The application of multi-port DC converters in DC microgrids (MGs) can effectively improve the integration and reliability of the system. This paper proposes an isolated three-port converter (TPC) with common low-voltage DC bus which is suitable for DC MGs. The proposed TPC is able to achieve bidirectional power transmission between the high-voltage side and the low-voltage side through the dual active bridge (DAB), while the power conversion of the low-voltage side is consisted of buck-boost converters. The number of power devices of the TPC is reduced by multiplex use of the power devices in the DAB. Meanwhile, interleaved structure is employed to reduce the current ripple at one port on low-voltage side. This paper analyzes the equivalent circuit model of the proposed TPC, then typical operating modes and key waveforms of the converter are presented. The phase-shifting control with duty-cycle adjustment method is adopted to realize bidirectional power transmission among the three ports. Finally, the power transmission characteristics of the TPC are verified by simulation and experimental studies, and the effectiveness of the proposed scheme is verified accordingly.