Research On Weak Grid LCL Grid-Connected Inverter Based On Composite Passive Controller

Countries in the world have an increasing demand for energy,and long-term dependence on non-renewable energy is not a long-term solution.At present,the demand for new energy is imminent.In recent years,photovoltaic power generation has received extensive attention from all walks of life.As one of the most important links in photovoltaic power generation systems,the grid-connected inverter is one of the most important links in the photovoltaic power generation system,which is a major difficulty for its design and control.In the process of grid connection of the system,it is inevitable to be affected by the impedance of the grid.Weak grids will cause irresistible problems to the system.In addition,the problem of LCL filter resonance spikes is also an urgent problem.In order to solve the above problems,and improve the static and dynamic performance of the system,and enhance the stability and robustness of the system,it is of great significance to study the appropriate system model and controller.This article compared the L-type filter with the LCL-type filter in the selection of the system topology.Through the analysis of the Bode diagram,the LCL-type filter with better suppression effect on high-frequency harmonics was determined.The control advantages and disadvantages of the three-phase LCL grid-connected inverter are briefly described.Based on the problem of resonance peaks caused by the filter,a more complex controller needs to be selected to effectively control the system.Aiming at the shortcomings of traditional PI controllers such as lack of anti-interference and stability,and the three-phase LCL grid-connected inverter as a non-linear system,it is proposed to introduce the passive control theory as a system controller.Established Euler-Lagrange mathematical models for three-phase LCL grid-connected inverters in strong and weak grids.Passive damping is used to obtain the passive control law,and simulations verify that passive control is in the system.Applicability.For the problem of system resonance,the passive damping method of the capacitor branch series damping resistor,the capacitive current and capacitive voltage proportional feedback active damping method,and the notch active damping method are combined with the passive controller to form a new Compound controller.The theoretical and simulation verifications of the three hybrid controllers were performed,and the results show that they have better stability and feasibility at smaller grid impedances.In different grid-connected occasions,the impedance of the power grid changes.Three types of hybrid controllers have been theoretically studied and verified by simulation.The hybrid controllers obtained by EL passive control and state feedback active damping have excellent robustness.Sex.The improved passive controller directly controls the grid-connected current to achieve grid-connected unit power factor of the system.Finally,through experimental research,it is observed that the system has a stable and smooth grid-connected current waveform under the conditions of sudden load increase,sudden load decrease,and full load.The improved passive controller can effectively suppress the resonance peak of the LCL filter.It has good static and dynamic performance under different grid impedances,which verifies the feasibility of the scheme.