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Interfacial Reaction in (Mg-37.5Al)/(Mg-6.7Nd) Diffusion Couples
Jiahong Dai,Shijun Shen,Bin Jiang,Jianyue Zhang,Qingshan Yang,Zhongtao Jiang,Hanwu Dong,Fusheng Pan 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.1
The solid-state diffusion reaction between Mg-37.5Al and Mg-6.7Nd was studied in the 623-673 K temperature range. A solid-liquid contact method was employed to produce diffusion couples. The Al4Nd, Al11Nd3, Al3Nd and Al2Nd intermetallic compounds form in the diffusion reaction layers of the couples. The formation of intermetallic compounds in the diffusion reaction layers is rationalized using the Miedema model. The local average compositions through the diffusion reaction layer were determined, and used to construct a semi-quantitative diffusion path on the isothermal Mg-Al-Nd ternary phase diagram at 673 K. The growth constants of the entire diffusion reaction layers were determined as 8.91 (±0.94)×10 -14 m 2 /s, 1.39 (±0.15)×10 -13 m 2 /s and 1.93 (±0.38)×10 -13 m 2 /s at 623 K, 648 K and 673 K, respectively. The activation energy Q for the growth of the entire diffusion reaction layers was 54±4.6 kJ/mol.
Bo Long,Yong Liao,YuFei Dai,LiJun Huang,Xin Lu,Yong Chen,FuSheng Li 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
Transformerless grid-connected inverters, due to their advantages in high efficiency, small volume and light weight, gain more research and interest in recent years. Due to the asymmetrical driving signal in pulse-width-modulation (PWM) caused by time-delay, zero-drift of the current sensors and imparities of the power transistors, etc. Output of the grid current contains dc component. As a result, power quality of the grid is degraded. In this paper, a dc component suppression scheme with recursive integral PI controller are introduced, according to the change tendency of tracking error, the coefficients of PI controller are regulated by BP neural network in real time, and the global optimization requirements are met. Sliding-Window-Double-Iteration-Method (SWDIM) is utilized for fast dc current extraction. Simulation results from a 2-kW three-phase grid-connected inverter confirm the effectiveness of the proposed scheme.
Bo Long,Wei Wang,Xin Lu,YuFei Dai,LiJun Huang,YuCheng Qian,Yong Chen,FuSheng Li 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
Conventional phase-shift controlled dual active bridge (DAB) converters which operate in discontinuous current mode (DCM) are hard to realize the zero-voltage switching (ZVS) due to the light load. This paper proposed an efficiency improvement method for the DAB converter with fix-frequency hybrid discontinue current mode (HDCM). By adopting the HDCM control method, synchronous rectification and wide load range ZVS of switching devices are realized simultaneously without changing the components of the conventional DAB power stage in DCM. Besides, to further improve the conversion ratio and efficiency, the voltage-doubled rectification (VDR) is adopted. The HDCM implementation method with a digital signal processor (DSP) is proposed. A 200W laboratory prototype is designed to validate the correctness of HDCM. Compared to the conventional DAB converter which operates in DCM, experimental results demonstrate that the efficiency was increased 1.2% at 10% rated load.
Bo Long,Chu Wang,ZiLin Zhu,Xin Lu,LiJun Huang,YuFei Dai,Yong Liao,FuSheng Li 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
In the grid-connected inverter controller system, conventional PI or PR controller decrease their lowfrequency gain and bandwidth to maintain the stability of the system. However, this degrades the disturbance rejection and current tracking capability. To solve this problem, this paper gives an H∞ robust control scheme based on Numerator Denominator Model method, which has the advantages of simplified current controller design procedure, can place the poles of closed-loop system at the desired place. By properly selecting the weight function, the proposed control scheme can not only achieve good robustness in disturbance rejection capability, but also gives a straight forward to design the dynamic performance. Simulation and experimental comparison results between PR and H∞ controller is demonstrated. The results prove that the proposed control scheme shows obviously improvements on the robustness of inverter and meanwhile does not lose advantages on the dynamic performance.
An Optimized Third Harmonic Injection Method for Three-Phase Cascaded H-Bridge Photovoltaic Inverter
Wang Mao,Xing Zhang,Tao Zhao,Yuhua Hu,Fusheng Wang,Zhiqiang Dai,Renxian Cao 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
The uneven irradiation and temperature in photovoltaic (PV) modules of three-phase cascaded H-bridge (CHB) inverters will cause the unbalanced output power between solar panels, resulting in unbalanced grid current between three phases. In addition, since each phase can be regarded as a single-phase inverter, the second harmonic voltage pulsation of dc-side capacitors is a problem to be solved. To solve these two problems, a third harmonic injection optimization method on the basis of fundamental frequency zero sequence is proposed in this paper. The third harmonic with the same amplitude of fundamental modulated wave signal is injected into the modulated wave signal when the amplitude of synthesized wave signal is no greater than unity. Otherwise, the amplitude of third harmonic is decreased correspondingly to ensure the amplitude of synthesized wave signal being unity. With this method, the dc-side voltage pulsation is effectively restrained and the power balancing limit of CHB inverter is expanded. The feasibility and effectiveness of this method are verified by an experimental prototype of a three-phase seven-level CHB inverter.
( Zhiyong Liu ),( Yinghua Wang ),( Lizhong Song ),( Yinyin Wang ),( Fusheng Dai ) 한국인터넷정보학회 2018 KSII Transactions on Internet and Information Syst Vol.12 No.1
In this paper, we propose a joint adaptive combining and variable tap-length multiuser detector (MUD) for amplify-and-forward (AF) underwater acoustic cooperative interleave-division multiple access (IDMA) communication system. The proposed MUD jointly realizes tap-length adjustment, adaptive combining, and multiuser detection. In contrast to the existing methods, the proposed detector can adaptively combine the received signals from different nodes at destination, and does not need the assumption that full and perfect channel state information (CSI) of all the links at the receiver is known. Moreover, the proposed detector can adaptively adjust the tap coefficient vector and tap-length of each branch according to the specific channel profile of each branch. Simulation results validate the feasibility and show the advantages of the proposed detector against existing counterparts.