Control Strategies for a Hybrid PV/Battery System with Grid-Connected and Island Mode

This paper has developed a hybrid PV/Battery system with the ability of grid-connected and island operating control, the objectives are to improve controllable grid-connected ability of PVs, reduce PVs output fluctuation due to changes of environmental factors such as solar intensity, regulate isolated network voltage and frequency with the participation of PVs. The converter consists of three DC/DC modules and one three-phase inverter module, and each module can achieve two-way flow of energy. This paper also proposes a control strategy for DC/DC converter with soft-start function, in order to solve the DC bus voltage control under no-load and light-load conditions. Firstly, energy flow of PV/Battery system in both grid-connected mode and stand-alone mode is analyzed, then control strategies for each module under different operation modes is proposed, and the control strategies is verified by actual devices.