Sliding Mode Control Strategy for Solar Charging of High Energy Lithium Batteries

Lithium-Ion (Li-Ion) batteries have been widely used in Electric vehicle (EV) and several other applications for their lightness and high performance. However, they imply a strict charging procedure. When a photovoltaic (PV) energy source is used, the charging task becomes more sensitive and necessitates a robust control strategy. In fact, the photovoltaic generator (PVG) is a highly nonlinear current source and depends on climatic variations. In this paper, a sliding mode control (SMC) strategy for solar charging of a high energy Li-Ion battery is presented. The control scheme is based on a cascaded control of a Current Fed (CF) synchronous buck converter powered with a PVG. It allows both Maximum Power Point tracking (MPPT) and output voltage or current regulation of the converter. The regulation is principally done by using the (PV) voltage as a control parameter. A charging algorithm providing the suitable PV reference voltage to the SM controller was proposed. Study and stability analysis of the proposed SMC were also included. The main feature of the proposed SMC is to include the PV reference voltage information in both the sliding surface, and in the equivalent control expression using the integral function. The validity of the control strategy was demonstrated through simulations under different radiation levels in both MPPT and constant current-constant voltage (CC-CV) charging modes.