This paper describes the general and efficient design method of an axial and a radial shim coils to correct field impurities of various harmonic orders in the imaging volume of Magnetic Resonance Imaging magnet. Shim coils are optimized by BCLSF subroutine of IMSL, which is the well-known commercial package for optimization, aiming at maximizing the magnitude of the desired field component as well as minimizing other field components. In order to evaluate their effect, the developed method was applied to the MRI magnet constructed in KERI.

This Paper presents the transient analysis of the single-phase line-start permanent magnet synchronous motor. To analyse the starting characteristics, the dynamic equation which is combined electric dynamic equations with mechanical dynamic equation is used. The electric dynamics are derived from the d-q axis voltages of stator and rotor respectively. Especially, symmetrical components transformation is used to consider unbalanced magnetic field which is produced by single-phase input. Non-linear d-q axis inductances according to current amplitude and current phase angle are calculated by Finite Element Method and applied to lumped parameter circuit. The analysis methods are validated by comparing simulated and experimental results.

The ever increasing density of adjustable speed drives(ASD) device with non-linear operating characteristics has been to put tremendous harmonic stress on end user's electrical application. All ASD controllers which employ solid state power devices cause harmonic currents in the source side line. This paper describes harmonic problems for use of ASD. In order to investigate the effect of harmonics caused by using of nonlinear load at the low voltage system, we fixed up simple load model and measured the voltage and current waveforms. Measurement results show that additional operation of linear load at the parallel bus with nonlinear load such as ASD is helpful to the reduction of harmonic influence.

This paper presents a multi output converter system that controls, simultaneously and independently, the separate Buck converter and Boost converter with the different specification by one DSP digital controller. As two separate converters are regulated by only one DSP, it is possible to achieve the simple digital control circuit for regulating multi output DC-DC converter. By setting the software switch state, PI and Fuzzy controller can be applied as a controller for each converter without any change of hardware. Also, it is included the control characteristics comparison between PI and Fuzzy controller. The control characteristics of each PWM DC-DC converter is validated by experimental results.

In this paper, we study a series active power filter to compensate current harmonics and unbalanced source voltages. Conventional control methods for compensating unbalanced source voltages use source voltages to calculate compensation voltages, and in addition use load voltages to regulate load voltages. But the proposed control method uses load voltage to compensate unbalanced source voltages and regulate load voltages. And we propose a control method to reduce current harmonics which can calculate compensation voltages directly from source currents and load voltages. By well-matched operation of two control methods, the series active power filter can compensate current harmonics, unbalanced source voltages, and regulate load voltages. We compose a combined system of the series active power filter and parallel passive filters to confirm a validity of proposed control methods. The results from experiments are presented to demonstrate effectiveness of the proposed method.

The trend of the regulations on environmental issues are getting tight. Responding to this trend new technologies such as moving electrodes, wide pitch and pulsed power supply are also introduced in the electrostatic precipitator(EP) systems. The introduction of wide pitch and moving electrodes enhances the system performance of the EPs by improving air-flow and by improving the ash reentrainment on rapping. The power supplies for the EPs developed up to date include thyristor-based dc or intermittent type, SMPS(switching mode power supply) type and the pulsed-power supply type. The use of the pulsed ones is known to improve dust-collecting efficiency of high resistivity ash and reduces back corona occurrence in the collecting plate. There are two kinds of pulsed-power supplies; one with pulsed transformers and the other with direct dc switching devices. The latter uses rotary spark gap switches or semiconductor switches. Both have the merits and demerits: the spark gap switches are simple and robust but has short life time, hence, high maintenance cost, whereas the semiconductor switches have long life time but are costly. In this study, A high voltage power supply with superimposing voltage pulse on dc source was developed for EPs. This study describes circuit topology, operating principle of the scheme, and analysis of experimental results on Dong-Hae Power Plant. The pulsed power supply consists of a variable dc power supply with ratings of 60kV, 800mA and pulse generator which is made of high voltage thyristor-diode switch strings, an LC resonant tank and a blocking inductor. The pulse generator generates variable pulse-voltage up to 70kV using a high frequency resonant inverter with a variable dc source. Two prototypes were built and tested on 250MW DongHae power plant to verify the possibility of the commercial use and the normal operation in the transient states.