• KIPS Transactions on Computer and Communication Systems
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• v.10 no.7
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• pp.199-204
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• 2021

Digital substation refers to a substation that digitizes functions and communication methods of power facilities such as monitoring, measuring, control, protection, and operation based on IEC 61850, an international standard for the purpose of intelligent power grids. Based on the intelligent operating system, efficient monitoring and control of power facilities is possible, and automatic recovery function and remote control are possible in the event of an accident, enabling rapid power failure recovery. With the development of digital technology and the expansion of the introduction of eco-friendly renewable energy and electric vehicles, the spread of direct current distribution systems is expected to expand. MVDC is a system that utilizes direct current lines with voltage levels and transmission capacities between HVDCs applied to conventional transmission systems and LVDCs from consumers. Converting existing lines in substations, where most power equipment is alternating current centric, to direct current lines will reduce transmission losses and ensure greater current capacity. The process bus of a digital substation is a communication network consisting of communication equipment such as Ethernet switches that connect installed devices between bay level and process level. For MVDC linkage to existing digital substations, the process level was divided into two buses: AC and DC, and a system that can be comprehensively managed in conjunction with diagnostic IEDs as well as surveillance and control was proposed.

• Journal of Power Electronics
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• v.16 no.3
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• pp.1176-1189
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• 2016

In this paper, a novel quasi-direct power control (Q-DPC) scheme based on a resonant frequency adaptive proportional-resonant (PR) current controller with a variable frequency resonant phase locked loop (RPLL) is proposed, which can achieve a fast power response with a unity power factor. It can also adapt to variations of the generator frequency in T-type Three-level shaft synchronous generator (SSG) converters. The PR controller under the static α-β frame is designed to track ac signals and to avert the strong cross coupling under the rotating d-q frame. The fundamental frequency can be precisely acquired by a RPLL from the generator terminal voltage which is distorted by harmonics. Thus, the resonant frequency of the PR controller can be confirmed exactly with optimized performance. Based on an instantaneous power balance, the load power feed-forward is added to the power command to improve the anti-disturbance performance of the dc-link. Simulations based on MATLAB/Simulink and experimental results obtained from a 75kW prototype validate the correctness and effectiveness of the proposed control scheme.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.195-198
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• 2006

The technology of Solar Power conversion System is defined as a solar cell that changes the sol ar energy into the direct electric energy, power conversion and control technology that convert the dc power into ac power The solar cell module, power conversion, and a control part in component parts consisting a solar power conversion system have influence on its performance. The roles of power conversion and a control part supply the direct current generated by solar cell module for a load with high efficiency as conveniently as possible in this study, the power conversion systen that can generate solar power using DSC module was developed and its characteristics was experimented. The characteristics of the DSC power conversion system including MOSFET and DSP micro processor, high speed devices, was simulated using Psim. According to the results, converter and inverter was manufactured in detail and the performance characteristics were studied.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.7
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• pp.809-815
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• 2016

In this paper, the electrical values of resistance, current, and voltage condition of reactivity is analyzed by applying the direct current (DC) voltage in medium for stem cell regeneration treatment. The voltage response by medium is related to electrical stimulation in the process of induction of differentiation for stem cell and the differentiation condition can be checked depending on the response of voltage condition. If the voltage level is lower in reacting response of a medium, the stem cell stimulation condition is stable, and if the voltage changing level is higher, the stem cell stimulation condition is unstable and a considerable loss will be resulted in the differentiation process. In this research, the optimization of electrical stimulation condition is expected for possible stem cell regeneration treatment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.2
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• pp.152-159
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• 2019

In general, a Doppler radar can measure only the velocity of a moving target. To measure the distance of a moving target, it is necessary to use a frequency-modulated continuous wave or pulse radar. However, the latter are very complex in terms of both hardware as well as signal processing. Moreover, the requirement of wide bandwidth necessitates the use of millimeter-wave frequency bands of 24 GHz and 77 GHz. Recently, a new kind of Doppler radar using multitone frequency has been studied to sense the distance of moving targets in addition to their speed. In this study, we show that distance sensing of moving targets is possible by adjusting only the frequency of a 2.4 GHz Doppler radar with low cost phase lock loop. In particular, we show that distance can be sensed using only alternating current information without direct current offset information. The proposed technology satisfies the Korean local standard for low power radio equipment for moving target identification in the 2.4 GHz frequency band, and enables multiple long-range sensing and radio-frequency identification applications.

• Journal of the Korea Society of Computer and Information
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• v.29 no.1
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• pp.195-209
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• 2024

The current road traffic signal controller developed in the 1990s has limitations in flexibility and scalability due to power supply problems, various communication methods, and hierarchical black box structures for various equipment and devices installed to improve traffic safety for road users and autonomous cooperative driving. In this paper, we designed a road traffic safety facilities equipment and devices integrated management system that can cope with the rapidly changing future traffic environment by solving the using direct current(DC) and power supply problem through the power over ethernet(PoE) technology and centralized data-driven control through message broker technology. In addition, a data-driven real-time control method for road traffic safety facilities equipment and devices operating based on time series data was implemented and verified.

• Journal of Electrical Engineering and Technology
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• v.7 no.4
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• pp.570-575
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• 2012

In a wireless communication RF transmitter, the output of a quadrature modulator (QM) is distorted by not only the linear imperfection features such as in/quadrature-phase (I/Q) input gain imbalance, local phase imbalance, and local gain imbalance but also the nonlinear imperfection features such as direct current (DC) offset and mixer nonlinearity related to in-band spurious signal. In this paper, we propose the unified QM model to analyze the combined effects of the linear and nonlinear imperfection features on the performance of the QM. The unified QM model consists of two identical nonlinear systems and modified I/Q inputs based on the two-port nonlinear mixer model. The unified QM model shows that the output signals can be expressed by mixer circuit parameters such as intercept point and gain as well as the imperfection features. The proposed approach is validated by not only simulation but also measurement.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.11 no.1
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• pp.10-15
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• 2012

Ultra wideband (UWB) technologies have been developed to exploit a new spectrum resource in substances and to realize ultra-high-speed communication, high precision geo-location, and other applications. The energy of UWB signal is extremely spread from near DC (Direct Current) to a few GHz. This means that the interference between conventional narrowband systems and UWB systems is inevitable. However, the interference effects had not previously been studied from UWB wireless systems to conventional wireless systems sharing the frequency bands such as broadcasting system. This paper experimentally evaluates the interference from two kinds of UWB sources, namely an orthogonal frequency division multiplex UWB source and an impulse radio UWB source, to a broadcasting transmission system. The S/N ratio degradation of broadcasting system is presented. From these experimental results, we show that in all practical cases UWB system can be coexisted 35m distance in-band broadcasting network.

• IEMEK Journal of Embedded Systems and Applications
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• v.12 no.2
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• pp.89-96
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• 2017

We develop an embedded system to measure various sensor data, control multiple motors, and communicate with mobile devices for system managements. Choosing TI AM3359 microprocessor featuring high processing performance, low power consumption, and various I/O device support, we design and build the embedded system hardware so that it supports multiple global positioning system (GPS) and gyro sensor modules to measure precise position; multiple pulse width modulation (PWM) outputs to control multiple direct current (DC) motors; a Bluetooth module to communicate with mobile devices. Then, we port the boot loader and device drivers to the built circuit board and construct the firmware development environment for the application programming. The performance of the designed and implemented embedded system is demonstrated by real motor control test using GPS and gyro sensor data and control parameters configured by a mobile device.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.645-648
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• 1991

In conventional sinusoidal wave PWM control, torque oscillation is a problem on account of harmonic component. This paper deals with the choice of line-to-line voltage modulation method, which is effective in using DC(direct current) source voltage and in controlling harmonic oscillation, and the pattern to reduce swiching loss through 1/3 pause of switching interral. So, this paper deals with valid realization of harmonic component and high torque response on variable load by simulation and experiments to compensate occurring problems when line-to-line modulation are applied to PWM inverter.