Ultrahigh step-up DC-DC converter for distributed generation by three degrees of freedom (3DoF) approach

This paper proposes a novel DC-DC converter topology to achieve an ultra-high step-up ratio while maintaining a high conversion efficiency. It adopts a three degree of freedom (3DoF) approach in the circuit design. It also demonstrates the flexibility of the proposed converter to combine with the features of modularity, electrical isolation, soft-switching, low voltage stress on switching devices, and is thus considered to be an improved topology over traditional DC-DC converters. New control strategies including the two-section output voltage control and cell idle control are also developed to improve the converter performance. With the cell idle control, the secondary winding inductance of the idle module is bypassed to decrease its power loss. A 400-W DC-DC converter is prototyped and tested to verify the proposed techniques, in addition to a simulation study. The step-up conversion ratio can reach 1:14 with a peak efficiency of 94% and the proposed techniques can be applied to a wide range of high voltage and high power distributed generation and DC power transmission.