Effect of Friction Coefficient on Relative Slippage of Fuel Cell Stack under Mechanical Impact Condition

A simplified finite element model for large polymer electrolyte membrane fuel cell (PEMFC) stack consisting of ten cells is established in order to investigate the internal structure deformation. It is found that the interface slippage occurs when the bipolar plate (BP) and membrane electrode assembly (MEA) are subjected to vertical impact acceleration. Based on this three-dimensional model, the influence of the friction coefficient between BP and MEA on the relative slippage can be analyzed efficiently. The division layer of relative slippage is found and its vibration rule is discussed. It is observed that increasing the magnitude of impact vibration has most significant effect on the movement of the division layer, and the two variables are linearly related when impact acceleration is greater than 5 g. This work provides important insight into the choice of the friction coefficient

An Improved Droop Control Strategy for Low-Voltage Microgrids Based on Distributed Secondary Power Optimization Control

To achieve accurate reactive power sharing and voltage frequency and amplitude restoration in low-voltage microgrids, a control strategy combining an improved droop control with distributed secondary power optimization control is proposed. The active and reactive power that each distributed generator (DG) shares is calculated by extracting load information and utilizing a power sharing ratio, and is reset to be the nominal power to recalculate droop gains. The droop control curves are reconstructed according to the nominal active and reactive power and the recalculated droop gains. The reconstructed active power-frequency droop control can regulate active power adaptively and keep frequency at a nominal value. Meanwhile, the reconstructed reactive power voltage droop control can reduce voltage amplitude deviation to a certain extent. A distributed secondary power optimization control is added to the reconstructed reactive power voltage droop control by using average system voltage. The average system voltage is obtained by using a consensus algorithm in a distributed, sparse communication network which is constituted by all controllers of DGs. As a result, accurate reactive power sharing is realized, average system voltage is kept at a nominal value, and all voltage amplitude deviations are further reduced. Due to the absence of a microgrid central controller, the reliability of the strategy is enhanced. Finally, the simulation results validate the proposed method

Three Representative Island Microgrids in the East China Sea: Key Technologies and Experiences

In recent years, providing green and reliable energy supply to islands has appeared in the strategic plans of many countries. This paper introduces three representative island microgrids that have been built and are operating in the East China Sea. Key technologies of the island microgrids are discussed, including the analysis of island resources and load, selection of energy storage, control strategies, and energy management systems. Through analyzing their operation data for one year, this paper demonstrates the impacts of the three microgrids from the perspectives of technology, economics, and sustainability. Summarizing the experiences and insights gained from their construction and operation, this paper provides references for the future development of island microgrid projects

CD spectroscopy as a fingerprint technique for the structural characterization and determination of absolute configurations of unsymmetric chiral Schiff base Ni(II) complexes

Unsymmetric Schiff base complexes have attracted more attention in recent years due to their diverse effects in catalytic reactions. Due to their high dissymmetry, unsymmetric metallosalen complexes are harder to prepare than symmetric ones. This means that X-ray crystallographic structural determination is sometimes unavailable, so their absolute configurations are determined by circular dichroism (CD) spectroscopy instead. Herein, some quadridentate unsymmetric metallosalen nickel(l]) complexes were synthesized and their structures were characterized by CD spectra. An empirical rule for assignment of the absolute configurations of tetra-coordinated pseudo-planar Ni(II) complexes was put forward. Furthermore, a fingerprint was found to judge whether the metallosalen complexes are symmetric or unsymmetric. (C) 2008 Elsevier Ltd. All rights reserved.Project of Innovation Foundation of Xiamen University [XDKJCX20061027]; National NSF of China [20773098, 20572061]; Projects of International Cooperation MOST [2006DFA43030]; Major Program of National Natural Science Foundation of China [20732004