Research On Nonlinear Composite Control Strategy Of Three-level Super Capacitor Energy Storage Converter

With the rapid development of the world economy,the demand for energy is increased,and renewable energy has been paid more and more attention,DC microgrid is rapidly developed.Due to the randomness of distributed energy and the uncertainty of load,the voltage fluctuation of DC microgrid will be caused.Because of the advantages of high power density and fast dynamie response,supercapacitor energy storage device is more suitable to be used to svppressing voltage fluctuation in DC microgrid.Based on this background,the non-linear composite control strategy of three-level supercapacitor energy storage system is studied in this paper.Firstly,the working principle of three-level bidirectional DC/DC converter is introduced·The characteristics of four different working inodes are analyzed.The input and output characteristics of three-level converter are deduced,By introducing the equivalent input current from the microgrid side,a unified mathematical model of three-level converter is established.It makes the design of the controller simplier.The two-direction operation mode can be realized by one controller.The logic judgment unit is omitted and the control cost is lower.Moreover,it does not depend on the microgrid side model,which improves the efficiency of the converter.Secondly,based on the unified mathematical model of three-level converter,the supercapacitor energy storage system is equivalent to a linear system with simple control by using the method of accurate linearization of state feedback.The combination of sliding mode variable structure control solves the dependence of exact linearization on exact model,and improves the robustness of the system.Aiming at the chattering problem of sliding mode variable structure control,fuzzy control is adopted to soften the control signal,so that the system has a certain self-regulation ability.A nonlinear composite discrete controller for three-level supercapacitor system is designed,and the influence of sampling time on the chattering of the system is analyzed.The control strategy is simulated and validated on the MATLAB simulation platform.Finally,the hardware platform and software program based on TMS320F28335 are designed,and the charging and discharging experiments of three-level supercapacitor energy storage system are completed.The correctness of the control algorithm is verified by the experimental results.