An active capacitor voltage control for symmetrical / non-symmetrical H-bridge flying capacitor multilevel inverter

Flying capacitor multilevel inverter (FCMLI) is one of the most well-known structure of multilevel inverters. In spite of its many advantages, it has some defects such as complex control and high volume because of its bulky capacitors. Furthermore, existing high number of power semiconductors in its structure makes it susceptible to failure. In this paper, to increase ratio of level numbers to components numbers, using of new asymmetrical structures of this inverter (AFCMLI) is suggested. To increase this ratio further, it is proposed to distribute DC link voltages unevenly. Taking these actions complicates control of the converter. To solve this problem, a method is proposed, which simplify control of the AFCMLI considerably. It is computationally very efficient, and it does not require any stored information from memory or a look-up table. Therefore, it permits on-line computation of the switching sequences. Furthermore, it is simply extendible to an arbitrary structure of AFCMLI with any number of levels and any DC link voltage combination without considerable modification. The performance of the proposed method is confirmed by a simulation using PSCAD/EMTDC^®. Based on the simulation studies, this method has satisfactory performance under various operating conditions.