Robust Power Flow Control of Grid-Connected Inverters

In this paper, an uncertainty and disturbance estimator (UDE)-based robust power flow control is developed for grid-connected inverters to achieve accurate power delivery to the grid. The model of power delivering with both frequency dynamics and voltage dynamics is derived at first. The UDE method is introduced into the controller design to deal with model uncertainties (e.g., output impedance and power angle), coupling effects, and external disturbances (e.g., the fluctuation of the dc-link voltage, the variation of output impedance/line impedance, and the variations of both frequency and amplitude in the grid voltage). Also, this controller does not need a voltage regulator or a current regulator and is easy for the implementation and parameter tuning through the design of the desired tracking error dynamics and the UDE filters. Experimental results are provided to show the effectiveness of the proposed method for different disturbance rejection scenarios, the low-voltage fault-ride through capability, and the weak grid operation capability. The good robustness of the UDE-based control is also demonstrated through the comparison with two other controllers: the proportional-integral controller and the active disturbance rejection controller.