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(Z(g)) to the inverter output impedance(Z(inv)). However, using Z(g)/Z(inv), 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with the change of grid impedance, which may lead to the traditional impedance-based stability criterion(TISC) is no longer applicable.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.