Research Of Fractional-Order Sliding Mode Control Based On Quasi-Z Source Grid-Connected Inverter

Since the 21 st century,green renewable and clean energy,represented by wind energy and solar energy,has gradually become the main energy source of mankind,at the same time,has changed the world’s energy production,transmission and consumption revolution.As the core equipment to realize energy conversion and control,grid-connected inverter can directly affect the stability and reliability of the renewable energy system,so the research on the control strategy of grid-connected inverter has become a hot spot.The typical nonlinear characteristics of power electronic devices are prone to bifurcation and chaos when the circuit parameters change,which seriously affects the safety and stability of the system.Therefore,nonlinear dynamic behavioral research has become an important branch.Based on the current status of analysis and control research on quasi-Z-source grid-connected inverter,a study on the analysis and design of the control system of the Z-source grid-connected inverter is conducted in this paper to further reveal the quasi-Z source,providing a new idea and approach for the analysis of nonlinear dynamics and controller design of quasi-Z-source grid-connected inverters.The main work of this paper are summarized:(1)An improved integral sliding mode control strategy of quasi-Z source grid-connected inverter is proposed.First introduce a variety of common photovoltaic inverters,focusing on the analysis of the working principle of the quasi-Z source inverter,the average state space equation,small signal model and discrete mapping model are derived.Aiming at the harmonic problem of the grid-connected current,a dual-loop integral sliding mode control strategy with the voltage loop and the current loop with power feedforward of the grid current is proposed basing on the average state space equation.The power feedforward can improve the response speed,the voltage outer loop can realize the stability of the DC voltage,and the current inner loop can eliminate the AC static error.Based on the simulation platform,the effectiveness of the improved integral sliding mode control strategy is verified.(2)A fractional-order sliding mode control strategy of quasi-Z source grid-connected inverter is proposed.Firstly,the current quality of the quasi-Z source grid-connected inverter is used as the control target.The fractional ordercontrol theory is applied to consider the effectiveness of the sliding mode control in the control of the nonlinear system,the fractional-order sliding mode control is designed.Fractional-order sliding mode control combines the advantages of fractional calculus and sliding mode control to further improve the quality of grid-connected current.Finally,the effectiveness of the fractional sliding mode control strategy is verified.(3)Fractional-order sliding mode chaos control of quasi-Z source circuit is proposed.Firstly,the discrete iterative mapping model is used to analyze the bifurcation chaos phenomenon in the quasi-Z source circuit by using bifurcation diagrams,phase orbit diagrams and other means.At the same time,the stability analysis is performed to obtain the stability domain.Finally,aiming at the nonlinear behavior of the quasi-Z source inverter,the nonlinear control of fractional sliding mode chaos control is performed to avoid possible bifurcation and chaos phenomena and ensure the stable operation of the quasi-Z source circuit.Finally,the effectiveness of the fractional sliding mode chaos control strategy is verified.