Unified power flow controllers and interphase power controllers (IPC) are power system devices for the load flow management of AC systems. This article discusses different theoretical and practical aspects of the IPC, which is a robust series controller and interconnection device consisting in each phase of two parallel impedances-one inductive and the other capacitive. The two impedances are normally connected in series to two phase-shifted voltages. The phase-shifting devices can be conventional or electronically switched phase-shifting transformers.