Feasibility Study of a Fully Decentralized Control Scheme for PV Cell-Level Cascaded H-Bridge Inverters

Photovoltaic (PV) cell-level inverters have recently gained popularity, as they provide individual maximum power point tracking and energy management, minimizing so the mismatch losses, caused by partial-shading, degradation effects and cell manufacturing variations in solar modules and arrays. In this article, a fully decentralized control scheme, applicable to PV cell-level inverters in cascaded H-bridge (CHB) configuration is presented. A feasibility study is carried out, considering individual PV cell inverter controllers, eliminating the need for data exchange among them, or with the central higher-level controller. At first, the overall concept of the control scheme in grid-tied operation is presented, highlighting the control, synchronization and cell-adjustment challenges. Two alternative controller configurations are presented and analyzed. The first one is based on the well-established sinusoidal pulse width modulation (SPWM) technique, with three different configurations i.e., (a) with active power maximization, (b) with reactive power regulation and (c) with reactive power minimization. The aforementioned schemes are analyzed and compared, highlighting their pros and cons. As for the second configuration, a multilevel-based self-synchronized/self-adjusted scheme is introduced, which minimizes switching losses and facilitates power line communication; however, power curtailment occurs in each cell. The mathematical analysis for the conduction angle calculation in each cell is presented. Finally, an experimental performance assessment for the aforementioned control strategies is performed (on a 4 cell CHB laboratory scale prototype), highlighting the advantages/disadvantages, as well as the implementation challenges of each one.