Research On Fractional Order Sliding Mode Control Method Of Photovoltaic Grid Connected Inverter

To improve the global energy shortage,optimize the energy power generation structure,protect the global environment and achieve sustainable development,new energy power generation technologies such as wind,light,water,geothermal and tidal energy have become the focus of research.Since solar energy has the advantages of clean,non-pollution,renewable and abundant reserves,photovoltaic power generation has been greatly developed.Grid-connected inverter is an important connection between photovoltaic power generation system and power grid.Its stability and performance will have a great impact on the results of grid-connected generation.Since grid-connected is usually susceptible to various external disturbances and internal parameter disturbances.Therefore,several key to improve the robustness of grid-connected inverter.The LCL-type three-phase grid-connected inverter is taken as the research object in thesis.In view of the robustness problems such as external disturbances encountered by the system,the following research contents are carried out on the basis of sliding mode control:（1）mode controller is designed to improve the robustness of the system;（2）For the chattering problem encountered in sliding mode control,a fractional-order sliding mode control is proposed to reduce the system chattering.and the fuzzy controller is designed to achieve fractional order adaptive;（3）A passive fractional order sliding mode control is proposed to further improve the robustness of the system.For the robustness of LCL grid-connected inverter,this paper designs a sliding mode controller based on LCL grid-connected inverter.Based on the mathematical model of LCL grid-connected inverter,the sliding mode surface and reaching law are designed.The stability and robustness of sliding mode control are analyzed theoretically.At the same time,the robustness of sliding mode control is verified by experiments.For the chattering problem in traditional sliding mode control,a fractional-order sliding mode controller is proposed in this paper.The chattering phenomenon of traditional sliding mode control can reduce the tracking accuracy and easily excite the unmodeled high frequency components in the system,which affects the stability of the system.Therefore,the fractional order term is introduced into the sliding surface to make the motion of the system state more gentle near the sliding surface,so that the chattering of the system state converges to the equilibrium point along the sliding surface is reduced,and the performance of the current controller and the robustness of the system are improved.Secondly,the fractional order sliding mode control law is discretized to make it more convenient for practical application.Then,aiming at the problem that the convergence effect of the system state is different under different fractional orders,a fuzzy controller is designed,so that the fractional order in the controller can change with the change of the system state,which further enhances the fractional order effect and improves the performance of the controller.Finally,the proposed fuzzy fractional-order sliding mode controller is applied to the inverter for experimental comparison to verify the robustness of the control system.Aiming at the robustness problems of LCL grid-connected inverter,such as large parameter disturbance and external disturbance,in order to further improve the robustness and stability of grid-connected inverter system and make the system output good grid current even under large parameter disturbance and external disturbance,a fractional order sliding mode control method based on passivity is proposed.The passivity-based control and fractional-order sliding mode control are combined.Due to the introduction of passivity theory,the stability of the system is linked to energy,and the stability of the system is improved.The fractional-order sliding mode control design of the system state is that the system state converges along the fractional-order sliding surface,which further enhances the robustness of the system.Finally,the effectiveness of the proposed controller is verified by experimental comparison.