Modeling Analysis And Control Research Of Fractional Order Dual Active Bridge Converter

As one of the representatives of high efficiency bidirectional DC converter,dual active bridge converter plays an important role in the electrified highway power supply scheme.Fractional calculus theory has seen a steady progression in recent years,the fractional characteristics of power electronic converters such as inductors and capacitors have also been further revealed.As the core device of the dual active bridge converter,the non-integer order of the inductor and capacitor has an important impact on its dynamic performance,frequency domain characteristics and control system design.The dual active bridge converter’s modeling and analysis are based on the ideal integer order of the inductor and capacitor,disregarding the fractional order characteristics of the component’s effect on converter performance,especially under the high-frequency development trend,The correlation analysis based on the integer order model is not accurate.The error caused by the model cannot be ignored.Therefore,this thesis takes the fractional order dual active bridge converter as the research object,and studies the fractional order modeling,the fractional order controller design and parameter optimization,and the current sharing under the staggered parallel IPOP structure of the dual active bridge converter.The main research contents are as follows:First of all,Analyzing the energy transmission principle and soft switching conditions of the dual active bridge converter,a single-phase-shifting control strategy is employed to address the issue that the traditional integer order model of the converter cannot precisely depict its characteristics in high frequency conditions.On this basis,Establishing a fractional order state space average model,the fractional calculus theory and state space average method are utilized to further derive control to output,input to output,control to state,and input to state transfer functions.Analysis of the effect of inductance and capacitance order on the converter’s amplitude frequency,phase frequency,and dynamic performance reveals that the order has a considerable influence on both the steady-state and transient performance.As order diminishes,the dynamic response speed is accelerated,overshoot is minimized,and adjustment time is shortened.Secondly,in order to further improve the control performance of the converter,a fractional-order PI~λ control strategy is designed based on the fractional-order state-space average model of the dual-active bridge converter and the transfer function from the control to the output of the fractional-order dual-active bridge converter.Because the integral order of the fractional PI~λ controller is adjustableλ ,the parameter adjustment mode is more flexible,but it is difficult to adjust,and it is difficult to achieve the desired effect.Aiming at this problem,the controller parameters are optimized by combining the advantages of genetic algorithm.The optimal fractional PI~λ controller parameters and PI controller parameters satisfying the absolute value integral of error(ITAE index)are obtained.Subsequently,it is verified in the simulation platform,and the adjustment time,input voltage disturbance,reference voltage disturbance and load disturbance are compared and analyzed respectively.The simulation results show that the fractional-order PI~λ controller makes the fractional-order double-active bridge converter system obtain better robustness and improves the dynamic performance of the converter.Finally,in order to solve the problem of unbalanced current in each phase of two-phase fractional order dual-active bridge IPOP combined converter in high-power scenarios,based on the current sharing idea without current sensor,a current sharing strategy suitable for two-phase interleaved parallel fractional order dual-active bridge combined DC converter is proposed.The current sharing principle is analyzed in detail and verified in the simulation platform.The current sharing strategy mainly includes the common phase shift duty cycle control stage Offset stage,calculation stage and current sharing control stage.The simulation results show that the fractional order dual active bridge converter can achieve effective current sharing between phases when the system parameters such as inductance and transformer ratio do not match.At the same time,through the introduction of interleaved parallel technology,the power density of each phase converter is effectively improved and the filter pressure is reduced.