• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.08a
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• pp.308-312
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• 1999

Developed the model equations which calculate roll force, roll power during hot rolling in real time. The variables which mainly effect on the roll force, roll power are shape factor, reduction, roll diameter, roll velocity, strip inlet temperature, carbon content of strip and strip-roll contact friction coefficient. Among these variables roll diameter, roll velocity, inlet temperature, carbon content and friction coefficient can be excluded in interpolated model equation by introducing equation of die force(F'), power(p') of the frictionless uniform plane strain compression which can be calculated without iteration. At the case of coulomb friction coefficient of 0.3, we evaluated coefficient of polynomial equations of {{{{ { F} over {F' } }}}}, {{{{ { Pf} over {Pd }, { Pd} over {P' } }}}} from the result of finite element analysis using interpolation. It was found that the change of values of {{{{ { F} over {F' }, { P} over {P' } }}}} with the friction coefficient tend to straight line which slope depend only on shape factor. With these properties, developed model equations could be extended to other values of coulomb friction coefficient. To verify developed roll force, roll power model equation we compared the results from these model equation with the results from these model equation with the results from finite element analysis in factory process condition.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.2168-2180
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• 2014

In this paper, a generalized power loss algorithm for multilevel neutral-point clamped (NPC) PWM inverters is presented, which is applicable to any level number of multilevel inverters. In the case of three-level inverters, the conduction loss depends on the MI (modulation index) and the PF (power factor), and the switching loss depends on a switching frequency, turn-on and turn-off energy. However, in the higher level of inverters than the three-level, the loss of semiconductor devices cannot be analyzed by conventional methods. The modulation depth should be considered in addition, to find the different conducting devices depending on the MI. In a case study, the power loss analysis for the three- and five-level NPC inverters has been performed with the proposed algorithm. The validity of the proposed algorithm is verified by simulation for the three-and five-level NPC inverters and experiment for three-level NPC inverter.

• Journal of Power Electronics
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• v.12 no.4
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• pp.578-586
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• 2012

In this paper a single-phase Cascaded H-Bridge (CHB) inverter for photovoltaic (PV) applications is presented. Based on the presented mathematical analysis, a novel controller is introduced which adjusts the inverter power factor (PF) and manipulates the distribution of the reactive power between the cells to enhance the operating range of the CHB inverter. The adopted control strategy enables tracking of the maximum power point (MPP) of distinct PV strings and allows independent control of the dc-link voltages. The proposed controller also enables the inverter to operate under heavily unbalanced PV conditions. The performance of the CHB inverter and the proposed controllers are evaluated in the PSCAD/EMTDC environment. A seven-level CHB-based grid connected laboratory prototype is also utilized to verify the system performance.

• Journal of the Korean Society of Industry Convergence
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• v.9 no.2
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• pp.133-139
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• 2006

Harmonics happened due to nonlinear systems such as UPS, SCR controlled motors, and fluorescent lighting in distribute power system is very important subject to optimal operation and control of power system. Harmonics sometimes make incorrect operation of protective relaying system under normal condition on power system. In this study, total harmonics distortion(THD) of power were measured and analyzed by the field test on electrical facilities which were installed at the rural industrial complex in Chungbuk province. In addition, the deprivation of power factor by harmonics and the content of THD which is measured at neutral line was researched.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.508-509
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• 2014

전력변환장치의 효율을 개선하기 위해 많은 연구가 이루어지고 있는 가운데, 본 논문에서는 3-레벨 인버터 중에서도 NPC 인버터와 T-타입 인버터를 사용한다. 각 인버터는 서로 다른 스위치 정격에 의해 손실 차이가 생기며, 또한 손실에 영향을 미치는 MI(Modulation Index), PF(Power Factor), 그리고 스위칭 주파수에 따라 손실의 크기가 좌우 되었다. 하지만 두 인버터는 각 구조의 특성상 NPC 의 경우 도통손실이 매우 크며, T-타입의 경우 스위칭 손실이 크게 나타난다는 모듈상의 한계가 있다. 본 논문에서는 인버터 구조에 따라 손실에 지배적으로 영향을 미치는 각 Device의 특성을 고려하여, 전력변환장치에서 발생되어지는 도통손실과 스위칭손실을 분석 하였다.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.36T no.3
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• pp.56-63
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• 1999

In this paper, we realize the active PFC(Power Factor Correction) system of BF (Boost Forward) converter with PWM-PFM control technique to control DC output voltage, and to control the input current with sinusoidal wave synchronized by the converter and inverter using power switching element, FET and IGBT. The control circuit of the suggested Boost converter is implemented with a microprocessor 80C196. After making the ratio of output voltage to current as 50V/1A and the duty ratio greater than 0.5. When input voltage is 30V and boost inductance is 1.1mH. We control the voltage changing rate according to the variation of load resistance using a PWM-PFM control technique. And finally we prove experimentally. PF can be improved up to 0.96 using the current shaping technique.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.12 no.1
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• pp.7-16
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• 2016

This paper presents the measurement and analysis results for the cooling performance of ground-coupled heat pump (GCHP) system using a cooling tower as a supplemental heat rejector. In order to demonstrate the performance of the hybrid approach, we installed the monitoring equipments including sensors for measuring temperature and power consumption, and measured operation parameters from May 1 to October 30, 2014. The results showed that the entering source temperature of brine returning from the ground heat exchanger was in a range of design target temperature. Leaving load temperatures to building showed an average value of $11.4^{\circ}C$ for cooling season. From the analysis, the daily performance factor (PF) of geothermal heat pumps ranged from 4.4 to 5.2, while the daily PF of hybrid GCHP system varied from 3.0 to 4.0 over the entire cooling season.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.611-616
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• 2001

This paper analyzed PFC of active clamp ZVS flyback converter by adding two methods PFC (power Factor Correction) circuit - two-stage and single-stage. The addition of active clamp circuit also provides a mechanism for achieving ZVS of both the primary and auxiliary switches. ZVS also limits the turn off di/dt of the output rectifier, reducing rectifier-switching loss and switching noise, due to diode reverse recovery. As a result, the proposed converters have characteristics of the reduced switching noise and high efficiency in comparison to conventional flyback converter. The simulation and experimental results show that the proposed converter improve the input PF of 300W ZVS flyback converter by adding single-stage, two-stage PFC circuit.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.538-541
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• 2001

This paper analyzed PFC of active clamp ZVS flyback converter by adding two method PFC (Power Factor Correction) circuit - Two-Stage and Single-Stage. It improves on Flyback converter's disadvantage - loss increasing by switching, noise increasing, high voltage stress of switch - by adding active clamp circuit. Simulation results show to improve the input PF of 300W ZVS flyback converter by adding Single-Stage, Two-Stage PFC circuit.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.15 no.6
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• pp.49-57
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• 2001

This paper analyzed PFC of active clamp ZVS flybark converter by adding two method PFC (Power Factor Correction) circuit-two-stage and single-stage. The addition of active clamp circuit also provide a mechanism fur achieving ZVS of both the primary and auxiliary switches. ZVS also limits the turn off di/dt of the output rectifier, reducing rectifier switching loss and switching noise, due to diode reverse recovery. As a results, the proposed converters have characteristics of the reduced switching noise and high efficiency in comparison to conventional flyback converter. The simulation and experimental results show that the proposed converters improve the input PF of 300[W] ZVS flyback converter by adding single-stage two-stage PFC circuit.