Research And Application Of ZVS And Flux Balance For Push-Pull Forward Converter

With the DC-DC converter being researched more and more widely and deeply, it is becoming a hot issue to improve the topology and the components of DC-DC converter, which is crucial to improve the performance and the efficiency of DC-DC converter, as well as satisfies the requirement of energy saving and environment protection.This article first describes and analyzes thoroughly the operation mode of the push-pull forward converter with clamp capacitor. Combined with the coupled inductor which is high focused in recent years, a novel push-pull forward converter with clamp capacitor and coupled inductor is then proposed, a highly efficient one that can achieve ZVS through the extra coupled inductor. The operation of the proposed converter is analyzed in detail, and the conditions to achieve ZVS are obtained. Besides, the EE core based coupled inductor in the topology is also researched thoroughly to reach a conclusion that the coupling coefficient leads to the best performance when selected around0.8. Some simulation based on Saber and the corresponding analysis validate the effectiveness of the proposed converter that it can achieve ZVS through an extra coupled inductor.The magnetic bias of the transformer for push-pull forward converter is analyzed in another part. Focused on converter with/without load respectively, it is concluded that the magnetic bias is independent with the load. How the magnetic bias occurs is then depicted in detail to summarize that the mismatch of the power device in the topology is the main cause, and this can be addressed to some extent by suppressing the stepped saturation of the transformer. Finally, a controller to force flux balancing based on the tuning of duty ratio and winding current is proposed to solve the problem of magnetic bias. Some simulation based on Saber validate the effectiveness of the proposed controller for flux balancing.In the last part of the article, a2.5kW prototype for the proposed push-pull forward converter is designed, and the corresponding efficiency curve and waveforms are provided. The efficiency of the proposed converter under nominal output can be as high as93%, and the actual waveforms match well with the theoretical analysis and simulation results. The experiment results validate the feasibility and efficiency of the proposed converter, as well as the stability and robustness of the controller for flux balancing. It is concluded that the proposed controller and the corresponding research provide some guidance for the future design of DC-DC converter.