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Impedance-based harmonics compensation with accurate harmonic power sharing in distorted microgrids
Pham, Minh-Duc,Lee, Hong-Hee The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.2
This paper presents an enhanced compensation strategy for distributed generation (DG) systems to simultaneously achieve accurate power sharing and harmonics compensation at the point of common coupling (PCC). In the proposed control strategy, the output impedance is modified at the fundamental and harmonic frequencies to compensate for the line impedance mismatches among DG units, which results in accurate power sharing. In addition, load harmonic currents are effectively adjusted by the DG units to effectively compensate the PCC voltage harmonics. Additionally, the DG equivalent impedance is regulated adaptively to ensure accurate harmonic power sharing even in the presence of sudden load changes. Furthermore, a distributed communication network is adopted instead of a central controller to increase the reliability and stability of the microgrid system. The proposed control strategy is applied to a prototype microgrid system, and its effectiveness and reliability are experimentally validated.
Pham, Minh-Duc,Lee, Hong-Hee The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.1
Inaccurate reactive power sharing and voltage distortion at the point of common coupling (PCC) always exist in a parallel inverter system due to feeder impedance mismatches and nonlinear load disturbances. An enhanced inverter control scheme through an output impedance adjustment is proposed to address these issues. Inverter output impedance is regulated considering fundamental and harmonic frequencies, and accurate power sharing and improved PCC voltage quality are realized at the steady state. In addition, the compensation scheme is easily applied in multiple parallel inverters without any prior knowledge of the feeder impedance. Experimental results with three parallel inverters validate the feasibility of the proposed control scheme.
Minh-Duc Pham,Hong-Hee Lee 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.6
Due to the mismatched line impedance among distributed generation units (DGs) and uncontrolled harmonic current, the droop controller has a number of problems such as inaccurate reactive power sharing and voltage distortion at the point of common coupling (PCC). To solve these problems, this paper proposes a resistive-capacitive virtual impedance control method. The proposed control method modifies the DG output impedance at the fundamental and harmonic frequencies to compensate the mismatched line impedance among DGs and to regulate the harmonic current. Finally, reactive power sharing is accurately achieved, and the PCC voltage distortion is compensated. In addition, adaptively controlling the virtual impedance guarantees compensation performance in spite of load changes. The effectiveness of the proposed control method was verified by experimental results.
Duc Minh Pham,김정권,이상철,홍성규,변석수,이상은 대한비뇨의학회 2020 Investigative and Clinical Urology Vol.61 No.4
Purpose: Whether active surveillance (AS) can be safely extended to patients with Gleason score (GS) 3+4 prostate cancer is highly debated. We examined the incidence and predictors of upgrading among patients with GS 3+4 disease. Materials and Methods: The study involved 377 patients with biopsy GS 3+4 who underwent robot-assisted laparoscopic radical prostatectomy (RP) from 2014 to 2018 at a single institution. We analyzed the rate of GS upgrading and used logistic regression to determine the predictors of upgrading. Results: A total of 168 (44.6%) patients with GS 3+4 experienced an upgrade in GS. In multivariable analysis, advanced age, prostate-specific antigen (PSA) level, PSA density (PSAD) and Prostate Imaging-Reporting and Data System version 2 (PI-RADS v2) score were significant predictors of GS upgrading. When structured into a predictive model that included age ≥65 years, PSA ≥7.7 ng/mL, PSAD ≥0.475 ng/mL2 and PI-RADS v2 score 4–5, the probability of GS upgrading ranged from 36.4% to 65.7% when one to four of these factors were included. Conclusions: A substantial proportion of patients with GS 3+4 prostate cancer were upgraded after RP. However, according to our model combining clinical and imaging predictors, patients with a low risk of GS upgrading may be eligible candidates for AS.
Pham, Minh-Duc,Lee, Hong-Hee The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.6
Due to the mismatched line impedance among distributed generation units (DGs) and uncontrolled harmonic current, the droop controller has a number of problems such as inaccurate reactive power sharing and voltage distortion at the point of common coupling (PCC). To solve these problems, this paper proposes a resistive-capacitive virtual impedance control method. The proposed control method modifies the DG output impedance at the fundamental and harmonic frequencies to compensate the mismatched line impedance among DGs and to regulate the harmonic current. Finally, reactive power sharing is accurately achieved, and the PCC voltage distortion is compensated. In addition, adaptively controlling the virtual impedance guarantees compensation performance in spite of load changes. The effectiveness of the proposed control method was verified by experimental results.
Cost-effective synchronization strategy for distributed generators in islanded microgrids
Pham, Minh-Duc,Hoang, Van-Tuan,Lee, Hong-Hee The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.3
A microgrid (MG) is an effective way to integrate various distributed generators (DGs) into a power distribution system. The synchronization of DG voltage with MG voltage is indispensable to prevent inrush currents before connection to a MG system and for working in parallel with other DGs in the MG. In the past, synchronization in terms of both phase and magnitude was realized using additional voltage sensors to measure the MG voltage. However, this increased the system cost. In this paper, a cost-effective synchronization strategy is proposed to allow a DG to connect with an islanded MG system without any additional voltage sensors. The feasibility and effectiveness of the proposed strategy were validated by experiment with a scaled-down islanded microgrid.
Duc-Hoc Tran,Long Luong-Duc,Minh-Tin Duong,Trong-Nhan Le,Anh-Duc Pham 한국CDE학회 2018 Journal of computational design and engineering Vol.5 No.2
Construction managers often face with projects containing multiple units wherein activities repeat from unit to unit. Therefore effective resource management is crucial in terms of project duration, cost and quality. Accordingly, researchers have developed several models to aid planners in developing practical and near-optimal schedules for repetitive projects. Despite their undeniable benefits, such models lack the ability of pure simultaneous optimization because existing methodologies optimize the schedule with respect to a single factor, to achieve minimum duration, total cost, resource work breaks or various combinations, respectively. This study introduces a novel approach called ‘‘opposition multiple objective symbiotic organisms search” (OMOSOS) for scheduling repetitive projects. The proposed algorithm used an opposition-based learning technique for population initialization and for generation jumping. Further, this study integrated a scheduling module (M1) to determine all project objectives including time, cost, quality and interruption. The proposed algorithm was implemented on two application examples in order to demonstrate its capabilities in optimizing the scheduling of repetitive construction projects. The results indicate that the OMOSOS approach is a powerful optimization technique and can assist project managers in selecting appropriate plan for project.
Ranking Quality Evaluation of PageRank Variations
팜민득(Pham Minh Duc),허준석(Jun-Seok Heo),이정훈(Jeong-Hoon Lee),황규영(Kyu-Young Whang) 大韓電子工學會 2009 電子工學會論文誌-CI (Computer and Information) Vol.46 No.5
PageRank 알고리즘은 구글(Google)등의 검색 엔진에서 웹 페이지의 순위(rank)를 정하는 중요한 요소이다. PageRank 알고리즘의 순위 품질(ranking quality)을 향상시키기 위해 많은 변형 알고리즘들이 제안되었지만 어떤 변형 알고리즘(혹은 변형 알고리즘들간의 조합)이 가장 좋은 순위 품질을 제공하는지가 명확하지 않다. 본 논문에서는 PageRank 알고리즘의 잘 알려진 변형 알고리즘들과 그들 간의 조합들에 대해 순위 품질을 평가한다. 이를 위해, 먼저 변형 알고리즘들을 웹의 링크(link) 구조를 이용하는 링크기반 방법(Link-based approaches)과 웹의 의미 정보를 이용하는 지식기반 방법(Knowledge-based approaches)으로 분류한다. 다음으로, 이 두 가지 방법에 속하는 알고리즘들을 조합한 알고리즘들을 제안하고, 변형 알고리즘들과 그들을 조합한 알고리즘들을 구현한다. 백만 개의 웹 페이지들로 구성된 실제 데이터에 대한 실험을 통해 PageRank의 변형 알고리즘들과 그들 간의 조합들로부터 가장 좋은 순위 품질을 제공하는 알고리즘을 찾는다. The PageRank algorithm is an important component for ranking Web pages in Google and other search engines. While many improvements for the original PageRank algorithm have been proposed, it is unclear which variations (and their combinations) provide the “best” ranked results. In this paper, we evaluate the ranking quality of the well-known variations of the original PageRank algorithm and their combinations. In order to do this, we first classify the variations into link-based approaches, which exploit the link structure of the Web, and knowledge-based approaches, which exploit the semantics of the Web. We then propose algorithms that combine the ranking algorithms in these two approaches and implement both the variations and their combinations. For our evaluation, we perform extensive experiments using a real data set of one million Web pages. Through the experiments, we find the algorithms that provide the best ranked results from either the variations or their combinations.