Three-phase step-down reversible AC-DC power converter

Bidirectional DC current flow is not a natural feature of the buck (step-down) switch-mode rectifier which leaves it at a disadvantage to boost (step-up) designs. A circuit topology is presented that allows bidirectional flow and which, by dual use of components, uses less devices than anti-parallel bridges. Sinusoidal current, controlled displacement factor and variable voltage transfer ratio are demonstrated in a 1.5 kVA prototype. Dynamic performance is investigated through simulation and experiment. A PI plus velocity controller is shown to be adequate provided care is taken over changing between rectification and inversion