Study On The Performance Of Pulsed Capacitors Based On The Theory Of Space Charge

As the most popular pulsed energy storage unit, the pulsed capacitor is one of the key components in pulsed power technology. Due to the high energy density, long lifetime and high reliability, metallized film capacitors have been the most widely used pulsed capacitors. Based on the theory of space charge, this paper focuses on the voltage-maintaining performance and lifetime characteristics of metallized BOPP film capacitors.Firstly, this paper analyses the formation of traps and space charge in dielectrics, as well as the relationship between the performance of pulsed capacitors and space charge. Based on the theory of energy band, the formation of traps and the process of trapping and detrapping are explained. Space charge can be formed by three ways: the electrode injection, the thermal dissociation of impurities and the space charge polarization. The voltage-maintaining performance of pulsed capacitors is related to the space charge polarization, and the lifetime characteristic is related to electrode injection.The voltage-maintaining performance of pulsed capacitors is studied. A simulation model is established according to the extended Debye model. And the comparison of simulation and measurement results shows that, when the temperature is between 25℃ and 70℃, the voltage is between 1kV and 3 kV, and the charging time is between 10 s and 80 s, the deviation of voltage drop percents of simulation value and measurement value is less than 2.5%, which verifies the feasibility of predicting the voltage drop by simulation. The influence factors of voltage-maintaining performance are investigated, and the results show that the rise of temperature and applied voltage, as well as the decrease of charging-keeping time, will weaken the voltage-maintaining performance of pulsed capacitors.Finally, the lifetime characteristics of pulsed capacitor are researched. The lifetime test platform is set up and conclusions are obtained that low repetitive frequency can shorten the lifetime of pulsed capacitors. Based on this conclusion, the injected space charge test platform, the system of TSDC, and the test platform of trap density are set up, and the relationship among repetitive frequency, the injection of space charge and the trap parameters is studied. Conclusions are drawn that at a lower repetitive frequency, the amount of space charge injected by electrode is larger. The increase of space charge at low repetitive frequency will accelerate the aging of the dielectrics and increase the trap energy and density, which will reduce the breakdown field strength and shorten the lifetime of the capacitor.