Virtual impedance-based equilibria suppression strategy for multi-inverter parallel grid-connected systems
摘要
With the increasing penetration of renewable energy, multiple inverters are connected in parallel to provide power to the utility grid. However, this results in two main challenges. First, the dynamic interaction between inverters and the utility grid can lead to oscillations. Second, the line impedance differences among inverters can cause power-sharing mismatch. To address these challenges, a novel dynamic interaction suppression strategy is proposed based on a virtual impedance model. The proposed strategy consists of two parts. The first part is a virtual impedance control method that aims to suppress the system oscillations caused by dynamic interaction and poor power sharing. The second part is an adaptive voltage compensator that restores PCC voltage and enhances power transmission efficiency. It is worth noting that the two components of the virtual impedance method, the active damper K and the virtual impedance Zv(s), have a synergistic control effect in suppressing dynamic interaction. The active damper K can suppress the dynamic interaction in the low–medium-frequency domain, while the dynamic interaction in the high-frequency band is suppressed by the virtual impedance Zv(s), mitigating the dynamic interaction across a wide frequency range. Investigation on key parameter variations is also conducted in this paper. Impedance analysis results and hardware-in-the-loop simulation results have verified the effectiveness and outstanding performance of the proposed strategy.