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The impedance-based method is widely used to analyze the instability issue of three-phase grid-tied converters. The precision of the impedance modeling method for converters is of great concern. This paper focuses on the accurate small-signal impedance of pulse width modulation (PWM) converters with digital control delay in the synchronous reference (dq) frame. Based on the closed-loop transfer function of the adopted converter, accurate modeling of digital control delay in dq frame is described in detail. Then the impedance measurement is executed to verify the advantage of the proposed model method. Moreover, the correctness and effectiveness of the theoretical analysis for predicting system stability are validated by time-domain simulations.
Zhan et al. (Sun,) studied this question.