Research of Photovoltaic Grid-connected and Islanded Storage System in DC Microgrid

The power of PV generator used in the DC microgrid is always fluctuating due to the irradiance and weather conditions. In order to enhance the DC microgrid's reliability, the system operation modes should be flexible depending on the conditions. In this paper, we research on a new type of photovoltaic system structure and its cooperative control scheme applied in the DC microgrid. With the new scheme, the new structure can operate in four modes depending on the PV and the AC grid conditions, which can optimize energy utilization and realize system stability. In this paper, the system structure, interfacing converters' modelling and control strategy are proposed at first, particularly the bidirectional high step up DC-DC converter which plays a key role in the DC micro grid. It connects the battery and the DC bus to achieve energy exchange between PV, grid and battery. Further, the various operation modes are proposed and analysed. In the end, a prototype is developed to verify the proposed structure and cooperative control scheme.