Stability Improvement of Grid-connected Converter with LCL Filter based on Capacitor Current Active Damping by Computational Delay Reduction

Nowadays, LCL filters utilization to suppress the grid-connected inverter switching harmonics is expanding and various methods such as capacitor current active damping scheme could be investigated to damp out these harmonics. However, the computational delays including control system, and PWM switching delays have significant effect on damping system stability. In most of LCL filter parameter designing schemes, the try and error methods are used, and the complicated calculations are needed for system stability considering grid impedance variation and delay effect. In this paper, at first a systematic method is provided for filter parameters designing by which better dynamic response and lower filter volume size are resulted and then, the step-by-step design procedure of grid-connected converter controller parameters with LCL filter by reducing the computational delay in inner (capacitor current feedback)- and outer control loop (grid current) is proposed for LCL filter resonance damping which is stable in case of severe variations in grid impedance. The simulation results by MATLAB/Simulink illustrate appropriate system operation.