Robust power flow control of grid-tied inverters based on the uncertainty and disturbance estimator

In this paper, an uncertainty and disturbance estimator (UDE)-based control is proposed to achieve accurate power flow control for grid-tied inverters (GTI). The power delivering dynamics is introduced at first after considering both frequency dynamics and voltage dynamics. Then the UDE algorithm is adopted to regulate both output voltage amplitude and frequency for accurate real power and reactive power control. With the adoption of the UDE method, the model uncertainty (e.g., power angle) and external disturbance (e.g., variations of grid frequency and grid voltage) can be compensated automatically. Moreover, this UDE-based dynamic power flow control can achieve self-synchronization without an extra synchronization unit (e.g., a phase-locked-loop) when the inverter is connected to the grid. In addition, the proposed controller is easy for implementation and parameter tuning through the designs of desired tracking error dynamics and UDE filters, while having the flexibility and performance of advanced control methodologies. The asymptotic stability of the closed-loop system is analyzed. Experimental results are provided for validation.