method. The result is that the switching loss is very low and the efficiency of system is high. The partial resonant circuit makes use of a inductor using step up and loss-less snubber capacitor. The circuit topology of the converter is simplified. Some simulative results on computer and experimental results are included to confirm the validity of the analytical results.