Understanding and Characterization of the Dynamic Characteristics of Grid-Connected Power Converters in Current Control Timescale

With the large-scale integration of converter-based grid-connected devices into power systems, a series of dynamic issues with unclear mechanisms have emerged, influenced by the characteristics of these devices. Mainstream converter gridconnected devices typically employ a terminal voltage phaselocked loop (PLL) structure for grid connection. During the initial stages of system disturbances, their current control loops act first to regulate the internal potential, thereby influencing the system’s dynamic response. However, the prevailing view based on the original current control structure assumes that the internal potential of converter grid-connected devices follows the frequency variations of the terminal voltage. This assumption overlooks the fundamental function and objective of current control, which is to adjust the internal potential based on the error between actual and expected active/reactive currents. Therefore, this paper aims to propose methods and frameworks for understanding and characterizing the dynamic characteristics of grid-connected power converters in current control timescale. Based on the original structure of current control in these devices, the difficulty in comprehending and characterizing their behavior are elucidated. By revealing the current control independently forms and regulates the AC internal potential based on AC current, the development of a current error excitation-internal potential response model is promoted. Additionally, the physical implication of how the PLL affects the realization of current control functions is clarified. Finally, through system simulations, the fundamental working process of current control in converter grid-connected devices is illustrated.