Transient response of three-phase voltage-source converters under grid-side faults

Three-phase voltage-source converters (VSC) are commonly used as a power flow interface in AC/DC hybrid power systems. The system may suffer from unpredictable transient disturbance from DC-side or grid-side faults. The nonlinear characteristics of VSCs have already been identified as exhibiting catastrophic bifurcation when there is a DC-side disturbance. In this paper, the transient response of a three-phase VSC under practical grid fault condition is studied. The converter will also exhibit a catastrophic bifurcation after the transient disturbance. The expanded AC current will cause excessive devise stress. A large-signal analysis is adopted to reveal the physical origin of the phenomenon and to locate the boundary of the instability. The phenomenon and the stability boundaries are verified by cycle-by-cycle simulations.