A new control scheme for LCL-type grid-connected inverter with a Notch filter

LCL filter is an effective solution to suppress harmonic current in grid-connected inverters. Unfortunately, it has resonance at certain frequency, which will result to system instability. In order to avoid stability problems, the resonance frequency of LCL filter can be damped using active techniques, which can eliminate dissipative elements but increase control complexity. A new designed notch filter offers an effective solution, but the variations of the grid impedance will degrade the damping effect. So tuning the quality factor becomes a good method to cope with the grid impedance variations and inproves the robustness. PI controller can obtain a higher gain at low frequency range, and acquire a good harmonic suppression. Simulation and experimental results verify the effectiveness of the proposed control method.