The project is applied to the hotel's power backup system, which consists of an energy management system (EMS), an energy storage battery pack, a battery management system (BMS), a DC / DC converter, 250KWPCS, AC distribution cabinets, and containers. The system has two modes, grid-connected and off-grid, which can be seamlessly switched to each other. It can not only supply power to the load, as a system regulation and support unit, but also as a load to absorb energy.