Accelerated Aging Test of Metallized Film Capacitors in Modular Multilevel Converter Based on Mission Profile Emulator

As a key component of the submodule (SM), capacitors play a crucial role with respect to the reliability of the modular multilevel converter (MMC) system. The accelerated aging test is an effective way to assess the availability and lifetime of capacitors. In typical floating aging tests of capacitors, the capacitors under test are subjected to small or no current ripples, constant DC voltage or sinusoidal voltage ripples, and high ambient temperature/humidity. These ideal testing conditions can no longer reflect the actual aging characteristics of capacitors in MMC applications, where the loading behaviors of capacitors are much more complex. Consequently, an accelerated aging test method for film capacitors based on mission profile emulation is proposed in this digest. The degradation process of capacitors is tested under the electrical and thermal stresses reproduced by a mission profile emulator (MPE) for one submodule of the MMC system. Compared with conventional aging tests, the capacitor under the realistic mission profile reveals a much faster aging rate and a crucial factor of short lifetime. These new discoveries provide a more correct understanding and estimation of the reliability performance of capacitors in the MMC system.