Optimization of distributed maximum power point tracking PV applications: The scan of the Power vs. Voltage input characteristic of the inverter

• In DMPPT PV applications, the energetic efficiency depends on the several factors.
• In the mismatched PV systems, the joint adoption of the CMPPT and DMPPT techniques is necessary.
• A new control technique for the optimization of DMPPT is proposed.
• The proposed technique is based on the scan of the Power vs. Voltage characteristic of the inverter.
• The first advantage of the proposed technique is the high energetic efficiency.

In order to overcome the drawbacks associated to mismatching operating conditions in PV systems it is possible to adopt one DC/DC converter (microconverter) for each PV module. The aim of microconverters is that of carrying out the Distributed Maximum Power Point Tracking (DMPPT), that is the MPPT of each PV module rather than of the whole PV field. Standard PV systems adopts instead central inverters which carry out the Central Maximum Power Point Tracking (CMPPT), that is the MPPT of the whole PV array. The DMPPT alone is not enough in order to get the actual maximization of the energetic efficiency of the PV system. Instead, it is necessary to couple the DMPPT technique with a suitable CMPPT technique. In this paper it will be shown how to properly optimize the CMPPT technique. In particular, the considered CMPPT technique is based on the periodic scan of the Power vs. Voltage characteristic seen at the input by the inverter. The aim of such a scan is to locate the optimal operating value of the bulk inverter voltage vb, that is the value of vb in correspondence of which the power extracted from the PV source is the maximum one. It will be shown that, despite of the apparent simplicity of such a CMPPT technique, much care is needed in order to avoid errors due to the peculiar shape assumed, under mismatching operating conditions, by the Power vs. Voltage characteristic seen at the input by the inverter. In fact, such a characteristic may exhibit the presence of multiple peaks and/or flat parts and/or nearly vertical portions which may easily lead the CMPPT technique to the error and, consequently, may cause a potentially significant waste of the available energy. The results of numerical simulations fully confirm the validity of the theoretical predictions.