In this paper, two new optimized common-mode voltage reduction PWM (CMVRPWM) strategies based on solving the established constrained nonlinear programming models in the time domain are proposed and analyzed. The proposed current ripple losses optimized CMVRPWM (CRLO-CMVRPWM) minimizes the mean-square values of the three-phase current ripples by calculating the optimized special solutions of the voltage-second balance equations under the designed switching sequences. CRLO-CMVRPWM can achieve better output waveform quality than the existing methods. The proposed switching losses optimized CMVRPWM (SLO-CMVRPWM) on-line optimizes the bus-clamping styles according to the phase currents to minimize the switching losses under different load power factors. Compared to the near-state PWM (NSPWM) with fixed bus-clamping styles, SLO-CMVRPWM can reduce more switching losses in broader range of the modulation index. Simulation and experiment results verify the superiority of the proposed strategies to the conventional ones. Index Terms-Common-mode voltage (CMV), constrained nonlinear programming, current ripple, linear modulation range, pulsewidth modulation (PWM), switching losses, voltage-source inverter (VSI). in 2009 and 2012, respectively.He is currently working toward the Ph.D. degree in power electronics and drives in China University of Mining and Technology.His current research interests include high-power three-level explosion-proof inverter modeling, fault-tolerance control of inverters.

Water pollution caused by Cu 2+ ions poses a significant threat to the ecosystem and human health, hence the development of highly cost-effective, highly operation-convenient and highly efficient natural polymer-based adsorbents is urgently needed. To overcome this serious problem, a novel cost-effective magnetic chitosan composite adsorbent (CsFeAC) was prepared with magnetic macroparticles and highly porous activated carbon carrier using the sol-gel method. Several methods, namely SEM, BET, FTIR, XRD, TGA and VSM, were applied to characterize the adsorbent. Batch tests were conducted to investigate Cu 2+ adsorption properties of CsFeAC at different pH values, contact time, initial Cu 2+ concentrations and temperatures. The adsorption fits better to the Langmuir isotherm and follows the pseudo-second-order model, suggesting that it is a monolayer adsorption and the rate-limiting step is the chemical chelating reaction. The saturated adsorption capacity is found to be 216.6 mg/g. Thermodynamics analysis suggests that the adsorption process is endothermic, with increasing entropy and spontaneous in nature. BET and XRD tests confirm that the higher specific surface area and lower crystallinity of CsFeAC significantly improve the absorption capacity and rate. FTIR spectra reveal that the amino and hydroxyl groups play an important role in the chelating adsorption. The supermagnetic property of CsFeAC facilitates its easy separation characteristic. Further recycling experiments show that CsFeAC still retains 95% of the original adsorption following the 5 th adsorption-desorption cycle. All these results demonstrate that CsFeAC is a promising recyclable adsorbent for removing Cu 2+ .

No abstract

This study aimed to develop a practical semi-empirical mathematical model of membrane fouling that accounts for cake formation on the membrane and its pore blocking as the major processes of membrane fouling. In the developed model, the concentration of mixed liquor suspended solid is used as a lumped parameter to describe the formation of cake layer including the biofilm. The new model considers the combined effect of aeration and backwash on the foulants' detachment from the membrane. New exponential coefficients are also included in the model to describe the exponential increase of transmembrane pressure that typically occurs after the initial stage of an MBR operation. The model was validated using experimental data obtained from a lab-scale aerobic sponge-submerged membrane bioreactor (MBR), and the simulation of the model agreed well with the experimental findings.