In the event of asymmetric faults in the power grid

virtual synchronous generator (VSG) will face problems such as three-phase current asymmetry

overcurrent

and transient instability. In response to the limitations of existing VSG research on symmetric operating conditions

this paper proposes a fault ride through control strategy that directly provides VSG asymmetric excitation reference under asymmetric faults in the power grid

relying on a three-phase four bridge arm topology. Firstly

the proposed control strategy freezes the reactive power loop

retaining only the active power loop

and comprehensively considers the VSG current limiting

voltage support capability

and system capacity to provide the optimal solution for the non-fault phase excitation reference amplitude at different fault depths; Secondly

based on the geometric relationship of the system phasor

the reference amplitude and power angle of the fault phase excitation are obtained. Then

considering the active power generated by both positive and negative sequence components

and taking into account the dynamic changes in excitation amplitude

a real-time dynamic adjustment method for active reference instructions was proposed based on the mechanism of the active reference on the system power angle

to control the power angle to reach the target value

ultimately forming a complete VSG asymmetric fault crossing collaborative control strategy. Finally

the paper conducts hardware in the loop semi physical experiments

and the experimental results show that the fault ride through strategy proposed in this paper can achieve three-phase current symmetry while suppressing overcurrent and improving transient stability.