Unified SISO Loop Gain Modeling, Measurement, and Stability Analysis of Three-Phase Voltage Source Converters.

Frequency-domain modeling is an effective technique in the dynamic analysis of power electronic converters-based power systems. In this paper, a unified single-input single-output (SISO) loop gain modeling for the three-phase grid-tied voltage source converters (VSCs) under both symmetric and asymmetric AC grids is presented, which facilitates the physical measurement and stability analysis. Based on the linear-time-periodic (LTP) modeling technique, the harmonic admittance model of the three-phase grid-tied VSC is developed in the stationary (αβ)-frame, which accurately captures the coupling dynamics. This model can be transformed into other existing models through coordinate transformations. According to the idea of mathematical induction, a two-by-two recursive admittance matrix (RAM) model is derived, which is easy to include frequency coupling components of arbitrary order. It is illustrated that the VSC admittance is coupled with the grid admittance due to the frequency coupling effect (FCE). Furthermore, the RAM is converted to its equivalent SISO models following the concept of loop gain. The system stability is thus assessed by the SISO stability criteria (e.g., Nyquist stability criterion). In addition, the loop gain allows the traditional SISO perturbation and measurement scheme to be used for detecting the stability margin information. Finally, simulation results verify the feasibility and correctness of the theoretical analysis presented above. [ABSTRACT FROM AUTHOR]