A method to overcome harmonic instability in grid-tied inverters employing active damping

Nowadays, grid-tied inverters are extensively employed in renewable energy applications for efficient conversion of power from DC to AC. To control these inverters, dual-loop current control with active damping is claimed to be one of the promising solutions to tackle grid impedance variations as well as to maintain the stable operation of the inverter connected to the grid. In recent literature, it is also proven that the unit PCC voltage feedforward loop along with dual-loop control can offer additional damping against LCL filter resonance. However, in our work, it will be shown how the addition of a full PCC voltage feedforward loop along with active damping pushes the inverter towards instability due to inverter-grid interaction. Furthermore, a cascaded dual low-pass filter will be designed to overcome the above problem. A grid-connected inverter with capacitive current feedback active damping along with a full voltage feedforward scheme is the system under study. The above findings are supported by frequency-domain analysis followed by simulations in MATLAB/SIMULINK platform.