Digital control strategy for a buck converter operating as a battery charger for stand-alone photovoltaic systems

This paper presents the design of a digital control strategy for a dc-dc type Buck converter used as an efficient lead acid battery charger in isolated electric photovoltaic systems. The strategy is designed to be implemented in a digital signal processor (DSP). The control acts depending on the state of charge of the batteries by regulating the drive duty cycle with the proper combination of incremental conductance MPPT technique and precise control of the battery current according to three charging stages, providing a joint solution which on one hand maximizes the production of solar energy available in the PV array, and on the other ensures a long battery lifetime, both aspects, which are generally investigated independently in technical literature, are treated simultaneously in our approach. The work explains in detail the converter modeling, the project of the compensator, as well as the development of MPPT used. Validation simulations are done via Matlab and experimental results from a prototype low power TMS320F2812 using a DSP from Texas Instruments, are provided and discussed, which show satisfactory performance of the proposed control system.