Modeling and control of a battery connected standalone photovoltaic system

This paper presents modeling and control of a standalone photovoltaic (PV) system in which a battery is used as a backup source for power management between the source and the load. Lead-acid battery is commonly used in high power PV applications due to its low cost and availability in large size. The modeling of PV system and lead-acid battery by using the corresponding equivalent circuits are discussed here. Three independent control loops are proposed to control the standalone PV system; MPPT control loop for extracting maximum power from PV module under different solar irradiation, battery control loop for bidirectional power flow between battery and dc-link through buck-boost converter to keep the input dc voltage constant, and inverter control loop for maintaining good voltage regulation and achieving fast dynamic response under sudden load fluctuations. The stability of the above control loops are verified by using Bode diagram. Finally the proposed method is applied to 2 kW, 110 V, 50 Hz, two-stage single-phase standalone PV system. The simulation and the experimental results are presented to validate the theoretical analysis, effectiveness and feasibility of the proposed control strategy.