Investigation of single-phase multilevel inverter based on series/parallel-connected H-bridges

This paper investigates a multilevel inverter composed of series/parallel-connected H-bridges. The presented structure can be used for applications in which is intended to use semiconductor switches with low voltage and low current rating. A comprehensive system model to control the circulating current, an overall control strategy to adjust the output voltage with constant magnitude and frequency, and a level-shifted PWM (LS-PWM) strategy based on a voltage vectors unidimensional and plane analysis are presented. The LS-PWM is capable of mitigating the low-frequency circulating current, thus generating multilevel voltage signal with low harmonic distortion, maximum number of levels, and low dv/dt. In addition, considering a wide range of values of voltages and currents and any power levels, the total converter losses are reduced compared with conventional multilevel converters. Two multilevel conventional inverters with same number of semiconductor switches are used for comparison. Simulation and experimental results demonstrate the feasibility of the studied converter.