An off-grid PV power generation system is generally composed of PV arrays, charge and discharge controllers, storage batteries, off-grid inverters, DC and AC loads. When there is solar illumination, the PV arrays will convert solar energy into electricity which will be supplied to the loads through the solar charge and discharge controllers, and the storage batteries will be charged at the same time. When there is no solar illumination, the storage batteries will supply power to DC load through the solar charge and discharge controllers. Meanwhile, the batteries will directly supply power to the independent inverters which will convert such power into AC power to supply to AC load.
Off-grid operation, also known as island operation, refers to the operation mode consisting of DG, energy storage device and load, which is disconnected from the main network distribution system in case of power grid failure or planned need. The energy storage converter PCS works in off-grid operation mode to continue power supply for the microgrid load, while the photovoltaic system continues to generate power when the power supply of the bus is restored, and the energy storage system usually only supplies power to the load.