Systematic Research On Magnetic-integration Techniqhes In Forward Converters

Due to the high requirements of the power converters, researchers can no longer optimize the performance only from the design of traditional circuit topology or control strategy, but also from the other aspects such as the package, heat dissipation, components and system integration. Meanwhile, the Magnetics–Integration techniques have attracted more and more attentions, for the Integrated Magnetics (IM) can help to reduce the core loss, core size, or ripple current compared with the Discrete Magnetics (DM). The forward converter is one of the most suitable topologies for low–to medium–power applications for its simplicity and good performance, however it has larger output ripple current comparing with the other doubled–ended primary topologies, and required a relatively large filtering inductor. Rational use of magnetic integration techniques can effectively solve these problems.Since the voltage across the transformer winding and inductor winding have the same polarity, the ac flux excited by the transformer winding and inductor winding can be positively coupled to reduce the output current ripples, therefore, a resonant reset forward converter with integrated magnetics (IM–RRF) and a winding reset forward converter with integrated magnetics (IM–WRF) are proposed in this paper. Based on analyzing the operating model of the IM–RRF and IM–WRF, the current ripples of different operating stages are obtained, and points out that it has five possibilities for the output current waveform. Furthermore, the IM reluctance condition, the smallest output current ripple condition and the design basis of IM is also obtained. Then, four 66W RRF and WRF prototype converters, with integrated magnetics and without, are built to verify the operation principle, and five kinds of IM corresponds to the above RRF and WRF are implemented and tested. The experimental results show that the output ripple current of IM converters on the condition thatΔiL₂=0 has been dropped by 50% compared with conventional one. Finally, the small–signal model of IM forward converter is founded and simulated, furthermore the steady–state performance and dynamic performance is analised to show that the converter with the integrated magnetics has better dynamic responding speed.