Closed-Loop Design for Standalone Photovoltaic-Battery Hybrid Power System

Abstract

The photovoltaic-battery hybrid power system is constructed with photovoltaic panels and a battery, which are connected to the load via a boost converter and a bidirectional buck/boost converter, respectively. Depending on the amount of available solar power, the photovoltaic panels may operate in a maximum power point tracking (MPPT) mode or off-MPPT mode to regulate the output voltage, and at the same time, the battery may provide power to the load or store energy from the solar power. The whole system is thus designed to operate with multiple operating modes. Compared to the system of single operating mode, the stability analysis and closed-loop design is much more difficult, as the control loops are usually coupled with each other and the design for stable operation of such system requires consideration of the stability conditions for all possible operating modes. To design the closed-loop, the commonly used small-signal analysis method based on averaged state-space is helpless here, and then the nonlinear analysis method with discrete-time mapping model is performed to evaluate the stability boundaries of the system. The parameters of the closed-loop are chosen in the stable region of the stability boundary diagrams. Moreover, a prototype is built and the experimental results are shown to verify the nonlinear analysis method in the design of closed-loop.