Pulse-Width Modulation Strategy for Common Mode Voltage Elimination with Reduced Common Mode Voltage Spikes in Multilevel Inverters with Extension to Over-Modulation Mode

Pham, Khoa-Dang,Nguyen, Nho-Van The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.3

This paper presents a pulse-width modulation strategy to eliminate the common mode voltage (CMV) with reduced CMV spikes in multilevel inverters since a high CMV magnitude and its fast variations dv/dt result in bearing failure of motors, overvoltage at motor terminals, and electromagnetic interference (EMI). The proposed method only utilizes the zero CMV states in a space vector diagram and it is implemented by a carrier-based pulse-width modulation (CBPWM) method. This method is generalized for odd number levels of inverters including neutral-point-clamped (NPC) and cascaded H-bridge inverters. Then it is extended to the over-modulation mode. The over-modulation mode is implemented by using the two-limit trajectory principle to maintain linear control and to avoid look-up tables. Even though the CMV is eliminated, CMV spikes that can cause EMI and bearing current problems still exist due to the deadtime effect. As a result, the deadtime effect is analyzed. By taking the deadtime effect into consideration, the proposed method is capable of reducing CMV spikes. Simulation and experimental results verify the effectiveness of the proposed strategy.

Pulse-Width Modulation Strategy for Common Mode Voltage Elimination with Reduced Common Mode Voltage Spikes in Multilevel Inverters with Extension to Over-Modulation Mode

Khoa-Dang Pham,Nho-Van Nguyen 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.3

This paper presents a pulse-width modulation strategy to eliminate the common mode voltage (CMV) with reduced CMV spikes in multilevel inverters since a high CMV magnitude and its fast variations dv/dt result in bearing failure of motors, overvoltage at motor terminals, and electromagnetic interference (EMI). The proposed method only utilizes the zero CMV states in a space vector diagram and it is implemented by a carrier-based pulse-width modulation (CBPWM) method. This method is generalized for odd number levels of inverters including neutral-point-clamped (NPC) and cascaded H-bridge inverters. Then it is extended to the over-modulation mode. The over-modulation mode is implemented by using the two-limit trajectory principle to maintain linear control and to avoid look-up tables. Even though the CMV is eliminated, CMV spikes that can cause EMI and bearing current problems still exist due to the deadtime effect. As a result, the deadtime effect is analyzed. By taking the deadtime effect into consideration, the proposed method is capable of reducing CMV spikes. Simulation and experimental results verify the effectiveness of the proposed strategy.

Critical Factors of Subcontractor Evaluation and Selection: A Case Study in Vietnam

VO, Khoa Dang,PHAM, Cuong Phu,PHAN, Phuong Thanh,VU, Ngoc Bich,DUONG, My Tien Ha,LE, Loan Phuc,NGUYEN, Quyen Le Hoang Thuy To Korea Distribution Science Association 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.3

A contractor or a main contractor is a company with full capacity to construct all project's works for the owner. A subcontractor is an organization that works with the main contractor to execute and complete work packages for the project. Selecting an effective subcontractor will help the efficiency and success of any projects in the construction industry. Therefore, this study identified subcontractor evaluation factors in Vietnam by collecting questionnaire survey data from engineers and staffs in the construction industry project environment. An exploratory factor analysis (EFA) was then performed to identify the critical factors when evaluating and selecting the subcontractor in construction projects. Moreover, when considering the impact level in terms of the average value, the research results showed that the most critical concern was the subcontractor's reputation. Furthermore, the top five factors affecting the sub-contractor evaluation and selection are (i) reputation, (ii) price, (iii) construction techniques, (iv) ability to implement projects according to commitments, and (v) subcontractor competence (the team of workers, technician staff, engineers with full capacity according to regulations). These research results provide an overall perspective that will help main contractors develop suitable subcontractors' evaluation and selection factors in their projects in the construction industry.

Exceptional case of Kasha's rule: Emission from higher-lying singlet electron excited states into ground states in coumarin-based biothiol sensing

Hien, Nguyen Khoa,Nhan, Doan Thanh,Kim, Won Young,Van Bay, Mai,Nam, Pham Cam,Van, Dang Ung,Lim, In-Taek,Kim, Jong Seung,Quang, Duong Tuan Elsevier 2018 Dyes and pigments Vol.152 No.-

<P><B>Abstract</B></P> <P>A coumarin-based fluorescent sensor (7-Acryloxy-4-methylcoumarin, <B>AMC</B>) for biothiols has been studied by a combination of quantum chemical calculation and experimental investigation. The <B>AMC</B> selectively reacts with mercapto biomolecules via Michael addition, which can be served as a ratiometric fluorescent sensor for thiol-containing biomolecules. The <B>AMC</B> sensor shows a selectivity towards biothiols with sensitivity in the order of cysteine > glutathione > homocysteine. Moreover, the <B>AMC</B> sensor can detect the cysteine concentration within the intracellular level. The results of the theoretical investigations on the electron excited states show that the lack of overlapping between MOs in transitions of the lower-lying singlet electron excited states and the small energy gap between electron excited states are the cause of fluorescence from the higher-lying singlet electron excited states, as an exception from Kasha's rule. The fluorescence from the higher-lying singlet electron excited states leads to marked fluorescence enhancement at long wavelength in the products of addition reaction of biothiols to <B>AMC</B> sensor.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A coumarin-derived ratiometric fluorescent sensor for the determination of biothiols via Michael addition was synthesized. </LI> <LI> Absorption and fluorescence characteristics were clarified on the basis of electronically excited states optimized geometries. </LI> <LI> The lack of overlap between MOs, and the small energy gap between electronically excited states lead to an exception of Kasha's rule. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Appropriation of Protocol for Laparoscopic Pancreaticoduodenectomy in Treatment of Periampullary Cancer

( Minh Hai Pham ),( Quan Anh Tuan Le ),( Hoang Bac Nguyen ),( Quang Hung Vu ),( Thai Ngoc Huy Tran ),( Hang Dang Khoa N Guyen ),( Thi Ngoc Sang Duong ),( Van Toan Tran ) 대한간학회 2020 춘·추계 학술대회 (KASL) Vol.2020 No.1

Aims: Laparoscopic pancreaticoduodenectomy (LPD) is considered as a safe and effective procedure in well - selected patients and appropriate surgical technique. Our aim is to evaluate suitability of using protocol for LPD in treatment of periampullary cancer at a single team. Methods: case series Results: Indication for LPD included 37 cases with resectable tumors which were classified basing on NCCN. All witness evaluation risk of complications with PREPARE score, ASA and evaluation risk of postoperative pancreatic fistula (POPF) with FRS classification. There were 2 open conversions because of vein resections, accounting for 5.4%. Standard lymphadenectomy was performed in all of 37 cases. In term of PREPARE score, major complications (Clavien - Dindo >= III) were 17.8%, 0% and 0% (5/28, 0/5 and 0/2 cases) in low risk, intermediate risk and high risk group, respectively. All of cases had ASA I or II. POPF happened 11.1% (1/9), 4.1% (1/24) and 50% (1/2) in low risk, intermediate risk and high risk group, respectively. Frozen section was needed for R0 margin. Retrieved lymph nodes was 8 - 18 with 12 lymph nodes in average. Conclusions: Indication for LPD with resectable tumors is acceptable. ASA I or II is a safe measure to select patient for LPD. FRS classification shows appropriation to evaluate risk of POPF.

Application of Electrocoagulation for Printing Wastewater Treatment: From Laboratory to Pilot Scale

Thuy, Nguyen Thi,Hoan, Nguyen Xuan,Thanh, Dang Van,Khoa, Pham Minh,Tai, Nguyen Thanh,Hoang, Quang Huy,Huy, Nguyen Nhat The Korean Electrochemical Society 2021 Journal of electrochemical science and technology Vol.12 No.1

This study reports for the first time the application of electrocoagulation (EC) from laboratory to pilot scales for the treatment of printing wastewater, a hazardous waste whose treatment and disposal are strictly regulated. The wastewater was taken from three real printing companies with strongly varying characteristics. The treatment process was performed in the laboratory for operational optimization and then applied in the pilot scale. The weight loss of the electrode and the generation of sludge at both scales were compared. The results show that the raw wastewater should be diluted before EC treatment if its COD is higher than about 10,000 mg/L. Pilot scale removal efficiencies of COD and color were slightly lower compared to those obtained from the laboratory scale. At pilot scale, the effluent CODs removal efficiency was 81.9 - 88.9% (final concentration of 448 - 992 mg/L) and color removal efficiency was 95.8 - 98.6% (final level of 89 - 202 Pt-Co) which proved the feasibility of EC treatment as an effective pre-treatment method for printing wastewater as well as other high colored and hard-biodegradable wastewaters.

Fabrication and modification of cellulose aerogels from Vietnamese water hyacinth for oil adsorption application

La Nam Phat,Tran Quoc Thang,Huynh Cam Nguyen,Dang Thi My Duyen,Dao Xuan Tien,Bui Dang Dang Khoa,Pham Tan Khang,Nguyen Thi Huong Giang,Hoang Minh Nam,Mai Thanh Phong,Nguyen Huu Hieu 한국화학공학회 2021 Korean Journal of Chemical Engineering Vol.38 No.11

Recycling biomass to cellulose aerogel (Cell-A) provides a promising approach to develop adsorbent materials for spilled-oil recovery. In this work, Cell-A was fabricated from Vietnamese water hyacinth via crosslinking methods using PVA as a crosslinker and freeze-drying process. Various cellulose to PVA ratios were investigated to obtain the optimal synthesis condition. The Cell-A was additionally modified by dip-coating in poly(dimethylsiloxane) (PDMS) and pyrolyzing to form PDMS-coated cellulose aerogels (Cell-AP) and carbon aerogels (CA), respectively. Results of the oil adsorption tests show that pyrolysis produced aerogels with greater adsorption capacity with an optimal mass ratio of 15 : 1 cellulose to PVA. Furthermore, the pseudo-second-order model was found to be more accurate than the pseudo-first-order model for the study of oil absorption kinetics. As a result, the modified cellulose aerogel is promising for replacing earth-unfriendly polymer-based oil sorbents due to their high oil absorption capacity.