Analysis, design, and evaluation of three-phase three-wire isolated ac-dc converter implemented with three single-phase converter modules

In this paper, a control method for three single-phase isolated ac-dc converter modules employed to implement an isolated three-phase, three-wire ac-dc converter is presented and its detailed design procedure provided. In the described control the input voltages of the Y-connected single-phase modules with floating common Y point are kept within a safe range by equalizing their input admittances. It is shown that for obtaining equal input admittances of the three PFC front stages, the outputs of the PFC voltage controllers should be equal. This is achieved by adjusting the reference currents of the current controllers in the output dc-dc stages. The performance of the presented control with both balanced and unbalanced source voltages, as well as with a phase fault (open or short circuit) is evaluated by Matlab/Simulink simulations and verified experimentally on a 6-kW prototype.