• Journal of Power Electronics
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• v.14 no.6
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• pp.1109-1118
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• 2014

A Fundamental Frequency Sorting Algorithm (FFSA) is proposed in this paper to balance the voltages of floating dc capacitors for Modular Multilevel Converters (MMCs). The main idea is to change the sequences of the CPS-PWM carriers according to the capacitor voltage increments during the previous fundamental period. Excessive frequent sorting is avoided and many calculating resources are saved for the controller. As a result, more sub-modules can be dealt with. Furthermore, it does not need to measure the arm currents. Therefore, the communication between the controllers can be simplified and the number of current sensors can be reduced. Moreover, the proposed balancing method guarantees that all of the switching frequencies of the sub-modules are equal to each other. This is quite beneficial for the thermal design of the sub-modules and the lifetime of the power switches. Simulation and experimental results acquired from a 9-level prototype verify the viability of the proposed balancing method.

• ETRI Journal
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• v.39 no.1
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• pp.62-68
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• 2017

In this paper, we present the design and characterization analysis of a cascode GaN field-effect transistor (FET) for switching power conversion systems. To enable normally-off operation, a cascode GaN FET employs a low breakdown voltage (BV) enhancement-mode Si metal-oxide-semiconductor FET and a high-BV depletion-mode (D-mode) GaN FET. This paper demonstrates a normally-on D-mode GaN FET with high power density and high switching frequency, and presents a theoretical analysis of a hybrid cascode GaN FET design. A TO-254 packaged FET provides a drain current of 6.04 A at a drain voltage of 2 V, a BV of 520 V at a drain leakage current of $250{\mu}A$, and an on-resistance of $331m{\Omega}$. Finally, a boost converter is used to evaluate the performance of the cascode GaN FET in power conversion applications.

• Proceedings of the KIPE Conference
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• 2006.06a
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• pp.488-491
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• 2006

In this paper proposed method of maximum power point tracking using boost converter for a connected single phase inverter with photovoltaic system. The maximum power point tracking control is based on generated circuit control MOSFET switch of boost converter and single phase inverter uses predicted current control to control four IGBT's switch in full bridge. The predicted current control provide current with sinusoidal wave shape and inphase with voltage. The generation control circuit allows each photovoltaic module to operate independently at peak capacity, simply by detecting of the output power of the system. Furthermore, the generation control circuit attenuates low-frequency ripple voltage, which is caused by the full-bridge inverter, across the photovoltaic modules. Consequently, the output power of system is increased due to the increase in average power generated by the photovoltaic modules. The effectiveness of the proposed inverter system is confirmed experimentally and by means of simulation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.8
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• pp.1193-1201
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• 2015

This paper presents a study of circulating current of modular multi-level converter (MMC) based a high voltage direct current (HVDC) system under unbalanced grid conditions. Due to the connection of a dependent DC source in each phase, the MMC system inherently generates the power ripple of double-line-frequency components in the AC-side and as a result, the additional sinusoidal current named circulating current flows through the each arm. Reliability improvement of HVDC system under an unbalanced grid condition is one of the important criteria. Generally, the modeling of the circulating current is based on the power relation between DC-side and AC-side. However, the method is not perfectly matched in the MMC system due to the difference of the structural characteristic. In this paper, improved modeling method of circulating current is proposed, which is based on the inner arm power. The proposed method is verified by several simulations to have good agreement of the circulating current components.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.9
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• pp.798-805
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• 2015

This paper proposes Relaxation Oscillator with Random Number Generator to minimize electromagnetic interference (EMI) noise. DC-DC Converter with Relaxation Oscillator is presented how much spurious noise effects to RF Receiver system. The main frequency of the proposed Relaxation oscillator is 7.9 MHz to operate it and add temperature compensation block to be applied to the frequency compensation in response to temperature changes. The DC-DC Converter Spurious noise is reduced up to 20 dB through changing frequency randomly. It is fabricated in $0.18{\mu}m$ CMOS technology. The active area occupies an area of $220{\mu}m{\times}280{\mu}m$. The supply voltage is 1.8 V and current consumption is $500{\mu}A$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11C
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• pp.963-969
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• 2008

This paper presents 6bit 100MHz Interpolation Flash Analog-to-Digital Converter, which can be applied to the Receiver of Wireless Tele-communication System. The 6bit 100MHz Flash Analog-to-Digital Converter simplifies and integrates S-R latch which multiplies as the resolution increases. Whereas the conventional NAND based S-R latch needed eight MOS transistors, this Converter was designed with only six, which makes the Dynamic Power Dissipation of the A/D Converter reduced up to 12.5%. The designed A/D Converter went through $0.18{\mu}m$ CMOS n-well 1-poly 6-metal process to be a final product, and the final product has shown 282mW of power dissipation with 1.8V of Supply Voltage, 100MHz of conversion rate. And 35.027dBc, 31.253dB SFDR and 4.8bits, 4.2bits ENOB with 12.5MHz, 50MHz of each input frequency.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.11B no.3
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• pp.104-111
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• 2001

The design procedures and experimental results of a single-stage electronic ballast using half-bridge resonant inverter are presented in this paper. The proposed topology is based on a single-stage ballast which combines a boost converter and a half-bradge series resonant inverter. High power factor is achieved by using the boost semi-stage operating in discontinuous conduction mode and inverter semi-stage operated above resonant frequency to provide zero voltage switching is empolyed to ballast the fluorescent lamp Experimental results from the ballast system with 36W fluorescent

• 전기의세계
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• v.30 no.7
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• pp.454-459
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• 1981

The aim of study in this paper is that in a system drive of the converter-inverter fed induction motor, the minimum input power can be maintained by control the voltage and frequency of the motor. In theoretical and experiment results describtion motor efficiency is improved by properly varying the ratio v/f. At lightly load condition, for example its efficiency was improved from 44% to 66% as the ratio of v/f varied from 1 to 0.57.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.32 no.3
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• pp.90-98
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• 1983

The method to improve the efficiency of a slightly loaded induction motor is suggested. It is based upon the optimal efficiency slip tracking by adjusting the voltage to frequency ratio(V/f). It is adopted the converter-inverter fed induction motor drive system. All the control loops are implemented bh the Z-80 microprocessor. By this method, 10% or more improvement is achieved at a few fraction of the full load.

• Journal of Electrical Engineering and Technology
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• v.10 no.2
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• pp.443-451
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• 2015

The stability of a multi-terminal direct current (MTDC) system is often influenced by its control strategy. To improve the stability of the MTDC system, the control strategy of the MTDC system must be appropriately adopted. This paper deals with estimating stability of a MTDC system based on the line-commutated converter based high voltage direct current (LCC HVDC) system with an inverter with constant extinction angle (CEA) control or a rectifier with constant ignition angle (CIA) control. In order to evaluate effects of two control strategies on stability, a MTDC system is tested on two conditions: initialization and changing DC power transfer. In order to compare the stability effects of the MTDC system according to each control strategy, a mathematical MTDC model is analyzed in frequency domain and time domain. In addition, Bode stability criterion and transient response are carried out to estimate its stability.