A Conservatism Improved Transient Stability Analysis of Grid-Following Converters Based on the Proposed Elliptic-Equal Area Criterion

The power electronics’ penetration in modern grids is rapidly increasing due to the growing proportion of renewable energy generation. As the important energy conversion interface, the stable operation of grid-tied converters is vital to the overall safe of the double-high power system. The prior arts have mainly focused on the varying negative damping in the phase-locked loop (PLL). Negative damping imposes energy into the system and is detrimental to system's transient stability and should not be neglected as the constant positive damping in synchronous generators. The deficiencies of the previous studies lie in the large conservatism of the criteria once considering the influence of negative damping. In this article, an elliptic-equal area criterion (EAC) is proposed to assess the damping impacts on the stable domain of the converter systems, which improves conservatism compared to previous transient stability criteria. In addition, a transient stability improved PLL is proposed by eliminating the negative damping term.