• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.2
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• pp.134-139
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• 2013

When the accident occurred in power distribution system, it needs to control efficiently the fault current according to the fault angle and location. The flux-lock type superconducting fault current limiters (SFCL) can quickly limit when the short circuit accidents occurred and be made the resistance after the fault current. The flux-lock type SFCL has a single triggering element, detects and limits the fault current at the same time regardless of the size of the fault current. However, it has a disadvantage that broken the superconductor element. If the flux-lock type SFCL has separated structure of the triggering element and the limiting element, when large fault current occurs, it can reduce the burden of power and control fault current to adjust impedance. In this paper, this system is composed by triggering element and limiting element to analyze operation of limiting current. When the fault current occurs, we analyzed the limiting and operating current characteristics of the two triggering current level, and the compensation characteristics of bus-voltage sag according to the fault angle and location.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.51 no.1
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• pp.15-22
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• 2002

This paper proposes a new power flow method for distribution system analysis by modifying the conventional back/forward sweep method using symmetrical components. Since the proposed method backward and forward sweeps with the variables expressed by symmetrical components, this method reduces computation time for matrix calculations; therefore, it is able to reduce the computational burden for real-time distribution network analysis. The proposed method was also developed to effectively analyze the unbalanced distribution system installing AVR(Auto Voltage Regulator), shunt capacitors. The proposed algorithm was compared with the conventional Back/forward Sweep method by applying both methods to three phase unbalanced distribution system of IEEE 123-bus model, and the test results showed that the proposed method would outperformed the conventional method in real-time distribution system analysis.

• Journal of Power Electronics
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• v.14 no.3
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• pp.413-420
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• 2014

The conventional Phase-Shift Full-Bridge (PSFB) converter has a serious voltage spike because of the ringing between the leakage inductance of the transformer and the parasitic output capacitance of the secondary side rectifier switches. To overcome this problem, an asynchronous active clamp technique employing an auxiliary DC/DC converter has been proposed. However, an exact analyses for designing the auxiliary DC/DC converter has not been presented. Therefore, the amount of power that is supposed to be handled in the auxiliary DC/DC converter is calculated through a precise mode analyses in this paper. In addition, this paper proposes a lossy snubber circuit with hysteresis characteristics to reduce the burden that the auxiliary DC/DC converter should take during the starting interval. This technique results in optimizing the size of the magnetic component of the auxiliary DC/DC converter. The operational principles and the theoretical analyses are validated through experiments with a 48V-to-30V/15A prototype.

• Journal of Power Electronics
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• v.19 no.2
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• pp.529-539
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• 2019

The modular multilevel converter (MMC) has become a promising topology for high-voltage direct current (HVDC) transmission systems. To control a MMC system properly, the ac-side current, circulating current and submodule (SM) capacitor voltage are taken into consideration. This paper proposes a low-computation indirect model predictive control (IMPC) strategy that takes advantages of the conventional MPC and has no weighting factors. The cost function and duty cycle are introduced to minimize the tracking error of the ac-side current and to eliminate the circulating current. An optimized merge sort (OMS) algorithm is applied to keep the SM capacitor voltages balanced. The proposed IMPC strategy effectively reduces the controller complexity and computational burden. In this paper, a discrete-time mathematical model of a MMC system is developed and the duty ratio of switching state is designed. In addition, a simulation of an eleven-level MMC system based on MATLAB/Simulink and a five-level experimental setup are built to evaluate the feasibility and performance of the proposed low-computation IMPC strategy.

• Nuclear Engineering and Technology
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• v.55 no.9
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• pp.3277-3290
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• 2023

Nuclear power plant (NPP) operations with multiple objectives and devices are still performed manually by operators despite the potential for human error. These operations could be automated to reduce the burden on operators; however, classical approaches may not be suitable for these multi-objective tasks. An alternative approach is deep reinforcement learning (DRL), which has been successful in automating various complex tasks and has been applied in automation of certain operations in NPPs. But despite the recent progress, previous studies using DRL for NPP operations have limitations to handle complex multi-objective operations with multiple devices efficiently. This study proposes a novel DRL-based approach that addresses these limitations by employing a continuous action space and straightforward binary rewards supported by the adoption of a soft actor-critic and hindsight experience replay. The feasibility of the proposed approach was evaluated for controlling the pressure and volume of the reactor coolant while heating the coolant during NPP startup. The results show that the proposed approach can train the agent with a proper strategy for effectively achieving multiple objectives through the control of multiple devices. Moreover, hands-on testing results demonstrate that the trained agent is capable of handling untrained objectives, such as cooldown, with substantial success.

• Nuclear Engineering and Technology
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• v.24 no.2
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• pp.183-192
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• 1992

An advanced load-follow operation mode, Mode K, is presented for the Korean Standardized Nuclear Power Plants. The Mode K utilizes a heavy worth bank dedicated to axial shape control independent of the existing regulating banks. In Mode K, the heavy bank provides a wide range of axial shape control and a monotonic relationship between its motion and the axial shape change, which makes it easy to automate axial shape control. The achievement of full automatic reactor power control both for the reactivity and power shape would reduce the burden due to load-follow operation on the operator. Also, it can accommodate the frequen-cy control, which requires the plant to respond to the unexpected demand. The Mode K design concepts were tested using simulation responses of Yonggwang Units 3&4, the reference plants for the Korean Standardized Nuclear Power Plants. The results illustrate that the Mode K is an adequate operation mode to provide practical load-follow capabilities for the Korean Standardized Nuclear Power Plants.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1A
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• pp.58-65
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• 2002

This paper deals with a delay problem in the endpoint detection of double-talk detection algorithm using correlation coefficient in the acoustic echo canceller. In case that past power is much bigger than current power like at the end of double-talking period, the power, estimated using forgetting factor, decreases slowly to cause a delay problem in the endpoint detection. In this paper, two methods are proposed to solve this problem. One is that the current power is periodically replaced by a new average power and the other is that the past power in recursive equation is periodically removed or replaced by other values. The simulation results show that proposed methods outperform conventional method in the endpoint of double-talking periods without increasing the computational burden much more.

• Nuclear Engineering and Technology
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• v.45 no.6
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• pp.731-744
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• 2013

Energy security is a topic of high importance to many countries throughout the world. Countries with access to vast energy supplies enjoy all of the economic and political benefits that come with controlling a highly sought after commodity. Given the desire to diversify away from fossil fuels due to rising environmental and economic concerns, there are limited technology options available for baseload electricity generation. Further complicating this issue is the desire for energy sources to be sustainable and globally scalable in addition to being economic and environmentally benign. Nuclear energy in its current form meets many but not all of these attributes. In order to address these limitations, TerraPower, LLC has developed the Traveling Wave Reactor (TWR) which is a near-term deployable and truly sustainable energy solution that is globally scalable for the indefinite future. The fast neutron spectrum allows up to a ~30-fold gain in fuel utilization efficiency when compared to conventional light water reactors utilizing enriched fuel. When compared to other fast reactors, TWRs represent the lowest cost alternative to enjoy the energy security benefits of an advanced nuclear fuel cycle without the associated proliferation concerns of chemical reprocessing. On a country level, this represents a significant savings in the energy generation infrastructure for several reasons 1) no reprocessing plants need to be built, 2) a reduced number of enrichment plants need to be built, 3) reduced waste production results in a lower repository capacity requirement and reduced waste transportation costs and 4) less uranium ore needs to be mined or purchased since natural or depleted uranium can be used directly as fuel. With advanced technological development and added cost, TWRs are also capable of reusing both their own used fuel and used fuel from LWRs, thereby eliminating the need for enrichment in the longer term and reducing the overall societal waste burden. This paper describes the origins and current status of the TWR development program at TerraPower, LLC. Some of the areas covered include the key TWR design challenges and brief descriptions of TWR-Prototype (TWR-P) reactor. Selected information on the TWR-P core designs are also provided in the areas of neutronic, thermal hydraulic and fuel performance. The TWR-P plant design is also described in such areas as; system design descriptions, mechanical design, and safety performance.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.10a
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• pp.331-339
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• 2008

Nowadays with advancement in technology and aging society, the number of disabled citizens is increasing. The disabled citizens always need a caretaker for daily life routines especially for mobility. In future, the need is considered to increase more. To reduce the burden from the disabled, various devices for healthcare are introduced using computer technology. The power wheelchair is an important and convenient mobility device. The demand of power wheelchair is increasing for assistance in mobility. In this paper we proposed a robotic wheelchair for mobility aid to reduce the burden from the disabled. The main issue in an autonomous wheelchair is the automatic detection and avoidance of obstacles and going to the pre-designated place. The proposed algorithm detects the obstacles and avoids them to drive the wheelchair to the desired place safely. By this way, the disabled will not always have to worry about paying deep attention to the surroundings and his path. User has a handheld bio-sensor monitoring system for get user's bio-signal. If user detects unusual signal, alarm send to protector.

• Journal of Advanced Navigation Technology
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• v.10 no.2
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• pp.138-144
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• 2006

In this paper, dual mode FET mixer for WiBro and wireless LAN(WLAN) applications has been designed in the form of dual gate FET mixer by using the cascode structure of two single gate pHEMTs. The designed dual gate mixer has been optimized to have variable conversion gain for WiBro and WLAN applications in order to save dc power consumption. The LO to RF isolation of the designed mixer is more than 20dB from 2.3GHz to 2.5GHz band. With the LO power of 0dBm and RF power of -50dBm, the mixer shows 15dB conversion gain. When RF power increases from -50dBm to -20dBm, the conversion gain decreases to -2dB from 15dB with bias change. The variable conversion gain has several advantages. It can reduce the high dynamic range requirement of AGC burden at IF stage. Also, it can save the dc power dissipation of mixer up to 90%.