In stand-alone photovoltaic (PV) systems, the battery chargers are important to warrantee the energy supply when the sunlight is not available. Such chargers need to perform the maximum power point tracking (MPPT) and to limit the derivative of the batteries charging current to extent their lifetime. This paper proposes a battery charging system formed by a Buck converter, a cascade control of the battery current and the PV panel voltage, and the Perturb and Observe (P&O) MPPT technique. The P&O generates the reference of the panel voltage for the external loop of the cascade control, implemented with a P regulator, whose control action is the reference of the batteries charging current. Such a current reference passes through a derivative limiter before reaching the internal current control loop, which is implemented by a sliding-mode controller (SMC). The paper includes transversality and reachability analyzes of the SMC, as well as the design procedure of the P regulator. The proposed system is validated by simulations in PSIM software to show its capacity to perform the MPPT and to limit the battery charging current derivative at the same time.
Battery charger; photovoltaic panel; Buck converter; sliding-mode control; current derivative limitation