Grid-Connected PV-Plants Based on a Distributed Energy-Storage System and a Multilevel Inverter

Abstract

An innovative architecture for grid-connected PV-plants is introduced and discussed, also on the basis of some recent studies of the Authors. A “distributed” energy storage system is introduced on the PV-plant, in order to obtain a distributed passive and reliable MPPT system together with a high level of availability for the plant generation. Furthermore, once a certain number of stable DC-voltage levels are made physically available on the PV-plant, a multilevel inverter is introduced for interconnecting the PV-plant with the grid, instead of a conventional PWM inverter. In order to contain the complexity of the multilevel inverter circuit, together with its costs and reliability, a cascaded H-bridge simplified architecture is proposed for it; furthermore, in order to optimize its performances and also the life of batteries that are utilized for supplying it, a “duty-cycle swapping” control logic, able to guarantee “uniform” charge-discharge cycles of batteries, is also introduced and utilized. Experimental tests and measurements are reported to show the usefulness of the proposed idea of inserting a distributed energy storage system on the PV-plant, while numerical simulations, operated by the MATLAB/Simulink tool, are utilized to investigate the performances of the simplified multilevel inverter also under critical solar irradiation conditions. Finally, some theoretical considerations are also developed about the intrinsic capabilities of the proposed architecture of the PV-plant to effectively satisfy some recent constraints introduced by the IEEE 1547.8 standard and also by the most recent Italian standards CEI 0-21 and CEI 0-16
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