Direct Power Flow Controller—A New Concept in Power Transmission

For power transmission in grid, a new concept of direct power flow controller (DPFC) was proposed based on single-stage ac–ac converter with controllable phase and amplitude. By connecting its regulated output compensation voltage with grid in series, DPFC is able to regulate the amplitude and phase angle of grid node voltage, and thus can effectively control active and reactive power flow in grid, respectively and simultaneously. Compared with unified power flow controller (UPFC), DPFC also has a parallel transformer and a series transformer but has no dc energy storage element that easily leads to high equipment failure rate. Furthermore, UPFC is similar to two-stage conversion circuit, while DPFC has only one-stage conversion circuit, which consists of three single-phase buck-type ac units and a three-phase output filter. With respect to the input voltage of DPFC basic circuit, the phase regulation range of its output compensation voltage is 60°, which is easy to extend to 360° with two selection switches changing the connection groups of the input and output transformer. The topology structure and operational principle of DPFC were presented, and the experimental results of a prototype showed its feasibility and verified the theoretical analysis of DPFC.