一种增强跟网型逆变器在弱电网下大信号稳定性的参考坐标系重匹配方法

The classical phase-locked loop (PLL)-based vector current control scheme has been widely used in grid-following (GFL) inverter systems. However, GFL inverters with this classical control scheme tend to be unstable under severe grid fault conditions, especially in weak grid cases. This article reveals that the PLL angle's dynamic is the main reason for instability. Specifically, the control dq frame and the system dq frame are synchronized easily in strong grid cases where the PLL angle's dynamic is relatively small, but the two dq frames have a risk of losing synchronization in weak grid cases where the PLL angle's dynamic is relatively large. To address this problem, this article proposes a reference frame rematching method, which can transform the original control dq frame into a new control dq frame that is almost identical to the system dq frame. So, the losing synchronization issue can be addressed. A significant advantage of the proposed method is that it can make sure that an equilibrium point exists during severe grid faults. Besides, it can achieve a seamless transition between normal and grid fault cases, without the need of grid fault detection. Simulations and experiments verify the effectiveness of the proposed method.