An LCL filter-based grid-interfaced three-phase voltage source inverter: Performance evaluation and stability anaylsis

Power converters in grid connection applications commonly employ Sinusoidal Pulse-Width Modulation (SPWM) technique. Passive filters are employed in order to attenuate the generated switching current ripples and reduces resonances between the grid and the inverter. The first-order (L), the second-order (LC), and the third-order (LCL) filters topologies are typical filters for grid connected Voltage Source Inverters (VSI). Practically, due to the system size, weight, and cost requirements, the LCL filter is the most commonly used among others for the integration of the three phase VSI into the grid. However, the control system stability is affected by the underdamping characteristic of the LCL filter therefore, it introduces to challenges to the control problem. Numerous control strategies such as repetitive, predictive, multiloop control, and hysteresis regulation have been proposed in order to improve the stability of the grid-connected VSIs. In this paper, the performance of the third order LCL filter-based gridconnected three-phase VSI is evaluated and the system stability is investigated using a two-loop control approach with both passive and active damping. The two-loop control considers the grid current as the outer loop while for the inner loop, different variables are considered such as capacitor voltage, capacitor current, and inductor current.