Single-stage AC-AC Converter With Controllable Phase and Amplitude

Single-stage ac-ac converter with controllable phase and amplitude (ACCPA) was proposed for power flow control in grid, whose output voltage phase and amplitude can be regulated, respectively and simultaneously, with respect to the input voltage. Single-stage ACCPA comprises of a three-phase input transformer, three single-phase buck-type ac units, a three-phase output filter and a three-phase output transformer, and can be connected to high-voltage grid. Compared with cascaded ACCPA and $\pi$ model ACCPA, which both have a two-stage circuit structure, single-stage ACCPA has a more simplified topology, less number of switches, and its conversion circuit is only one stage. In order to cancel out third harmonic voltage, triangular connection ( $\Delta$ type) is adopted for capacitors of the three-phase output filter, and then the output voltages only contain fundamental component. By adjusting 3 control parameters in the duty ratio of single-stage ACCPA, the phase and amplitude of its output voltage can be regulated independently. A family of single-stage ACCPA having different regulation range can be obtained, if different connection group of input and output transformer is selected. The operational principle of single-stage ACCPA was analyzed in detail, and a prototype was developed. Its experimental results were coincident with the theoretical analysis.