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A Generalized Loss Analysis Algorithm of Power Semiconductor Devices in Multilevel NPC Inverters
Alemi, Payam,Lee, Dong-Choon The Korean Institute of Electrical Engineers 2014 Journal of Electrical Engineering & Technology Vol.9 No.6
In this paper, a generalized power loss algorithm for multilevel neutral-point clamped (NPC) PWM inverters is presented, which is applicable to any level number of multilevel inverters. In the case of three-level inverters, the conduction loss depends on the MI (modulation index) and the PF (power factor), and the switching loss depends on a switching frequency, turn-on and turn-off energy. However, in the higher level of inverters than the three-level, the loss of semiconductor devices cannot be analyzed by conventional methods. The modulation depth should be considered in addition, to find the different conducting devices depending on the MI. In a case study, the power loss analysis for the three- and five-level NPC inverters has been performed with the proposed algorithm. The validity of the proposed algorithm is verified by simulation for the three-and five-level NPC inverters and experiment for three-level NPC inverter.
DC-Link Capacitance Minimization in T-Type Three-Level AC/DC/AC PWM Converters
Alemi, Payam,Yoon-Cheul Jeung,Dong-Choon Lee IEEE 2015 IEEE transactions on industrial electronics Vol.62 No.3
<P>In this paper, a novel control algorithm that minimizes the dc-link capacitance in the T-type three-level back-to-back converter is proposed. For this, the charging and discharging currents through the capacitor should be minimized, which can be achieved by utilizing the power balance of the ac/dc converter. Then, the voltage variation in the dc-link is also decreased, which makes a significant reduction in the size of dc-link capacitors. With this scheme, the electrolytic capacitors can be replaced by film capacitors, which are of higher power density, longer lifetime, and higher reliability. The effectiveness of the proposed strategy has been verified by the simulation and experiment results for a 3-kW T-type three-level ac/dc/ac pulsewidth modulation converter system with a 50- μF film capacitor in the dc-link.</P>
Active Damping of LLCL Filters Using PR Control for Grid-Connected Three-Level T-Type Converters
Alemi, Payam,Jeong, Seon-Yeong,Lee, Dong-Choon The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.3
In this paper, an active damping control scheme for LLCL filters based on the PR (proportional-resonant) regulator is proposed for grid-connected three-level T-type PWM converter systems. The PR controller gives an infinite gain at the resonance frequency. As a result, the oscillation can be suppressed at that frequency. In order to improve the stability of the system in the case of grid impedance variations, online grid impedance estimation is applied. Simulation and experimental results have verified the effectiveness of the proposed scheme for three-phase T-type AC/DC PWM converters.
Alemi, Abdolali,Hanifehpour, Younes,Joo, Sang Woo Hindawi Limited 2011 Journal of nanomaterials Vol.2011 No.-
<P>Based on the complex decomposition approach, a simple hydrothermal method has been developed for the synthesizing of Sb2S3nanorods with high yield in 24 h at<SUP>150∘</SUP>C. The powder X-ray diffraction pattern shows the Sb2S3crystals belong to the orthorhombic phase with calculated lattice parametersa=1.120 nm,b=1.128 nm, andc=0.383 nm. The quantification of energy dispersive X-ray spectrometric analysis peaks give an atomic ratio of 2 : 3 for Sb : S. TEM and SEM studies reveal that the appearance of the as-prepared Sb2S3is rod-like which is composed of nanorods with the typical width of 30–160 nm and length of up to 6 μm. High-resolution transmission electron microscopic (HRTEM) studies reveal that the Sb2S3is oriented in the [10-1] growth direction. The band gap calculated from the absorption spectra is found to be 3.29 ev, indicating a considerable blue shift relative to the bulk. The formation mechanism of Sb2S3nanostructures is proposed.</P>
Abdolali Alemi,Leila Kafi-Ahmadi,Ali Akbar Khandar,Amin Salem 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.6
Glass in the system 5In2O3.94Na2B4O7 was fabricated via a melt quenching technique. The amorphous nature of the quenched glass was confirmed by X-ray powder diffraction. The infrared spectrum shows no boroxol ring formation in the structure of this glass. Differential thermal analysis shows a glass transition temperature of 696 oC and a crystallization temperature of 1151 oC. A cerium–zirconium mixed oxide Ce0.75Zr0.25O2 and Eu-doped cerium-zirconium mixed oxide were obtained by a solid-state method. Then the glass powder and Eu-doped cerium-zirconium mixed oxide were mixed. The mixture was heated in a crucible. The glass-ceramic sample was obtained by pouring the melts onto stainless steel plates. The samples obtained were annealed at 450 oC for 1 h to remove the thermal strain. Gas phase catalytic oxidation of toluene was studied over these nanostructures. The results showed that the catalytic activity of Eu0.01Ce0.74Zr0.25O1.995 was higher than Ce0.75Zr0.25O2 for conversion of toluene. Differential thermal analysis for a glass-ceramic sample shows a glass transition temperature of 648 oC and a crystallization temperature of 1134 oC. A scanning electron microscopy study of the glass-ceramic indicates that the crystallized glass consists of crystals with an average diameter of about 86 nm dispersed in glassy regions.
Power Loss Comparison in Two- and Three-Level PWM Converters
Payam Alemi,Dong-Choon Lee 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
This paper presents a fair comparison of power losses in two-level and NPC three-level PWM converters using different switching devices. Conduction losses for IGBT and diode are calculated as a function of modulation index and power factor. Switching losses are calculated as a function of the switching frequency. Three-level converters give a lower total power loss compared with two-level converters. Cost comparison has shown the two-level configuration is about 25% cheaper than the three-level configuration.
Active Damping of LLCL Filters Using PR Control for Grid-Connected Three-Level T-Type Converters
Payam Alemi,Seon-Yeong Jeong,Dong-Choon Lee 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.3
In this paper, an active damping control scheme for LLCL filters based on the PR (proportional-resonant) regulator is proposed for grid-connected three-level T-type PWM converter systems. The PR controller gives an infinite gain at the resonance frequency. As a result, the oscillation can be suppressed at that frequency. In order to improve the stability of the system in the case of grid impedance variations, online grid impedance estimation is applied. Simulation and experimental results have verified the effectiveness of the proposed scheme for three-phase T-type AC/DC PWM converters.
Minimization of DC-Link Capacitance for NPC Three-level PWM Converters
Payam Alemi,Dong-Choon Lee(이동춘) 전력전자학회 2011 전력전자학술대회 논문집 Vol.2011 No.7
This paper presents a control algorithm that minimizes the DC-link capacitance by decreasing the capacitor current. The capacitor current can be nullified by a feedback compensation term which is calculated from the power balance in the AC/DC converter. As a result, voltage variation in the DC-link is reduced further, which makes a large reduction in the size of DC-link capacitors which are expensive and have limitations in life time. Simulations are performed with two 80uF DC-link capacitors, which can be replaced by film capacitors.
A Generalized Loss Analysis Algorithm of Power Semiconductor Devices in Multilevel NPC Inverters
Payam Alemi,Dong-Choon Lee 대한전기학회 2014 Journal of Electrical Engineering & Technology Vol.9 No.6
In this paper, a generalized power loss algorithm for multilevel neutral-point clamped (NPC) PWM inverters is presented, which is applicable to any level number of multilevel inverters. In the case of three-level inverters, the conduction loss depends on the MI (modulation index) and the PF (power factor), and the switching loss depends on a switching frequency, turn-on and turn-off energy. However, in the higher level of inverters than the three-level, the loss of semiconductor devices cannot be analyzed by conventional methods. The modulation depth should be considered in addition, to find the different conducting devices depending on the MI. In a case study, the power loss analysis for the three- and five-level NPC inverters has been performed with the proposed algorithm. The validity of the proposed algorithm is verified by simulation for the three-and five-level NPC inverters and experiment for three-level NPC inverter.
Comparison of Different Methods for Line Impedance Estimation
Payam Alemi(알레미파얌),Bo-hwan Seo(서보환),Dong-Choon Lee(이동춘) 전력전자학회 2010 전력전자학술대회 논문집 Vol.2010 No.7
This paper surveys recent works in line impedance estimation. Inverters used in distribution system are often connected to the grid through LCL filter. Different methods are investigated for estimating the line impedance. Advantages and disadvantages with brief summary for each method are presented. Simulation results for a specified grid are shown for two main different methods and the results are compared with estimation error.