Ok-Hwan Kim

A Study on the Improved Stability of Inverter through History Management of Semiconductor Elements for Power Supply

This study suggested the methods to check a proper replacement time, etc. by managing operation data of IGBT used as switching element of inverter for improving the stability of inverter, which was checked through practical experiment. This study accumulated and recorded data such as operation time of IGBT and temperature of radiator for the use in setting, etc. of proper replacement time by checking the data through an indicator. Methods and systems suggested in this study will be also easily used in various sectors using other electric system and semiconductor switching elements for power.

Characteristics Analysis and Library Development for Common Lamps by Using PSPICE Modeling

Recently, common lamps have been used in a variety of fields, including simple illumination science, and their domain of use is increasingly widening. In this study, we configure a library through modeling and verify its accuracy through simulations for widely used and representative lamps such as CCFL, fluorescent lamps, and HID lamps. On the basis of our experiments, we also perform a lamp simulation using PSPICE, which allows us to take advantage of the lamp library easily.

PV System for Medical Devices in the Hospital

In this thesis, a boost chopper using pv system and PWM(Pulse Width Modulation) voltage type power converter were constructed to provide a pleasant environment to the patients in the hospital wards by controlling temperature, humidity and air-conditioning and heating. For the stable modulation of solar cell, synchronizing signal and control signal were processed using one chip microprocessor. Power converter system was constructed with booster chopper and voltage source inverter and test was carried out for both devices. Constant voltage control method was used to track a maximum power point at boost converter control. For the inverter control, synchronizing signal and control signal were processed by microprocessor according to the switching theory of SPWM(Sinusoidal pulse Width Modulation), directions to each sector and stable modulation. Test was carried out for inverter control using SPWM control method. In addition, grid voltage was detected and this grid voltage and inverter output were operated at the same phase for the phase locking with PWM voltage source inverter so that surplus power could be linked to grid. This characteristics were applied on the temperature and humidity sensors in the general buildings and buildings of specific purpose such as hospitals. The good dynamic characteristic of inverter could be obtained by these applications.

Electric Braking Control System to Secure Braking Force in the Wide Speed Range of Traction Motor

In this paper, a vehicle stopping method using an electric brake until a traction motor is stopped is studied. At the moment of vehicle stop, electric brake is changed to control mode wherein torque is reduced at a low speed. Gradient is controlled by estimating the load torque of motor thereby traction motor is not rotated after stop. In addition, coasting operation and brake test were performed from normal-opposite operation and start using a small-scale model comprising the inertial load equipment and the power converter. Further, traction motor was made to be equipped with a suspension torque. Pure electric braking that makes traction motor stopped by an air brake at the time of stop was also implemented. Constant torque range and constant power range were expanded during braking so that braking force was secured with the electric brakes even in high speed region. Therefore, vehicle reduction effect could be expected by reducing parts related with an air brake which is not used frequently by using a pure electric brake in the M car in wide speed region. Further, maintenance of brake system could be reduced, Besides ride comfort of passenger in the electric rail car, energy efficiency improvement, and noise reduction effect could be additionally expected.