In this article we introduce a mathematical algorithm for the optimization of the doping distribution in power semiconductor devices in order to increase the breakdown voltage and decrease the on-state resistance of these devices. The algorithm is based on the computation of the doping sensitivity functions of the breakdown voltage and on-state resistance and uses a gradientbased iterative method to compute the optimum doping profile in metal-oxide-semiconductor field-effect transistors (MOSFET), insulted gate bipolar transistors (IGBT), p-n junctions, etc. Since the optimization is performed using gradient descents it is perfectly suited for the optimization of doping concentration at all the nodes of finite element discretizations simultaneously (in which the number of nodes can be as large as 10 4 -10 6 ). Due to the large simulation time of each individual device, traditional heuristic optimization methods such as genetic algorithms, swarmoptimization, or evolutionary algorithms are practically impossible to use (traditional heuristic optimization algorithms are used when the number of optimization variables is smaller than 10). Numerical results for the doping sensitivity functions of the breakdown voltage and on-state voltage are presented and discussed for a standard IGBT device.
In this article we develop a mathematical model and analyze the variability of discharge characteristics and impedance spectra in Li-air batteries with organic electrolyte. These batteries are well known to display a large variability of their characteristics from battery to battery (particularly of their specific capacity, energy and power densities), however, the exact reasons of this variability are still under investigation. Our model shows that the intrinsic variability of the pore microstructure which include the variability of the porosity and specific area from one macroscopic location to another macroscopic location inside the same battery and from one battery to another battery can be, at least in part, responsible for the large discrepancy of the results reported in the literature for the discharge characteristics and impedance spectra. It is shown that, while the variance of the specific capacity decreases slightly when the discharge current of the cell is increasing, the relative varianceto-mean ratio increases dramatically.
The energy router composed of double active bridge (DAB) can interconnect multiple voltage level AC distribution network through DC lines to form AC/DC hybrid distribution network. The fault types of the system are diverse and the fault characteristics are complex. This paper studies the fault characteristics of the system in detail. The single-phase grounding fault of AC network side and single-phase grounding fault of AC valve side occurred in the system. This paper explored the impact of the AC side of the system after the above failure, and make a detailed comparative analysis. The results show that DAB can isolate the influence of AC side fault, and provide theoretical basis for the selection of grounding mode and the design of protection system for AC/DC hybrid distribution network.
The doping sensitivity functions provide a powerful tool to analyze the effects of doping variations on the parameters of power semiconductor devices. They can be coupled with gradient-based optimization algorithms to design the doping profiles in power devices and are instrumental in the statistical analysis of these devices. In this article we discuss about applications of the doping sensitivity functions in power devices. We focus mostly on maximizing the breakdown voltage and minimizing the on-state resistance and on the numerical evaluation of the acceptor and donor sensitivity functions of the breakdown voltage. Simulation results are presented and analyzed for a standard insulated gate bipolar transistor.
A three dimensional quasi-state numerical model of fluid flow ,heat transfer process in the melted pool for composite coating was developed ,and the temperature profile were successfully calculated by finite element software. Numerical results show that when the laser power is 1.5KW, the coating melts and the matrix does not melt, forming good shape; when the laser power is 1.6KW, the thermal stress increase, the binding of substrate and coating occurs crack, the experiment is agreement with that calculated.
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