Interfacial behaviors in Cu/molten Sn–58Bi/Cu solder joints under coupling with thermal and current stressing

Fengjiang Wang,Hong Chen,Dongyang Li,Zhijie Zhang,Xiaojing Wang 대한금속·재료학회 2019 ELECTRONIC MATERIALS LETTERS Vol.15 No.1

The interfacial behaviors of Cu/molten Sn–58Bi/Cu solder joints under the coupling eff ect of a temperature gradient and thecurrent stressing have been investigated. The most obvious change of the interfacial behaviors under the individual electromigration(EM) and thermomigration (TM) in molten solder was the asymmetrical growth of interfacial Cu–Sn intermetalliccompounds (IMCs), which grew rapidly as the stressing time prolonged. The growth rates of the interfacial IMCs inducedby TM under a temperature gradient of 40 °C/cm were slightly faster than EM under the current density of 0.5 × 10 4 A/cm 2 . However, the microstructure evolution and interfacial behaviors changed obviously when the thermal was distributedunevenly across the entire solder stripe under current stressing. It was found that there was a Bi-rich layer adhered to theanode side and a distributed Cu 6 Sn 5 phase existed in the solder matrix when the anode and the cold end were at the sameend. Additionally, a large number of Bi-blocks and Cu–Sn IMCs were dramatically observed in the solder matrix when theanode and the hot end were on the same side. The main reason for this result may be attributed to the signifi cant change ofthe diff usion of Bi atoms under the thermo-electric coupling conditions. In the initial melting stage of solder, the Bi atomsin molten Sn–58Bi solder rapidly diff used to the anode and then began to be reversely dissolved into the solder matrix. Theexperimental results proved the additional temperature gradient played a positive or negative role on the reverse dissolutionof Bi atoms in the heat preservation process.

Elimination of the State-of-Charge Errors for Distributed Battery Energy Storage Devices in Islanded Droop-controlled Microgrids

Wang, Weixin,Wu, Fengjiang,Zhao, Ke,Sun, Li,Duan, Jiandong,Sun, Dongyang The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.4

Battery energy storage devices (ESDs) have become more and more commonplace to maintain the stability of islanded power systems. Considering the limitation in inverter capacity and the requirement of flexibility in the ESD, the droop control was implemented in paralleled ESDs for higher capacity and autonomous operation. Under the conventional droop control, state-of-charge (SoC) errors between paralleled ESDs is inevitable in the discharging operation. Thus, some ESDs cease operation earlier than expected. This paper proposes an adaptive accelerating parameter to improve the performance of the SoC error eliminating droop controller under the constraints of a microgrid. The SoC of a battery ESD is employed in the active power droop coefficient, which could eliminate the SoC error during the discharging process. In addition, to expedite the process of SoC error elimination, an adaptive accelerating parameter is dedicated to weaken the adverse effect of the constraints due to the requirement of the system running. Moreover, the stability and feasibility of the proposed control strategy are confirmed by small-signal analysis. The effectiveness of the control scheme is validated by simulation and experiment results.

Dual-Side Circulating Currents Free TPS Control for Dual Active Bridge DC-DC Converter and Its Implementation

Fengjiang Wu,Guizhong Wang,Xiaoguang Li 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

In this paper, a novel triple phase-shift (NTPS) modulation is proposed first to eliminate the dual-side circulating currents of isolated dual-active bridge DC-DC converter. Furthermore, the current stress of the proposed NTPS control when the phase shift is tuned in two regions is derived and compared with each other and the best tuning region of the phase shift is determined to achieve the optimal current characteristics. The steady-state and transient performance of two implementation methods of NTPS control are discussed and the better one is determined. The corresponding experimental results of the proposed NTPS control validate its accuracy and validity.

Elimination of the State-of-Charge Errors for Distributed Battery Energy Storage Devices in Islanded Droop-controlled Microgrids

Weixin Wang,Fengjiang Wu,Ke Zhao,Li Sun,Jiandong Duan,Dongyang Sun 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.4

Battery energy storage devices (ESDs) have become more and more commonplace to maintain the stability of islanded power systems. Considering the limitation in inverter capacity and the requirement of flexibility in the ESD, the droop control was implemented in paralleled ESDs for higher capacity and autonomous operation. Under the conventional droop control, state-of-charge (SoC) errors between paralleled ESDs is inevitable in the discharging operation. Thus, some ESDs cease operation earlier than expected. This paper proposes an adaptive accelerating parameter to improve the performance of the SoC error eliminating droop controller under the constraints of a microgrid. The SoC of a battery ESD is employed in the active power droop coefficient, which could eliminate the SoC error during the discharging process. In addition, to expedite the process of SoC error elimination, an adaptive accelerating parameter is dedicated to weaken the adverse effect of the constraints due to the requirement of the system running. Moreover, the stability and feasibility of the proposed control strategy are confirmed by small-signal analysis. The effectiveness of the control scheme is validated by simulation and experiment results.

Improved virtual quadrature-coordinate EPLL considering input harmonics and DC offset

Yin, Dong,Wang, Guizhong,Wu, Fengjiang,Guo, Zhizhong The Korean Institute of Power Electronics 2020 JOURNAL OF POWER ELECTRONICS Vol.20 No.1

The two-phase quadrature-coordinate enhanced phase-locked loop (QC-EPLL) possesses a better transient performance than the standard single-phase EPLL. In this paper, a virtual QC-EPLL (VQC-EPLL) based on signal delay method is proposed to realize using QC-EPLL to estimate the synchronization information of the single-phase grid. Furthermore, the effect of the input harmonics and DC offset on the VQC-EPLL is originally derived and it reveals these nonideal conditions causes the unexpected periodical ripple in the estimated amplitude, phase angle and frequency. Furthermore, the improved approach, including the DC offset estimator and finite impulse response filter is proposed to eliminate these effect. Detailed experimental results verify the correctness and feasibility of the theoretical analysis and proposed improved approach.

The Effects of Job Crafting on Task and Contextual Performance: Focusing on the Mediating Effect of Work Engagement

Feng JIANG,Li WANG,Lei YAN 한국유통과학회 2022 The Journal of Industrial Distribution & Business( Vol.13 No.5

Purpose: Research on job crafting has thus far focused on how alter job demand and resources behaviors relate to employee task performance. However, job crafting behaviors do not necessarily have an impact only on task performance, but also on employees’ contextual performance, a phenomenon that has little research in job crafting research. Therefore, this study aims to investigate the effect of job crafting on task performance or contextual performance and the mediating effect of work engagement between them in the Chinese context. Research design, data and methodology: In order to achieve the above research goals and test the proposed hypotheses, we used a cross-sectional design and a self-administered questionnaire to collect quantitative data from September 8, 2021 to September 27, 2021 among knowledge workers in Shandong Province various financial companies and finally analyzed 211 questionnaires. Descriptive statistics and research model analysis were performed using SPSS 25.0 Version and AMOS 27.0 Version to test the developed hypotheses. Results: The results are as follows; firstly, the study showed that job crafting of employees had a significant positive impact on task performance and contextual performance. Secondly, the higher job crafting of employees, the higher their work engagement. Thirdly, this study showed that work engagement of employees had a positive impact on task performance and contextual performance. Fourthly, we predicted and found that work engagement of employees had a positive mediating effect between job crafting and task performance and a positive mediating effect between job crafting and contextual performance. Overall, this study showed that the proactive job crafting behaviors of employees enhance their engagement for their work, which in turn improves task performance and contextual performance. Conclusions: This paper develops job crafting research by exploring the positive impact of job crafting on employees' task performance or contextual performance through their work engagement. It also proposes that both job crafting behaviors and work engagement are important approaches to improve employees' task performance or contextual performance. Practical implications for organizations, such as increasing employee' work engagement, as well as the limitations and suggestions are concluded for the future research directions.