Abstract: A three-port delta AC/AC converter is proposed for the three-port flexible interconnection of distribution networks.Firstly, the topology of the three-port delta AC/AC converter is described. Compared with the three-port back-to-back modular multilevel converter（MMC）, the number of bridge arms in the proposed topology is reduced by half. Secondly, the working principle of the three-port delta AC/AC converter is analyzed, and its mathematical model is established, while its operation characteristics are studied by phasor diagram method. Thirdly, the control strategy is designed according to the application requirements of flexible multi-state switch（FMSS）. According to the current regulation characteristics of the third bridge arm, the flexible power distribution between the two input feeders is realized based on the power demand of the output feeder. Finally, the validity of the proposed topology of the three-port delta AC/AC converter and the mathematical model, as well as the effectiveness of the control strategy, are verified by the simulation.