Three-Phase Synergetically Controlled Current DC-Link AC/DC Buck-Boost Converter With Two Independently Regulated DC Outputs

A three-phase current DC-link AC/DC buck-boost converter, composed of a three-phase current-source recti-fier (CSR) front-end and a three-level DC/DC-stage, can provide two independently regulated DC outputs. A conventional synergetic control strategy, which coordinates the modulation of the CSR and the DC/DC converter stage to achieve minimum overall switching losses, is extended to the case of two independent DC outputs, retaining all advantageous features, such as seamless transitions between operating modes and modulation schemes. The extended synergetic control strategy allows loss-optimum operation [i.e., reduced number of switching instants due to clamping of a phase of the CSR-stage (switching only two out of the three phases, i.e., 2/3-PWM) or individual clamping of the DC/DC-stage's two half-bridges and minimum possible DC-link current] for any operating point, especially also for two different output voltages and/or two different loads. Finally, experimental confirmation of the proposed control scheme using a 10 kW demonstrator system is provided. Operating in the boost-mode at a total output voltage of 800 V, the proposed synergetic control achieves a significant measured efficiency improvement over a wide load range, e.g., from 95.7 % to 96.9 % (1.2 %) at 2 kW and from 97.9 % to 98.4 % (0.5 %) at 10 kW, which is largely independent of output voltage asymmetries and load asymmetries.