Research On The Optimization Of Dynamic Characteristics Of Input Series Output Parallel Dual Active Bridge

Medium and low voltage DC power transmission systems have attracted more and more attention due to its ability to connect DC loads and renewable resources such as photovoltaic,wind power and energy storage devices with fewer power conversion stages.Loads connected to DC bus vary,whic h leads to the problem that the input voltage and output load fluctuate greatly,and at the same time challenges the dynamic response speed of the system.At present,the high-power dual DC-DC converter in the medium and low voltage DC transmission system mostly adopts the input-series-output-parallel dual active bridge.The control strategy of this structure converter is mainly based on the power balance control of PI.There are still two problems to be solved yet: one is that the response speed of the system is affected by the integral link,and the other is the design of compensation parameters become complicated when the number of system modules increases.For this reason,an adaptive finite control set model predictive control is adopted in this dissert ation.By establishing a predictive model for a single module and input-series-output-parallel dual active bridge composed of multiple modules,the dynamic characteristics of the starting process,load switching and input voltage fluctuation are improved.For the single-module bi-directional active bridge module,the mode analysis and operation characteristics analysis are given in one switching cycle using the dual-phase shift control,and small-signal model of the module is established.Small signal modeling is carried out for the isop-dab composed of multiple modules.The power balance condition and the working principle of the multi-module double-loop control strategy are analyzed.The double-loop decoupling is realized and the closed-loop parameter design is simplified.When traditional control is used in single-module and isop-dab,the dynamic response of the system is slow and modeling of the system is complex.To better improve the problems mentioned above,double adaptive model predictive control strategy for single module and dual power flow adaptive model predictive control for the isop-dab are put forward.The error ender steady state is analyzed and correspondent revision is given.Finally,the detailed workflow of the proposed control strategy is designed.A type-Ⅱ compensator is designed for the single-module bidirectional active bridge,and a double-loop accurate voltage equalizer is designed for the isop-dab.In the design process of the compensator,the factors such as low frequency gain,medium frequency bandwidth,high frequency attenuation and crossover frequency are considered comprehensively.In order to verify the effectiveness of the proposed control strategy,a simulation was carried out,and a 25 W experimental platform was built.Thr ough the comparison of the simulation and experiment between the traditional control method and the proposed method,it was verified that the proposed method has better dynamic characteristics in the starting process,load switching and input voltage fluctuation are improved.