Exact Maximum Power Point Tracking of Grid-Connected Partially Shaded PV Source Using Current Compensation Concept

Under partially shaded conditions, series connection of photovoltaic (PV) modules results in the flow of lowest current in the string corresponding to the most shaded module, reducing the overall power output. Power output can be maximized by incorporating module-level “distributed” maximum power point tracking (DMPPT) wherein the current of each module is compensated by regulating its voltage at the respective maximum power point (MPP) value by connecting a dc-dc converter in parallel. Existing current compensation schemes are either too complex or inaccurate. This paper proposes a novel DMPPT scheme using current compensation, which is simple to implement and yet provides an accurate compensation, resulting in exact maximum power point tracking (MPPT). In the proposed scheme, each PV module is resonated through a special arrangement in the shunt-connected flyback dc-dc converter. The secondary-side diode in the flyback converter is replaced by a power mosfet with an antiparallel diode. The converter operates in two modes: resonant MPPT mode and normal flyback mode. An intelligent controller tracks the MPP of the modules while they resonate. An output switch decouples the PV source from the grid momentarily, while the MPP is tracked. All the results of this work, including experimental validation, are presented.