Research On Control Strategy And Stability Based On LCL-type Grid-connected Inverter

Since modern times,fossil energy has injected a steady stream of vitality into the prosperity and development of human society,but we should also rationally see that the uncontrolled exploitation and utilization of fossil energy（oil,coal）will cause the world to suffer from energy and environmental crises.To solve such crises,countries are actively seeking new energy（solar energy,tidal energy,etc.）that can be used by humans.As the energy exchange interface between renewable energy power generation units and the grid,grid-connected inverters play a very important role in the safe,stable and high-quality operation of distributed power generation systems.First,it introduces the significance of the development of distributed power generation technology,and the definition and characteristics of the technology,and then explains the characteristics,networking types,and control methods of microgrid technology.Taking grid-tied inverter with an LCL filter as the object of elaboration,the research status of its control scheme under different power grid conditions is introduced.Then,the main structure and system composition of the LCL grid-connected inverter system are introduced,and the peak resonance and filtering characteristics of the LCL filter are explained.Several damping schemes to suppress resonance of LCL filter are summarized,and several typical passive damping methods are compared and analyzed in terms of structure,filtering effect and power loss.Furthermore,a current control method based on parameterized stabilization controller and H₂norm of error signal is proposed.In this method,the parametric stabilization controller is used to ensure the internal stability,and then the method determines the free parameters of the stabilization controller and open-loop gain coefficient by designing the H₂ norm of the error signal and open-loop gain,so that the system has a fast dynamic response and zero steady-state error.This scheme can effectively reduce the interference of the grid voltage on the grid current,and the system can quickly and accurately output a three-phase balanced sinusoidal current within a half cycle under different operating conditions when the reference current changes suddenly.Finally,Aiming at the problem that the inherent resonance of LCL filter increases the difficulty of stable operation of the inverter,based on the analysis of steady-state and transient models of grid-tied inverters,a Lyapunov-theory based disturbance compensation scheme is proposed.The steady-state modulation function is derived and designed by using the state variable as a constant at steady state.When the disturbance occurs,the disturbance modulation function is designed according to the transient model.Moreover,the introduction of the gain coefficient k in the disturbance modulation function overcomes the limitation of less freedom,and can increase the adjustment dimension of the inverter.The proposed disturbance compensation scheme has global stability,good dynamic response and Anti-disturbance ability.