• Journal of Power Electronics
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• v.9 no.3
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• pp.365-376
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• 2009

In this paper, the implementation of a three-phase shunt active power filter is presented. The filter is essentially three independent single-phase current-controlled voltage source inverters (CC-VSI) with a common DC bus. The CC- VSI is operated to directly control the AC grid current to be sinusoidal and in phase with the grid voltage without detecting the load currents. The APF consists of a current control loop, which shapes the grid currents to be sinusoidal and a voltage control loop, which regulates the active power balance of the system. The experimental results indicate that the active filter is able to handle predominantly the harmonics, as well as the unbalance and reactive power, so that the grid currents are sinusoidal, in phase with the grid voltages and symmetrical.

• Journal of Power Electronics
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• v.17 no.1
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• pp.272-281
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• 2017

The DC circuit breaker is essential for supplying stable DC power with the advent of DC transmission/distribution and sensitive loads. Compared with mechanical circuit breakers, which must interrupt a very large fault current due to their slow breaking capability, a solid-state circuit breaker (SSCB) can quickly break a fault current almost within 1 [ms]. Thus, it can reduce the damage of an accident a lot more than mechanical circuit breakers. However, previous DC SSCBs cannot perform the operating duty, and are not economical because many SCR are required. Therefore, this paper proposes a new DC SSCB suitable for DC grids. It has a low semiconductor conduction loss, quick reclosing and rebreaking capabilities. As a result, it can perform the operating duties of reclosing and rebreaking. The proposed DC SSCB is designed and implemented so that it is suitable for home dc distribution at a rated power of 5 [kW] and a voltage of 380 [V]. The operating characteristics are confirmed by simulation and experimental results. In addition, this paper suggests design guidelines so that it can be applied to other DC grids. It is anticipated that the proposed DC SSCB may be utilized to design and realize many DC grid systems.

• Journal of Electrical Engineering and Technology
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• v.10 no.2
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• pp.529-538
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• 2015

Due to the high efficiency and compact mechanical structure, direct drive variable speed generators are used for power conversion in wind turbines. The wind energy conversion system (WECS) considered in this paper consists of a permanent magnet synchronous generator (PMSG), uncontrolled rectifier, dc-dc boost converter controlled with maximum power point tracking (MPPT) and adaptive hysteresis controlled voltage source inverter (VSI). For high utilization of the converter's power capability and stabilizing voltage and power flow, constant DC-link voltage is essential. Step and search MPPT algorithm which senses the rectified voltage ($V_{DC}$) alone and controls the same is used to effectively maximize the output power. The adaptive hysteresis band current control is characterized by fast dynamic response and constant switching frequency. With MPPT and adaptive hysteresis band current control in VSI, the DC link voltage is maintained constant under variable wind speeds and transient grid currents respectively.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.5
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• pp.750-756
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• 2017

This paper presents a method for DC voltage control of HVDC system connection of offshore wind farms. In the event of fault in AC grid, HVDC system need to meet LVRT regulations. When HVDC system meet LVRT regulation, unbalance is caused between power input and power output for DC link. Therefore, LVRT regulation lead to DC voltage increase of HVDC system. To control the DC voltage increase, the chopper resistor can be suggested. In this paper, DC voltage suppression is proposed using chopper resistor and de-loading. The effectiveness of the chopper resistor was verified using PSCAD/EMTDC.

• Progress in Superconductivity and Cryogenics
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• v.18 no.4
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• pp.30-34
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• 2016

In this study, a SFCL-combined DC circuit breaker system was proposed by applying the current-limiting technology for DC circuit breaking. The SFCL-combined circuit breaker system consists of a mechanical DC circuit breaker combined with superconductors. To ensure the reliable structure and operation of the SFCL-combined circuit breaker system, a simulation grid was designed using the EMTDC/PSCAD program, and simulation was conducted. The results showed that the SFCL-combined DC circuit breaker system with superconductors limited the maximum fault current by 37%. In addition, the burden on the DC circuit breaker was decreased by 87%.

• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.1805-1811
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• 2017

Recently, DC systems are considered as efficient electric power systems for renewable energy based clean power generators. This discloses several critical issues that are required to be considered before the installation of the DC systems. First of all, voltage/current switching stress, which is aggravated by large fault current, might damage DC circuit breakers. This problem can be simply solved by applying a superconducting fault current limiter (SFCL) as proposed in this study. It allows a simple use of insulated-gate bipolar transistors (IGBTs) as a DC circuit breaker. To evaluate the proposed resistive type SFCL application to the DC circuit breaker, a DC distribution system is composed of the practical line impedances from the real distribution system in Do-gok area, Korea. Also, to reflect the distributed generation (DG) effects, several DC-to-DC converters are applied. The locations and sizes of the DGs are optimally selected according to the results of previous studies on DG optimization. The performance of the resistive type SFCL applied DC circuit breaker is verified by a time-domain simulation based case study using the power systems computer aided design/electromagnetic transients including DC (PSCAD/ EMTDC(R)).

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.11
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• pp.68-76
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• 2014

This paper presents an offset error compensation algorithm for the accurate phase angle of the grid voltage in single-phase grid-connected inverters. The offset error generated from the grid voltage measurement process cause the fundamental harmonic component with grid frequency in the synchronous reference frame phase lock loop (PLL). As a result, the grid angle is distorted and the power quality in power systems is degraded. In addition, the dq-axis currents in the synchronous reference frame and phase current have the dc component, first and second order ripples compared with the grid frequency under the distorted grid angle. In this paper, the effects of the offset and scaling errors are analyzed based on the synchronous reference frame PLL. Particularly, the offset error can be estimated from the integrator output of the synchronous reference frame PLL and compensated by using proportional-integral controller. Moreover, the RMS (Root Mean Square) function is proposed to detect the offset error component. The effectiveness of the proposed algorithm is verified through simulation and experiment results.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.287-288
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• 2016

기존 자가발전 운동기구의 경우, 가변저항을 사용하여 운동강도를 조절하기 때문에 Generator에서 생성된 에너지가 모두 소모되는 문제점이 있다. 또한 계통연계형 자가발전 운동기구의 경우에는 에너지 회수는 가능하지만 운동 강도 조절이 불가능한 단점이 존재한다. 따라서 본 논문에서는 계통연계를 통해 에너지 회수가 가능하고, 운동 강도 조절이 가능한 자가발전 운동기구용 DC/DC 컨버터를 제안한다. 제안회로는 가변저항을 사용하지 않고 입력임피던스를 통해 운동 강도를 조절하기 때문에 높은 에너지를 생성할 수 있고 계통연계를 통해 에너지 회수도 가능한 장점이 있다. 본 논문에서는 제안된 회로의 이론적 특성을 분석하고 모의실험을 통해 확인하였으며, 계통연계형 자가발전 운동기구에 적용하여 실험을 통해 우수성을 검증하였다.

• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.553-554
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• 2011

환경오염의 의한 지구온난화가 세계적 이슈가 되고 있으며 화석연료의 고갈 등으로 기존의 자동차들이 점점 설 자리를 잃어 가는 게 현재 상황이다. 따라서 화석연료 자동차를 대체해야하는 많은 새로운 형태의 자동차가 제시 되고 있는데 그중에 현재 가장 경쟁력과 경제성을 가진 전기자동차가 대두되고 있는 시점에 이를 충전하기 위한 여러 장치들이 나오고 있다. 그중에 우리는 3상계통 인버터와 고효율 DC-DC 컨버터로 구성 된 충전기를 소개하고자한다.

• Proceedings of the KIEE Conference
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• summer
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• pp.1161-1165
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• 2004

The fundamental digital control of utility-connected PV inverter are presented with detailed analysis and simulation and experimental results. PLL controller using virtual two phase detector, current controller of DC-DC converter, dc link voltage controller and inverter current controller are discussed. The novel PLL controller using virtual two phase detector can detect the information of utility voltage instantaneously and is not sensitive to the noise. Current controller of DC-DC converter, dc link voltage controller and inverter current controller are the conventional methods. We have constructed utility-Connected PV Inverter and applied to those controllers. The simulation and experimental results demonstrate an excellent performance in the single-phase grid-connected operation.