Research On The Function Integration And Dynamic Performance Improvement Of Three-level Flying-capacitor Buck Converter

Compared with the traditional Buck topology, the Three-level Flying-capacitor Buck topology has the advantages such as lower voltage stresses and smaller output filters, leading to higher power density. In recent years, the Three-level Flying-capacitor Buck converter has received extensive attention. However, the flying capacitor needs to be pre-charged to half of the input voltage before the converter works. Otherwise, the power devices may suffer from overvoltage problems. Currently, only a few pre-charging methods can use for reference and their practicality is not strong enough. Meanwhile, various industrial applications demand that DC/DC converters should have better dynamic performance. Therefore, it is meaningful to further improve the dynamic performance of the converter.The reliable operation of the Three-level Flying-capacitor Buck converter requires various auxiliary networks. However, these networks are relatively independent, i.e. each network is useful under specific condition, which means that the component utilizations are not high. To overcome this disadvantage, this paper first proposes a function-integrated auxiliary passive network. The design of input capacitor pre-charging circuit, the flying-capacitor pre-charging circuit and RCD snubber circuits are integrated. In this way, components in these auxiliary networks can realize several functions, thus improving the component utilizations. On this basis, this paper proposes a further-improved auxiliary active network which decouples the parameter design. Not only the active network holds the advantage of function integration, but also fully overcomes the disadvantages of the passive network, thus enhancing the versatility.In order to further improve the dynamic performance of the Three-level Flying-capacitor Buck converter, this paper proposes a transient control strategy based on redundancy mode, i.e. introducing transient control on the steady-state controller basis. When the load varies, the inductor current adjusts quickly to reduce the output voltage fluctuations. The proposed control strategy holds concise principle and is easy to apply, offering a complement for steady-state controller and further improving the dynamic performance of the converter.Finally, a 1.3k W power rating prototype has been built. The experimental results match the simulation results very well. The proposed auxiliary circuit and transient control strategy have been fully verified.