• Journal of Power Electronics
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• v.19 no.2
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• pp.560-568
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• 2019

This paper studies the inherent relationship between currents and zero-sequence components. Then a precise algorithm is proposed to calculate the injected zero-sequence component to control the DC-Link neutral-point voltage balance, which can result in a more efficient and flexible neutral point voltage balance with a desirable performance. In addition, it is shown that carried-based PWM with the calculated zero-sequence component scheme can be equivalent to space-vector pulse-width modulation (SVPWM). Based on the proposed method, the optimal zero-sequence component of the feasible modulation indices is analyzed. In addition, the unbalanced load limitation of the DC-Link neutral-point voltage balance control is also revealed. Simulation and experimental results are shown to verify the validity and practicality of the proposed algorithm.

• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.34-36
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• 2020

본 논문은 전기자동차용 탑재형 충전기에 사용되는 능동 전력 디커플링 회로의 커패시턴스 저감 기법을 제안한다. 탑재형 충전기의 허용 DC-link 전압 리플과 커패시턴스 사이의 관계를 분석하고, 허용 리플 크기에 따른 최적 커패시턴스의 크기를 도출한다. 제안하는 설계 기법은 시뮬레이션 및 실험 결과를 기반으로 검증한다.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.437-439
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• 1996

In this paper, an UPS system using high-frequency link AC to DC converter is Proposed. The AC to DC converter has sinusoidal input current and high power factor. In this UPS system, the waveform of the output voltage has smaller harmonic contents than those of a conventional UPS system. In this paper, an operating principle of the system is presented. This new control technique of the UPS system is capable of providing a wide range regulated output DC voltage compared with the conventional UPS system. Performance of the system carried out through theoretical and experimental means.

• Proceedings of the KIEE Conference
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• 1997.07c
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• pp.1133-1136
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• 1997

This study established AC-DC system model including DC Link, and then BC Link equation was derived from the model. The equation was included into the calculational algorithm of AC system and solved using fast decoupled method. To minimize the line loss of AC-DC system, optimum theory was applied to the equations.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.367-368
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• 2015

This paper introduces a shunt active power filter with a small DC bus capacitor by adding additional low-pass filter (LPF). The DC link voltage fluctuation is impressively suppressed with a small value in spite of the low value of DC-link capacitor under the steady-state condition. Consequently, the cost and volume of power converter are significantly reduced thanks to the reduced value of DC-bus capacitor. On the other hand, an indirect control strategy is used to maintain grid-side current when non-linear loads are connected to the system. By using proportional-integral (PI) and modified repetitive controller (RC) in dq0 frame, the calculation time is greatly decreased by 6 times compared with the conventional RC, and the number of measurement devices is also minimized. As a result, the acquired total harmonic distortion (THD) is lower than 2% regardless of the load conditions. Simulation results are carried out in order to verify the effectiveness of the proposed control strategy.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.6
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• pp.563-569
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• 2002

This paper proposes an inverter for the grid-connected photovoltaic system based on the transformer-less inverter. This system consists of a high frequency DC-DC converter, high frequency transformer, diode bridge rectifiers, a DC filter, a low frequency inverter, and an AC filter. The 20kHz switched high frequency converter is used to generate bipolar PWM pulse, and the high frequency transformer transforms its voltage twice, which is subsequently rectified by diode bridge rectifiers for a full-wave rectified 60 Hz sine wave power output. Even though the high frequency link system needs more power semiconductors, a reduced size, light weight, and saved parts cost make this system more comparative than other power conditioning systems due to elimination of 60Hz transformer.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.9
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• pp.1617-1624
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• 2006

This paper presents system modeling, modified space vector PWM implementation and design of a closed loop controller of the Z-source inverter which consists of L and C components and shoot-through zero vectors for DGS. Zero vector periods of SVPWM utilized to boost DC-link voltage instead of conventional DC/DC converter and transformer. Only two shoot-through vut(nn are used for DC link voltage control during one switching period without loss of non-zero vectors. Discrete time sliding mode controller, robust servomechanism controller are designed to realize fast and no-overshoot current response and a steady state voltage error. Simulation results are shows the effectiveness of the proposed algorithm.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.11a
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• pp.387-390
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• 2005

A This paper presents a novel three-phase current-fed Pulse Width Modulation converter with switched- capacitor type resonant DC link commutation circuit operating PWM pattern strategy under a design consideration of low-pass filter, which can operate on the basis of the principle of zero current soft-switching commutation. In the first place, the steady-state operating principle of this converter with a new resonant DC link snubber circuit is described in connection with the equivalent operation circuit, together with the practical design procedure of the switched-capacitor type resonant DC link circuit is discussed from a theoretical viewpoint on the basis of a design example for high-power applications. The actively delayed time correction method to compensate distorted currents due to a relatively long resonant commutation time is newly implemented in the open loop control scheme so as to acquire the new optimum PWM pattern. Finally, the experiment or set-up in laboratory system or this converter is concretely demonstrated herein to confirm a zero current soft-switching commutation of this converter. The comparative evaluations between current-fed hard switching PWM and soft-switching PWM converters are carried out from a viewpoint of their PWM converter characteristics.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.2B no.3
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• pp.81-89
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• 2002

The sensorless AC motor drive is a popular topic of study due to the cost and reliability of speed and position sensors. Most sensorless algorithms are based on the mathematical modeling of motors including electrical variables such as phase current and voltage. Therefore, the accuracy of such variables largely affects the performance of the sensorless AC motor drive. However, the output voltage of the SVPWM-VSI, which is widely used in sensorless AC motor drives, has considerable errors. In particular, the SVPWM-VSI is error-prone in the low speed range because the constant DC link voltage causes poor resolution in a low output voltage command and the output voltage is distorted due to dead time and voltage drop. This paper investigates a novel high-performance strategy for overcoming these problems in a sensorless ac motor drive. In this paper, a variation of the DC link voltage and a direct compensation for dead time and voltage drop are proposed. The variable DC link voltage leads to an improved resolution of the inverter output voltage, especially in the motor's low speed range. The direct compensation for dead time and voltage drop directly calculates the duration of the switching voltage vector without the modification of the reference voltage and needs no additional circuits. In addition, the proposed strategy reduces a current ripple, which deteriorates the accuracy of a monitored current and causes torque ripple and additional loss. Simulation and experimentation have been performed to verify the proposed strategy.

• Proceedings of the KIPE Conference
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• 2009.11a
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• pp.219-221
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• 2009

태양전지 어레이(PV-array)로부터 발전되는 DC 전력을 AC로 변환시켜 계통으로 발전시키는 역할을 하는 태양광 발전 시스템용 PCS의 스위칭 회로 Topology로는 일반적으로 3상 풀브리지 회로가 사용된다. 이러한 3상 풀브리지 회로 시스템의 수명예측을 위해 DC link 단의 커패시터의 커패시턴스를 계산하여 커패시턴스의 감소정도를 이용하여 전체 시스템의 수명을 예측하게 된다. 이러한 커패시터의 상태를 추정하기 위해서는 시스템을 정지시킨 후 커패시터를 분리하여 커패시턴스를 측정하는 방법, 특정 주파수의 전류(일반적으로 저주파)를 주입하고 주입한 전류의 주파수에 해당하는 전류 및 전압을 검출하여 capacitance 연산하는 방식등이 이용된다. 시스템을 정지시킨 후 커패시터를 분리하여 커패시턴스를 측정하는 방법은 번거로우며, 전류 주입을 이용한 방식은 불필요한 고조파 전류가 계통으로 침투하는 단점을 가진다. 그러므로 본 연구에서는 모듈타입 PCS 이용시 계통으로 고조파 침투가 없는 비침투 커패시턴스 계산 알고리즘을 제안한다.