The conventional interphase power controller (IPC) can control the power flow of the transmission line. In this paper, a novel topology for IPC, called the unified interphase power controller (UIPC), is introduced. In this topology, the phase-shifting transformers (PSTs) are replaced by voltage-source converters. In this paper, the transient behavior of UIPC is modeled and investigated. The results are compared with the simulation results of IPC and UPFC. It is shown that UIPC has all of the capabilities of IPC and UPFC, such as power-flow control, fault current limitation, voltage isolation, and local bus voltage regulation simultaneously. The results also reveal that UIPC increases the variations range of control variables of IPC and, as a result, the range of variations of active and reactive powers