An Equivalent Impedance Measurement Method for Grid-connected Distributed Power Supply System Based on Superposition Theorem

In the distributed generation system, the grid impedance will seriously affect the stability of the grid-connected inverter, and the accurate measurement method of grid impedance is the key technology to realize the high-performance adaptive control of grid-connected inverter in weak grid situations. Most of the existing methods are designed for grid inverters, active measurement will have an impact on system operation and power quality, while passive measurement methods have problems such as large calculation and low accuracy. Based on the limitations of the existing methods, this paper carries out the research on the passive measurement method of grid impedance suitable for both grid-following inverters and grid-type inverters, firstly, constructs an impedance model of distributed power supply dual-machine grid-connected, and analyzes the characteristics of dual-machine grid-connected operation. Then, based on the two-machine grid-connected model, an impedance calculation method based on the superposition theorem is proposed. Finally, through the comparison and analysis of the simulation platform and the existing methods, the results show that the proposed method can quickly and accurately calculate the grid line impedance in the two-machine grid-connected system, and can be applied to the grid impedance calculation of both the grid inverter and the configuration inverter.