The purpose of this paper is to mimic, using the Monte Carlo Simulation, the electron avalanche growth by tracking individual paths of charged particles; the effect of space charge is included by solving the Poisson equation. An electronic avalanche is produced, when an electric field, sufficiently intense, is applied to a gas. At some stage of formation of free electrons and ions; the electronic avalanche becomes a conductor channel, and then self sustainment of the discharge. The simulation is carried out in O2 gas for two different pressures, under the effect of uniform electrical fields. The streamer breakdown criterion for the different applied uniform fields is examined.
We present in this paper a comparative study between two control strategies of electrical machines: Direct Torque Control (DTC-SVM), and Predictive Direct Torque Control (MPDTC). The first algorithm based on PI controllers, where the torque and the flux are regulated by a PI controller; we present a conception method of the PI controllers, associated with the flux and the torque regulation loops and gives analytical formulas for the proportional and integral gains. We also present in the second algorithm. The Predictive Direct Torque Control based on the linearization input-output of the machine. The technique of the linearization is used to give a model linearized and uncoupled from the machine for the anticipation of future behavior of the output. Following the formulation of both approaches, their implementation in the Matlab-Simulink environment has been treated. It has been found that the second approach MPDTC yields high dynamic performances in the whole speed range. These performances are characterized by a low torque ripple. However, requires much more CPU time than the first one.
In this work, we introduced a new robust hybrid control to an induction motor (IM), based on the theory of fuzzy logic and variable structure with sliding-mode control (SMC). As the variations of both control system parameters and operating conditions occur, the conventional control methods may not be satisfied further. Fuzzy tuning schemes are employed to improve control performance and to reduce chattering in the sliding mode. The combination of these two theories has given high performance and fast dynamic response with no overshoot. As it is very robust, it is insensitive to process parameters variation and external disturbances.
The aim of this paper consists of presenting optimization criteria of coil dimensions and the exciting field frequency in order to improving eddy current probe sensitivity for small and deep cracks under fasteners. To accomplish this task, we have studied the influence of coil inner radius, coil height and exciting frequency on probe sensitivity. Then, an algorithmic searching technique is applied to determine the optimal values of the previous parameters. Hence, the obtained results have revealed that the optimum inner radius corresponds exactly to the fastener head outer radius. Furthermore, it has been noticed that as well as the coil height is reduced while keeping the same number of turns, the probes sensitivity increases. Indeed, the use of stacking flat micro-coils is well adapted. In addition, the calculation of the optimum values of the frequency demonstrate that this parameter depend relatively on the defect position, its radial and vertical depth.
