Nonlinear controller design and stability analysis under power management of autonomous PV systems

A stable controller and power management design for an autonomous photovoltaic (PV) system that includes battery storage devices is proposed in this paper. Both the PV and the storage system are interfaced to a dc load, each via a dc/dc boost power electronic converter. To proceed with the system stability analysis, the complete nonlinear dynamic model of the composite system is developed by taking into account the PV source, battery and converters dynamics. It is shown that the open-loop system has the passivity property, which is preserved in the closed-loop form by suitably designing proportional-integral controllers for the duty-ratio inputs of the power converters. Based on this property, a new sequential method is developed that provides a Lyapunov function capable to prove input-to-state stability (ISS) for the closed-loop system. The ISS property is finally combined with an appropriate power management strategy to guarantee stable operation of the complete autonomous PV system. Simulation results under two different scenarios verify the theoretical analysis and the good performance of the system.