Lock‐Up Problem in the Current‐Limiting Mode of the Grid‐Forming Converter With Priority‐Based Limiter and Its Solution

ABSTRACT As a voltage‐source‐type device, the output current of a grid‐forming converter without a current limiter is determined by the external circuit status. When a short‐circuit fault occurs in the grid, the converter may burn out because of the large current. Therefore, it's necessary for grid‐forming converters to be equipped with current limiters. For the grid‐forming converter employing the priority‐based current limiter, this study found that the lock‐up problem in the current‐limiting mode may occur; that is, the converter cannot switch back from the current‐limiting mode to normal mode if the fault is cleared in a relatively short period of time. This is caused by the impact of the line current dynamics. It causes the converter to enter the current‐limiting mode early, making the maximum power angle smaller than the angle in which the converter can exit the current‐limiting mode. A strategy to overcome this lock‐up problem by reasonably setting the proportional gain of the proportional‐integral (PI) controller in the voltage loop is provided, which essentially reduces the lower boundary of the angle at which the current‐limiting mode can exit to be equal to or less than the fault occurrence power angle. The effectiveness of the strategy is demonstrated through numerical simulations.