An emergency control considering current limitation and transient stability of virtual synchronous generator

With the increasing application of renewable energy sources (RESs), more and more grid-connected voltage-source converters (VSCs) in the grid need to operate in a “grid-forming” manner. However, when large disturbances occur in the grid, grid-connected converters may lose synchronization and cause the current to exceed set limits. To ensure the stable and safe operation of VSC during large disturbances and to improve the power supply capacity during voltage dips of RES, this paper proposes an emergency control method that takes into account the virtual synchronous generator (VSG) current limit and transient stability based on a large-signal mathematical model of the VSG during fault and normal states. The method divides the operation area of the VSG into non-emergency area and emergency area. If the operating point is in the non-emergency region after a fault, only the active power reference value is changed to avoid current exceeding the limit and transient instability; if the operating point is in the emergency region, the current exceeding the limit and transient instability are avoided by changing the active power reference value and adding in the virtual impedance. Finally, the effectiveness of the proposed control strategy is verified by simulation.