Power Balance Control Scheme of Cascaded H-Bridge Multilevel Inverter for Grid-Connection Photovoltaic Systems

A cascaded H-bridge multilevel inverter has been applied in large scale photovoltaic systems, with the features of modular, distributed maximum power point tracking control scheme and so on. However, the power of photovoltaic modules supplied to each phase of the inverter may be different, introduced by the different irradiance levels and ambient temperatures, leading to the asymmetric grid currents. To deal with the issue, this paper analyzes and compares two different zero sequence component injection methods, and proposes a novel method in which obtaining the amplitude and phase angle of zero sequence component via the directly calculated power errors against above two solutions' drawbacks. So this method possesses clearest physical principle, best dynamic behavior and capacity of providing accurate results to suppress unbalanced power. Finally, the simulation results of a three-phase 5-level cascaded H-bridge inverter validate the effectiveness and feasibility of the developed ideal.