Harmonic-Domain SISO Equivalent Impedance Modeling and Stability Analysis of a Single-Phase Grid-Connected VSC

This article presents a harmonic-domain single-input single-output (SISO) equivalent modeling technique for the impedance modeling and stability analysis of a single-phase grid-connected voltage-source converter (VSC). The basis is a conversion technique that transforms a harmonic transfer function (HTF)-based model into a SISO equivalent model while preserving all the information of frequency couplings. The proposed SISO modeling concept is useful for understanding the meaning and consequence of SISO impedance measurement of an interconnected system with frequency couplings, which further enables a simpler impedance measurement and impedance-based analysis. Applications of this method for the VSC model reduction and stability characteristic analyses are presented. From these results, useful conclusions regarding the accuracy of three types of reduced-order VSC impedance models and the stability effects of the VSC control with and without compensation for dc voltage variation are obtained. The presented examples of applications demonstrate how the proposed SISO modeling technique facilitates a simpler and efficient impedance-based analysis. Finally, experimental results verify the validity of the proposed VSC-SISO admittance and corresponding analyses.