Numerical simulation of output short-circuit capacitor discharge of intrinsically safe switching transistor converter

Abstract

When the intrinsically safe switching converter adopts the IEC spark experimental device for opening and closing explosive test evaluation, the output circuit can be equivalent to a capacitor circuit. In order to study the micro characteristics in the process of short-circuit discharge, the capacitor circuit is equivalent to the same amount of charge according to the law of charge conservation, A two-dimensional plate-to-plate electrostatic model with tungsten wire as anode and cadmium disk as cathode in explosive gas gap is established by particle method (PIC / MCC). The discharge processes of dielectric breakdown, spark discharge and spark maintenance are simulated, and the correctness and feasibility are verified. By analyzing the number of charged particles, the spatial distribution of particles and the change of electric field intensity in the electrode gap, the discharge process of the first three stages of capacitor short-circuit discharge is explained. It is found that the dielectric breakdown in the discharge process of capacitor circuit is only related to the electric field intensity formed by the plate voltage in the electrode gap. When the field enhancement factor is 100 and the field strength is greater than 2x10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> v/m, there is field emission between the electrodes, and the electrode gap can be broken down. The critical breakdown spacing of the electrode plate is 1.2um During the discharge process, the number of electrons in the gap first increases rapidly, then increases slowly, and then decreases slowly after reaching the peak. When the external capacitance is greater than lpF, the number of electrons increases by 1X10? for every 10pF increase. Based on the flat two-dimensional model, this paper analyzes the change trend of electric field in the discharge process, and obtains that the electric field intensity of capacitor in the spark maintenance stage is a fixed value, which is independent of the capacitance value. When the electric field intensity is 9x10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> v/m, the voltage will not drop and maintain at 9V, and the capacitor discharge is in the spark maintenance stage.