Numerator-Denominator Model Based H ∞ Robust Control for LCL Filter-Based Grid-Connected Inverters under Weak Grid Conditions

In the grid-connected inverter controller system, conventional PI or PR controller decrease their low-frequency gain and bandwidth to maintain the stability of the system. However, this degrades the disturbance rejection and current tracking capability. To solve this problem, this paper gives an H _∞ robust control scheme based on Numerator Denominator Model method, which has the advantages of simplified current controller design procedure, can place the poles of closed-loop system at the desired place. By properly selecting the weight function, the proposed control scheme can not only achieve good robustness in disturbance rejection capability, but also gives a straight forward to design the dynamic performance. Simulation and experimental comparison results between PR and H _∞ controller is demonstrated. The results prove that the proposed control scheme shows obviously improvements on the robustness of inverter and meanwhile does not lose advantages on the dynamic performance.