Extended operating range of PV module-level CHB inverter

In this paper an enhanced distributed maximum power point tracking (DMPPT) algorithm, along with an improved hybrid modulation method for a photovoltaic (PV) module-level Cascaded H­Bridge (CHB) inverter, is proposed. The advantages and drawbacks of the CHB topology in distributed PV generation systems are highlighted. The main benefits are related to the higher granularity of the PV power control, which mitigates mismatch effects, thus increasing the power harvesting. Nevertheless, heavy unbalanced configurations need to be properly addressed by means of dedicated control action. The proposed control strategy allows to overcome the operating limits of PV CHB inverter, by integrating in the MPPT algorithm a limitation of the individual cell modulation index. Experimental tests carried out on a laboratory prototype of a single­phase seven­level PV CHB inverter, evidence the effectiveness of the proposed control and modulation approach in terms of extended operating range and MPPT efficiency.