Research Of Full-bridge Isolated Bidirectional DC-DC Converter Applied To Power Electronic Transformer

The Power Electronic Transformer is considered to be the core component of the future development of the power grid in the direction of intelligence,flexibility and interaction.It is an intelligent power electronic device with multiple functions Compared to the traditional power frequency transformers such as electrical isolation,power regulation and control,voltage conversion and renewable energy grid connection.But the Dual Active Bridge DC/DC Converter has broad application prospects as an intermediate grade widely used in PET because of its excellent high power density,soft switching characteristics and electrical isolation.This article takes DAB as the research object.The control strategy of the converter is optimized and simplified to achieve the purpose of reducing complexity,accelerating response speed and improving efficiency through the disassembly analysis of the working state and the one-to-one correspondence of mathematical algebraic expressions.First,the working principle and basic power characteristic analysis of single phase shift,extended phase shift and double phase shift are introduced in this paper.The basic concepts of current effective value,inductor current stress and return power are drew out.The working process is divided into sixth,eighth and tenth working states under three control strategies.The expressions of transmission power and current stress are derived from the segmented instantaneous mathematical expressions of the inductor current.Secondly,the modified control strategy of Lagrange extreme value converter is proposed.The problems are avoided fundamentally compared with the commonly used analytical methods such as solving the expressions of shifting D₂ and output power,shifting D₁ and voltage regulation ratio are complicated,the optimization strategy is more segmented,and it is not easy to implement.At the same time,it also avoids the more complex closed-loop system design.By discarding the condition that the partial derivative of the Lagrange multiplier?is zero,the intersection point of several plane intersections can be quickly obtained to determine the optimal trajectory.Thereby the optimal phase shift angle is obtained.Moreover,the inductor current stress and current effective value are analyzed and compared under the three control strategies,and the control strategy of the return power under the extended phase shift is also optimized under the premise of control variables.Finally,the main circuit,control circuit,high-frequency transformer and external given circuit are designed and a hardware experiment platform is built.The main component selection calculation process and circuit structure are briefly described.The verification experiment of the optimized control strategy of the inductor current stress and the effective value of the current is compared on the premise of the control variables under the three control methods on the platform.And the existing simulation waveforms are verified to verify the correctness of the theoretical deduction feasibility.