An innovative perturb, observe and check algorithm for partially shaded PV systems

The performance of every photovoltaic (PV) module constituting a PV system can be slightly or strongly different from each other. This factual functioning of PV systems results in some new effects to bear in mind, including the appearance of new peak power points on the output P-V characteristic. However, traditional Maximum Power Point Tracking (MPPT) control methods do not manage these phenomena and can get lost easily. Even though many papers have been reported recently in relation to new MPPT control techniques, none of these solves satisfactorily the problem of local Maximum Power Points (MPPs). In fact, despite their complexity, the operating point is likely to converge on a local MPP under certain conditions reducing significantly the global efficiency of the PV system. In order to overcome this drawback, a new MPPT is proposed consisting of a traditional Perturb & Observe (PO) algorithm but improved with a second stage able to detect these anomalies on the PV generator curve. With this aim, the casuistry of the problem of local MPPs has been analyzed in depth. From the obtained conclusions a new checking stage has been developed and tested. The experimental results carried out have shown not only the capability to find the real MPP under any circumstance but also the facility to get it in a fast and reliable way.