• Proceedings of the KIEE Conference
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• 2008.11a
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• pp.217-219
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• 2008

Among the Flexible AC Transmission Systems (FACTS) devices, Unified Power Flow Controller (UPFC) is considered as the most powerful and versatile one as it provides simultaneous, real time control of the transmission parameters, voltages, impedances, and phase angles which determine the power flow in AC transmission systems. This paper presents modelling of UPFC and describes its characteristics. The UPFC implemented in this paper is based on Sinusoidal Pulse Width Modulation (SPWM) and Electro-Magnetic Transients Program (EMTP)/ATPDraw is used to model and analyze it. The simulation results confirm advantages of UPFC in operational performance with respect to the steady state Power flow regulation and the transient stability control.

• Journal of Power Electronics
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• v.1 no.1
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• pp.48-55
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• 2001

This paper describes a switching-level simulation model and scaled hardware model for SSSC, which is useful for analyzing the dynamic interaction between the SSC and the power transmission system. A detailed simulation model with EMTP was developed to verity the SSSC operation with control system, and its increasing capability of power transmission through the line for a typical one-machine infinite-bus system. The simulation results of the developed model are compared with the experimental results froma scaled model fo 2KVA rating for evaluation the whole system operation.

• Journal of Power Electronics
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• v.9 no.5
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• pp.667-678
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• 2009

The PWM (Pulse Width Modulation) control signals have a drawback in that their power spectrum tends to be concentrated around the switching frequency and the resulting harmonic spikes cause an EMI (Electromagnetic Interference) and switching losses in semiconductors, etc. The SDM (Sigma-Delta Modulation) is a type of switching modulation used to reduce these harmonic spikes, and several SDM schemes are investigated in this paper. In the DSDM (Dithered SDM), the SDSDM (Space-Dithered SDM) and TDSDM (Time-Dithered SDM), the signals are classified by the location of their random dither additions. In these schemes, the switching frequency is spread by a random dither generator placed on the input or the output parts. Experimental results are presented where the advantages of the new proposed CDSDM (Combined Dithered SDM) are confirmed by applying to a buck converter.

• Journal of Power Electronics
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• v.16 no.4
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• pp.1504-1512
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• 2016

This paper presents a new single-phase asymmetrical cascaded multilevel DC-link inverter. The proposed inverter comprises two stages. The main stage of the inverter consists of multiple similar cells, each of which is a half-bridge inverter consisting of two switches and a single DC source. All cells are connected in a cascaded manner with a fixed neutral point. The DC source values are not made equal to increase the performance of the inverter. The second circuit is a folded cascaded H-bridge circuit operating at a line frequency. One of the main advantages of this proposed topology is that it is a modular type and can thus be extended to high stages without changing the configuration of the main stage circuit. Two control schemes, namely, low switching with selective harmonic elimination and sinusoidal pulse width modulation, are employed to validate the proposed topology. The detailed approach of each control scheme and switching pulses are discussed in detail. A 150W prototype of the proposed system is implemented in the laboratory to verify the validity of the proposed topology.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.1104-1107
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• 1992

Voltage controlled current regulated PWM(pulse width modulation) of VSI (voltage source inverter) is proposed. Adopting one degree of freedom, the voltage, the current controller shows much more improvement than conventional ones not using this method. The voltage controller or this proposal needs load's parameters, torque value, rotational speed. This voltage controller is located at converter part which links AC source and DC bus. With this proposed method, duty ratio of the inverter's switching is nearly unity for all speed and torque range. Hence, this method gets many advantages such as reducing current ripple, thermal loss, and noises and improving control performances. Theoretical approach to this voltage-current controller is performed, and the results are presented.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.10
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• pp.1858-1864
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• 2011

This paper suggests a control technique of the sensorless brushless DC (BLDC) motor drive for a vehicle fuel pump application. The sensorless technique based on a comparator and a potential start-up method with high starting torque are proposed. The comparator is used to generate the commutation signals in phase with the three-phase back-EMFs. The rotor position is aligned at standstill for maximum starting torque without an additional sensor and any information of motor parameters. Also, the stator current can be easily adjusted by modulating the pulse width of the switching devices during alignment. Some experiments are implemented on a single chip 16-bit DSP controller to demonstrate the feasibility of the sensorless techniques.

• Journal of Mechanical Science and Technology
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• v.17 no.11
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• pp.1608-1615
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• 2003

This paper studies on the linearization of a looper system in hot strip mills, that plays an important role in regulating a strip tension or a strip width. Nonlinear dynamic equations of the looper system are analytically linearized by a static feedback linearization algorithm with a compensator. The proposed linear model of the looper is validated by a comparison with a linear model using Taylor's series. It is shown that the linear model by static feedback well describes nonlinearities of the looper system than one using Taylor's series. Furthermore, it is shown from the design of an ILQ controller that the linear model by static feedback is very useful in designing a linear controller of the looper system.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.1
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• pp.150-157
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• 1999

In this study, the loader was completed that has 4-wheel gear driven drivetrain of study (Ⅰ), the 4-wheel steering with power wheel type, all-wheel traction system, and joy-stick type lever for hydraulic control valve. From driving test of the developed 4WD and 4WS type loader, we obtained that the minimum circling radius and the necessary width in circling motion reduced about 40% and 33% compared with 2WS type loader. Also, all-wheel traction system could keep the tires glued to the ground with greater stability, the power steering allowed a smoother operation, and the joy-stick type lever offered easily to control. Thus, the developed loader having these functions was very fit in a small cattle shed or rugged ground.

• Journal of the Korean Society of Combustion
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• v.3 no.1
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• pp.1-10
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• 1998

Lots of techniques are adopted for a flame stabilization and a high-load combustion. But the techniques being used were passive control method which have to change combustor shape like pilot flame, flame stabilizer, pressure profile, etc. Active control method which is not necessary to transform its shape is employed. Acoustical excitation is broadly used for its convenience in changing frequency and intensity. Both acoustical excitation and flame stabilizers were adopted to study their relationship. So, we investigated flammability limits. Flame visualization. And mean temperature in the condition of various frequencies, intensities, and flame stabilizers. As a consequence, flammability limit were advanced in acoustically excited flame at some frequencies. Coherent structure was extended to the downstream region through acoustical excitation and a size of vortice was curtailed. Also width of recirculation zone was magnified. In addition, Effects of acoustical excitation was stood out at 25mm flame stabilizer rather than another ones.

• Proceedings of the KIEE Conference
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• 2007.10c
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• pp.175-177
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• 2007

This paper presents for the torque characteristics and improving the efficiency of driving system of electric bicycle which applied IEWPM(Independently Excited Winding Permanent Magnet) motor. IEWPM motor can expand the number of phase from 3 phases to multiphase like SRM motor because stator windings are unconnected directly. BLDC motor raise rotor'-s electromagnetic torque per unit volume by using Spoke type permanent magnet. By using two photo sensor per phase and applying excited width, advance angle and bipolar control, we confirmed higher torque at a low speed, higher out-put at a high speed, and efficiency improvement at a wide speed control area.