PV plants with distributed MPPT founded on batteries

Abstract

This paper introduces and tests a new way of using batteries within a PV plant endowed with a distributed maximum power point tracker (DMPPT). Batteries are used in a distributed framework and they can make possible both the conventional energy storage service and the optimisation of the PV generation. As well known, energy storage is on the basis for solving a lot a problems that are emerging on distribution grids due to the rapid consolidation of the distributed generation. In this paper, it is shown as in PV plants the energy storage availability together with a properly selected value of the rated voltage of batteries can simply avoid generation losses caused by variations on both grid/load operating conditions and also on solar irradiance levels; a further regulation of the rated voltage of batteries, obtained by means of DC/DC converters, can compensate also for generation losses caused by variations on working temperature of PV cells. Finally, batteries used in a distributed framework can guarantee the generation optimisation also in presence of relevant mismatches among PV modules of the whole PV field. In comparison with PV plants with conventional DMPPT (with no energy storage or with a centralized energy storage) the DC voltage at the input terminal of the inverter is very stable and no dangerous overvoltages occur not even in case of strong mismatches among powers generated by different PV modules of a PV field, so the generation of the maximum power is always possible and major costs for batteries acquisition and maintenance can be easily justified. Experiments on a small-power prototype and Pspice numerical simulations are used to demonstrate the usefulness and the practical interest of the proposal.