Study on the Stability Analysis Method of Grid-connected Converters in Full Operating Range

The research on operation stability of grid-connected converter (GCC), the core equipment of distributed new energy power generation, in full working range has important theoretical and practical value. At present, impedance-based method and state-space based method are commonly used in the stability study of GCC; while analysis results under rated operating conditions are widely used to guide the design of the controller in the whole static operating area. However, GCCs often show different operating characteristics in different power ranges. For example, in a photovoltaic plant in Qinghai Province, the voltage and current at the point of common coupling (PCC) tend to have waveform distortion when the output power reaches about 65% of its rated value. Therefore, it is of great significance to study the operation characteristics of GCC in full operating range. However, existing typical stability analysis methods, including impedance-based method and state-space method, are only used when modeling at a single working point. There are less researches related to extend the existing methods to the full operating range. This paper proposes a stability region-based method to analyze the stability of GCC in full operating range. First, the operating point is introduced into the modeling process as a variable through the multiple coupling effect between dq axes and the dynamic characteristics of phase locked loop (PLL). Then, a single-input single-output (SISO) transfer function model of the converter is constructed, which includes the operating point variables. Based on the proposed model, the stable working domain of the system can be analyzed intuitively, as well as the influence mechanisms of system parameters on stable domain. The simulation and experimental results verify the validity of the model and the theoretical analysis. © 2023 Chinese Society for Electrical Engineering. All rights reserved.