Modified Single-Carrier Multilevel SPWM and Online Efficiency Enhancement for Single-Phase Asymmetrical NPC Grid-Connected Inverter

In this paper, a modified single-carrier and multimodulation sine pulse width modulation (MSCMM-SPWM) is proposed to simplify the implementation of the single-phase asymmetrical neutral-point clamped grid-connected inverter (ANPC-GCI) for the PV generation system application. Furthermore, the expressions of the total switching loss and grid current total harmonic distortion (THD) of ANPC-GCI controlled by the proposed MSCMM-SPWM are derived. Then taking the grid current THD meet the grid-connected standard in the entire operational range as the constraint, an efficiency enhancement scheme for ANPC-GCI based on online adjusting the carrier frequency and the obtained THD expression is proposed. The control configuration of ANPC-GCI, including the proposed MSCMM-SPWM and online efficiency enhancement scheme, is designed. The detailed experimental results verify the correctness and feasibility of the proposed MSCMM-SPWM and the efficiency enhancement scheme.