Research On Predictive Current Control Of Photovoltaic Energy Storage System Based On Disturbance Observer

In an independent photovoltaic(PV)power generation system,the change of PV output power,linear or nonlinear load mutations,etc.,will have a certain impact on the DC bus voltage,which will affect the normal operation of the other loads on the DC bus.The voltage fluctuation on DC bus can be suppressed effectively by connecting energy storage devices.For energy storage devices,the bidirectional DC-DC converter is a bridge connecting DC bus and energy storage medium.The various disturbance problems in the PV energy storage system can be solved through reasonable control of the bidirectional DC-DC converter.In this paper,a predictive current control method for the bidirectional DC-DC converter based on disturbance observer is studied for PV energy storage system.The DC bus voltage fluctuation caused by the volatility of PV output and the uncertainty of load is solved by this method.The dynamic and steady-state performance and anti-interference ability of PV energy storage system are improved effectively by the method.The specific contents of this paper are as follows:Firstly,the research status of bidirectional DC-DC converter is introduced from two perspectives of circuit topology and control method,and the development process and research status of predictive current control method and disturbance observer are introduced.Secondly,the working principle of the non-isolated bidirectional half-bridge DC-DC converter is introduced in detail,and the mathematical model of bidirectional DC-DC converter in Boost and Buck modes are established respectively.Thirdly,the design process of finite control set predictive current controller is given,and the essential problem of unfixed switching frequency in finite control set predictive current control method is analyzed.Then the continuous control set predictive current controller is designed and its stability is analyzed.And the predictive control delay compensation is realized.Then,the multi-source disturbance characteristic of the PV energy storage system is analyzed,and the equivalent load current is used as the interference for feedforward compensation to improve the anti-interference ability of the system.The equivalent load current is obtained by the designed nonlinear disturbance observer.Finally,in order to verify the feasibility and effectiveness of the proposed control method,the simulation and experimental verification of two types of predictive current control methods and the continuous control set predictive current control method based on disturbance observer are carried out.Through simulation and experimental comparison of PV energy storage system under various working conditions,it is verified that the continuous control set predictive current control method based on disturbance observer can improve the dynamic and steady-state performance and anti-interference ability of the PV energy storage system effectively.