Multilevel inverter with improved basic unit structure for symmetric and asymmetric source configuration

Abstract

An improved multilevel inverter (MLI) topology using a new basic unit structure with a reduced number of components is proposed in this study. Its single compact module is made up of two basic units connected to the left and right sides of a packed H-bridge. The topology produces 9-Level output when operated symmetrically and 17-Level output when operated asymmetrically. Identical magnitude of DC sources is used for the symmetrical operation, while non-identical magnitudes in a trinary sequence are used for the asymmetrical operation. The low-frequency modulation scheme is applied for the switching control where the switching angles are pre-calculated. The mathematical formulations for the switching are also considered to reduce the total harmonic distortion (THD) at the output. The proposed topology is also found to be superior in terms of the required number of switches per output level and total blocking voltage compared to conventional and recently reported MLIs. With these merits, real-time installation of the proposed topology will potentially require lesser space and become cheaper. The feasibility of the proposed topology is validated for its 9-Level and 17-Level operations through experimental verification on output characteristics, THD, blocking voltage, power-sharing and efficiency.