A fault current limiting control strategy for GFM converters based on directional current command

Abstract

The grid-forming （GFM） control technology is instrumental in enabling converters to provide frequency and voltage support response akin to synchronous generators， thus bolstering the stability of the new power system. Nonetheless， a notable challenge lies in delivering grid support during fault current limiting. To this end， a strategy for fault current limiting in GFM converters based on measuring terminal and internal differential voltage orientation is proposed. In this approach， the angles of the positive and negative sequence current commands lag 90° behind the positive and negative sequence voltage differences. Additionally， the maximum magnitude of the synthesized vector of the current commands aligns with the converter’s overcurrent capability， which is equivalent to the generation of positive and negative sequence adaptive virtual inductance by control， respectively. This method obviates the need for direct virtual inductance value calculations and can maximize the maximum support capacity of the converter to realize the fault current characteristics resembling those of synchronous generators. The proposed fault current limiting strategy is validated by a simulation system built through PSCAD/EMTDC. The simulation outcomes affirm the strategy’s efficacy in delivering substantial grid support to the AC system while limiting fault currents.

Keywords

• new power system
• converter control
• gfm control
• fault current limiting
• differential voltage orientation