Modeling of Grid-Connected VSC Based on Power Angle for Synchronization Stability Analysis

As grid-connected Voltage Source Converters (VSCs) are extensively employed as interfaces for integrating renewable energy generation into the grid, the synchronization stability problem between them and the grid has become the focus of current research. This paper proposes a power angle of grid-connected VSC from a current source perspective, drawing with the power angle concept of the synchronous machine. This definition is grounded in the intrinsic properties of the controlled current source characteristic of grid-connected VSC. Subsequently, a Heffron-Phillips-like model is established based on the power angle, encompassing the DC voltage control (DVC) and phase-locked loop (PLL) control loops. Referring to the synchronous machine synchronous damping torque analysis method, the additional branch dominated by the PLL control loop is simplified into two parts: additional synchronization power and additional damping power. This distillation leads to a second-order dynamics equation form for the grid-connected VSC, facilitating the study of synchronization stability under small disturbances through the analysis of the damping coefficient. Lastly, the paper discusses the impact of grid strength and control parameters on the damping coefficient of the grid-connected VSC, corroborating the analytical findings with simulation results.