Bifurcation Analysis of Standalone Photovoltaic-Battery Hybrid Power System

Standalone photovoltaic-battery hybrid power systems are attractive renewable power generation systems, a popular form of which is based on a photovoltaic system and a battery connected to an output dc bus via a buck converter and a bidirectional buck/boost converter, respectively. Due to variation of the available sunlight intensity, the battery voltage and load condition, the system´s structures and operating modes are switched from time to time. The dynamic behavior is thus quite complex, and the design for stable operation of the system requires consideration of the stability conditions for all possible operating modes. This paper studies the dynamic behavior of this system and reveals the smooth and non-smooth bifurcation phenomena. Under certain conditions, when the system switches its operating mode, a non-smooth bifurcation, manifested as a jump from stable to unstable behavior, has been observed and verified with full-circuit simulations. Moreover, a detailed analysis based on averaged modes is performed to identify the two types of bifurcation and evaluate the stability boundaries of the system. The results provide useful insights and information about the behavior of the system and the interacting effects of control parameters on the design of the control loops.