Enhancing the reliability of single-phase CHB-based grid-connected photovoltaic energy systems

This paper presents a single-phase Cascaded H-Bridge (CHB) inverter for photovoltaic (PV) applications. The adopted control strategy allows the independent control of each dc-link voltage, enabling the tracking of the maximum power point (MPP) of each solar panel. Based on the presented mathematical analysis, the stable operation boundaries of the inverter under unbalanced operation conditions, without any additional controller is explored. A novel reactive power controller is also proposed that enhances the operating range of the CHB inverter. The proposed reactive power controller enables the inverter to operate under unbalanced solar panel conditions, i.e. the worst case, when one panel becomes completely shaded. Performance of the CHB inverter and the corresponding controllers are evaluated based on the digital time domain simulation studies in the PSCAD/EMTDC environment.