Research On The Control Method Of Single-phase LCL Inverter Under Weak Grid

As the energy crisis and environmental issues become more and more serious,distributed energy such as wind powe r and solar power are steadily growing.As the key equipment connecting the distributed generation system and the utility grid,the grid-connected inverter plays an important role in the distributed generation system.In grid-connected inverters,a filter is needed to attenuate the switching harmonics.The LCL-type output filter is widely used because it has higher attenuation capability than the L-type filter and the LCtype filter at high-frequency harmonics.Because the inverter plays a role in the locat ion of the grid,it has lowfrequency harmonic components,and long-distance transmission lines and transformers and other equipment factors make the actual grid have non-negligible impedance,resulting in the weak grid characteristics of the power grid.The LCL inverter control method was studied.The mathematical model of LCL filter was established,and the influence of parasitic parameters on its stability was analyzed.The limiting condition of LCL value was analyzed.The parameter design process was gi ven.The active damping and feedback mechanism of capacitive current and capacitive voltage were theoretically analyzed.At the same time,in order to ensure that the grid-connected current accurately tracks the grid voltage,a second-order generalized integral algorithm is used to generate a virtual quadrature signal to construct a phase-locked loop.The theory deduces the output impedance of the inverter based on capacitive current feedback active damping PR control.The influence of various parameter changes in the system on its frequency characteristics is studied.The output impedance of the inverter meets the demand characteristics by setting the filter parameters and control parameters.The comprehensive consideration of determining the PR parameters and discretizing them.Impedance analysis method is used to analyze the stability of the inverter under the weak power grid,and it is concluded that the output impedance of the inverter and the grid impedance have a certain phase margin at the crossover frequency in order to make the system run stably.Before the grid voltage is used The feed-forward additional compensation control strategy improves the phase angle margin of the output impedance of the inverter,avoids the occurrence of resonance,stabilizes the system,and is verified through simulation.Finally,a single-phase inverter experiment platform with TMS320F2 8335 as the control chip was set up.The hardware circuit and software control algorithm were designed and verified by experiments.The exp erimental results verify the validity of the application of the forward voltage compensation of the grid voltage in this paper under the weak grid.