Research On Energy Management Of Dual Active Bridge-Supercapacitor Energy Storage System Based On Hybrid Model Predictive Control

Supercapacitors are widely used in energy storage systems requiring fast response due to their advantages of high power-density,long life,fast charge and discharge speed,safety and reliability,and no pollution.In order to realize the bidirectional flow of energy in an energy storage system,a bidirectional DC/DC converter is generally required.Dual active bridge(DAB)converters can achieve soft switching operation over a wide voltage range,and can use transformer turns ratio to obtain output of high gain.The DAB converter has the advantages of high power-density,high efficiency,symmetrical structure,two-way energy transmission,and simple control.Therefore,it is very suitable for energy storage systems containing supercapacitors.However,if the supercapacitor does not match the DAB converter,the supercapacitor's advantage of fast dynamic response will not be realized.Therefore,aiming at this problem,a hybrid model predictive control strategy is proposed to control the dual active bridge-super capacitor(DAB-SC)energy storage system,which is to improve the overall response speed of the system.Firstly,through the analysis of supercapacitors,dual active bridges and their control methods,the importance of fast dynamic response of DAB converters in dual active bridge-supercapacitor energy storage systems is clarified.Based on the structure of the dual active bridge-supercapacitor energy storage system,the working principle of the system is analyzed.By analyzing the working principle of supercapacitors and the characteristics of commonly used supercapacitor equivalent circuit models,an equivalent model of supercapacitors suitable for this subject is established.And the system's energy management strategy is proposed.Secondly,based on the single-phase shift control method,the working principle of the DAB converter is analyzed in detail.According to the working principle of the DAB converter,the equivalent model of the converter in different switching states is obtained.And the supercapacitor equivalent model is integrated into the equivalent model of the converter in different switching states,so as to obtain the state space model of the system.Thirdly,by comparing the advantages and disadvantages of different fast response control methods,the Model Predictive Control(MPC)method is selected for analysis,and a hybrid model predictive control strategy incorporating supercapacitor equivalent model parameters is proposed.That is,by establishing a hybrid prediction model that incorporates supercapacitor equivalent resistance and capacitance parameters,setting a reference trajectory,and solving the objective function,the optimal control amount of the phase shifting duty ratio D of the converter is obtained.Then by optimizing the control amount D,the overall response time of the energy storage system is reduced to quickly respond to energy fluctuations on the bus side.Lastly,the effectiveness of the proposed method is verified by simulation and experiments.The simulation was performed using MATLAB/Simulink simulation platform.The simulation results show that compared with the single model predictive control method of DAB,the hybrid model predictive control method proposed in this paper can reduce the response time by about 0.4ms when the supercapacitor voltage is within the normal voltage range.Through the established experimental platform,experiments were performed under the conditions that the bus voltage was lower than the lower limit and the supercapacitor was within the normal voltage range.The experimental results show that,compared with the single model predictive control method of DAB,the hybrid model predictive control method proposed in this paper can reduce the response time by 14 ms,the response speeds were increased by 29.2%.And the correctness and effectiveness of the proposed method were verified.