Grid-connected single-phase multi-level inverter

Recently, great attention has been addressed for multilevel inverters, as they exhibit low total harmonic distortion (THD) in the output voltage and low electromagnetic interference (EMI). This paper proposes a single-phase five-level pulse width modulation (PWM) inverter for grid connection. The proposed PWM technique has some switches operated at fundamental line frequency and the others operate at inverter switching frequency. The proposed inverter has advantages of less number of components and low THD compared with the conventional multilevel inverter. The inverter operational principles and the switching functions are analyzed in this paper. Moreover, a proportional integral (PI) current control algorithm is designed and implemented in DSPACE DS1103 to keep the current injected into the grid sinusoidal and in-phase with the grid voltage for unity power factor. Simulation and experimental results prove the powerful merits of the proposed multi-level inverter and the capabilities of the proposed PWM technique.