Abstract: A low-frequency AC（LFAC） transmission scheme based on the active modular multilevel matrix converter（M3 C） is proposed, which can reduce the influence of faults occurring at one side of the low frequency or power frequency AC system on the other side. First, the topology of the active M3 C is introduced, and the mathematical model of the active M3 C is derived. Then,based on the derived mathematical model, a control system of the active M3 C is designed, and the fault isolation strategy of the LFAC transmission system as well as the state of charge（SOC） balance control strategy of the energy storage unit is proposed.Finally, an electromagnetic-transient simulation model of the low-frequency transmission system based on the active M3 C for offshore wind power is built in PSCAD/EMTDC. Simulation tests are carried out for typical working conditions such as different kinds of AC system faults and the SOC balance process of the energy storage unit, and the effectiveness of the proposed scheme is verified.