• Journal of Power Electronics
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• v.13 no.6
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• pp.1058-1069
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• 2013

This paper proposes and designs a new output filter called an LCFL filter for application to three phase three wire shunt active power filters (SAPF). This LCFL filter is derived from a traditional LCL filter by replacing its capacitor with a C-type filter, and then constructing an L-C-type Filter-L (LCFL) topology. The LCFL filter can provide better switching ripple attenuation capability than traditional passive damped LCL filters. The LC branch series resonant frequency of the LCFL filter is set at the switching frequency, which can bypass most of the switching harmonic current generated by a SAPF converter. As a result, the power losses in the damping resistor of the LCFL filter can be reduced when compared to traditional passive damped LCL filters. The principle and parameter design of the LCFL filter are presented in this paper, as well as a comparison to traditional passive damped LCL filters. Simulation and experimental results are presented to validate the theoretical analyses and effectiveness of the LCFL filter.

• Journal of Power Electronics
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• v.17 no.4
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• pp.1058-1070
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• 2017

This paper proposes a novel active damping scheme to suppress LCL-filter resonance with only grid-current feedback control in grid-connected voltage-source converters. The idea comes from the concept of the model reference adaptive control (MRAC). A detailed theoretical derivation is given, and the effectiveness of this method is explained based on its physical nature. According to the control structure of this method, the active damping compensator, which is essentially a second order resonant integrator (SORI) filter, provides an effective solution to damp LCL resonance and to eliminate the need for additional sensors. Compared with extra feedback methods, the cost and complexity are reduced. A straightforward tuning procedure for the active damping method has been presented. A stability analysis is illustrated in the discrete domain while considering a one-step delay. Finally, experimental results are presented to validate the analysis and to demonstrate the good performance of the proposed method.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.4
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• pp.296-308
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• 2010

This paper proposes a design of the three-parallel converter system and grid-connection technique for a PMSG based wind turbine systems. The back-to-back converter of the PMSG based wind turbine system is directly connected to the grid so that both the power devices and the filters are needed to have large power ratings. The three-parallel converter configuration can reduce the required power ratings of the devices and filters. However, the three-parallel converter can cause circulating currents. These circulating currents can be suppressed by sellecting proper inner inductance at each leg. An LCL filter design is used to meet the THD regulations. The latent resonance caused by the LCL filter is compensated by an active damping method without additional loss. The decline of the power quality caused by the unbalanced and distorted grid voltages is also compensated with an additional compensation algorithm. The simulation and experimental results show that the proposed system and compensation methods are effective for the wind turbine systems.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.295-296
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• 2016

본 논문은 LCL 필터를 사용하는 계통연계형 인버터에 커패시터 전류 피드백 방식의 능동댐핑을 적용한 안정도 향상 방안를 분석하였다. 커패시터 전류 피드백 방식은 커패시터에 저항을 병렬 연결한 수동댐핑과 동일한 특성을 나타내며, 안정도 해석에 $1.5T_s$의 연산 및 PWM 시지연을 고려하였다. 주파수 응답 특성과 이산시간 영역에서 근궤적을 이용하여 안정도를 해석하며, 필터 공진을 저감시키기 위한 능동댐핑의 이득 $k_d$의 범위를 산정하였으며 PSIM 시뮬레이션과 5kW 계통연계형 실험을 통해 필터 공진에 대한 저감 효과를 검증하였다.

• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.30-31
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• 2011

본 논문은 LCL필터를 이용한 분산전원용 계통연계형 PCS의 공진 억제 기법들을 비교 분석하였다. 주요 비교대상은 기존의 커패시터 전류를 읽어오는 가상 저항 기법과 커패시터 전압을 읽어오는 공진 억제 기법이며, 각 기법의 장단점과 정상상태 THD 분석을 모의 실험으로 비교하였다.

• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.42-43
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• 2011

PV Simulator는 제한된 작업공간에서 태양광발전계통의 주요 설비인 Power Conditioning System (PCS)의 성능을 평가하거나, 제품 출하 전 PCS의 고장유무를 검사하는데 필수적인 장비이다. 최근에 IEC에서 EN50530규정에 따라 PCS의 MPPT평가도 중요하게 되어 동특성이 우수한 PV Simulator가 요구되고 있다. 현재 출시되고 있는 PV Simulator는 대부분 리니어 방식으로서 안정된 출력을 갖지만 효율이 나쁘다는 단점이 있다. 본 논문에서는 효율을 높이기 위한 스위칭 방식 PV Simulator의 전력회로와 출력용 LCL필터를 설계하고 그 특성을 검증한다.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1179-1180
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• 2011

본 논문은 재생에너지의 고전압크기 변환에 적용하기 위해 출력 정류 다이오드 뒤에 LCL 공진회로를 갖는 푸시풀 컨버터를 나타내었다. 푸시풀 컨버터의 공진회로는 두 배의 스위칭 주파로 동작함으로 공진요소의 값이 작아도 되어 소형 경량이다. 제안된 푸시풀 컨버터 토포로지는 낮은 전압에서 높은 전압까지 안정된 전압을 얻을 수 있다. 실험 컨버터는 입력전압 24[V], 전류 80-A, 출력전압 320[V] 출력 1.5[kW]이고 동작 주파수 20 [kHz]에서 양호하게 동작하였고 시뮬레이션과 실험 결과가 잘 일치함을 볼 수 있다.

• Proceedings of the KIPE Conference
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• 2001.12a
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• pp.194-197
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• 2001

In this paper, the design method of LCL filter at the AC input side of a voltage fed active power filter is proposed. The characteristics of harmonics suppression and current control performance of active power filter are described using the analysis of the relation of these characteristics and DC voltage, switching frequency, and AC inductor values. The design examples are shown and the validity of the proposed design method is verified through the PSIM simulation.

• Journal of Power Electronics
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• v.16 no.4
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• pp.1587-1597
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• 2016

A novel active damping strategy for the LCL filter resonance is proposed using the grid current and the capacitor voltage. The proposed technique is deduced in the continuous time domain and a discussion for its discrete implementation is presented. According to the proposed technique, instability of the open loop system, which results in non-minimum phase behavior, can be avoided over wide range of resonant frequencies. Moreover, straightforward co-design steps for both the fundamental current regulator and the active damping loops can be used. A numerical example along with experimental results are introduced to validate the proposed strategy performance over wide range of resonant frequencies.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1165-1177
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• 2018

This paper investigates the active damping of grid-connected LCL filter resonance using high-pass filter (HPF) of the grid current. An expression for such HPF is derived in terms of the filter components. This expression facilitates a general study of the actively damped filter behavior in the discrete time domain. Limits for the HPF parameters are derived to avoid the excitation of unstable open loop poles since such excitation can reduce both the damping performance and the system robustness. Based on this study, straightforward co-design steps for the active damping loop along with the fundamental current regulator are proposed. A numerical example along with simulation and experimental results are presented to verify the theoretical analyses.