Reconstruction of impedance-based stability criterion in weak grid

Impedance-based analysis is widely used to study the stability of grid-connected inverter system in a weak grid. And the stability of the system is characterized by the ratio of the grid impedance(Zg)to the inverter output impedance(Zinv) However, using Zg/Zinv to represent the phase margin (PM) of the system is inaccurate. Meanwhile, with the development of grid-connected inverter adaptive control strategy, the inverter control loop parameters will be adjusted dynamically with the change of grid impedance, which may lead to the traditional impedance-based stability criterion(TISC) is no longer applicable. In view of the shortcomings of traditional impedance-based analysis method, the impedance-based stability criterion is reconstructed in this paper. The reconstructed impedance-based stability criterion (RISC) can not only accurately represent the stability margin of the system, but also has good applicability to grid-connected inverters with variable control parameters. Simulations validate the theoretical analysis.