The nonlinear coupling characteristic of modular multilevel converter（MMC） results in power oscillation under asymmetric conditions. A fault ride-through strategy based on average model of MMC system was proposed in this paper. By decoupling the circulating current

DC current and zero sequence current controller from the AC current controller

the unbalanced power caused by asymmetric AC fault was consumed inside the converter instead of propagating to the DC side. By realizing the energy management for distributed capacitor

those were balanced that the capacitor voltages of each valve

each bridge arm

each phase unit and each converter

improving stability of HVDC system under asymmetric conditions. The simulation results for the proposed strategy of PSCAD/EMTDC indicate that the characteristics of the non-faulty side converter are the same as those under the power flow step condition

and the faulty side converter still maintains good performance.