• Combined stability analysis with quantitative methods and 3D visualization. • Synchronization instability mechanisms and dominant factors are investigated. • The coupling support effect between positive and negative sequences is revealed. • Negative-sequence active current is necessary for stability and voltage support. • A current phase-angle setting method for voltage support and stability is proposed. Synchronization stability in power systems with high renewable penetration has become an increasingly important issue. However, studies on the mechanism of PLL-dominated synchronization stability under unbalanced fault conditions remain limited, and clear guidelines for positive-sequence and negative-sequence current injection to enhance synchronization stability are still lacking. Accordingly, existence conditions for the system equilibrium point that account for positive–negative sequence coupling effects are derived, a stability margin index is constructed, and a three-dimensional visualization analysis method is proposed. On this basis, the dominant factors leading to the loss of the equilibrium points are identified, and the influence of positive-sequence and negative-sequence currents on the existence of the equilibrium point is clarified. The analysis reveals the mutual supporting effect of positive- and negative-sequence currents on the opposite-sequence equilibrium point and further demonstrates the necessity of negative-sequence active current injection for voltage support and enhanced synchronization stability in grids with high resistance-to-reactance ratios. Furthermore, a setting method for positive-sequence and negative-sequence current references is proposed. It simultaneously achieves voltage support and enhances synchronization stability. Finally, the theoretical analysis and the proposed method are validated through hardware-in-the-loop experiments.
Liu et al. (Wed,) studied this question.