Grid-Forming Converter Overcurrent Limiting Strategy Based on Additional Current Loop

Abstract

Compared with current source converters, voltage source converters (grid-forming converters) have better frequency support capabilities, voltage support capabilities, and regulation performance, thus they have broad application prospects. However, the grid-forming (GFM) converter has insufficient current control ability, and it easily causes problems such as overcurrent issues when a fault occurs. Thus, this insufficiency is one of the most important challenges the GFM converter is faced with. Aiming to solve the problems mentioned above, this paper proposes a control method of a GFM converter achieved with a low-pass filter structure and an additional current loop. The additional current loop controls the dq-axis current components by acting on the outer loop to generate appropriate phase and voltage amplitude reference. The low-pass filter structure is used to solve the system frequency stability problem caused by the inclusion of the additional current loop. On the premise of ensuring that the system frequency meets the grid-connection requirements, the proposed strategy rapidly limits the output current within the allowable range and guarantees expected voltage source characteristics of the converter during the fault period. Finally, the effectiveness and superiority of the proposed control strategy are verified by MATLAB/Simulink simulations.

Keywords

• grid-forming converter
• current limiting
• low-pass filter
• voltage support
• frequency stabilization