I. Introduction
Grid forming inverters are considered to be one of the solutions for power grid with high-share of power electronic interfaces [1]. The output current of a traditional grid following inverter tracks the phase angle of the grid voltage, which can be approximated as a controlled current source [2]. The grid following inverter calculates the phase angle of the grid voltage by using technologies such as phase-locked loop (PLL). PLL will lose stability in a weak grid. The grid forming inverter synchronizes with the grid voltage by simulating a synchronous generator, so it can be approximated as a controlled voltage source [3]. Its grid adaptability is better than grid following inverter, it can even operate independently in an island grid.