High power factor transformerless single-stage single-phase ac to high-voltage dc converter with voltage multiplier

This study proposes a transformerless single-stage single-phase ac to high-voltage dc converter based on Cockcroft-Walton (CW) voltage-multiplier circuit with only adding one bi-directional switch and one boost inductor. This study also derives a new method of circuit representation for CW voltage multiplier, which simplifies the equivalent circuit and is convenient for simulation. Compared with conventional CW voltage multiplier, the proposed converter provides half-wave symmetry and low-distorted line current, improved power factor at the ac source and a regulated dc output voltage for wide load range. In addition, a current-fed analysis approach is used to derive a general expression of the output voltage ripple as function of the load to facilitate the design of the system parameters. A commercial average-current-control continuous conduction mode power factor correction integrated circuit (IC) is used to implement the control strategy of the proposed converter that does not need the multiplier and sensing of the input ac voltage; this strategy simplifies the design and reduces the control circuit components. A 500 W prototype is built for testing. Both simulation and experimental results demonstrate the validity of the proposed converter.