The IM-TTF Converter Based On AC Flux Positive Coupling

Forward convertor is widely used in the field of communications, computer, aeronautics and astronautics for its simple structure, high reliability, galvanic isolation between input and output, and so on. As an important part of high frequency DC/DC converter, magnetic components limit improvement of power density and performance. Due to the advantage of reducing volume, weight, power loss of magnetic components and output ripple current, improving output dynamic characteristic etc, MIT is subjected to more and more concern.Based on reducing output ripple current by AC flux positive coupling of transformer and output inductor, a series of IM forward converter are derived in this thesis as solution for low utilization of transformer core, high output ripple current in the conventional high frequency forward converter. And taking two-transistor forward converter, which is widely used in medium- to-high power occasion as example, research on application of MIT is performed in target for reducing volume, weight of magnetic components and output ripple current.First of all, conventional converter topologies and key techniques of high frequency DC/DC converter are introduced, indicating that performance of converter can be improved by MIT. Based on the analysis about the flux characteristic of magnetic components in forward converter and using principle of superposition, it is concluded that AC flux positive coupling can reduce output ripple current, so that a series of IM forward converter are derived. Two-transistor forward converter is taken as example, and its principle and influence on ripple current and efficiency by MIT are analyzed; design rule of IM components is presented as well. Finally, prototypes of IM-TTF and DM-TTF with 240~300V input and 28.5V/30A output are implemented and tested. It is proved that IM solution can reduce output ripple current and volume of magnetic components, but decrease of magnetizing inductance of IM transformer has negative influence on efficiency, especially when input voltage is high.