Abstract：Traditional stability methods have extensively discussed the stability of grid-connected inverters (GCI) at specific operating points. However, due to the fluctuation of new energy output and the randomness of load switching, the operating point of GCI exhibits significant time-varying characteristics. There are substantial differences in the stability of GCI under different working conditions. PQ control is a common control strategy for GCI, which has the characteristics of multi-loop coupling, multiple time scales, and strong nonlinearity compared to single-current control. To clarify the dynamic attributes of GCI, a stability analysis method of GCI with PQ control based on the stable operating region is proposed. The stable operating region can directly characterize the stability of the whole working range of the system. Firstly, the mutual couples among the control loops, such as phase-locked loop (PLL), power loop, and current loop, are considered. The operating point variables are introduced into the small signal model of GCI by the PLL and power calculation sessions. The PQ control GCI model with embedded operating point variables is derived. It can comprehensively and accurately describe the stability of the inverter system over the full operating range. Secondly, considering the power circuit constraint, the stable operating region of GCI is constructed by numerical analysis. The stability of all operating points in the operating range can be visually obtained. Furthermore, the effects of external system parameters (e.g., grid impedance, grid voltage) and internal control parameters (PLL bandwidth) on stability are analyzed. The difference in the stable operating region between GCI with PQ control and GCI with current control is compared. Finally, the theoretical analysis is verified by simulation and experiment. The following conclusions can be drawn from the simulation analysis. (1) The dynamic characteristics of the power outer loop, current loop, PLL, and the coupling effect between the dq-axis are considered. The working point is introduced for modeling, and the multivariable closed-loop transfer function model is derived. The model can directly analyze the system's stability under time-varying operating points, avoiding the complicated process of repeated modeling. (2) The closed-loop transfer function model based on embedded operating point variables can accurately characterize the stable operating region of the system. It can be used to analyze the trend of grid impedance, grid voltage, and phase-locked loop bandwidth in the stable operating region. A significant difference exists between the stable operating region of the GCI with PQ control and the GCI with current control at higher grid voltages and lower PLL bandwidths. (3) Based on the obtained stable operating region, the stability information of the system under time-varying operating conditions can be obtained intuitively. The stable operating region analysis shows that the stable operating region positively correlates with the grid resistance and voltage, while negatively correlating with the grid inductance and PLL bandwidth. In the analyzed power range, the sensitivity of stable operating region to grid voltage changes is similar. However, the sensitivity of stable operating region to PLL bandwidth variation is greater in higher power ranges.
罗宇航, 肖凡, 郑宇婷, 谢伟杰, 涂春鸣. 基于稳定域的PQ控制并网逆变器稳定性分析方法[J]. 电工技术学报, 2025, 40(22): 7334-7348.
Luo Yuhang, Xiao Fan, Zheng Yuting, Xie Weijie, Tu Chunming. Stability Analysis Method of Grid-Connected Inverter with PQ Control Based on Stable Operating Region. Transactions of China Electrotechnical Society, 2025, 40(22): 7334-7348.
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