Small-signal Stability Analysis of VSCs with Neative-sequence Current Control Based on LTP and HSS Theory

In many countries, the negative sequence current control (NSCC) has been the national standard for connecting renewable energy to power systems. At the same time, the original relationship of voltage source converters (VSCs), commonly used in renewable power generation, shows inherent periodic time-varying characteristics. Considering the pros and cons of the different small-signal models for nonlinear time-varying systems, the comprehensive analysis based on linear time periodic (LTP) and harmonic state-space (HSS) models are introduced to studying the small-signal stability of power systems dominated by VSCs with NSCC. Considering the advantages of the LTP model in stability determination, the stable domains of control parameters are described. Additionally, the structural effect of the decoupled double synchronous reference frame (DDSRF), widely used for separating positive and negative sequences, is compared. Then, considering that the HSS model is a linear time-invariant (LTI) model, and its stability mechanism analysis method is mature, we characterize the interaction among controls based on the participation factor analysis. These comprehensive analysis results are beneficial for understanding the impact of NSCC on system dynamics and provide theoretical support for the optimization of NSCC and DDSRF. Finally, case studies validate the effectiveness of the analysis results.