Modeling, Analysis, and Testing of Transient Characteristics of the Distributed Photovoltaic Closing to the Distribution Grid

The penetration rate of distributed photovoltaics in medium and low voltage distribution networks is increasing obviously. Traditionally, distributed photovoltaics have been considered as current sources, but they only hold true during steady-state operation. If there is an abnormal grid voltage or transient transition during the initial PV closing to the distribution grid, distributed photovoltaics cannot be considered as current sources. In response to this issue, this paper first analyzes the transient equivalent model of distributed photovoltaics, theoretically derives and simulates its transient characteristics at the initial moment of grid connection, and further conducts experimental tests to obtain actual experimental data. The results show that in the initial moment of grid connection of distributed photovoltaics, the transient process not only needs to consider the zero input response and zero state response at the initial moment of closing, but also no longer exhibits current source characteristics. The overvoltage impact caused by the transient moment of closing is severe, which has a great impact on the power supply quality of low-voltage users and the healthy operation of grid connected transformers.