Current Issue : July - September Volume : 2019 Issue Number : 3 Articles : 5 Articles
In this study, in order to explore the failure mode of ZnO varistors under multiple lightning\nstrokes, a five-pulse 8/20...........
The increase in demand for clean, safe, and environmentally friendly renewable energy\nsources faces several challenges such as system design and reliable operations. DC microgrid (MG)\nis a promising system due to higher efficiency and natural interface to renewable sources. In the\nhierarchical control of DC Microgrid, the V-I droop control is deployed usually in primary control\nlevel for common load sharing between converters. However, conventional droop control causes\nimproper current sharing, voltage variations, and circulating current regulation due to the presence of\ndroop and line resistance between converters. The aim of this paper is to presents the primary control\nlevel design of buck converters in current mode control according to the concepts of time constant and\ntime delay, and secondary control design for parallel operations in distributed manners by combining\nmethods, namely, low bandwidth communication (LBC), circulating current minimization techniques,\nand average voltage/current control. Moreover, different time delays are used for two converters to\ntestify the effects of communication delays on current sharing and voltage restoration. The simulation\nis done for 2 * 2.5 KWdc parallel buck converters in PLECS (a Simulation software used for high\nspeed simulation for power electronics) environment which shows excellent results in minimizing\ncirculation currents, enhancing proportional current sharing, and restoring the grid voltage....
We establish a novel hybridmodel of a continuous conductionmode buck converterwith a constant power load based on themixed\nlogical dynamical modeling method. Based on the proposed model, the influence of the constant power loadâ??s negative impedance (RCPL) on the dynamics of the buck converter with a constant power load is studied by computing bifurcation diagrams and the\nspectrum of the largest Lyapunov exponents with the variation of the absolute value of RCPL. Numerical results show that the\nsystemâ??s bifurcations exhibit two different types of behavior, namely, Hopf bifurcations and state jumping. Moreover, the accuracy\nand effectiveness of the established mathematicalmodel are verified via simulation and experimental results. Because of including\ndifferent discrete mappings of the system exhibited in different working modes in a unified model, the proposed hybrid model\nsolves the problemof choosing different discretemappings according to different working models.That is, the hybridmodel in this\npaper provides a new unified model for future research on the dynamic properties and design of controllers for such systems....
The brushless director current (DC) motor is a new type of mechatronic motor that has been developed rapidly with the\ndevelopment of power electronics technology and the emergence of new permanent magnet materials. Based on the speed\nregulation characteristics, speed regulation strategy, and mathematical model of brushless DC motor, a parameter optimization\nmethod of proportional-integral (PI) controller on speed regulation for the brushless DC motor based on particle swarm\noptimization (PSO) algorithm with variable inertia weights is proposed. The parameters of PI controller are optimized by PSO\nalgorithm with five inertia weight adjustment strategies (linear descending inertia weight, linear differential descending inertia\nweight, incremental-decremented inertia weight, nonlinear descending inertia weight with threshold, and nonlinear descending\ninertia weight with control factor). The effectiveness of the proposed method is verified by the simulation experiments and the\nrelated simulation results....
This paper concerns the modeling of eddy current losses in conductive materials in the\nvicinity of a high-frequency transformer; more specifically, in two-dimensional problems where a high\nratio between the object dimensions and the skin-depth exists. The analysis is performed using the\nSpectral Element Method (SEM), where high order Legendreâ??Gaussâ??Lobatto polynomials are applied\nto increase the accuracy of the results with respect to the Finite Element Method (FEM). A convergence\nanalysis is performed on a two-dimensional benchmark system, for both the SEM and FEM. The\nbenchmark system consists of a high-frequency transformer confined by a conductive cylinder and is\nfree of complex geometrical shapes. Two different objectives are investigated. First, the discretizations\nat which the relative error with respect to a reference solution is minimized are compared. Second,\nthe discretizations at which the trade-off between computational effort and accuracy is optimized are\ncompared. The results indicated that by applying the SEM to the two-dimensional benchmark system,\na higher accuracy per degree of freedom and significantly lower computation time are obtained with\nrespect to the FEM. Therefore, the SEM is proven to be particularly useful for this type of problem....
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