Shin-Hyeong Choi

A Study on Device Development for Electrical Fire Protection on Open Phase of Three-Phase Motor

In the three-phase power system using the three-phase motor, when any one-phase is open-phase, the unbalanced current flows and the single-phase power supplied by power supply produces overcurrent to motor coil. As a result, the enormous damage and electrical fire can be given to the power system. Recently, the thermal over-current relay (THR) or electronic motor protection relay (EMPR) is mostly used as the open-phase detection device of the three-phase motor. When the over-current or overheat of electric line is generated, it detects and operates circuit breaker, but there is the defect that the sensing speed is slow, the operation can be sometimes failed, and the precision is decreased. In order to improve these problems, this paper is proposed a new control circuit topology for openphase protection using semiconductor devices. Therefore, the proposed open-phase protection device (OPPD) enhances the sensing speed and precision, and has the advantage of simple fitting in the three-phase motor control panel in the field, as it manufactures into small size and light weight. As a result, the proposed OPPD protects the three-phase motor, minimizes the electrical fire from openphase, and contributes for the stable driving of the power system. The performance and confidence of the proposed OPPD is confirmed by a great variety of the experiments of operation characteristic.

A Study on Visitors Tracking Method Using Wireless Communication

Wireless sensor networks are rapidly growing. Wireless sensor networks are composed of a large number of radio frequency equipped sensor devices that autonomously form networks through which sensor data is transported. These sensor devices are used in various real life applications. Recent advances in wireless communications and electronics have enabled the development of low-cost, low-power, small-size sensor nodes. These sensor nodes are deployed in a wide area and are used to monitor a given field of interest for changes in the environment. Location tracking in wireless sensor networks is an important application area. The focus of this paper is on location tracking using wireless communication. In this paper, we present a visitor tracking method based on wireless sensor networks.

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.

Estimation of Activity Energy Expenditure According to the Position of User's Smart Phone

Energy expenditure of a person closely corresponds to the amount of physical activity. Recently, due to the advance in sensor and electronic technology, we can measure physical activity using portable electronic devices. Smart phones are well equipped with useful sensors such as accelerometers and orientation. In this paper, we present estimation method of activity energy expenditure using a smart phone and use the accelerometer inside a smart phone as a sensitive element able to identify activity.

Design and Implementation of a Field Inspection Management System Based on Wireless Sensor Networks

Various errors and failures occur every day in the plant field. However these errors have been managed manually by field inspector. In this paper, we present a design and implementation of a field inspection management system based on wireless sensor networks. This system works on a portable embedded device. To develop the field inspection management system, we analyzed work tasks and process in the plant field. In addition, we propose security measures for preventing information stealing and alteration in the embedded system. Through this system, we can manage effectively error information collected in the field.

Design and Implementation of the Prevention System of Molds Growth Using Wireless Sensor Networks

Due to the advances in memory and processing capacity of embedded systems, wireless communications, and size of the devices, many researchers are growing more and more interested in wireless sensor networks (WSN). WSN have a large number of nodes with a sensor board, and wireless communication board, and have been applied to many fields. Summer is the season when much personal and property damage arises from various natural disasters such as the heat being reminiscent of subtropical climate and flooding from heavy rain due to global warming. This unusual temperature affects our lives much besides causing natural disasters. Recently, many problems have occurred with respect to hygiene and beauty of view especially due to growing of various molds in the residential environment. In the heat of summer, the damages from molds become serious due to the effect of temperature and humidity according to seasonal characteristics. In this paper, we build a wireless sensor network with some sensors such as temperature and humidity. And then we design and implement the prevention system of molds growth which can predict and prevent molds production in indoor environment.

Development of the Prediction System of Condensation Based on Wireless Communications

Due to advances in microelectromechanical system (MEMS), many smart sensors have been developed. A large number of sensors build a wireless sensor network and can communicate with each other. Wireless sensor networks help monitor objects in our environment, and many researches about this technology are in progress. Condensation is a phenomenon that water vapor contained in the air condenses and makes water droplets. This is caused by the complex action of a variety of factors, including the temperature difference between indoor and outdoor and excessive indoor moisture, so it is never easy to identify the cause and establish measures for the actual building. In this paper, a system is presented to predict and alert condensation promptly and accurately, considering the causes and prevention of condensation. In this paper, a system will be developed to collect and monitor environmental information causing condensation, in real time using a wireless sensor network in order to build a system to prevent condensation. The users are expected to use this system to easily identify the cause of condensation and take actions based on the cause-specific alarm messages in order to alleviate aesthetics and hygiene problems due to condensation.

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.

An Android Phone Workplace Management System

Power plants need quite a wide area of the site. In the power plants, various types of machinery and equipment are distributed throughout the workplace, to manage them checking the operation is necessary on a regular time interval. In general, the workplace inspector writes error data by hand and then inputs them to information system. In this paper, we present an Android platform’s workplace management application design, which makes it possible to manage failure or error data of the workplace.

The Security Process Model of Embedded Systems

Embedded systems for specific purposes perform certain roles in various environments. Security of embedded systems is becoming a paramount concern, and once a problem occurs in embedded systems, can lead to fatal accidents. Therefore, we need security policy for embedded systems. However, due to the limited size and performance, security techniques developed for enterprise and desktop computing might not satisfy embedded application requirements. In this paper, we analyze existing security policies and divide malicious attacks into three sections, and then present the security process model of embedded systems.