• The Transactions of the Korean Institute of Power Electronics
• /
• v.25 no.3
• /
• pp.213-218
• /
• 2020

In this study, we propose a control algorithm to reduce the unbalanced characteristics of a three-phase system power caused by the unbalanced load of the AC electric railway. Then, we verify its performance through the design of a power compensator and experiments applying it. Like electric railway systems, a Scott transformer is applied, and the load and single-phase back-to-back converters are connected to the M-phase and T-phase outputs. The back-to-back converter monitors the difference in active power between the unbalanced loads in real-time and compensates for the power by using bidirectional characteristics. The active power is performed through PI control in the synchronous coordinate system, and DC link overall voltage and voltage balancing control are controlled jointly by M-phase and T-phase converters to improve the responsiveness of the system. To verify the performance of the proposed power compensation device, an experiment was performed under the condition that M-phase 5 kW and T-phase 1 kW unbalanced load. As a result of the experiment, the unbalance rate of the three-phase current after the operation of the power compensator decreases by 58.66% from 65.04% to 6.38%, and the excellent performance of the power compensator proposed in this study is verified.

• KEPCO Journal on Electric Power and Energy
• /
• v.1 no.1
• /
• pp.33-38
• /
• 2015

Energy storage systems (ESSs) have been utilized widely in the world to optimize the power operation system and to improve the power quality. As lithium secondary batteries are the main power supplier for ESSs, it is very important to predict its cycle and power degradation behavior. In particular, the power, one of the hardest electrochemical properties to measure, needs lots of resources such as time and facilities. Due to these difficulties, computer modelling of lithium secondary batteries is applied to predict the DC-IR and power value during charging and discharging as a function of state of charge (SOC) by using pulse-based measurement methods. Moreover, based on the hybrid pulse power characteristics (HPPC) and J-Pulse (JEVS D 713, Japan Electric Vehicle Association Standards) methods, their electrochemical properties are also compared and discussed.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.66 no.2
• /
• pp.357-362
• /
• 2017

Among the lithium metal oxides for asymmetric hybrid supercapacitor, $Li_4Ti_5O_{12}(LTO)$ is an emerging electrode material as zero-stain material in volume change during the with the charging and discharging processes. The pulverized LTO powder was observed to show the enhanced capacity from 120 mAh/g to 156 mAh/g at C-rate (10, 100 C). Hybrid supercapacitor module(48V, 416F) was fabricated using an asymmetric hybrid capacitor with a capacitance of 7500F. As a result of the measurement of C-rate characteristics, the module shows that the discharge time is drastically reduced at more than 50C, and the ESR and voltage drop characteristics are increased. The energy density and power density were reduced under high C-rate conditions. When designing asymmetric hybrid supercapacitor module, the C-rate and ESR should be considered As a result of measuring the 5 kw UPS, it was discharged at the current of 116A~170A during the discharge in the voltage range of 48V~30V, and the compensation time at discharge was measured to be about 33.2s. Experimental results show that it can be applied to applications related to stabilization of power quality by applying hybrid supercapacitor module.

• Journal of the East Asian Society of Dietary Life
• /
• v.24 no.2
• /
• pp.190-200
• /
• 2014

In this study, the antioxidant activity and quality characteristics of the Korean traditional food jeung-pyun made with ju-bak powder were investigated. Jeung-pyun added with 10% ju-bak powder had a total polyphenol content of 54.27%, DPPH free radical scavenging activity of 91.98%, reducing power of 0.51% and SOD-like antioxidant activity of 18.21%. Jeung-pyun added with ju-bak powder had a moisture content of 52.65 to 46.94%, crude fat content of 1.61 to 1.29%, crude protein content of 3.50 to 4.66%, crude ash content of 0.68 to 0.82% and dietary fiber content of 0.12 to 1.46%. Ju-bak powder added with jeung-pyun had a pH level from 4.86 to 4.39. As ju-bak content increased, the pH decreased significantly. Color L value were 78.82 to 68.67. As ju-bak content increased, the Color L value content decreased significantly; a value ranged from -1.89 to 0.69 and b value from 2.99 to 14.25. As ju-bak content increased, the color content significantly increased. As ju-bak content increased, the volume significantly decreased (ranged from 42.50 to 30.00 mL), hardness, gumminess and chewiness significantly increased, and cohesiveness significantly decreased. From SEM, as ju-bak content increased, the pores merged and collapsed, whereas the number of pores decreased and pore size became larger. Sensory evaluation of color, flavor, taste, texture, appearance, cell uniformity and overall acceptability for various levels of ju-bak powder showed that 10% had the highest acceptability. Therefore, 10% ju-bak power added with jeung-pyun has both high antioxidant capacity and sensory acceptability.

• Journal of information and communication convergence engineering
• /
• v.1 no.3
• /
• pp.163-168
• /
• 2003

This paper presents a cascade multilevel PWM rectifier without the isolation transformers for energy build-up at each inverter modules. The features and advantages of the proposed PWM rectifier can be summarized as follows; I) It realizes the high power high voltage AC/DC power conversion, 2) It uses no transformer which is bulky and heavy, 3) It has hybrid structure so that switching devices can be effectively utilized, 4) It produces high quality AC current even in high power high voltage applications, 5) The input power factor remains unity by simple modulation index control. The multilevel rectifier is analyzed by using the circuit DQ transformation whereby the characteristics and control equations are obtained. Finally, it will be shown that the system simulation reveals the validity of analyses.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.56 no.3
• /
• pp.457-464
• /
• 2007

Micro-Grid comprising Micro-Sources supplying several $kW{\sim}MW$ power to local customers is environmentally friendly and reliable. This paper deals with the development of simulation models of Micro-Grid on the PSCAD/EMTDC platform for analyzing various aspects of the interaction of the Micro-Grid. The developed switching level model adopts the space vector PWM. Both switching level and power frequency Micro-Source models are developed, which shows that power frequency modeling is sufficient for analyzing the phenomena of interest. Control characteristics of the Micro-Sources with the parameter and load power variation are analyzed for power quality enhancement. The simulation results show that the developed models are effective for studying Micro-Grid.

• Journal of Electrical Engineering and Technology
• /
• v.11 no.1
• /
• pp.55-64
• /
• 2016

The development of high-speed rail (HSR) has had a major impact on the power supply grid. Based on the monitored waveforms of HSR, a pattern recognition approach is proposed for the first time in this paper to identify the operating conditions. To reduce the data dimensions for monitored waveforms, the principal component analysis (PCA) algorithm was used to extract the characteristics and their waveforms from the monitored waveforms data. The dynamic time wrapping (DTW) algorithm was then used to identify the operating conditions of the HSR. Cases studies show that the proposed approach is effective and feasible, and that it is possible to identify the real-time operating conditions based on the monitored waveforms.

• Journal of the Korean Operations Research and Management Science Society
• /
• v.41 no.1
• /
• pp.113-126
• /
• 2016

This study investigates the effect of power dynamics on R&D and market performances. Various types of relationships in a supply chain are considered. An R&D company offering new technology for product quality and a manufacturer responsible for both production and sales are utilized as subjects. The company with bargaining power differs with respect to the supply chain situation in practice, and no fixed single relationship and supply chain structure exist. However, only a few studies have considered the various relationships among players in a supply chain and their effects on performance. Therefore, we propose three models with different supply chain structures and power dynamics among players. This study contributes to the academia and supply chain practice by revealing the different characteristics of supply chain models.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
• /
• 1994.11a
• /
• pp.14-16
• /
• 1994

The development of proton exchange membrane fuel cells(PEMFCs) with high energy efficiencies and high power densities is gaining momentum because their performance characteristics are attractive for terrestrial(power sources for electrical vehicles, stand-by power), space and underwater application[1]. Fuel cells are capable of running on non-petroleum fuels such as methanol, natural gas or hydrogen and also have major impact on improving air quality. They virtually eliminate particulates, NO$_{x}$, SO$_{x}$, and significant reduce hydrocarbons and carbon monoxide. Especially, fuel cell-battery hybrid power sources appear to be well suited to overcome both the so-called battery problem(low energy density) and the fuel cell problem(low power density)[2].[2].

• Journal of Power Electronics
• /
• v.15 no.4
• /
• pp.1074-1084
• /
• 2015

These days, the widespread use of sensitive loads and distributed generators makes the solid-state circuit breaker (SSCB) an essential component in power circuits to achieve a high power quality for AC Grids. In traditional AC SSCB using SCRs, some auxiliary mechanical devices are required to make the reclosing operation possible before fault recovery. However, the proposed AC SSCB can break quickly and then be reclosed without auxiliary mechanical devices even during the short-circuit fault. Moreover, its fault current breaking time is short and its SSCB reclosing operation is fast. This results in a reduction of the economic losses due to fault currents and power outages. Through simulations and experiments on short-circuit faults, the performance characteristics of the proposed AC SSCB are verified. A design guideline is also suggested to apply the proposed AC SSCB to various AC grids.