Revisit SISO Impedance-Based Stability Analysis of Single-Phase Grid-Tied Converters

This article analyzes the stability of a single-phase grid-tied converter under droop control with harmonic-domain single-input-single-output (SISO) impedance-based method. The SISO impedance model has been widely used because it is easier to measure compared with multi-input-multi-output (MIMO) impedance matrix. However, the issue of right-half-plane poles (RHPPs) in SISO impedance was not paid much attention in some previous studies, which may result in stability misjudgment. This article analyzes the root causes of the misjudgment and presents a revised SISO impedance-based stability criterion for single-phase grid-tied converter systems. The proposed criterion supplements how to accurately identify the number of RHPPs in SISO impedance. A grid-tied converter system under droop control is constructed for stability analysis and to verify the correctness of the proposed stability analysis method. Both simulation and experimental results indicate that the previous SISO impedance-based stability criterion ignoring RHPPs gives the wrong stability judgment, and the proposed one gives the correct result.