LCL filter design based on non-minimum-phase stability region for grid-connected inverters in weak grid
The resonant stability problems of LCL filter have become big challenges for grid-connected inverter in weak grid. This paper takes the effect of non-minimum phase time delay on the ratio between resonance frequency and sampling frequency into account and use it to design the LCL filter. Both LCL resonance frequency and inverter-side inductor and filter capacitor related L1C resonance frequency are limited to a specific stability region considering the following factors: different computation delay, inductance variation and grid impedance variation in a large range. Associated with the maximum current ripple expression for inverter-side inductance calculation, three expressions can establish a simple and robust method to calculate LCL filter parameters without active damping. Simulation and experimental results are provided to validate the correctness of the developed model and control scheme.