• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.938-943
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• 1998

The induction motor of the electric vehicles is controlled based on the vector control method to obtain good torque control characteristics. In the conventional vector control system, the field exciting current should be kept on a constant value to keep a stable flux level. This method has a liability that core loss becomes increasing at the light load region. To solve this liability, the efficiency maximizing control method of the vector controlled induction motor is proposed in thid paper. We developed light weight water cooled 60kW induction motor drive system which adopts our method and fabricated a conversion electric car for actual vehicle test. We demonstrate the usefulness of drive system by comparing its driving mode with conventional field oriented system and an efficiency maximizing controlled induction motor.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.3
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• pp.69-74
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• 2007

Flux level is low in the maximum efficiency control of a stator flux-oriented control of induction motor under the light load. In this cast if the loaf torque is suddenly increased, torque component current is limited to the low level by torque-limit condition because of the low flux level. In this paper, a technique to solve the problem is proposed.

• Proceedings of the KIPE Conference
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• 2003.11a
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• pp.85-89
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• 2003

Many single-stage PFC(power-facto.-correction) ACHC converters suffer from the high link voltage at high input voltage and light load condition. In this paper, to suppress the link voltage, a novel high power factor high efficiency PFC AC/DC converter is proposed using the single controller which generates two gate signals so that one of them is used far gate signal of the flyback DC/DC converter switch and the other is applied to the Boost PFC stage. A 130w prototype for LCD monitor adapter with universal input $(90-265V_{rms})$ and 19.5V 6.7A output is implemented to verify the operational principles and performances. The experimental results show that the maximum link voltage stress is about 450V at 270Vac input voltage. Moreover, efficiency and power factor are over $84\%$ and 0.95, respectively, under the full load condition.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.49 no.8
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• pp.35-40
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• 2012

In DC-DC converters, a PWM/PFM dual mode control method is commonly used to maintain a high efficiency over a wide range of load variation. Since the control mode is selected according to the load condition, the chip area is increased due to additional circuit for mode control and the optimum efficiency cannot be achieved around the mode transition point. To solve such problems, a new integrated control method is proposed in this paper, in which a PLL is used in the current mode PWM control circuit instead of an oscillator. The proposed integrated control method is verified through a design of a buck converter using PSIM simulation. Simulation of the complete buck converter circuit by Cadence Spectre showed a maximum efficiency of 94.7% at a load current of 250mA and an efficiency of 85.4% at a load current of 10mA under the light load condition.

• Journal of Power Electronics
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• v.17 no.6
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• pp.1454-1468
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• 2017

In this study, a new dual-active soft-switching converter is proposed to improve conversion efficiency and extend the load range for an MTEM electromagnetic transmitter in geological exploration. Unlike a conventional DC/DC converter, the proposed converter can operate in passive soft-switching, single-active soft-switching, or dual-active soft-switching modes depending on the change in load power. The main switches and lagging auxiliary switches of the converter can attain soft-switching over the entire load range. The conduction and switching losses are greatly reduced compared with those of ordinary converters under the action of the cut-off diodes and auxiliary windings coupled to the main transformer in the auxiliary circuits. The conversion efficiency of the proposed converter is significantly improved, especially under light-load conditions. First, the working principle of the proposed converter is analyzed in detail. Second, the relationship between the different operating modes and the load power is given and the design principle of the auxiliary circuit is presented. Finally, the Saber simulation and experimental results verify the feasibility and validity of the converter and a 50 kW prototype is implemented.

• Journal of Power Electronics
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• v.18 no.1
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• pp.45-55
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• 2018

It is usually difficult for dual-active-bridge (DAB) dc-dc converters to operate efficiently at light loads. This paper presents an in-depth analysis of a DAB with triple-phase-shift (TPS) control under the light load condition to overcome this problem. A kind of operating mode which is suitable for light load operation is analyzed in this paper. First, an analysis of the zero-voltage-switching (ZVS) constraints for the DAB converter has been carried out and a reasonable dead-band setting method has been proposed. Secondly, the basic operating characteristics of the converter are analyzed. Third, under the condition of satisfying the ZVS constraints, both the reactive power and the root mean square (RMS) value of the current are simultaneously minimized and a particle swarm optimization (PSO) algorithm is employed to analyze and solve this optimization problem. Lastly, both simulations and experiments are carried out to verify the effectiveness of the proposed method. The experimental results show that the converter can effectively achieve ZVS and improved efficiency.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.06a
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• pp.10-11
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• 2020

Currently, the most used forms, such as euro form and aluminum form, has many problems. There are issues with noise of construction site because of existing forms' material and issues with safety because of heavy weight. To solve these problems, there are many researches on using plastic and composite materials on the formwork. However, plastic has lower tensile strength than the steel and aluminum and composite materials are expensive. Therefore, constructors are avoid to use the forms with new materials. The purpose of this study is to develop light-weight plastic form to solve these existing problems by using ABS with optimized design. To verify, the study measured the amount of deflection from developed form through a load test. The test result showed a deflection of 1.15mm when 1.4ton was loaded in the middle of form. The result of the study verified that the usage of ABS and optimized design effectively reduced the weight and noise. Also, it's performance was verified through the load test.

• Proceedings of the KIPE Conference
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• 1996.06a
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• pp.71-75
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• 1996

As the Three-level ZVS PWM DC-DC converter operates likewise full-bridge ZVS PWM DC-DC converter and the blocking voltage of each switching device is a half of the DC-link voltage, it is suitable for the high imput voltage applications. However, it has some problems as follows; The blocking voltage of each devices is unbalanced and it causes the power losses of the inner switching devices to be increased. Also, it has narrow load range so that the switching losses and the efficiency are reduced as it goes to the light load. This paper presents an nove Three-level ZVS PWM DC-DC converter, which can reduce the overvoltage of the outer switches, eliminate the unbalance of the voltage sharing between the switches at turn-off due to the stray inductances, and operate from no load to full load. The characteristics and the performances of the proposed Three-level ZVS PWM DC-DC converter are verified by simulation and experimental results

• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.307-309
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• 2000

This paper presents development of program for mid-tong term load forecasting in region and district respectively. In this program, at first, the region is classified by KEPCO branch which can be analyzed in light of curl·elation between load characteristics and economic indicator and then, prediction for load density in each region was performed by scenario of economic, population and city plan. Secondly, prediction for load density in each district is performed by methodology which is based on land use method. Finally efficiency for prediction work in each KEPCO branch could be identified by applying the developed program to the Seoul city in real.

• Proceedings of the KIPE Conference
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• 2006.06a
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• pp.25-27
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• 2006

This paper proposes a new full ZVS-range asymmetrical half bridge converter. It uses the variable transient current build-up technique with the load variations. The current build-up is accomplished by using the secondary synchronous switch control. Due to the blocking capacitor in secondary side, the voltage applied to leakage inductor varies with the load variations during current build-up period. Therefore, the unnecessary current build-up of leakage inductor current in heavy load condition is prevented and more current build-up in medium and light load condition is achieved for ZVS operation. That is, the variant current build-up with the load variation is accomplished for the ZVS operation. Furthermore, the DC offset of the transformer magnetizing current is also eliminated and the utilization of magnetic core is maximized.