Development Of 270V28V Bidirectional DCDC Converter

The bidirectional DC converter can be used in the aircraft electrical system.It uses a device that can realize the two functions of battery charging and emergency discharging,which helps reduce the weight of the system.This paper takes a 270 V / 28 V DC / DC bidirectional converter as the research object,and studies the converter topology and the control method,which is significant and has great value of engineering application.This paper adopts a two-stage topology solution.The high-voltage side uses an LLLC resonant converter to achieve a high voltage ratio,and the low-voltage side uses an interleaved bidirectional Buck / Boost converter to achieve the function of stable voltage.The DSP is used as a control chip to implement all digital control.The main contents of the thesis include:The bidirectional LLLC + Buck / Boost two-stage topology is used to analyze the working principle of the circuits at each stage.Also this paper uses the extended description function method and state space averaging method to model LLLC and interleaved bidirectional Buck / Boost,At the same time,it designs the closed-loop design and analyzes cascade stability analysis of two-stage converter were performed.The paper proposes an adaptive frequency conversion control method based on coupled inductors,which realizes the soft switching of the upper and lower switches in the bidirectional Buck/ Boost topology,reducing the voltage spikes.Taking the minimum loss under the maximum load as the optimization goal,a reasonable coupling coefficient is selected.Also a control method for adaptive load changing switching frequency is proposed to improve the efficiency of the circuit under light load conditions,which is testified in this paper.Finally,the paper designs the main circuit parameters of the switching device of the bidirectional DC/DC converter,such as the magnetic components,the filter capacitors and so on.It also optimizes the dead time and auxiliary inductance of LLLC.A 2000 W principle prototype is developed,which realizes bidirectional energy conversion with a full-load step-down efficiency of 94.5% and a step-up efficiency of 93.8%.