Simple scanning methods for a Global-MPP determination in a PV string

Partial shading and/or mismatch of photovoltaic (PV) modules can cause multiple maxima to occur in their power-voltage curves which can mislead conventional Maximum Power Point Tracking (MPPT) algorithms. This relates both to residential installations and large-scale power plants and can result in significant drop in the overall energy yield. To overcome this problem, a new approach generally referred to as Global Maximum Power Point Searching (GMPPS) has emerged. GMPPS methods based on power-voltage curve scanning are able to obtain optimum operating point in a very short time, regardless of the irradiation profile. This paper presents two methods utilizing external circuitry in order to scan the power-voltage curve of the PV string and determine its maximum power. First method utilizes a MOSFET acting as variable resistive load, whereas the latter is based on forcing the PV current using an switched inductor. Simulation study followed by the experimental verification is presented for both methods.