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Due to the defects of the way of the traditional grid power supply, microgrid arises at the historic moment. At present, DC microgrid is an effective solution to integrate renewable energy sources which are DC power supply with DC loads. In allusion to the power unbalance intra-microgrid and the wide fluctuation of DC bus voltage due to unstable output of DC micro resources in DC microgrid, A DC microgrid structure consisting of photovoltaic generation system, hybrid energy storage systems and AC main grid, is researched in this paper. A novel power management strategy for this DC microgrid is proposed. The control strategy divides the DC bus voltage into seven ranges by six critical voltage values which are employed as the represents of power states, and according to the range which the bus voltage belongs to, the operation mode of the system can be automatically judged and switched freely. A hybrid energy storage system in this microgrid that contains two complementary type storage elements—battery and super-capacitor, can enhance the reliability and flexibility of the system based on their special supply logical. Experimental results show that above-mentioned control strategy is feasible through the MATLAB/SIMULINK simulation platform.

This paper discussed the advantages and challenges of DC microgrid for commercial building. The data obtained from the DC microgrid constructed at Xiamen University shows that DC microgrid with rooftop solar system is an efficient way to power varies DC loads inside the building. The capacity of the solar system on the rooftop normally will be enough to power the LED light loads in commercial buildings, even for high rise buildings. In order to power heavy loads such as air conditioning and EV charging stations, extra power are required, which can be obtained from the BIPV on the sidewall, glass window, or adjacent parking lots. To ensure the stable bus voltage and continuous operation of the DC microgrid, a suitable energy storage unit and two way AC/DC invertors are needed. Therefore we believe to use the solar power only for the matched DC loads, and keep existing AC power in the building to power the rest loads (or an AC and DC hybrid microgrid) maybe a more viable solution. The economical analysis shows that installation cost of a DC microgrid system is about $2.2/W, which is becoming a marketable technology.

The number and variety of electric vehicles connected to grid continue to grow rapidly, which results in a heavy burden on grid. To solve this problem, the concept of V2G (Vehicle to Grid) that electric vehicles could act as a new power source for grid was proposed. With distributed renewable energy developing fast recent years, charging EVs is a good way to use it. The DC micro-grid program being conducted at the Xiamen University (China) consists of a 150kW peak photovoltaic system. A unique charging station has been proposed designed on the basis of the DC micro-grid, featuring three-way energy flow among the power grid, PV modules and electric vehicles. The paper proposes a charging station based on DC micro-grid which also can provide V2G service. The control strategy of converters is investigated. Finally, simulation based on MATLAB is built to validate the availability and effectiveness of the proposed system and control strategy.