Research On State-Feedback Control Technology For Grid-Connected Inverter With LCL Filter

Taking the grid-connected inverter circuit with LCL filter as the research object,the influence mechanism of LCL filter’s resonant characteristics and digital control delay characteristics on the stable operation of the system is studied in this paper.State reconfiguration and state-feedback control method are adopted to improve the system stability and the parameters adaptability on the basis of reducing the number of current sensors.The stability problem caused by the inherent resonance of the LCL filter,the grid impedance variation and the digital time delay will affect the stable operation of the LCL grid-connected inverter system.In order to solve these problems,first of all,the state differential equation and the state diffenrence equation for the LCL filter are separately established.As for the consideration of digital delay,the order of the LCL grid-connected inverter control system is extended to form the four order difference state space model.Secondly,the state-feedback characteristics are analyzed,and the damping characteristics of all state-feedback variables and the limitation of state-feedback parameters for different LCL filter parameters are discussed based on the above model.The influences of the grid voltage,the capacitance voltage and the common coupling point voltage on the system operation characteristics are respectively analyzed and compared to improve the system stability and the parameters adaptability,hence,a state-feedback control method with active damping characteristics is researched.The common coupling point voltage vpcc is used as a system state,the improvement effect of this state-feedback variable on the stability problem is analyzed,the problem is introduced by the impedance fluctuation of the grid-side.In addition,the state-feedback characteristics of inverter current iL1 and grid current iL2 are evaluated respectively,a state reconstruction method is provided,which relies on the sampling values of vpcc and iL2.Meanwhile,the order of the space model is virtually enlarged to improve the system stability and the parameter adaptability.Finally,the simulation and experimental verification of the research contents in this paper are carried out based on MATLAB/Simulink simulation software and the experimental platform with TMS320C6713 as the control core,which aims to compare and analyze the theoretical analysis and experimental results.Contrast and analysis of the simulation and experimental results are discussed,and it confirms that theoretical analysis and experimental results are consistent.The conclusion verifies that the research contents in this paper are correct and the control method is effective and feasible.