• Journal of Power Electronics
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• 제17권3호
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• pp.821-834
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• 2017

This paper reports on a single-inductor multiple-output step-up converter with digital control. A systematic analog-to-digital-controller design is explained. The number of digital blocks in the feedback path of the proposed converter has been decreased. The simpler digital pulse-width modulation (DPWM) architecture is then utilized to reduce the power consumption. This architecture has several advantages because counters and a complex digital design are not required. An initially designed unit-delay cell is adopted recursively for the construction of coarse, intermediate, and fine delay blocks. A digital limiter is then designed to allow only useful code for the DPWM. The input voltage is 1.8 V, whereas output voltages are 2 V and 2.2 V. A co-simulation was also conducted utilizing PowerSim and Matlab/Simulink, whereby the 55 nm process was employed in the experimental results to evaluate the performance of the architecture.

• Journal of Power Electronics
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• 제18권1호
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• pp.70-80
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• 2018

A novel strategy based on a zero common mode voltage pulse-width modulation (ZCMV-PWM) technique and zero-sequence circulating current (ZSCC) feedback control is proposed in this study to eliminate ZSCCs between three-level neutral point clamped (NPC) voltage source inverters, with common AC and DC buses, that are operating in parallel. First, an equivalent model of ZSCC in a three-phase three-level NPC inverter paralleled system is developed. Second, on the basis of the analysis of the excitation source of ZSCCs, i.e., the difference in common mode voltages (CMVs) between paralleled inverters, the ZCMV-PWM method is presented to reduce CMVs, and a simple electric circuit is adopted to control ZSCCs and neutral point potential. Finally, simulation and experiment are conducted to illustrate effectiveness of the proposed strategy. Results show that ZSCCs between paralleled inverters can be eliminated effectively under steady and dynamic states. Moreover, the proposed strategy exhibits the advantage of not requiring carrier synchronization. It can be utilized in inverters with different types of filter.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 추계학술대회 논문집
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• pp.9-10
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• 2016

최근 급속한 산업 발달로 인하여 기존의 수 MW급 대용량 인버터가 산업용 팬, 컴프레서, 고속 철도 시스템 등 여러 분야에 사용되면서 이와 관련된 대용량 인버터 연구가 활발히 진행 중이다. 이런 대용량 인버터는 고효율과 직병렬의 구성된 전력용반도체 소자를 동시다발적으로 제어되어야하기 때문에 멀티레벨 인버터의 구조가 가장 적합하다. Cascaded H-bridge 멀티레벨 인버터는 커패시터와 다이오드를 사용하지 않고 스위치만으로 구성하며, 필터를 따로 구성하지 않아도 정현파와 유사하게 전압을 출력할 수 있다. 이로 인해 고주파 감소 및 각 셀을 직렬로 연결하여 입력전압보다 높은 출력전압을 얻을 수 있다. 또한, 스위칭 방법에 따라 동일한 Cascaded H-bridge 멀티레벨인버터 토폴로지에서도 각 THD와 온도에 따른 손실이 달라질 수 있다. Cascaded H-bridge 멀티레벨 인버터에서 이용하는 스위칭 방식은 첫 번째로 유니폴라 방식을 기본으로 한 Phase-shift가 있다. 이는 180도 위상차를 갖는 2개의 레퍼런스 파형과 위상천이가 된 캐리어 파형의 비교로 PWM (Pulse Width Modulation) 을 수행한다. 두 번째 방식으로는 Level-shift가 있다. 이는 캐리어 파형을 IPD (In-Phase Disposition) 방식으로 수직적으로 대역폭이 연속적이게 나열하여 레퍼런스 파형과 비교하는 PWM방식이다. 본 논문에서는 Phase-shift와 Level-shift 방식에 따른 Cascaded H-bridge 인버터와 NPC (Neutral Point Clamped) 인버터를 결합한 토폴로지에서의 온도에 따른 손실을 분석하고, 시뮬레이션을 통하여 비교 분석하였다.

• Journal of Power Electronics
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• 제17권4호
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• pp.1048-1057
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• 2017

An indirect matrix converter (IMC) is a modern power generation system that enables a direct ac/ac conversion without the need for any bulky and limited lifetime electrolytic capacitor. This system also allows four-quadrant operation, generation of sinusoidal output voltage waveforms with variable frequency and amplitude, and control of input power factor. This study proposes a pulse-width modulation-based sliding-mode controller to achieve unity input-power factor operation of the IMC independently of the active power exchanged with the grid, as well as a fast dynamic response. The designed equivalent control law determines, at each sampling period, the appropriate q-axis component of the modulated input current to be injected into the grid through the LC input filter. An integral term of the error is included in the expression of the sliding surface to increase the accuracy of the control method. A double space vector modulation method is used to synthesize the direction of the space vector of the input currents as required by the sliding-mode controller and the space vectors of the target output voltages. Simulation and experimental results are provided to show the effectiveness and evaluate the performance of the proposed control method.

• Smart Structures and Systems
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• 제18권3호
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• pp.405-423
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• 2016

In this study, the feasibility of using telecommunication single-mode optical fiber (SMF) as a distributed fiber optic strain and crack sensor was evaluated in concrete pavement monitoring. Tensile tests on various sensors indicated that the $SMF-28e^+$ fiber revealed linear elastic behavior to rupture at approximately 26 N load and 2.6% strain. Six full-scale concrete panels were prepared and tested under truck and three-point loads to quantify the performance of sensors with pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA). The sensors were protected by precast mortar from brutal action during concrete casting. Once air-cured for 2 hours after initial setting, half a mortar cylinder of 12 mm in diameter ensured that the protected sensors remained functional during and after concrete casting. The strains measured from PPP-BOTDA with a sensitivity coefficient of $5.43{\times}10^{-5}GHz/{\mu}{\varepsilon}$ were validated locally by commercial fiber Bragg grating (FBG) sensors. Unlike the point FBG sensors, the distributed PPP-BOTDA sensors can be utilized to effectively locate multiple cracks. Depending on their layout, the distributed sensors can provide one- or two-dimensional strain fields in pavement panels. The width of both micro and major cracks can be linearly related to the peak strain directly measured with the distributed fiber optic sensor.

• 전기전자학회논문지
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• 제25권3호
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• pp.517-527
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• 2021

본 논문에서는 단일칩 마이컴을 이용한 위상변위 방식 직류-직류 전력변환기를 제안한다. 제안한 전력변환기의 1차측은 위상변위 방식에 의하여 단극성 펄스폭변조(unipolar PWM)로 동작하는 풀브리지 전력구조이며, 2차측은 4개의 다이오드로 구성된 풀브리지 전파정류기이다. 제안한 전력변환기의 제어는 단일칩 마이컴에 의해 수행되고, 그 MOSFET 스위치들은 부트스트랩 회로에 의해 구동된다. 그래서 전력변환기의 전체 시스템은 간단하다. 제안한 전력변환기는 공진회로와 저지커패시터를 이용하여 고효율을 달성한다. 본 논문에서는 먼저, 제안한 전력변환기의 전력회로의 동작을 각 동작모드를 따라 설명한다. 그리고 제안한 전력변환기의 전력회로 설계방식을 보이고 제안한 전력변환기를 동작시키는 마이컴 상의 소프트웨어 제어 알고리즘과 피드백 및 스위치 구동 회로에 관하여 간략히 설명한다. 그 후, 본 논문에서 제시한 설계와 구현방식에 의하여 설계하고 제작된 시제품 전력변환기의 실험결과를 통하여 제안한 전력변환기의 동작 특성을 입증한다. 실험결과에서 약 92% 정도의 최고 효율을 얻었다.

• Journal of Power Electronics
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• 제19권4호
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• pp.922-933
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• 2019

The arm inductance (AI) of a modular multilevel converter (MMC) affects both the fault and circulating current magnitudes. In addition, it has an impact on the inverter efficiency and harmonic content. In this study, the AI of a three-phase MMC is optimized in a novel way in terms of DC voltage utilization, harmonics and efficiency. This MMC has 10 submodules (SM) per arm and the power circuit topology of the SM is a half-bridge. The optimum AI is adopted and verified in an MMC that has 100 SMs per arm. Then the phase shift (PS) and phase disposition (PD) pulse width modulation (PWM) methods are investigated for better DC voltage utilization, efficiency and harmonics. It is found that similar performances are obtained for both modulation techniques in terms of DC voltage utilization. However, the total harmonic distortion (THD) of the PS-PWM is found to be 0.02%, which is slightly lower than the THD of the PD-PWM at 0.16%. In efficiency calculations, the switching and conduction losses for all of the semiconductor are considered separately and the minimum efficiency of the 100-SM based MMC is found to be 99.62% for the PS-PWM and 99.64% for the PD-PWM with the optimal value of the AI. Simulation results are verified with an experimental prototype of a 6-SM based MMC.

• 한국정보기술학회논문지
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• 제16권11호
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• pp.115-121
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• 2018

근적외선을 이용한 형광 영상은 방사능에 대한 걱정이 없고 수술 중 실시간으로 영상 확인이 가능한 장점이 있다. 따라서 감시림프절 생검에 형광 영상을 이용하는 실험이 활발히 진행되고 있다. 형광 영상장비는 LED, 카메라와 같은 고발열 부품이 사용되어 안정적인 발열 억제 수단으로 수랭 방식의 쿨링 시스템을 사용하고 있다. 형광 영상장비에서 수랭 쿨링 시스템은 큰 부피를 차지하여 장비의 소형화 측면에서는 단점이 된다. 장비의 소형화를 위해 공랭 쿨링 방식을 이용할 경우 발열이 문제가 된다. 본 논문에서는 장비의 소형화를 위해 PWM 제어를 이용한 공랭 방식을 적용하여 실험을 했고, 장비를 장시간 사용해도 문제가 없는 일정한 품질의 형광 영상과 발열 억제 성능을 확인했다.

• 마이크로전자및패키징학회지
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• 제27권4호
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• pp.113-117
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• 2020

논문에서는 고분자 나노구조 필름의 기계적 물성을 향상하기 위하여 광열효과를 이용한 열처리 공정을 응용하여 나노임프린트로 제작된 고분자 나노구조 필름의 기계적 물성에 미치는 영향을 규명하였다. Hybrid resin과 UV 나노임프린트을 이용하여 저반사 나노구조를 성형하고 IPL (intense pulsed light)를 이용하여 열처리를 수행한 뒤, 제작된 나노구조 필름의 투과율과 내스크래치성을 평가하여 나노구조의 성형성과 기계적 물성의 변화를 관찰하였다. 나노패턴의 특성에 의해서 나노구조의 투과율은 550 nm 파장에서 97.6%로 고투과율의 기능을 확인하였으며, IPL을 이용한 열처리를 진행한 경우 Hotplate를 이용한 열처리보다 경도는 0.51 GPa로, 0.27 GPa로 열처리한 시편에 비해 1.8배 향상하였으며, 동일 실험 조건에서 탄성율은 Hotplate 이용 시 4 GPa에서 IPL 이용 시 5.9 GPa로 1.4배 증가하였다.

• Journal of Periodontal and Implant Science
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• 제52권3호
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• pp.242-257
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• 2022

Purpose: This study investigated periodontal ligament (PDL) restoration in osseointegrated implants using stem cells. Methods: Commercial pure titanium and zirconium oxide (zirconia) were coated with beta-tricalcium phosphate (β-TCP) using a long-pulse Nd:YAG laser (1,064 nm). Isolated bone marrow mesenchymal cells (BMMSCs) from rabbit tibia and femur, isolated PDL stem cells (PDLSCs) from the lower right incisor, and co-cultured BMMSCs and PDLSCs were tested for periostin markers using an immunofluorescent assay. Implants with 3D-engineered tissue were implanted into the lower right central incisors after extraction from rabbits. Forty implants (Ti or zirconia) were subdivided according to the duration of implantation (healing period: 45 or 90 days). Each subgroup (20 implants) was subdivided into 4 groups (without cells, PDLSC sheets, BMMSC sheets, and co-culture cell sheets). All groups underwent histological testing involving haematoxylin and eosin staining and immunohistochemistry, stereoscopic analysis to measure the PDL width, and field emission scanning electron microscopy (FESEM). The natural lower central incisors were used as controls. Results: The BMMSCs co-cultured with PDLSCs generated a well-formed PDL tissue that exhibited positive periostin expression. Histological analysis showed that the implantation of coated (Ti and zirconia) dental implants without a cell sheet resulted in a well-osseointegrated implant at both healing intervals, which was confirmed with FESEM analysis and negative periostin expression. The mesenchymal tissue structured from PDLSCs only or co-cultured (BMMSCs and PDLSCs) could form a natural periodontal tissue with no significant difference between Ti and zirconia implants, consequently forming a biohybrid dental implant. Green fluorescence for periostin was clearly detected around the biohybrid implants after 45 and 90 days. FESEM showed the invasion of PDL-like fibres perpendicular to the cementum of the bio-hybrid implants. Conclusions: β-TCP-coated (Ti and zirconia) implants generated periodontal tissue and formed biohybrid implants when mesenchymal-tissue-layered cell sheets were isolated from PDLSCs alone or co-cultured BMMSCs and PDLSCs.