27-Level asymmetric multilevel inverter for photovoltaic energy conversion

This paper presents a novel structure to inject the electric energy from photovoltaic modules to the grid based on a 27-level asymmetric multilevel inverter. This work proposes mixing existing approaches based on string and central inverters to implement a hybrid structure that generates highly sinusoidal waveforms. Indeed, the presented structure allows for a staircase AC voltage waveform with a low level of harmonic distortion, which is a key feature for photovoltaic energy conversion. The proposal is supported with theoretical analyses that include system modeling and a suitable control strategy to track both the active and reactive power. A low power proof-of-concept prototype was built to validate the properness of the proposal. Several dynamic tests were performed, such as severe load impacts, partial shading and fault ride-through capability.