Enhanced Active Power Balancing Capability of Grid-Connected Solar PV Fed Cascaded H-Bridge Converter

Cascaded H-bridge converter is a promising solution for the next generation large-scale photovoltaic (PV) system having both active and reactive power exchange capacity. However, one challenge with this converter is unbalanced power generation among the clusters or cells due to variation in radiation level, temperature, dusting on PV cells etc. In order to inject balanced power to the grid, in this paper, a controlled exchange of reactive power is proposed so that the converter can work with unbalanced power generation within the clusters. The magnitude of reactive power exchange is derived and necessary conditions to prevent overmodulation are discussed. In addition, the magnitude of zero voltage is derived taking into account both active and reactive power exchange with the grid. By exchanging reactive power, the converter can also be used during low-voltage ride-through condition. This paper introduces a novel representation of unbalanced power generation using the barycentric coordinate system which helps to identify regions in the power plane which require the exchange of reactive power. The proposed method is verified through computer simulation and in a laboratory prototype.