• 전기학회논문지
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• 제56권6호
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• pp.1071-1079
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• 2007

In this paper, a novel space vector control method for isolated multi-level inverter using 3-phase low frequency transformers is proposed. This method is based on the simplification of the space-vector diagram of a five-level inverter using calculated table into fully programming method. The execution time of the proposed method is about same as that of the method using calculated table. Also, the proposed method is easily applied to other case level inverter. We applied this method into the 3-phase IHCML inverter using common arm. It makes possible to use a single DC power source due to employing low frequency transformers. In this inverter, the number of transformers could be reduced compare with an exiting 3-phase multi-level inverter using single phase transformer. In addition, this method generates very low harmonic distortion operation with nearly fundamental switching frequency. Finally, We tested multi-level inverter to clarify electric circuit and reasonableness through Matlab simulation and experiment by using prototype inverter.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.126-131
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• 2001

This paper deals with implementation of inverter systems for DC power regeneration, which can regenerate the excessive DC power from DC bus line to AC supply in substations for traction systems. From the viewpoint of both power capacity and switching losses, a three-phase square-wave inverter system is adopted. To control the regenerated power, the magnitude and phase of fundamental output voltages should be appropriately controlled in spite of the variation of input DC voltage. Inverters are operated with modified a-conduction mode to fix the potential of each arm. The overall system consists of the line-to-line voltage and line current sensors, an actual power calculator using d-q transformation method, a complex power controller with PI control scheme, a gating signal generator for modified $\alpha-conduction\;mode\;with\;\delta\;and\;\alpha$, a DPLL for frequency followup, and power circuit.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.346-351
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• 2002

Noise of the VVVF inverter and DC/DC converter, which are the most dominant noise sources of maglev train at low speed, is studied, The coils inside inverter and converter are excited by electro-magnetic forces, which results in core vibration and generations of the noise. It is found that the spectra of the noise show many harmonics, where there exist several different fundamental frequencies. Some noise reducing techniques are known for the transformer noise such as changing stiffness and using different core materials, which make less electrostatic responses, and consequently less noise. In this study, it is shown that the most effective and feasible noise reducing method is to increase the switching frequencies of the inverter and converter, where peaks in higher frequency are significantly reduced.

• Journal of Power Electronics
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• 제16권5호
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• pp.1752-1762
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• 2016

To achieve higher reliability in the modular multilevel converters (MMC) for HVDC transmission systems, the internal condition of the DC capacitors of the submodules (SM) needs to be monitored regularly. For an online estimation of the SM capacitance, a controlled AC current with double the fundamental frequency is injected into the circulating current loop of the MMC, which results in current and voltage ripples in the SM capacitors. The capacitor currents are calculated from the arm currents and their switching states. By processing these AC voltage and current components with digital filters, their capacitances are estimated by a recursive least square (RLS) algorithm. The validity of the proposed scheme has been verified by simulation results for a 300-MW, 300-kV HVDC system. In addition, its feasibility has been verified by experimental results obtained with a reduced-scale prototype. It has been shown that the estimation errors for both the simulation and experimental tests are 1.32% at maximum.

• 한국광학회지
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• 제16권2호
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• pp.152-158
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• 2005

출력거울로 GRM(Gaussian reflectivity mirror)을 채택한 불안정 공진기를 구성하여 그 Q-스위치 출력의 특성을 분석하였다. 입력 전기에너지가 55J 일 때 1064 nm의 기본파장에서 470 mJ, 532 nm의 제2고조파 파장에서 280 mJ의 출력 에너지를 얻었다. 출력빔의 발산각은 1.7 mrad 이었으며 근접장 영역에서 Top-Hat 형태의 빔을 얻을 수 있었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 학술대회 논문집 전문대학교육위원
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• pp.21-25
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• 1999

This paper proposes a novel control strategy of SVC(Static var compensator) using cascade multilevel inverter. To control the reactive power instantaneously, the dq-dynamic system model is described and analyzed. A single pulse pattern based on the SHE(Selective Harmonic Elimination) technique is determined from the look-up table to reduce the line current harmonics and a rotating fundamental frequency switching scheme is applied to adjust the DC capacitor voltage at the scheme level. From the simulation, it is verified that this proposed control scheme make the dynamic control response of SVC fast, the current harmonics low, and the DC capacitor voltage balanced.

• 한국전자파학회논문지
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• 제24권8호
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• pp.798-804
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• 2013

본 논문에서는 고주파 회로 모델링을 이용하여 전기자동차의 LDC로부터 방출되는 전도성 전자파 잡음을 시스템-레벨에서 분석하였다. 관련 전도 방출의 주요 원인은 LDC에서 사용하는 펄스폭 변조 방식의 100 kHz 스위칭 동작에 기인하며, 이러한 전도 방출은 공통-임피던스 결합 및 유도성 결합을 통해 AM/FM 주파수 대역에서의 무선주파수 간섭을 유발한다. 이러한 문제를 분석하기 위해 LDC를 구성하고 있는 MOSFET과 고압 커패시터, 고전압 케이블과 버스 바에 대한 기본 회로는 물론, 각 부분에서 존재하는 기생 성분 및 비선형 특성을 해석하여 LDC 전체를 포함한 시스템-레벨의 고주파 등가회로 모델을 제안하였다. 이러한 모델을 이용하여 시뮬레이션과 측정을 비교하여 유사성을 검증하였다. 향후 이러한 접근 방법이 전기자동차의 전자파 적합성 설계에 효과적으로 사용될 수 있을 것으로 기대한다.

• Journal of Electrical Engineering and Technology
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• 제12권4호
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• pp.1484-1494
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• 2017

We present a two-stage inverter with high step-up conversion ratio engaging modified finite-set Model Predictive Control (MPC) for utility-integrated photovoltaic (PV) applications. The anticipated arrangement is fit for low power PV uses, the calculated efficiency at 150 W input power and 19 times boosting ratio was around 94%. The suggested high-gain dc-dc converter based on Cockcroft-Walton multiplier constitutes the first-stage of the offered structure, due to its high step-up ability. It can boost the input voltage up to 20 times. The 3S current-source inverter constitutes the second-stage. The 3S current-source inverter hires three semiconductor switches, in which one is functioning at high-frequency and the others are operating at fundamental-frequency. The high-switching pulses are varied in the procedure of unidirectional sine-wave to engender a current coordinated with the utility-voltage. The unidirectional current is shaped into alternating current by the synchronized push-pull configuration. The MPC process are intended to control the scheme and achieve the subsequent tasks, take out the Maximum Power (MP) from the PV, step-up the PV voltage, and introduces low current with low Total Harmonic Distortion (THD) and with unity power factor with the grid voltage.

• 한국조명전기설비학회지:조명전기설비
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• 제2권2호
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• pp.59-63
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• 1988

고정 AC 전력전원에서 PWN(Pulse Width Modulation) 기법은 전압과 기본파 주파수를 가변 시키는 데 이용되어 왔다. 종래의 PWN 기법은 전류수, 필터크기 등의 문제점 때문에 PWN 출력 전압파형을 모터 구동 등의 제어 대상에 응용하는 연구가 진행되었다. 그러나 본 논문에서는 출력단 고속 스윗칭 소자를 사용하여 캐리어 주파수를 10(KHz)-45(KHz)까지 정현 PWN 시키고, 인버터의 출력단 파형은 소용량LPF(Low Pass Filter)를 사용하여 PAM(Pulse Amplitude Modulation)을 얻어냈다. 정현 PWN 제어 회로는 속응성과 제어성을 고려하여 마이크로 프로세서와 아날로그 회로로 혼합구성 하였다. 그리고 실험 결과는 변조도 0.6-1.0까지 변할 때 전압 파형을 관찰했다.

• Journal of Power Electronics
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• 제16권1호
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• pp.297-309
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• 2016

Grid-connected inverters (GCIs) with an LCL output filter have the ability of attenuating high-frequency (HF) switching ripples. However, by using only grid-current control, the system is prone to resonances if it is not properly damped, and the current distortion is amplified significantly under highly distorted grid conditions. This paper proposes a synchronous reference frame equivalent proportional-integral (SRF-EPI) controller in the αβ stationary frame using the parallel virtual resistance-based active damping (PVR-AD) strategy for grid-interfaced distributed generation (DG) systems to suppress LCL resonance. Although both a proportional-resonant (PR) controller in the αβ stationary frame and a PI controller in the dq synchronous frame achieve zero steady-state error, the amplitude- and phase-frequency characteristics differ greatly from each other except for the reference tracking at the fundamental frequency. Therefore, an accurate SRF-EPI controller in the αβ stationary frame is established to achieve precise tracking accuracy. Moreover, the robustness, the harmonic rejection capability, and the influence of the control delay are investigated by the Nyquist stability criterion when the PVR-based AD method is adopted. Furthermore, grid voltage feed-forward and multiple PR controllers are integrated into the current loop to mitigate the current distortion introduced by the grid background distortion. In addition, the parameters design guidelines are presented to show the effectiveness of the proposed strategy. Finally, simulation and experimental results are provided to validate the feasibility of the proposed control approach.