标题：Mechanism underlying constant amplitude oscillation of grid-tied voltage source converters

作者：Jianhang Zhu ; Shicong Ma ; Xuan Gong ; Jiabing Hu

摘要：Small-signal stability is one of the main issues for the safe operation of power system. The traditional studies mainly focus on stability determination of power system, but the issue after system oscillation divergence is seldom involved, which may cause system collapse and trigger protective actions, or oscillate at a constant amplitude with a certain frequency. In this paper, the mechanism of small-signal instability diverging to constant amplitude oscillation (CAO) is studied for grid connected converters, which only considers the nonlinear factors introduced by phase-locked loop (PLL) controller. Based on the nonlinear analysis method of Lyapunov exponent, the CAO is caused by the nonlinear limit cycles, which is investigated for the first time, and the period of nonlinear limit cycle dose not correspond to the unstable modal frequency of small-signal analysis. When the system oscillates stably with constant amplitude, the system model cannot be described by linear-time invariable (LTI) model in constant speed reference frame of base frequency, then the linear-time periodic (LTP) theory is introduced into this case. Based on the Floquet theory, the eigenvalue locus of LTP model in time-domain illustrates the process of unstable system at constant steady-state operating point diverging to a stable system at steady-state trajectory. Finally, the validity of the analysis is verified by simulation.

发表于：8th Renewable Power Generation Conference (RPG 2019)